Article

Intrasexually selected weapons

June 2018
Biological reviews of the Cambridge Philosophical Society 94(6)

DOI:10.1111/brv.12436

Authors:

Alejandro Rico-Guevara

University of Washington Seattle

Kristiina J. Hurme

University of Washington Seattle

We propose a practical concept that distinguishes the particular kind of weaponry that has evolved to be used in combat between individuals of the same species and sex, which we term intrasexually selected weapons (ISWs). We present a treatise of ISWs in nature, aiming to understand their distinction and evolution from other secondary sex traits, including from ‘sexually selected weapons’, and from sexually dimorphic and monomorphic weaponry. We focus on the subset of secondary sex traits that are the result of same‐sex combat, defined here as ISWs, provide not previously reported evolutionary patterns, and offer hypotheses to answer questions such as: why have only some species evolved weapons to fight for the opposite sex or breeding resources? We examined traits that seem to have evolved as ISWs in the entire animal phylogeny, restricting the classification of ISW to traits that are only present or enlarged in adults of one of the sexes, and are used as weapons during intrasexual fights. Because of the absence of behavioural data and, in many cases, lack of sexually discriminated series from juveniles to adults, we exclude the fossil record from this review. We merge morphological, ontogenetic, and behavioural information, and for the first time thoroughly review the tree of life to identify separate evolution of ISWs. We found that ISWs are only found in bilateral animals, appearing independently in nematodes, various groups of arthropods, and vertebrates. Our review sets a reference point to explore other taxa that we identify with potential ISWs for which behavioural or morphological studies are warranted. We establish that most ISWs come in pairs, are located in or near the head, are endo‐ or exoskeletal modifications, are overdeveloped structures compared with those found in females, are modified feeding structures and/or locomotor appendages, are most common in terrestrial taxa, are frequently used to guard females, territories, or both, and are also used in signalling displays to deter rivals and/or attract females. We also found that most taxa lack ISWs, that females of only a few species possess better‐developed weapons than males, that the cases of independent evolution of ISWs are not evenly distributed across the phylogeny, and that animals possessing the most developed ISWs have non‐hunting habits (e.g. herbivores) or are faunivores that prey on very small prey relative to their body size (e.g. insectivores). Bringing together perspectives from studies on a variety of taxa, we conceptualize that there are five ways in which a sexually dimorphic trait, apart from the primary sex traits, can be fixed: sexual selection, fecundity selection, parental role division, differential niche occupation between the sexes, and interference competition. We discuss these trends and the factors involved in the evolution of intrasexually selected weaponry in nature.

The evolution of sexually dimorphic traits in ecological gradients: an interplay between natural and sexual selection in hummingbirds

Article

Full-text available

Dec 2022
Proc Biol Sci

Traits that exhibit differences between the sexes have been of special interest in the study of phenotypic evolution. Classic hypotheses explain sexually dimorphic traits via intra-sexual competition and mate selection, yet natural selection may also act differentially on the sexes to produce dimorphism. Natural selection can act either through physiological and ecological constraints on one of the sexes, or by modulating the strength of sexual/social selection. This predicts an association between the degree of dimorphism and variation in ecological environments. Here, we characterize the variation in hummingbird dimorphism across ecological gradients using rich databases of morphology, colouration and song. We show that morphological dimorphism decreases with elevation in the understorey and increases with elevation in mixed habitats, that dichromatism increases at high altitudes in open and mixed habitats, and that song is less complex in mixed habitats. Our results are consistent with flight constraints, lower predation pressure at high elevations and with habitat effects on song transmission. We also show that dichromatism and song complexity are positively associated, while tail dimorphism and song complexity are negatively associated. Our results suggest that key ecological factors shape sexually dimorphic traits, and that different communication modalities do not always evolve in tandem.

Weapon shape variation of male morphotypes in two freshwater prawn species genus Macrobrachium (Decapoda: Palaemonidae)

Article

Jun 2022
ANIM BIOL

Many animal groups can develop weapons that originate from specialized modifications in different body regions. Decapods are a classic example of organisms that develop these weapons. In this group, we can find specific appendages modified to claws that are used during agonistic conflicts, as is the case between dominant and submissive male morphotypes in freshwater prawns. Our study aimed to analyze the shape, size, and morphological integration of claw components (propodus and dactyl) in male morphotypes of two freshwater prawn congeners (Macrobrachium amazonicum and M. brasiliense). Claws of the prawns were photographed and marked with landmarks and semilandmarks for the acquisition of shape variables. The shape of the propodus and dactyl was statistically different between almost all morphotypes of the two species. The size of structures differed statistically between all morphotypes. The claws of almost all morphotypes showed a high degree of morphological integration; however, statistical differences were observed only between the morphotypes of M. brasiliense. The variation in the shape and degree of morphological integration of the claws between the morphotypes of M. amazonicum was less evident when compared to the morphotypes of M. brasiliense, which may be related to distinct patterns in the development of chelipeds of each species, that is, homochely and heterochely, respectively. Thus, the exaggerated development of a cheliped (heterochely) can cause greater variation in the shape of this structure, also influencing the degree of morphological integration between its components, as evidenced in this study.

Positive allometry of sexually selected traits: Do metabolic maintenance costs play an important role?

Article

Full-text available

May 2021

Ummat Somjee

Sexual selection drives the evolution of some of the most exaggerated traits in nature. Studies on sexual selection often focus on the size of these traits relative to body size, but few focus on energetic maintenance costs of the tissues that compose them, and the ways in which these costs vary with body size. The relationships between energy use and body size have consequences that may allow large individuals to invest disproportionally more in sexually selected structures, or lead to the reduced per‐gram maintenance cost of enlarged structures. Although sexually selected traits can incur energetic maintenance costs, these costs are not universally high; they are dependent on the relative mass and metabolic activity of tissues associated with them. Energetic costs of maintenance may play a pervasive yet little‐explored role in shaping the relative scaling of sexually selected traits across diverse taxa. Large animals generally have lower relative rates of energy use compared to small ones. In many diverse groups, large animals also invest in disproportionately larger sexually selected traits. The economy of energy gained by large size may play an important role in shaping the positive scaling of sexually selected traits.

Do reproductive characteristics of the species explain differences in the investment in weapon size present in males?

Article

Nov 2022

Sexually selected traits, such as male weapons, are highly variable in shape and size across species. However, little is known about the mechanisms that may govern this variation. Because males with greater investment in weapon size tend to win more fights, but also pay higher costs related to weapon development and maintenance, larger weapons should be expected only in species in which victory in male–male fights generate reproductive benefits that outweigh investment costs. Here, we hypothesized that the reproductive characteristics that increase the chances of winners to access females or to fertilize eggs will favor the evolution of larger weapons. To evaluate this hypothesis, we conducted a meta‐analysis using arthropods as model organisms. To measure investment in weapon size, we gathered both Pearson correlation coefficient and the standardized (but non centralized) slope values for the relationship between weapon size and body size. We found that none of the reproductive characteristics we investigated was related to male weapon size. Thus, it seems that greater certainty of accessing a female or fertilizing female eggs with a victory does not modulate the investment in male weapon size. Perhaps the cost–benefit ratio between weapon size investment and reproductive success is not the main factor driving the variation in weapon size. Little is known about the mechanisms driving variation in male weapon size across species. We hypothesized that reproductive characteristics that increase the chances of male winners to copulate/fertilize females would favor a greater investment in weapons size. Using a meta‐analytical approach, we found that the variation in weapon size was unrelated to the investigated reproductive characteristics. We argue that the way weapons are used during contests may be more important than the species’ reproductive characteristics to explain weapon size variation.

The hidden links between animal weapons, fighting style, and their effect on contest success: a meta‐analysis

Article

Jul 2022

In many species that fight over resources, individuals use specialized structures to gain a mechanical advantage over their rivals during contests (i.e. weapons). Although weapons are widespread across animals, how they affect the probability of winning contests is still debated. According to theory, understanding weapon function during contests is essential to: (i) understanding its importance in determining the winner, and (ii) identifying what weapon traits (e.g. weapon length versus shape versus performance) are most relevant for contest success. However, quantitative evaluations of how weapon function affects the extent to which weapon traits influence contest success are still lacking. Here, we first develop an individual‐based model to evaluate how increasing the influence of the weapon in determining the winner translates to differences between winners and losers. Then, we use a meta‐analysis to identify: (i) whether different weapon measures influence contest outcome differently; (ii) how animals use their weapons during fights – i.e. weapon function; and (iii) if weapon function correlates to how weapons influence contest outcome. Our model showed that, as weapons increased the chance of determining the winner, the mean difference between winners and losers also increased. Therefore, in our meta‐analysis we used the mean trait difference between winners and losers as a proxy for the extent to which weapons influence contest success. The literature search identified 49 suitable studies, containing information for 52 species, totalling 107 effect sizes. Four main patterns emerged. First, most of the literature focuses on linear measures of weapons, while performance measures are concentrated on Crustacea and Squamata; other types of measures were rare. Second, differences between winners and losers in linear measurements were greater than differences in performance measurements when all species were combined (and when we used only a subset). Third, species that bear weapons almost always perform visual/tactile displays before engaging in physical contact. And fourth, while the way individuals display their weapons did not influence the importance of weapon size on contest outcomes, fighting style predicted when differences between winners and losers would be higher. Species that used their weapons to push or lift (even when combined with other functions) showed greater differences between winners and losers when compared to species that used their weapons to impact, pierce, pull or squeeze. Overall, our results show that we have an incomplete understanding of animal weapons built mostly on weapon size and a few select taxa. Thus, we should start focusing on measuring weapons according to how they are used during contests and in a wider diversity of species. One way forward is to conduct studies that integrate weapon morphology to weapon function to ensure we are measuring the most ecologically relevant variables.

Article

Full-text available

Apr 2022

A dominance hierarchy is the set of ranks occupied by species within an assemblage. Species with a high position within the dominance hierarchy tend to dominate subordinate species in contests for access to resources. In hummingbirds, greater weight and wing disc loading have been associated with highest ranks within the dominance hierarchy. Nevertheless, the limit to which the difference between the weight of contending species represents a competitive advantage has not yet been determined. Here, we determined the dominance hierarchy of a hummingbird assemblage exploiting the most abundant floral resource (Palicourea padifolia, Rubiaceae) in a cloud forest of central Veracruz, Mexico. Specifically, we tested whether species weight and wing disc loading influence the dominance hierarchy. Additionally, we tested whether the flowers visited per foraging bout increases with species weight and dominance. We further tested whether weight, wing disc loading, and the genetic relatedness between contenders influenced the dominance relationships in species-pair interactions. Our results indicate that the hierarchy is positively influenced by weight. Hummingbirds visited similar number of flowers regardless their weight or their dominance. Nevertheless , the probability that the heaviest contender won contests was positively associated with the differences of weight and genetic relatedness between contenders. Contrarily, the probability that the contender with greatest wing disc loading won contests was positively associated with differences of weight and negatively associated with the relatedness between contenders. However, these models only explained between 22% and 34% of the variation, respectively. Our results demonstrate that the weight was the major contributor to high dominance values. However, future studies should include (1) the temporal variability of the weight and (2) experimental predictor variables such the burst power of the hummingbirds to evaluate its effects on the dynamics of dominance hierarchies in hummingbird assemblages. All the hummingbird species present in the studied assemblage have developed wide behavioral mechanisms that compensate their morphological differences, which allow them to coexist, even when they compete for the access to the same resource.

Biomechanics influence sexual dimorphism in the giant mesquite bug, Thasus neocalifornicus

Article

Dec 2021
ZOOLOGY

In many species, males possess specialized weaponry that confers benefits during male-male combat. Because male weapons are often disproportionately larger versions of preexisting body parts, females often possess reduced versions of male weaponry. Most research focuses exclusively on sexual dimorphism in the size of male and female weapons, even though other aspects such as weapon performance can also explain the evolution of weapon sexual dimorphism. In the giant mesquite bug, Thasus neocalifornicus, males wield exaggerated hindlegs that aid in locomotion and are used as weapons to generate forceful squeezes during combat. However, female T. neocalifornicus hindlegs are relatively inconspicuous and only used for locomotion. To understand the intricacies of weapon sexual dimorphism in T. neocalifornicus hindlegs, we measured the allometry of their hindlegs morphology, biomechanics, and performance. Males and females had relatively similar sized legs when concerning only linear measurements: hindleg length did not differ between the sexes (both for intercept and slope), but males do have relatively wider hindlegs (greater intercepts). Regarding performance, however, males were relatively and proportionally stronger than females. Furthermore, the output lever of male hindlegs scales hypoallometrically and the tibial spine maintains its position as the hindlegs grows, both of which maintain the hindlegs’ biomechanical efficiency as they increase in size. Overall, our finding demonstrates that selection on the performance and biomechanics of sexually selected weapons can influence the expression of sexual dimorphism, by exaggerating some aspects of the weapons morphology—but constraining others.

Runaway evolution from male‐male competition

Article

Full-text available

Feb 2022
ECOL LETT

Wondrously elaborate weapons and displays that appear to be counter to ecological optima are widespread features of male contests for mates across the animal kingdom. To understand how such diverse traits evolve, here we develop a quantitative genetic model of sexual selection for a male signaling trait that mediates aggression in male‐male contests and show that an honest indicator of aggression can generate selection on itself by altering the social environment. This can cause selection to accelerate as the trait is elaborated, leading to runaway evolution. Thus, an evolving source of selection provided by the social environment is the fundamental unifying feature of runaway sexual selection driven by either male‐male competition or female mate choice. However, a key difference is that runaway driven by male‐male competition requires signal honesty. Our model identifies simple conditions that provide clear, testable predictions for empirical studies using standard quantitative genetic methods. Biologists and the public are captivated by extravagant traits used during male‐male contests for mates. Elaborations such as weapons, showy signals, and complex courtship are curious because they don't obviously contribute to survival, and in many instances would seem to work to attract predation. We provide a quantitative genetic model that shows how such elaboration can evolve, and when populations will shoot past an optimum leading to runaway evolution.

Killing conspecific adults in mammals

Article

Jul 2021
Proc Biol Sci

Mammals kill both conspecific infants and adults. Whereas infanticide has been profusely studied, the killing of non-infants (adulticide) has seldom attracted the attention of researchers. Mammals kill conspecific adults by at least four, non-exclusive reasons: during intrasexual aggression for mating opportunities, to defend valuable resources, to protect their progeny and to prey upon conspecifics. In this study, we test which reason is most likely to explain male and female adulticide in mammals. For this, we recorded the presence of adulticide, the ecological and behavioural traits, and the phylogenetic relationship for more than 1000 species. Adulticide has been recorded in over 350 species from the most important Mammalian clades. Male adulticide was phylogenetically correlated with the presence of size dimorphism and intrasexually selected weapons. Female adulticide was phylogenetically associated with the occurrence of infanticide. These results indicate that the evolutionary pathways underlying the evolution of adulticide differ between sexes in mammals. Whereas males commit adulticide to increase breeding opportunities and to compete with other males for mating, females commit adulticide mainly to defend offspring from infanticidal conspecifics.

Weapon performance drives weapon evolution

Article

Jan 2021

Many sexually selected traits function as weapons, and these weapons can be incredibly diverse. However, the factors underlying weapon diversity among species remain poorly understood, and a fundamental hypothesis to explain this diversity remains untested. Although weapons can serve multiple functions, an undeniably important function is their role in fights. Thus, a crucial hypothesis is that weapon diversification is driven by the evolution of weapon modifications that provide an advantage in combat (e.g. causing more damage). Here, we test this fighting-advantage hypothesis using data from 17 species of coreid bugs. We utilize the fact that male–male combat in coreids often results in detectable damage, allowing us to link different weapon morphologies to different levels of damage among species. We find that certain weapon morphologies inflict much more damage than others, strongly supporting the fighting-advantage hypothesis. Moreover, very different weapon morphologies can inflict similarly severe amounts of damage, leading to a weapon performance landscape with multiple performance peaks. This multi-peak pattern could potentially drive different lineages towards divergent weapon forms, further increasing weapon diversity among species. Overall, our results may help explain how sexually selected weapons have evolved into the diversity of forms seen today.

Males armed with big weapons win fights at limited cost in ant-mimicking jumping spiders

Article

Full-text available

Dec 2022

A core assumption of sexual selection theory is that sexually selected weapons, specialized morphological structures used directly in male contests, can improve an individual’s reproductive success but only if the bearer can overcome associated costs, the negative effects on the bearer’s fitness components. However, recent studies have shown that producing and wielding exaggerated weapons may not necessarily be costly. Rather, some traits can be selected for supporting, or compensating for, the expense of producing and wielding such exaggerated weapons. In the ant-mimicking jumping spider Myrmarachne gisti, exaggerated chelicerae are borne only by adult males and not females, showing sexual dimorphism and steep positive allometry with body size. Here, we determine the potential benefits of bearing exaggerated chelicerae during male contests and explore the potential for costs in terms of prey -capture efficiency and compensation between chelicera size and neighbouring trait size. While males with longer chelicerae won most of their malemale contests, we found no significant differences in prey -capture efficiency between males and females regardless of whether prey were winged or flightless. Males’ elongated chelicerae thus do not impede their efficiency at capturing prey. Furthermore, we found that the sizes of all neighbouring traits are positively correlated with chelicera size, suggesting that these traits may be under correlational selection . Taken together, our findings suggest that M. gisti males armed with the exaggerated chelicerae that function as weapons win more fights at limited cost for performance in prey -capture and compensate for neighbouring structures.

Sexual dimorphism in the methane seep-dwelling Costa Rican yeti crab Kiwa puravida (Decapoda: Anomura: Kiwaidae)

Article

Full-text available

Nov 2022

Deep-sea chemosynthesis-based ecosystems support unique biological communities, but human impacts are an increasing threat. Understanding the life-history traits of species from deep-sea chemosynthesis-based ecosystems can help to develop adequate management strategies, as these can have impacts on ecological responses to changes in the environment. Here we examined the occurrence of sexual dimorphism in the yeti crab Kiwa puravida, an endemic species from the Costa Rican Pacific margin that aggregates at active methane seeps and depends on chemosynthetic bacteria for nutrition. The two morphological features examined included the claws, suspected to be under sexual selection and used for defense, and the carpus of the second pereopod not suspected to be under sexual selection. A total of 258 specimens, 161 males, 81 females, 16 juveniles, were collected from Mound 12 at 1,000-1,040 m depth in 2017 and 2018 and analyzed. We found that males have larger and wider claws than females, while there were no differences in carpus length. These results suggest that claw weaponry is under sexual selection in K. puravida, which is probably related to the mating system of this deep-sea species. This is the first attempt to study the reproductive biology of K. puravida, and additional observations will be necessary to shed more light on this matter.

Sizing up swords: Correlated evolution of antlers and tusks in ruminants

Article

Full-text available

Nov 2022
J Mamm Evol

Many sexual weapons used in sexual combat and/or as visual displays of dominance (e.g., antlers, horns) show positive allometry with body size, but allometry in species with more than one sexual weapon is not well studied. We examined the static and evolutionary allometric relationships between body size and tusks (pure combat weapons) and/or antlers (both a visual signal and combat weapon) from thirty-three artiodactyl species including the muntjaks and tufted deer (Muntiacinae), which uniquely have both antlers and tusks. In Muntiacinae species, we found a positive static allometric relationship between antler length and skull length, whereas tusk size scaled isometrically, suggesting greater energy investment in antlers as signals over tusks as combative weapons when both are present. Evolutionarily, we found that in species with only one weapon (either solely tusked or solely antlered), their weapon scaled with positive allometry with body mass, and the relationship for antlers levels off at larger body sizes. When we included the dual-weaponed Muntiacinae species, the positive allometric trend for tusks was not conserved, resulting in an isometric relationship, suggesting the possession of antlers negatively affects the energy investment in tusks as weapons. Overall, our findings show that species that possess dual weapons invest less energy in each weapon relative to single-weaponed species.

Static allometries do not reflect evolutionary allometry in exaggerated weaponry of male New Zealand sheetweb spiders ( Cambridgea spp.)

Article

Full-text available

Sep 2022

Across the animal kingdom, exaggerated weaponry is frequently used by one sex to contest access for potential mates. Within species, if disproportionate investment in weaponry confers an advantage to larger individuals, this may result in positive static allometry. It is predicted that the same selective pressures may also lead to positive evolutionary allometry, where larger species bear disproportionately large weapons on average, compared with smaller species. Furthermore, in species with stronger sexual selection, the static allometries of those weapons are expected to steepen. All adult males across the New Zealand sheetweb spider genus Cambridgea bear exaggerated chelicerae, which are used to compete for control of females' webs. Here, we characterize the distribution of chelicera lengths within each sex of 12 Cambridgea species to show that chelicerae almost always exhibit positive static allometry in males while female chelicera lengths are consistently isometric. We use comparative phylogenetic methods to demonstrate that the slopes of static allometries steepen in males of larger species but that the ratio of average chelicera length to cephalothorax width is tightly conserved across taxa, leading to an isometric evolutionary allometry. While static allometries indeed steepen in larger species, possibly due to stronger sexual selection, this conservation of relative trait size suggests that chelicera length is subject to other stabilizing selective pressures. Changes to species body plans might be constrained, while still allowing for disproportionate investment in weapon traits in the upper range of intraspecific body sizes.

Evaluation of Body Size Indicators for Morphological Analyses in Two Sister Species of Genus Dorcus (Coleoptera, Lucanidae)

Article

Full-text available

Sep 2022
J INSECT SCI

The relationship between trait and body size, i.e., the scaling relationship or static allometry, is an essential concept for investigating trait size. However, usage of an inappropriate body size indicator can lead to misinterpretation of morphology. In this study, we examined several possible body size indicators in two closely related stag beetle species, Dorcus rectus and Dorcus amamianus. We raised animals in captivity and used pupal weight as a measure of true, or overall body size, and then evaluated six adult morphological traits to test whether these traits could be reliably used as body size indicators in static scaling relationship comparisons. We analyzed two comparisons, between sexes in same species and between species in same sex. We showed that the most appropriate body size indicators differ depending on the comparisons. Our results indicated that the scaling relationship of focal traits could be over- or under-estimated depending on which body size indicators are used.

White-edged cowards: high-pitched treefrogs will be attacked by those with orange legs

Article

Sep 2022
BEHAVIOUR

Raoni Rebouças

Anurans are one of the most diverse groups of animals, with single and multi-modal communication forms commonly used to settle disputes over territory and to attract females. Thus, I aimed to evaluate if male white-edged treefrogs tend to attack smaller individuals and which morphometric factor is related to it. Advertisement calls of this species were recorded and used in a four-choice experiment with the emission of artificially designed calls. I evaluated which speaker individuals approached and if morphometric variables could predict it. I observed that individuals approached significantly more often towards the high-pitched call than other treatments, and the frequency to do so was predicted by the extension of orange colour in their legs. These results indicate that smaller individuals are actively excluded from calling sites.

Human third-party observers accurately track fighting skill and vigour along their unique paths to victory

Article

Full-text available

Sep 2022

Sexual selection via male-male contest competition has shaped the evolution of agonistic displays, weaponry, and fighting styles, and is further argued to have shaped human psychological mechanisms to detect, process, and respond appropriately to cues of fighting ability. Drawing on the largest fight-specific dataset to date across the sports and biological sciences ( N = 2765 fights), we examined how different indicators of fighting ability in humans reflect unique paths to victory and indicate different forms of perceived and actual resource-holding power (RHP). Overall, we discovered that: (1) both striking skill and vigour, and grappling skill and vigour, individually and collectively predict RHP; (2) different RHP indicators are distinguished by a unique path to victory (e.g., striking skill is a knockout-typical strategy, whereas grappling vigour is a submission-typical strategy); and (3) third-party observers accurately track fighting skill and vigour along their unique paths to victory. Our argument that different measures of RHP are associated with unique paths to victory, and third-party observers accurately track fighting vigour and skill along their unique paths to victory, advance our understanding not only of human contest competition, but animal contest theory more broadly.

Dual function and associated costs of a highly exaggerated trait in a cichlid fish

Article

Full-text available

Nov 2021

Exaggerated secondary sexual characteristics are apparently costly and seem to defy natural selection. This conundrum promoted the theory of sexual selection. Accordingly, exaggerated secondary sexual characteristics might be ornaments on which female choice is based and/or armaments used during male–male competition. Males of many cichlid fish species, including the adaptive radiation of Nicaraguan Midas cichlids, develop a highly exaggerated nuchal hump, which is thought to be a sexually selected trait. To test this hypothesis, we conducted a series of behavioral assays in F2 hybrids obtained from crossing a species with a relatively small hump and one with an exaggerated hump. Mate-choice experiments showed a clear female preference for males with large humps. In an open-choice experiment with limited territories, couples including large humped males were more successful in acquiring these territories. Therefore, nuchal humps appear to serve dual functions as an ornament for attracting mates and as an armament for direct contest with rivals. Although being beneficial in terms of sexual selection, this trait also imposes fitness costs on males possessing disproportionally large nuchal humps since they exhibit decreased endurance and increased energetic costs when swimming. We conclude that these costs illustrate trade-offs associated with large hump size between sexual and natural selection, which causes the latter to limit further exaggeration of this spectacular male trait.

Contrasting selection pressure on body and weapon size in a polygynous megaherbivore

Article

Full-text available

Oct 2021
BIOL LETTERS

Sexual size dimorphism (SSD) is a common morphological trait in ungulates, with polygyny considered the leading driver of larger male body mass and weapon size. However, not all polygynous species exhibit SSD, while molecular evidence has revealed a more complex relationship between paternity and mating system than originally predicted. SSD is, therefore, likely to be shaped by a range of social, ecological and physiological factors. We present the first definitive analysis of SSD in the common hippopotamus ( Hippopotamus amphibius ) using a unique morphological dataset collected from 2994 aged individuals. The results confirm that hippos exhibit SSD, but the mean body mass differed by only 5% between the sexes, which is rather limited compared with many other polygynous ungulates. However, jaw and canine mass are significantly greater in males than females (44% and 81% heavier, respectively), highlighting the considerable selection pressure for acquiring larger weapons. A predominantly aquatic lifestyle coupled with the physiological limitations of their foregut fermenting morphology likely restricts body size differences between the sexes. Indeed, hippos appear to be a rare example among ungulates whereby sexual selection favours increased weapon size over body mass, underlining the important role that species-specific ecology and physiology have in shaping SSD.

Armed stem to stinger: A review of the ecological roles of scorpion weapons

Article

Full-text available

Sep 2021
J VENOM ANIM TOXINS

Scorpions possess two systems of weapons: the pincers (chelae) and the stinger (telson). These are placed on anatomically and developmentally well separated parts of the body, that is, the oral appendages and at the end of the body axis. The otherwise conserved body plan of scorpions varies most in the shape and relative dimensions of these two weapon systems, both across species and in some cases between the sexes. We review the literature on the ecological function of these two weapon systems in each of three contexts of usage: (i) predation, (ii) defense and (iii) sexual contests. In the latter context, we will also discuss their usage in mating. We first provide a comparative background for each of these contexts of usage by giving examples of other weapon systems from across the animal kingdom. Then, we discuss the pertinent aspects of the anatomy of the weapon systems, particularly those aspects relevant to their functioning in their ecological roles. The literature on the functioning and ecological role of both the chelae and the telson is discussed in detail, again organized by context of usage. Particular emphasis is given on the differences in morphology or usage between species or higher taxonomic groups, or between genders, as such cases are most insightful to understand the roles of each of the two distinct weapon systems of the scorpions and their evolutionary interactions. We aimed to synthesize the literature while minimizing conjecture, but also to point out gaps in the literature and potential future research opportunities.

Beards Increase the Speed, Accuracy, and Explicit Judgments of Facial Threat

Article

Full-text available

Dec 2021

Objectives To test whether intra-sexual selection has influenced perceptions of male facial hair. We predicted that beards would increase the speed and accuracy of perceptions of angry but not happy facial expressions. We also predicted that bearded angry faces would receive the highest explicit ratings of masculinity and aggressiveness, whereas higher prosociality ratings would be ascribed to clean-shaven happy faces.MethodsA total of 106 participants, ranging from 17 to 59 years of age (M = 27.27, SD = 10.03); 59 were female and 47 were male (44.3%) completed an emotion categorization tasks and an explicit ratings task. Participants viewed faces of the same men when bearded, clean-shaven, and 10 days of natural growth (i.e. stubble) when posing angry and happy facial expressions.ResultsAngry facial expressions were categorised most rapidly and with the greatest accuracy on bearded faces, followed by faces with stubble then clean-shaven faces. Conversely, happy facial expressions were categorised most rapidly and with the greatest accuracy on clean-shaven faces, followed by stubbled faces then bearded faces. Irrespective of facial expression, full bearded faces received the highest ratings of masculinity followed by faces with stubble then clean-shaven faces. Aggressiveness ratings were highest for angry faces with full beards, followed by angry faces with stubble, with clean-shaven angry faces receiving the lowest ratings. In contrast to our prediction, bearded smiling faces were rated as significantly more prosocial than stubbled and clean-shaven smiling faces.Conclusions These findings contribute further evidence that men’s beardedness represents an intra-sexually selected badge of status that enhances nonverbal threat potentially by augmenting underlying masculine facial structures.

No risk to scrambling? Mating tactic does not affect the frequency of leg autotomy in a New Zealand harvestman

Article

Jul 2021
ANIM BEHAV

Intense sexual selection on males may drive the evolution of exaggerated weaponry, typically used in contests for females or reproductive sites. In some species, males have discontinuous variation in weapon morphology that is accompanied by alternative reproductive tactics (ARTs). Major males with enlarged weapons usually exhibit a mating tactic based on female or resource defence, which makes them relatively sedentary. Minor males with reduced or absent weapons may exhibit a scramble competition mating tactic, which involves increased movement in search of females. Thus, the main costs paid by majors involve the expression/maintenance of exaggerated structures and potential injuries during contests. In turn, the main costs paid by minors are likely related to increased exposure to predation during mate search, yet this cost has rarely been considered for minors. Harvestmen are an arachnid group with diverse male weaponry, including many cases of male polymorphism associated with ARTs. Species of the suborder Eupnoi use leg autotomy as a common antipredator defence. Here we investigated whether leg autotomy (a proxy for predation risk) is more frequent in minors of the weapon polymorphic harvestman Forsteropsalis pureora, which has three male morphs with drastically different cheliceral size and morphology. Leg autotomy was very common, with 54% of wild-caught individuals missing at least one leg (mostly leg II), but we found no evidence for differential predation risk between male morphs during adulthood. In a predator simulation experiment, we found no difference in the likelihood or latency to autotomize a leg between male morphs or leg types (legs I, II, III or IV). However, males already missing legs were more reluctant to autotomize an additional leg. Our results suggest that while leg autotomy is a common antipredator strategy, with no difference between male tactics, costs are compounded as additional legs are autotomized and males may strategically decide not to autotomize in future predator encounters.

Tests of the positive and functional allometry hypotheses for sexually selected traits in the Jamaican field cricket

Article

May 2021
BEHAV PROCESS

Sexually selected traits, including threat signals, have been shown to scale steeply positively with body size because their exaggeration maximizes honest signalling. However, the functional allometry hypothesis makes the opposite prediction for some weapons: because the biomechanics of force applied in their use may favor relatively smaller size, sexually selected weapons may exhibit negative allometry. Tests of these ideas in insects have largely focused on holometabolous species, whose adult body size is entirely dependent on nutrients acquired during the larval stage. In contrast, hemimetabolous insects may exhibit different patterns of allometry development because they forage throughout development, between successive moults. Here, we tested complementary and competing predictions made by the positive and functional allometry hypotheses, regarding intrasexually selected trait allometry in a hemimetabolous insect, the Jamaican field cricket (Gryllus assimilis). As expected, head width (a dominance and/or combat trait) was more positively allometric than non-sexually selected traits. In contrast, and consistent with the functional allometry hypothesis, mouthparts (weapons) were either isometric or negatively allometric. We also tested whether trait allometry responded to rearing diet by raising males on either a high protein diet or a high carbohydrate diet; we predicted stronger positive allometry under the high protein diet. However, diet did not influence allometry in the predicted manner. Overall, our results support the functional allometry hypothesis regarding sexually selected trait allometry and raise intriguing possibilities for integrating these ideas with recent paradigms for classifying intrasexually selected traits.

Cost-Reducing Traits for Agonistic Head Collisions: A Case for Neurophysiology

Article

Apr 2021
INTEGR COMP BIOL

Synopsis Many animal species have evolved extreme behaviors requiring them to engage in repeated high-impact collisions. These behaviors include mating displays like headbutting in sheep and drumming in woodpeckers. To our knowledge, these taxa do not experience any notable acute head trauma, even though the deceleration forces would cause traumatic brain injury in most animals. Previous research has focused on skeletomuscular morphology, biomechanics, and material properties in an attempt to explain how animals moderate these high-impact forces. However, many of these behaviors are understudied, and most morphological or computational studies make assumptions about the behavior without accounting for the physiology of an organism. Studying neurophysiological and immune adaptations that covary with these behaviors can highlight unique or synergistic solutions to seemingly deleterious behavioral displays. Here, we argue that selection for repeated, high-impact head collisions may rely on a suite of coadaptations in intracranial physiology as a cost-reducing mechanism. We propose that there are three physiological systems that could mitigate the effects of repeated head trauma: (1) the innate neuroimmune response; (2) the glymphatic system, and (3) the choroid plexus. These systems are interconnected yet can evolve in an independent manner. We then briefly describe the function of these systems, their role in head trauma, and research that has examined how these systems may evolve to help reduce the cost of repeated, forceful head impacts. Ultimately, we note that little is known about cost-reducing intracranial mechanisms making it a novel field of comparative study that is ripe for exploration.

Complex vocal learning and three-dimensional mating environments

Preprint

Full-text available

Jan 2021

Jan Verpooten

Complex vocal learning, the capacity to imitate new sounds, underpins the evolution of animal vocal cultures and song dialects and is a key prerequisite for human speech and song. Due to its relevance for the understanding of cultural evolution and the biology and evolution of language and music, the trait has gained much scholarly attention. However, while we have seen tremendous progress with respect to our understanding of its morphological, neurological and genetic aspects, its peculiar phylogenetic distribution has remained elusive. Intriguingly, animals as distinct as hummingbirds and humpback whales share well-developed vocal learning capacity in common with humans, while this ability is quite limited in nonhuman primates. Yet, solving this ‘vocal learning conundrum’ may shed light on the constraints ancestral humans overcame to unleash their vocal capacities. To this end I consider major constraints and functions that have been proposed. I highlight an especially promising ecological constraint, namely the spatial dimensionality of the environment. Based on an informal comparative review, I suggest that complex vocal learning is associated with three-dimensional habitats such as air and water. I argue that this is consistent with recent theoretical advances – i.e., the coercion-avoidance and dimensionality hypotheses – and with the long-standing hypothesis that mate choice is a major driver of the origin and evolution of complex vocal learning. However, I stress that multiple functions may apply and that quantitative phylogenetic comparative methods should be employed to finally resolve the issue.

NATIONAL INTERRELATIONSHIPS FROM THE VIEWPOINT OF BIOLOGIST

Article

Dec 2020

ALEXANDER V. SIROTKIN

This review presents an original hypothesis, which explains the existence of current nationalism in the modern globalized society by biological rules of hierarchy and competition between the genotypes. Due to its innate character, it cannot be completely deleted from the social life, but the understanding its biological origin can avoid its negative expressions in the multinational communities.

Evaluating drivers of female dominance in the spotted hyena

Article

Full-text available

Dec 2022

Introduction Dominance relationships in which females dominate males are rare among mammals. Mechanistic hypotheses explaining the occurrence of female dominance suggest that females dominate males because (1) they are intrinsically more aggressive or less submissive than males, and/or (2) they have access to more social support than males. Methods Here, we examine the determinants of female dominance across ontogenetic development in spotted hyenas ( Crocuta crocuta ) using 30 years of detailed behavioral observations from the Mara Hyena Project to evaluate these two hypotheses. Results Among adult hyenas, we find that females spontaneously aggress at higher rates than males, whereas males spontaneously submit at higher rates than females. Once an aggressive interaction has been initiated, adult females are more likely than immigrant males to elicit submission from members of the opposite sex, and both adult natal and immigrant males are more likely than adult females to offer submission in response to an aggressive act. We also find that adult male aggressors are more likely to receive social support than are adult female aggressors, and that both adult natal and immigrant males are 2–3 times more likely to receive support when attacking a female than when attacking another male. Across all age classes, females are more likely than males to be targets of aggressive acts that occur with support. Further, receiving social support does slightly help immigrant males elicit submission from adult females compared to immigrant males acting alone, and it also helps females elicit submission from other females. However, adult females can dominate immigrant males with or without support far more often than immigrant males can dominate females, even when the immigrants are supported against females. Discussion Overall, we find evidence for both mechanisms hypothesized to mediate female dominance in this species: (1) male and female hyenas clearly differ in their aggressive and submissive tendencies, and (2) realized social support plays an important role in shaping dominance relationships within a clan. Nevertheless, our results suggest that social support alone cannot explain sex-biased dominance in spotted hyenas. Although realized social support can certainly influence fight outcomes among females, adult females can easily dominate immigrant males without any support at all.

Functional morphology of prey capture in stream-dwelling sailfin silversides (Telmatherinidae) based on high-speed video recordings

Article

Full-text available

Oct 2022
ZOOMORPHOLOGY

Understanding how ecology shapes the evolution of morphological traits is a major goal in organismal biology. By quantifying force of motion, hypotheses on the function of fundamental tasks of animals like feeding can be tested. Ray-finned fishes use various feeding strategies, classified into three main feeding modes: suction, ram and manipulation. While manipulation feeders are usually distinct in morphology and feeding behavior, differentiation between suction and ram feeders is often fine-scaled and transitional. Previous studies have identified different feeding modes and biomechanical adaptations on interspecific and intersexual levels in lake-dwelling sailfin silversides, species of a Sulawesi freshwater radiation. Functional feeding morphology of stream-dwelling species remained in contrast unstudied. We hypothesized that different requirements of riverine habitats favor the evolution of alternative functional adaptations in stream-dwelling sailfin silversides. To test this hypothesis, we investigated feeding of two phenotypically distinct riverine species, Telmatherina bonti and Marosatherina ladigesi, and their sexes, by high-speed videos and biomechanical models. The kinematic approaches identify T. bonti as ram feeder and M. ladigesi as suction feeder. Surprisingly, the biomechanical models of the jaw apparatus provide contradicting results: only one out of three studied parameters varies between both species. Contrarily to lake-dwelling Telmatherina, sexes of both species do not differ in feeding biomechanics. We conclude that T. bonti predominantly uses ram feeding while M. ladigesi primarily uses suction feeding as its main hunting strategy. Feeding biomechanics of stream-dwelling sailfin silversides are less distinct compared to lake-dwelling species, likely due to different trophic ecologies or less stable ecological conditions.

Variable evidence for convergence in morphology and function across avian nectarivores

Article

Sep 2022

Nectar‐feeding birds provide an excellent system in which to examine form‐function relationships over evolutionary time. There are many independent origins of nectarivory in birds, and nectar feeding is a lifestyle with many inherent biophysical constraints. We review the morphology and function of the feeding apparatus, the locomotor apparatus, and the digestive and renal systems across avian nectarivores with the goals of synthesizing available information and identifying the extent to which different aspects of anatomy have morphologically and functionally converged. In doing so, we have systematically tabulated the occurrence of putative adaptations to nectarivory across birds and created what is, to our knowledge, the first comprehensive summary of adaptations to nectarivory across body systems and taxa. We also provide the first phylogenetically informed estimate of the number of times nectarivory has evolved within Aves. Based on this synthesis of existing knowledge, we identify current knowledge gaps and provide suggestions for future research questions and methods of data collection that will increase our understanding of the distribution of adaptations across bodily systems and taxa, and the relationship between those adaptations and ecological and evolutionary factors. We hope that this synthesis will serve as a landmark for the current state of the field, prompting investigators to begin collecting new data and addressing questions that have heretofore been impossible to answer about the ecology, evolution, and functional morphology of avian nectarivory. This article is protected by copyright. All rights reserved.

Contamination effects on sexual selection in wild dung beetles

Article

Jun 2022
J EVOLUTION BIOL

Sexual selection influences the expression of secondary sexual traits, which are costly to produce and maintain and are thus considered honest indicators of individual con-dition. Therefore, sexual selection could select for high-quality individuals able to re-spond to stressful conditions, with impacts on population- level fitness. We sampled dung beetles from 19 pastures and investigated if contamination by herbicides and veterinary drugs modifies male investment in sexually selected traits and has asso-ciated population- level effects. We measured horn size, condition dependence (i.e. size-corrected body mass) and allometry, besides abundance and sexual size dimor-phism in three species: Copris incertus, Euoniticellus intermedius and Digitonthophagus gazella. In contrary to our expectations, horn size was independent of contamination and individual condition. However, strong positive allometric relationships were re-duced by herbicide contamination for C. incertus and D. gazella and were increased by ivermectin for C. incertus, revealing differential investment in horn production ac-cording to body size in contaminated habitats. At the population level, large- horned C. incertus males were more abundant in contaminated pastures, potentially revealing a case of evolutionary rescue by sexual selection or a plastic response to higher popu-lation densities. Finally, chemical compounds affected the sexual size dimorphism of all three species, with potential effects on female fecundity or intrasexual selection. Together, our findings indicate that contamination interferes with sexual selection processes in the wild, opening new questions regarding the role of sexual selection in favouring species persistence in contaminated environments.

Large eastern grey kangaroo males are dominant but do not monopolize matings

Article

Full-text available

Jun 2022
BEHAV ECOL SOCIOBIOL

Group-living species are often organized into social dominance hierarchies, where high-ranking individuals have priority of access to resources, including estrous females. Traits associated with male dominance status should thus be correlated with reproductive success, but, with the exception of research on some primates, studies with both behavioral data to determine dominance hierarchies and a pedigree to identify male siring success are rare. For a wild population of sexually dimorphic eastern grey kangaroos Macropus giganteus, we characterized the social hierarchy over 6 non-consecutive years to investigate the relationship between male dominance and yearly reproductive success. Dominance hierarchies were steep, linear, and stable over time. Asymmetries in body mass and size between contestants were strong predictors of contest outcomes, and these morphological traits were positively correlated with dominance status. Males did not spatially avoid each other but tended to fight with individuals of similar size, suggesting that when asymmetries were large, contests were unlikely. Dominance status was under strong sexual selection, despite moderate monopolization of paternities by highly dominant males. Overall, these results suggest that body size and weapons are important determinants of dominance status and male reproductive success but that other traits play a considerable role. A clear-cut dominance hierarchy and strong selection on dominance status do not necessarily lead to monopolization of reproduction by the most dominant males in this strongly sexually dimorphic species.

Aggressive behaviour in the skyhoppers of the Australian Alps

Article

Full-text available

Aug 2022
EVOL ECOL

The evolution of male-male aggression is of interest because at its extreme it can be very energetically costly, leave males vulnerable to preadtors, and give rise to weaponry such as exaggerated traits. In grasshoppers (Acrididae), one group stands out as exceptionally aggressive, the skyhoppers ( Kosciuscola ) in which males bite, kick, mandible flare, and wrestle each other for access to females or when females are laying eggs. In this study we asked whether there is variation in aggressive behaviour among four skyhopper species and aimed to determine whether the traits used in fighting bear signatures of sexual selection in their size, variability, and allometric scaling. We found clear differences in the numbers and types of aggressive behaviours among species. Kosciuscola tristis and K. usitatus were the most aggressive, K. cognatus was the least aggressive, and K. tristis was the only species that performed the ‘mandible flare’ behaviour. Mandible size was larger among the three species that showed aggressive behaviour, all except K. cognatus , and was negatively allometric for all species possibly suggesting a functional size constraint. Pronotum size was different among most species and K. tristis ’ pronotum was the largest and borderline positively allometric perhaps suggesting that pronotum size is related to aggressive behaviour but the nature of that relationship remains obscured. Our study suggests that further work investigates skyhoppers’ aggressive behaviour and how it varies with ecology, and paves the way for establishing them as a model system in the evolution of aggressive behaviour.

Body size and canine size do not confer a competitive advantage in male rhesus macaques

Article

Mar 2022
ANIM BEHAV

Male armaments are hypothesized to have evolved under intrasexual selection. Such traits may function as signals, weapons, or both, in male–male mating competition. Primate sexually dimorphic canine teeth and body size are two potentially weaponized traits whose function as a signal and/or weapon remains unclear, largely due to the difficulty of collecting detailed measurements of morphology on large free-ranging mammals. Rhesus macaques, Macaca mulatta, are an interesting study system in which to investigate how such traits function because they experience relatively low levels of direct male–male mating competition compared to other members of their subfamily. Furthermore, male dominance rank is largely based on a queuing system rather than on the outcome of intermale aggressive encounters. We leveraged a novel data set of behavioural observations and morphometric data from free-ranging rhesus macaques to investigate the function of sexually dimorphic canine teeth and body mass as weapons and/or signals. We tested whether canine height or body mass was correlated with dominance rank, whether similarity in any of these factors influenced the occurrence or outcome of agonistic interactions between male–male dyads and whether either of these traits predicted the likelihood of winning an agonistic interaction. Neither canine height nor body mass was related to dominance rank. Similarity in dominance rank, but not in morphology, predicted the occurrence of agonism between dyads. Agonistic encounters between males more similar in dominance rank were more likely to be characterized by aggression rather than submission. Dominance rank, but not canine height or body mass, predicted the likelihood of winning an agonistic interaction. Our results suggest that canine height and body mass do not confer a strong competitive advantage in male rhesus macaques and add to a growing body of evidence indicating that weaponized traits do not always seem to function either in fights or as signals in male–male combat.

Size variation, allometry and mating success in Aotearoa|New Zealand kelp flies (Coelopidae)

Article

Full-text available

Aug 2022
EVOL ECOL

The need to respond quickly to the presence of an ephemeral resource required for breeding is often a feature of scramble competition mating systems. Scramble competition mating systems can feature extreme levels of sexual conflict and coercive mating by males. As a result, sexual selection can act on various traits used by males to overcome female resistance behaviours. Selection on these traits may result in significant intra and intersexual size variation and sexual dimorphism. Additionally, traits that influence mating success in males often show positive static allometry. Kelp flies (Coelopidae) are a small family of Diptera which specialise on wrack (beach cast marine macroalgae), a highly ephemeral resource. The mating system of these flies involves high levels of sexual conflict, with females rejecting all male mating attempts. In this study we describe intra and intersexual size variation and static allometry of traits in two of Aotearoa|New Zealand’s species, Coelopella curvipes and Chaetocoelopa littoralis . In addition, we investigate the mating behaviour of C. littoralis under ecologically relevant mating conditions. We found high levels of variation in both species with significant evidence of sexual dimorphism across all traits measured in C. littoralis, and in mid tibia length in C. curvipes . Furthermore, mid tibia length in both species exhibits positive static allometry and is disproportionally larger in larger males, suggesting that this trait in particular may be under strong sexual selection. We found that larger male C. littoralis which attempt to mate are significantly more likely to mate successfully demonstrating a large-size advantage in this species similar to findings across the Coelopidae. However, we only found a non-significant trend towards a mating advantage for males with longer mid-tibiae. We discuss these findings with reference to the population dynamics and ecology of these species.

Variation in allometry along the weapon-signal continuum

Article

Full-text available

Aug 2022
EVOL ECOL

Structures used in intrasexual competition span a continuum, with pure weapons that are used exclusively in physical fights at one extreme and pure aggressive signals that are used exclusively to assess and threaten rivals at the other. We propose this weapon-signal continuum offers a framework for understanding the variation in allometric slopes among intra-sexually selected structures. We predict allometric slopes will become steeper as the relative importance of signaling increases, because aggressive signaling will favor the evolution of hypervariable structures that facilitate the assessment of subtle differences in body size. We provide preliminary empirical support for the continuum hypothesis using species with different types of armaments and offer suggestions for how to test the weapon-signal continuum among closely related species.

Flight hampers the evolution of weapons in birds

Article

Full-text available

Mar 2022
ECOL LETT

Birds are a remarkable example of how sexual selection can produce diverse ornaments and behaviours. Specialised fighting structures like deer's antlers, in contrast, are mostly absent among birds. Here, we investigated if the birds’ costly mode of locomotion—powered flight—helps explain the scarcity of weapons among members of this clade. Our simulations of flight energetics predicted that the cost of bony spurs—a specialised avian weapon—should increase with time spent flying. Bayesian phylogenetic comparative analyses using a global spur dataset corroborated this prediction. First, extant species with flight-efficient wings (which presumably fly more frequently) tend to have fewer or no bony spurs. Second, this association likely arose because flying more leads to more frequent evolutionary loss of spurs. Together, these findings suggest that, much like pneumatic bones, absence of weaponry may be another feature of the avian body plan that allows birds to efficiently explore the aerial habitat.

Behavior, ecology and territory of the chestnut-bellied hummingbird, Saucerottia castaneiventris, in the xerophytic vegetation of the Chicamocha canyon of Colombia

Article

Full-text available

Dec 2021

The Chestnut-bellied Hummingbird Saucerottia castaneiventris is an endemic hummingbird of Colombia, currently categorized as Near Threatened (NT) globally and as Vulnerable (VU) in Colombia. We characterize the territorial defense and foraging behaviors of S. castaneiventris hummingbird during different seasons of the year, and we determined the size of the S. castaneiventris territory and its relationship with floral abundance at different times of the year. We made four field trips between 2008 and 2009 and registered 19 individuals from S. castaneiventris . Of these, 10 were in the rainy periods, distributed in five territories (one male and one female for each). Eight were in the dry period (July), distributed in four territories. And one individual was in the dry period of February, which did not settle in any of the identified territories. Territorial defense occupied a large part of species’ time. The nectar drinking, and insect hunting were the most frequent activities. The most common floral resources were Opuntia dillenii , Tillandsia sp. and Aloe vera . The hummingbirds Chlorostilbon gibsoni and Doryfera ludoviciae shared habitats with S. castaneiventris and there were fluctuations in encounter rates between the seasons ( C. gibsoni ER: 20–7.5 and D. ludoviciae and ER: 0.0–2.5). Territories ranged between 1800 and 3800 m ² for the dry season and between 1500 and 6500 m ² for the rainy season. Our results provided primary information on the ecology of S. castaneiventris and form the basis for the formulation of conservation strategies for the species and for its habitats..

Body injuries in male morphotypes of the Amazon River prawn (Macrobrachium amazonicum)

Article

Nov 2021
MAR FRESHW BEHAV PHY

Fights between individuals in a population can be motivated by several factors, such as disputes over food, shelter and sexual partners. The present study aimed to evaluate the pattern of injury occurrence in the Amazon River prawn (Macrobrachium amazonicum). Prawns and environmental factors were sampled monthly, from February 2012 to September 2013, in the Tietê River, São Paulo, Brazil. Individuals were classified into eight different demographic classes and analyzed macroscopically for body injuries, which were separated into four categories (0–4). From the 2,234 prawns collected, 124 presented one or more types of physical damages. The males of dominant castes presented the highest amount of injuries, suggesting that these groups get involved more frequently in disputes. Possibly, reproductive events are a strong stimulus for the occurrence of fights in freshwater prawns since the greatest amount of injuries was observed in the period of reproductive peaks.

A new classification of mammalian uni-male multi-female groups based on the fundamental principles governing inter- and intrasexual relationships

Article

Full-text available

Nov 2021
BEHAV ECOL SOCIOBIOL

Polygyny is the most common mating system in mammals, and many species form uni-male multi-female groups (UM-MF units). Polygynous systems are traditionally distinguished according to male reproductive strategies, such as “resource defense” or “female defense,” both of which are often described in the literature as forming “harems.” However, this focus on male strategies, and the use of umbrella terms to describe them, lumps together societies that fundamentally differ in their ontogeny, stability, and relationships. Integrating foundational theories of mating strategies with the principles governing relationship dynamics, driven by both male and female strategies and modulated by male-female conflicts of interest, we propose a new framework for classifying the diversity of UM-MF units. We differentiate UM-MF groups in terms of average female kinship within the group and length of male tenure to define general classes with distinct predictions for the nature of inter- and intrasexual relationships. We propose a narrower definition for the “true harem” along with new terminology to describe the other three classes: “benign consortship,” “coterie,” and “coercive consortship.” Using socioecological data for 40 mammalian species from 27 families, we found our framework was able to successfully predict patterns of female-female cooperation and the presence of coercive male-female relationships. Finally, we refine our framework, identifying subclasses of the main four classes and propose hypotheses about the underlying causes of observed patterns. By focusing on the nature of within group relationships, this framework provides a powerful lens for asking broad, comparative evolutionary questions about social evolution and socioecology.

Sexual selection in a sexually dimorphic species: effect of body size on reproductive success and offspring sex ratio in kangaroos

Thesis

Full-text available

Oct 2021

Luca Montana

Sexual selection is responsible for some of the most extravagant traits found in the animal kingdom, as they confer a fitness advantage in terms of access to mates. Large body size in males of many polygynous species should provide a mating advantage through its association with dominance rank and, ultimately, access to females. Recent evidence from multiple species, however, questions this generalization, suggesting instead a weak relationship between male size and reproductive success. That empirical evidence suggests a need to develop new theory to explain patterns of male reproductive success. This thesis meets this challenge by examining if and how sexual selection acts on a polygynous sexually dimorphic species. I used a combination of behavioral, morphological, spatial, and reproductive data on marked individuals from a long-term longitudinal study of eastern grey kangaroos (Macropus giganteus) to explore which ecological and demographic factors influence the association between body size and dominance, siring chances and reproductive success, and relate the effect of paternal body size to offspring sex and maternal allocation. First, I needed to understand if body size is positively associated with dominance status, as individual rank is assumed to be a decisive factor granting priority access to receptive females. By analyzing the outcome of about 2,300 male-male agonistic interactions across six years (2010-2011 and 2015-2018), chapter 2 shows that kangaroo males formed yearly linear, steep, and stable dominance hierarchies based on body size. Dominance status was, however, only moderately correlated with yearly reproductive success. This finding strongly suggests that body size is not the only factor influencing reproductive success on this species, possibly indicating weak sexual selection on body size. To determine what factors other than body size may influence siring success, I examined if males had an upper reproductive threshold set by their mating opportunity. If a male does not encounter a female, he cannot father her offspring. Most studies of sexual selection, however, assume that all males in a population have equal access to all females. Chapter 3 thus uses spatial data collected over 9 years (2010-2018) to show that ecological variables such as mating opportunity, quantified by the spatial overlap between each male-female pair, residency on the breeding site, and an accurate estimation of the competitive environment influence individual siring chances. Next, I quantified sexual selection on body size, its fluctuation across years and according to mating opportunity and residency, and the strength of reproductive inequality. Chapter 4 shows that sexual selection was overall stabilizing and there was no evidence of temporal fluctuation or fluctuation caused by mating opportunity, and only limited variation caused by differences in residency. Despite weak reproductive inequality, sexual selection acted strongly on body size. Finally, I redirected my attention to recent findings showing that fathers can influence offspring sex and maternal allocation. Chapter 5 thus examined if paternal body size, which is strongly sexually selected, affected offspring sex ratio or maternal differential allocation. The results indicated that maternal and paternal influences modulated each other, as light mothers conceived sons when the father was heavy, conversely, heavy mothers conceived sons when the father was light. Maternal sex-specific allocation was independent of paternal size. I found that despite a stable linear social hierarchy, the most dominant males did not monopolize paternities, possibly because they did not have the opportunity to do so. It is important to emphasize that strong sexual selection does not necessarily lead to contemporary high variance in reproduction, as the phenotypes selected will determine the strength of selection. By reporting a rare occurrence of non-linear sexual selection on body size experienced by a sexually dimorphic species, this thesis underlines the necessity of simultaneous study of pre- and post-copulatory sexual selection. Moreover, it provides a solid contribution to our understanding of sexual selection by highlighting the importance of underrated ecological and demographic factors such true mating opportunity, generated by spatial overlap, and effective number of competitors faced by each male.

Sizing Up Swords: Correlated Evolution of Antlers and Tusks in Ungulates

Preprint

Full-text available

Aug 2021

Most sexual weapons in sexual combat and visual displays of dominance (e.g., antlers, horns) show positively allometry with body size for both growth during development and evolution across species, but allometry in species with more than one sexual weapon is unstudied. We examined the allometric relationships between body size and tusks (pure combat weapons) and/or antlers (both a visual signal and combat weapon) from forty-three artiodactyl species including the muntjaks (Muntiacinae), which uniquely have both antlers and tusks. We found that in Muntiacinae antler length scales positively allometrically with skull length, whereas tusk size scales isometrically suggesting greater energy investment in antlers as signals over tusks as combative weapons when both are present. Interspecifically, we found that species who possess only one weapon (either solely tusked or solely antlered) scaled positively allometrically with body mass, and the latter relationship levels off at larger body sizes. In our tusk analysis, when we included Muntiacinae species the positive allometric trend was not conserved resulting in an isometric relationship suggesting the possession of antlers negatively affect the energy investment in tusks as weapons. Overall, our findings show that species that possess dual weapons unproportionally invest energy in the development and maintenance of their multiple weapons.

Interactions Between Figs and Gall-Inducing Fig Wasps: Adaptations, Constraints, and Unanswered Questions

Article

Full-text available

Aug 2021

Renee Borges

The ancient interaction between figs (Ficus, Moraceae) and their pollinating fig wasps is an unusual example of a mutualism between plants and gall-inducing insects. This review intends to offer fresh perspectives into the relationship between figs and the diversity of gall-inducing sycophiles which inhabit their enclosed globular inflorescences that function as microcosms. Besides gall-inducing pollinators, fig inflorescences are also inhabited by other gall-inducing wasps. This review evaluates the state of current knowledge on gall-induction by fig wasps and exposes the many lacunae in this area. This review makes connections between fig and gall-inducing wasp traits, and suggests relatively unexplored research avenues. This manuscript calls for an integrated approach that incorporates such diverse fields as life-history theory, plant mate choice, wasp sexual selection and local mate competition, plant embryology as well as seed and fruit dispersal. It calls for collaboration between researchers such as plant developmental biologists, insect physiologists, chemical ecologists and sensory biologists to jointly solve the many valuable questions that can be addressed in community ecology, co-evolution and species interaction biology using the fig inflorescence microcosm, that is inhabited by gall-inducing mutualistic and parasitic wasps, as a model system.

Damage from intraspecific combat is costly

Article

Aug 2021

When individuals engage in fights with conspecifics over access to resources, injuries can occur. Most theoretical models suggest that the costs associated with these injuries should influence an individual’s decision to retreat from a fight. Thus, damage from intraspecific combat is frequently noted and quantified. However, the fitness-related costs associated with this damage are not. Quantifying the cost of fighting-related damage is important because most theoretical models assume that it is the cost associated with the damage (not the damage itself) that should influence an individual’s decision to retreat. Here, we quantified the cost of fighting-related injuries in the giant mesquite bug, Thasus neocalifornicus. We demonstrate that experimentally simulated fighting injuries result in metabolic costs and costs to flight performance. We also show that flight costs are more severe when the injuries are larger. Overall, our results provide empirical support for the fundamental assumption that damage acquired during intraspecific combat is costly.

Sexual size dimorphism and life history traits in an island-mainland system: an overview of the lizard genus Microlophus

Article

Full-text available

Jul 2021

Opposing life history strategies are a common result of the different ecological settings experienced by insular and continental species. Here we present a comprehensive compilation of data on sexual size dimorphism (SSD) and life history traits of Microlophus , a genus of lizards distributed in western South America and the Galápagos Islands, and test for differences between insular and continental species under life history theory expectations. Contrary to our predictions, we found no differences in SSD between localities or evidence that Microlophus follows Rensch’s rule. However, as expected, head dimensions and maturity sizes were significantly larger in insular species while continental species had larger clutches. Our results show that Microlophus exhibits some of the patterns expected from an island-mainland system, but unexplained patterns will only be resolved through future ecological, morphological and behavioural studies integrating both faunas.

Exaggerated sexually selected weapons maintained with disproportionately low metabolic costs in a single species with extreme size variation

Article

Jul 2021

Larger individuals typically have lower mass‐specific metabolic rates compared to small ones (hypometric scaling). This trend is most evident across species where body‐size differences can be extreme. Yet, within‐species studies are critical to decipher the morphological and physiological mechanisms responsible. However, the relatively small range in body and appendage size found within many species of the same life‐stage often precludes such intra‐specific comparisons. Sexually selected weapons are among the most exaggerated traits in nature; these traits can account for a large portion of body mass and contribute to whole‐body energetic maintenance costs. Often larger individuals possess disproportionally larger weapons relative to their body size, yet little is known about how large individuals meet the predicted increased energetic demands of maintaining disproportionately large weapons. New Zealand giraffe weevils, Lasiorhyncus barbicornis (Coleoptera:Brentidae) exhibit an extreme 30‐fold range in male body mass as well as hypermetric scaling of sexually selected rostra used as weapons in male‐male competition. We compare intra‐ and inter‐specific resting metabolic rates by compiling measurements across 26 arthropod species whose size ranges overlap with L. barbicornis. The scaling of metabolic rate across this pooled interspecific sample was not significantly different from the intraspecific scaling of metabolic rate we found in L. barbicornis (slope of log‐log relationship with body mass = 0.67). Male and female L. barbicornis had a similar scaling of metabolic rate with body size, despite differing substantially in the scaling of rostra, legs and antennae. However, large structures that scaled with positive allometry in males (rostra and legs) were increasingly composed of cuticle in larger individuals. The largest males invest ~60% less metabolically active tissue into rostra (weapons) compared to the smallest males. Our findings reveal hypometric scaling relationships of inter‐ and intra‐specific metabolic rates across a shared size range in a diverse group of arthropods. Our intraspecific study uncovers a tremendous difference in weapon architecture as individuals scale up in size; we find that large males bear disproportionally larger weapons at a lower relative metabolic cost. This cost‐saving mechanism may play a key role in shaping the hypermetric scaling of sexually selected traits.

Mechanoethology: The Physical Mechanisms of Behavior

Article

Full-text available

Jun 2021

Research that integrates animal behavior theory with mechanics—including biomechanics, physiology, and functional morphology—can reveal how organisms accomplish tasks crucial to their fitness. Despite the insights that can be gained from this interdisciplinary approach, biomechanics commonly neglects a behavioral context and behavioral research generally does not consider mechanics. Here, we aim to encourage the study of “mechanoethology,” an area of investigation intended to encompass integrative studies of mechanics and behavior. Using examples from the literature, including papers in this issue, we show how these fields can influence each other in three ways: 1) the energy required to execute behaviors is driven by the kinematics of movement, and mechanistic studies of movement can benefit from consideration of its behavioral context; 2) mechanics sets physical limits on what behaviors organisms execute, while behavior influences ecological and evolutionary limits on mechanical systems; and 3) sensory behavior is underlain by the mechanics of sensory structures, and sensory systems guide whole-organism movement. These core concepts offer a foundation for mehanoethology research. However, future studies focused on merging behavior and mechanics may reveal other ways by which these fields are linked, leading to further insights in integrative organismal biology.

Developmental Nutrition Affects the Structural Integrity of a Sexually Selected Weapon

Article

Jun 2021

Males in many species engage in physical combat over access to mates, and sexual selection has led to the evolution of weapons to enhance contest performance. The size of these often-elaborate structures is known to be exquisitely sensitive to nutrition. However, we know very little about the degree to which nutrition affects other attributes of animal weapons that can be crucial to fighting. In this study, we investigated the impact of natural dietary variation on weapon structural integrity in a fighting insect, Narnia femorata (Hemiptera: Coreidae). Males in this species display their enlarged, spiny hind legs to other males, and these legs serve as weapons in aggressive physical contests where they are used to strike and squeeze opponents. N. femorata feeds on the fruit of prickly pear cactus and sets up territories on this plant. In North Central Florida the prickly pear Opuntia mesacantha spp. lata blooms and begins to produce fruits in April and May. N. femorata has multiple, overlapping generations while the green fruits slowly ripen over the next several months. We examined insects reaching adulthood at two nearby time points in this range, June and July, to test the influence of the nutrition provided by ripening green cactus fruit on weapon size and its ability to resist puncture. We also raised insects on cactus with red, ripe fruit for comparison. We found a striking effect of cactus fruit phenology on weapons. Insects raised with the more mature green fruit (those in the second cohort) had 71% larger weapon area and 4.4 times greater puncture resistance than those raised on the early green fruit (those in the first cohort). In contrast, insects raised on red, ripe fruit were moderate in size, had high puncture resistance, and they changed little phenotypically from the first to second cohort. Increased structural integrity of the hind femur weapon was associated with the increased body size that came with better nutrition. This pattern highlights that cuticle thickness increased or its material properties changed when weapons were larger. Importantly, effects of nutrition on puncture resistance also transcended size. Insects of the same size had greater structural integrity if they received superior nutrition. Sexually selected weapons are often used as visual signals to conspecifics before fights, and this work hints that the size of the weapons may be a poor signal of weapon performance when nutrition is variable.

Bene“fit” Assessment in Pollination Coevolution: Mechanistic Perspectives on Hummingbird Bill–Flower Matching

Article

Full-text available

May 2021
INTEGR COMP BIOL

One of the reasons why flowering plants became the most diverse group of land plants is their association with animals to reproduce. The earliest examples of this mutualism involved insects foraging for food from plants and, in the process, pollinating them. Vertebrates are latecomers to these mutualisms, but birds, in particular, present a wide variety of nectar-feeding clades that have adapted to solve similar challenges. Such challenges include surviving on small caloric rewards widely scattered across the landscape, matching their foraging strategy to nectar replenishment rate, and efficiently collecting this liquid food from well-protected chambers deep inside flowers. One particular set of convergent traits among plants and their bird pollinators has been especially well studied: the match between the shape and size of bird bills and ornithophilous flowers. Focusing on a highly specialized group, hummingbirds, we examine the expected benefits from bill-flower matching, with a strong focus on the benefits to the hummingbird and how to quantify them. Explanations for the coevolution of bill-flower matching include 1) that the evolution of traits by bird-pollinated plants, such as long and thin corollas, prevents less efficient pollinators (e.g., insects) from accessing the nectar, and 2) that increased matching, as a result of reciprocal adaptation, benefits both the bird (nectar extraction efficiency) and the plant (pollen transfer). In addition to nectar feeding, we discuss how interference and exploitative competition also play a significant role in the evolution and maintenance of trait matching. We present hummingbird-plant interactions as a model system to understand how trait matching evolves and how pollinator behavior can modify expectations based solely on morphological matching, and discuss the implications of this behavioral modulation for the maintenance of specialization. While this perspective piece directly concerns hummingbird-plant interactions, the implications are much broader. Functional trait matching is likely common in coevolutionary interactions (e.g., in predator-prey interactions), yet the physical mechanisms underlying trait matching are understudied and rarely quantified. We summarize existing methods and present novel approaches that can be used to quantify key benefits to interacting partners in a variety of ecological systems.

Do sexually selected weapons drive diversification?

Article

Mar 2021

Sexual selection is often thought to promote speciation. This expectation is largely driven by the fact that sexually selected traits can influence mating patterns and contribute to reproductive isolation. Indeed, some comparative studies have shown that clades with sexually selected traits have increased rates of speciation and diversification. However, these studies have almost exclusively focused on one mechanism of sexual selection: female choice. Another widespread mechanism is male‐male competition. Few empirical studies (if any) have investigated the role of this alternative mechanism in driving diversification. Nevertheless, recent reviews have suggested that male‐male competition can increase speciation rates. Here, we investigated whether traits associated with precopulatory male‐male competition (i.e. sexually selected weapons) have promoted speciation and diversification in insects. We focused on three clades with both weapons and suitable phylogenies: leaf‐footed and broad‐headed bugs (Coreidae+Alydidae; ∼2,850 species), stick insects and relatives (Phasmatodea; ∼3,284 species), and scarab beetles (Scarabaeoidea; ∼39,717 species). We found no evidence that weapon‐bearing lineages in these clades have higher rates of speciation or diversification than their weaponless relatives. Thus, our results suggest that precopulatory male‐male competition may not have strong, general effects on speciation and diversification in insects, a group encompassing ∼60% of all described species. This article is protected by copyright. All rights reserved

Complex vocal learning and three-dimensional mating environments

Article

Full-text available

Apr 2021
BIOL PHILOS

Jan Verpooten

Complex vocal learning, the capacity to imitate new sounds, underpins the evolution of animal vocal cultures and song dialects and is a key prerequisite for human speech and song. Due to its relevance for the understanding of cultural evolution and the biology and evolution of language and music, the trait has gained much scholarly attention. However, while we have seen tremendous progress with respect to our understanding of its morphological, neurological and genetic aspects, its peculiar phylogenetic distribution has remained elusive. Intriguingly, animals as distinct as hummingbirds and humpback whales share well-developed vocal learning capacity in common with humans, while this ability is quite limited in nonhuman primates. Yet, solving this ‘vocal learning conundrum’ may shed light on the constraints ancestral humans overcame to unleash their vocal capacities. To this end I consider major constraints and functions that have been proposed. I highlight an especially promising ecological constraint, namely the spatial dimensionality of the environment. Based on an informal comparative review, I suggest that complex vocal learning is associated with three-dimensional habitats such as air and water. I argue that this is consistent with recent theoretical advances—i.e., the coercion-avoidance and dimensionality hypotheses—and with the long-standing hypothesis that mate choice is a major driver of the evolution and origin of complex vocal learning. However, I stress that multiple functions may apply and that quantitative phylogenetic comparative methods should be employed to finally resolve the issue.

Age estimation of camel in Nigeria using rostral dentition A R T I C L E I N F O

Article

Full-text available

Jan 2013

The study aimed at providing information in estimating the age of camel using rostral dentition through the phenomenon of teeth eruption and wearing, thought, only way to age an animal accurately is to know the date of birth but where these records are not available various anatomical features are used to estimate age. A total of 1100 camels of both sex were used for the purpose of the study. Records were obtained between April to July 2010 on daily visit to the Sokoto metropolitan abattoir. Investigation showed that at birth, there were no teeth, at 9 month, all the deciduate teeth have erupted. At 4 years, all the deciduate incisors and canine have worn down. At 7 years, all the permanent incisors and canine teeth have erupted. At 12 years, all the permanent incisors are in wear, while At 15 years, all the permanent incisors and canine teeth have worn down. At 20 years, all the permanent teeth are down and clearly separated from each other.

Age estimation of camel in Nigeria using rostral dentition A R T I C L E I N F O

Article

Full-text available

Jan 2013

Patterns of cranial sexual dimorphism in the yellow-bellied toad (Bombina variegata, Bombinatoridae)

Article

Full-text available

Jun 2018
NORTH-WEST J ZOOL

This study provides first insight into patterns of adult cranial size and shape sexual dimorphism in the yellow-bellied toad (Bombina variegata). Our results revealed significant cranial sexual size and shape differences in this species, with a very small impact of allometry on the shape diversity. The pattern of cranial sexual dimorphism indicates early differentiation of the sexes followed by parallel growth trajectories. Males have a larger cranium than females. Shape differences between the sexes are pronounced in the trophic part of the cranium. In comparison to females males have the lateral part of the nasal displaced posteriorly, a shorter anterior pterygoid process and the posterior part of the quadratojugal and pterygoid displaced toward the snout. Therefore, males have a wider but shorter posterior part of the cranium. Adaptation to divergent trophic niches driven by natural selection rather than sexual selection could have led to sexual size and shape differences in the yellow-bellied toad. However, further analysis of cranial variation patterns including ontogenetic aspects of cranial variation and ecological niche analyses are crucial to elucidate how different developmental and evolutionary mechanisms act on the cranium and result in size and shape sexual dimorphism.

Combat in a cave-dwelling wētā (Orthoptera: Rhaphidophoridae) with exaggerated weaponry

Article

Full-text available

Apr 2018

Animals sometimes possess extraordinarily enlarged or specialized structures used as weaponry for intrasexual combat. The way in which an animal's mating system leads to the diversity of exaggerated armaments we see in nature is a matter of current and ongoing research. Central to this enquiry is the question of how animal weapons are involved in assessment: how, when and why is the decision made to retreat from a contest by combatants fighting over their future fertilization success? We investigated the agonistic role of highly elongated male hindlegs in an Orthopteran insect found in dense aggregations in New Zealand caves: the cave wētā, Pachyrhamma waitomoensis (Rhaphidophoridae). We found a large degree of sexual dimorphism in the hindlegs. In contests among males in the field, males with longer hindlegs were more likely to win contests, while body size did not influence contest outcome. We also assessed the influence of winner, loser and relative hindleg length on contest escalation, finding that fights among males with greater differences in leg length were resolved by less-escalated contests. In addition, the level of contest escalation was positively correlated with the loser's, but not the winner's, leg length, matching the predictions of self-only models of animal assessment.

While males fight, females choose: male phenotypic quality informs female mate choice in mammals

Article

Full-text available

Apr 2018

Theoretical support exists for an exaggerated male structure to serve as both a weapon for intrasexual competition and as an ornament to signal quality and promote female choice. However, there is little, if any, evidence to support this theory in maleemale competition breeding systems. Using white-tailed deer, Odocoileus virginianus, as a model species, we manipulated antler size on males while controlling for body size and age and allowed 25 oestrous females the opportunity to choose between pairs of segregated males with either large or small antlers. By segregating males, we were able to remove any intrasexual male competition and isolate the effects of female choice. Using various behavioural indications of female choice, we demonstrate that females prefer males with large antlers to those with small antlers. Because antler size is heritable in deer, this female preference for larger antlers may be adaptive by increasing the reproductive success of her male offspring. Our unique antler manipulation study supports the armament-ornament model where male weapons can simultaneously serve as ornaments to females and weapons in maleemale competition breeding systems.

Is there evidence for a trade-off between sperm competition traits and forelimb musculature in the western grey kangaroo?

Article

Full-text available

Feb 2018

Males may use tactics before, during and after mating to increase their reproductive success. With finite energy resources available, theory predicts that there should be a trade-off between investment in pre-copulatory traits (e.g. body size, armaments) and post-copulatory traits (e.g. testes size, spermatogenic efficiency). Western grey kangaroos (Macropus fuliginosus) are found in large, labile mixed-sex groups, in which the males show a dominance hierarchy. Males show indeterminate growth, and will reach up to six times the body mass of females. While the largest males use their size as a reproductive advantage, forelimb musculature further aids male-male contest, female attraction and/or female coercion. Under a trade-off scenario, we therefore predicted that larger, more muscular males would show less investment in sperm competitive traits. Consistent with this prediction, more muscular males showed decreased spermatozoa velocity. However, muscularity was also positively correlated with mass of two pairs of bulbourethral accessory glands, as well as mass of the penis and its muscles of erection. Seasonal changes in muscularity and accessory gland masses were also evident. Male kangaroos therefore invest in multiple reproductive traits on which selection can work.

The evolution of tail weaponization in amniotes

Article

Full-text available

Jan 2018

Weaponry, for the purpose of intraspecific combat or predator defence, is one of the most widespread animal adaptations, yet the selective pressures and constraints governing its phenotypic diversity and skeletal regionalization are not well understood. Here, we investigate the evolution of tail weaponry in amniotes, a rare form of weaponry that nonetheless evolved independently among a broad spectrum of life including mammals, turtles and dinosaurs. Using phylogenetic comparative methods, we test for links between morphology, ecology and behaviour in extant amniotes known to use the tail as a weapon, and in extinct taxa bearing osseous tail armaments. We find robust ecological and morphological correlates of both tail lashing behaviour and bony tail weaponry, including large body size, body armour and herbivory, suggesting these life-history parameters factor into the evolution of antipredator behaviours and tail armaments. We suggest that the evolution of tail weaponry is rare because large, armoured herbivores are uncommon in extant terrestrial faunas, as they have been throughout evolutionary history.

The Behavior and Reproductive Physiology of a Solitary Progressive Provisioning Vespid Wasp: Evidence for a Solitary-Cycle Origin of Reproductive Castes

Article

Full-text available

Jan 2018

The emergence of queens and workers from solitary antecedents mark a major evolutionary transition in the history of life. The solitary progressive provisioning wasp Synagris cornuta, a member of the subfamily Eumeninae (basal to eusocial vespid wasps), alternates between behavioral states characterized as queenlike and worker-like. Akin to a queen in eusocial wasps, a S. cornuta female initiates construction of a cell into which she oviposits and then, similar to a worker, cares for the brood as it develops. The ovarian groundplan (OGP) hypothesis for caste origins predicts that these behavioral states are associated with cyclical changes in ovarian status, where females performing queenlike tasks have eggs and those performing worker-like tasks possess only small oocytes. Our findings show strong support for the OGP hypothesis: the ovaries of S. cornuta females undergo differential oogenesis depending on the behavioral phase: the largest oocyte in the ovaries of females building a cell progresses faster compared to that of females attending brood. Yet contrary to the OGP hypothesis, neither juvenile hormone nor ecdysteroids is associated with the reproductive cycle. Finally, the cuticular hydrocarbon profile showed no link with ovarian status, suggesting that fertility signals evolved subsequent to the emergence of group living.

Immune function and the decision to deploy weapons during fights in the beadlet anemone Actinia equina

Article

Full-text available

Dec 2017

The ability to mitigate the costs of engaging in a fight will depend on an individual's physiological state. However, the experience of fighting itself may in turn affect an individual's state, especially if the fight results in injury. Previous studies found a correlation between immune state and fighting success, but the causal direction of this relationship remains unclear. Does immune state determine fighting success? Or does fighting itself influence subsequent immune state? Using the beadlet anemone Actinia equina, we disentangle the cause and effect of this relationship, measuring immune response once pre-fight and twice post-fight. Contrary to previous findings, pre-fight immune response did not predict fighting success, but rather predicted whether an individual used its weapons during the fight. Furthermore, weapon use and contest outcome significantly affected post-fight immune response. Individuals that used their weapons maintained a stable immune response following the fight, while those that fought non-injuriously did not. Furthermore, although winners suffered a similar reduction in immune response to losers immediately post-fight, winners began to recover pre-fight levels within 24 hours. Our findings indicate that immune state can influence strategic fighting decisions and moreover that fight outcome and the agonistic behaviours expressed can significantly affect subsequent immunity.

Sexual Dimorphism in the Lampshade Spider Hypochilus thorelli (Araneae: Hypochilidae)

Article

Full-text available

Sep 2017

Recent comparative analyses of sexual size dimorphism in web-building spiders have not included data from the Hypochilidae, an ancient group of spiders in which half of the species have geographic distributions that are restricted to the Appalachian Mountains. Females are slightly larger than males as measured by cephalothorax width, but male leg 1 is much longer than that of females. We document the development of this dimorphism in the field and discuss the possible adaptive significance of this trait.

A short note on the use of humeral spines in combat in Espadarana prosoblepon (Anura: Centrolenidae).

Article

Full-text available

Jan 2014

Alexander Krohn

Selection on an extreme weapon in the frog legged leaf beetle (Sagra femorata)

Article

Full-text available

Aug 2017
EVOLUTION

Biologists have been fascinated with the extreme products of sexual selection for decades. However, relatively few studies have characterized patterns of selection acting on ornaments and weapons in the wild. Here, we measure selection on a wild population of weapon-bearing beetles (frog legged leaf beetles: Sagra femorata) for two consecutive breeding seasons. We consider variation in both weapon size (hindleg length), and in relative weapon size (deviations from the population average scaling relationship between hindleg length and body size), and provide evidence for directional selection on weapon size per se and stabilizing selection on a particular scaling relationship in this population. We suggest that whenever growth in body size is sensitive to external circumstance such as nutrition, then considering deviations from population-level scaling relationships will better reflect patterns of selection relevant to evolution of the ornament or weapon than will variation in trait size per se. This is because trait-size versus body-size scaling relationships approximate underlying developmental reaction norms relating trait growth with body condition in these species. Heightened condition-sensitive expression is a hallmark of the exaggerated ornaments and weapons favored by sexual selection, yet this plasticity is rarely reflected in the way we think about – and measure – selection acting on these structures in the wild. This article is protected by copyright. All rights reserved

ALLOMETRIC PREDICTION OF LIVE WEIGHT IN THE ALPACA

Article

Full-text available

Jan 1987

Divergent competitive phenotypes between females of two sex-role-reversed species

Article

Full-text available

Jun 2017
BEHAV ECOL SOCIOBIOL

Sara Lipshutz

Divergent phenotypes between lineages in the early stages of speciation can promote or impede reproductive isolation. Although divergence in male competitive morphology and behavior has been explored for many hybridizing lineages, it is less known how divergence between females influences hybridization. Here, I compare competitive phenotypes between females of two hybridizing, sex-role-reversed jacana species in Panama. Previous work suggests Jacana spinosa females monopolize mating in the hybrid zone, potentially through a competitive advantage. I tested whether J. spinosa females have a more competitive phenotype than Jacana jacana females. I compared morphological traits related to territoriality and measured aggressive behavior using territorial intrusion simulations: the first aggression assay in a shorebird. I also quantified these traits in males, to confirm previous studies reporting males as smaller and less aggressive than females in both species. As predicted, J. spinosa females had larger body mass and longer wing spurs than J. jacana females. J. spinosa females were also more aggressive than J. jacana females. Male J. spinosa had longer wing spurs than male J. jacana, but there was no difference in male body mass between the species, and J. spinosa males were more aggressive than J. jacana males. Additionally, male J. spinosa was more aggressive than female J. spinosa, suggesting mixed support for females as competitively dominant to males and indicating the need for additional experimental work on sex differences in Jacana. Significance statement Historically, research on the role of mating behavior in hybridization has focused on competitive males and choosy females. Although female-female competition is widespread and has important fitness consequences for many species across numerous taxa, little is known about the role of female competition in mediating hybridization between closely related lineages. I compare morphological and behavioral traits related to competition between two hybridizing species of jacanas, tropical shorebirds with sex-role reversal. I find that J. spinosa females have a more competitive morphological phenotype and higher aggression than J. jacana females, which may allow them a competitive advantage in obtaining and defending territories and mates in the hybrid zone. These patterns align with a pattern of asymmetrical introgression of J. spinosa mitochondrial DNA previously described in the hybrid zone, as well as findings from other hybrid zones in which male-male competition can potentially explain asymmetric patterns of gene flow from the more dominant species into the less dominant species.

Sexual dimorphism in osteoderm expression and the role of male intrasexual aggression

Article

Full-text available

Jun 2017
BIOL J LINN SOC

The functional significance of osteoderms, body plates embedded in the skin of various extinct and extant tetrapods, has been studied widely in the past, leading to the advancement of a plethora of hypotheses to explain their presence. Whereas the emphasis of most studies is on the role of osteoderms as protection against predators, alternative hypotheses remain largely unexplored. This study investigates whether male intrasexual aggression might contribute to variation in osteoderm expression, using the Cape cliff lizard Hemicordylus capensis as model organism. Micro-computed tomography was used to examine ontogenetic variation and sexual dimorphism in osteoderm expression in two study populations that were assumed to display contrasting levels of male aggression. Our results show that osteoderms in the trunk develop at the onset of sexual maturity, or after, in a lateral to medial fashion. A clear difference in osteoderm volume between males and females was detected, with osteoderm volume being significantly higher in males than in females, regardless of locality. Higher levels of intrasexual aggression, inferred from bite force data, appear to be present in individuals from the southern locality, and this appears to coincide with high osteoderm expression. In summary, although osteoderm expression has long been regarded a result of natural selection, our findings suggest that these structures might instead be sexually selected.

Relating form to function in the hummingbird feeding apparatus

Article

Full-text available

Jun 2017

Alejandro Rico-Guevara

A complete understanding of the feeding structures is fundamental in order to study how animals survive. Some birds use long and protrusible tongues as the main tool to collect their central caloric source (e.g., woodpeckers and nectarivores). Hummingbirds are the oldest and most diverse clade of nectarivorous vertebrates, being a perfect subject to study tongue specializations. Their tongue functions to intraorally transport arthropods through their long bills and enables them to exploit the nectarivorous niche by collecting small amounts of liquid, therefore it is of vital importance to study its anatomy and structure at various scales. I focused on the portions of the hummingbird tongue that have been shown to be key for understanding their feeding mechanisms. I used histology, transmission and scanning electron microscopy, microCT, and ex-vivo experiments in order to advance the comprehension of the morphology and functioning of the hummingbird feeding apparatus. I found that hummingbird tongues are composed mainly of thin cornified epithelium, lack papillae, and completely fill the internal cast of the rostral oropharyngeal cavity. Understanding this puzzle-piece match between bill and tongue will be essential for the study of intraoral transport of nectar. Likewise, I found that the structural composition and tissue architecture of the tongue groove walls provide the rostral portion of the tongue with elastic properties that are central to the study of tongue-nectar interactions during the feeding process. Detailed studies on hummingbirds set the basis for comparisons with other nectar-feeding birds and contribute to comprehend the natural solutions to collecting liquids in the most efficient way possible.

SEXUAL SELECTION ON BODY SIZE AND SHAPE IN THE WESTERN HARVESTER ANT, POGONOMYRMEX OCCIDENTALIS CRESSON

Article

Full-text available

Apr 1999
EVOLUTION

Mating in social insects has generally been studied in relation to reproductive allocation and relatedness. Despite the tremendous morphological diversity in social insects, little is known about how individual morphology affects mating success. We examined the correlation of male size and shape with mating success in the western harvester ant, Pogonomyrmex occidentalis. Larger males had significantly higher mating success in two independent collections of males at mating aggregations. We also detected significant linear and nonlinear selection on aspects of male shape that were consistent across years. These shape components are independent of size, suggesting that male mating success is a complex function of size and shape. Successful males had elongate thoraxes and short mandibles relative to males collected at random at the lek. Overall, mated males also had longer postpetioles relative to body size, but there was also evidence of nonlinear selection on relative postpetiole length in both years. We found no evidence of assortative mating based on size or multivariate shape measures in either year, but in one year we found weak assortative mating based on some univariate traits.

THE SOCIAL SIGNIFICANCE OF AVIAN WINTER PLUMAGE VARIABILITY

Article

Full-text available

Dec 1975
EVOLUTION

Sievert Rohwer

Mites: Ecology, Evolution and Behaviour

Book

Sep 1999

European Earwig Forficula auricularia Linnaeus (Insecta: Dermaptera: Forficulidae): EENY483/IN875, 10/2010

Article

Nov 2010

John L. Capinera

EENY-483, a 6-page illustrated fact sheet by John L. Capinera, is part of the Featured Creatures collection. It describes this predatory, omnivorous insect with pincer-like cerci (forceps) – distribution, description and life cycle, behavior, hosts, damage, and management. Includes references. Published by the UF Department of Entomology and Nematology, October 2010. EENY483/IN875: European Earwig Forficula auricularia Linnaeus (Insecta: Dermaptera: Forficulidae) (ufl.edu)

Age estimation of camel in Nigeria using rostral dentition A R T I C L E I N F O

Article

Jan 2013

CHARACTER DISPLACEMENT IN AUSTRALIAN DASYURID CARNIVORES: SIZE RELATIONSHIPS AND PREY SIZE PATTERNS

Article

Dec 1997
ECOLOGY

Menna Jones

The Biology of Centipedes

Book

Aug 1981

J. G. E. Lewis

This is a comprehensive account of centipede biology providing a critical review of the work covering anatomy, behaviour, reproduction and life history, predators and parasites, physiology, ecology and taxonomy. It is an important source-book of particular value to scientists working directly with this group and to soil ecologists and those more generally interested in arthropods, arthropod affinities and their evolution. This is a book from an internationally respected scientist and includes many first-hand accounts of his own work both on temperate and tropical species.

Energetic Consequences of Sexual Size Dimorphism in White Ibises (Eudocimus albus)

Article

Oct 1987

Keith L. Bildstein

Size Dimorphism, Intrasexual Competition, and Sexual Selection in Wattled Jacana (Jacana Jacana), A Sex-Role-Reversed Shorebird in Panama

Article

Apr 2004

We studied sexual size dimorphism, intrasexual competition, and sexual selection in an individually marked population of Wattled Jacanas (Jacana jacana) in the Republic of Panama. Males are the sole incubators of eggs (28-day incubation) and primary providers of chick care (50–60 days). Females were 48% heavier than, and behaviorally dominant over, males. Females also showed greater development of secondary sexual characters (fleshy facial ornamentation and wing spurs) than males. Both sexes defended territories throughout the year against same-sex conspecifics. Competition for territorial space was intense, and many individuals of both sexes did not become breeders. Resident females further competed with one another to accumulate multiple mates, resulting in a mating system of simultaneous polyandry. Female and male residents (territory holders) were larger, heavier, and more ornamented than adult floaters of the same sex. Larger and heavier females also had more mates than smaller females. Body size was thus a critical predictor of success in intrasexual competition for territories (both sexes) and for mates (females). Three measures of sexual selection—(1) sex difference in the opportunity for sexual selection, (2) female-to-male ratio of potential reproductive rates, and (3) operational sex ratio—each indicated that sexual selection is currently operating more strongly on females than on males (female-to-male ratios ranged from 1.43:1 to 2.22:1). Values of 1.61:1 and 1.43:1 represent the first published quantitative estimates of the opportunity for sexual selection for any sex-role-reversed bird. Our study supports the theory that when increased parental care entails reduced opportunities for future reproduction, asymmetries in parental care behaviors of the sexes can influence the intensity of competition for mates and the direction and strength of sexual selection.

A new species of arboreal toad (Anura: Bufonidae: Chaunus) from Madidi National Park, Bolivia

Article

Aug 2006

A new arboreal species of the Chaunus veraguensis group is described for the humid montane forest of Madidi National Park, in northern Bolivia. The new species differs from other species in the group by the combination small size, long and slender extremities, webbed hands, conspicuous tympanic membrane, well developed parotoid glands, absence of large glands on dorsum and extremities, nuptial excrescences of males composed of pungent spines on dorsal surface of thumb, greenish-brown coloration on dorsum with red warts in life, and green iris. It is only known from two nearby localities in the Serranía Eslabón, Department La Paz. An operational key for species in the C. veraguensis group is provided.

Review of the genus Petropedetes Reichenow, 1874 in Central Africa with the description of three new species (Amphibia: Anura: Petropedetidae)

Article

Jan 2010

We review and summarize the present knowledge on Central African Petropedetes, discuss their taxonomy and describe three new species. We synonymise one name: P. newtonii is a junior synonym of P. johnstoni. Frogs from the African mainland, namely Cameroon and eastern Nigeria, assigned to “P. newtonii” in more recent literature, were misidentified. They are herein described anew as Petropedetes vulpiae sp. nov. Two further new taxa are morphologically similar to other described species. Petropedetes euskircheni sp. nov. is morphologically close to P. parkeri but differs foremost in the smaller size of the femoral glands in adult males. P. juliawurstnerae sp. nov. is morphologically similar to P. perreti and P. cameronensis. It can be distinguished from P. perreti by its less developed webbing and from P. cameronensis by the size of its tympanum and the occurrence of a tympanic papilla in males. A key to adult males of the currently known Central African Petropedetes species is given and an outlook on potential further new taxa is provided.

Breeding tubercles of Phoxinus (Teleostei: Cyprinidae): Morphology, distribution, and phylogenetic implications

Article

May 1996
J MORPHOL

Studies of the skin with scanning electron microscopy (SEM) reveal a diverse morphology in breeding tubercles among species of Phoxinus. Based mainly on the fine structure of the surface of tubercles, nine morphotypes, coded as letters A-I, occur in Phoxinus. Most of the morphotypes are common to all Phoxinus species, but type E is present only on the dorsum of the head of P. phoxinus, type H on the breast scale of female P. phoxinus, and type I on the pectoral fin in P. erythrogaster. Multicellular breeding tubercles bearing unicellular projections, identified as unculiferous tubercles are found in type H and probably types F and G. The distribution of tubercles on head, body, and fins is described and compared among Phoxinus species. Breeding tubercles in Phoxinus and other minnow genera are compared in order to interpret the phylogenetic implication of the tuberculation in Phoxinus. The deeply embedded breast scales and the breeding tubercles on their apical margins, and a series of tubercles on the apical margins of lateral scales of the caudal peduncle in breeding males of Phoxinus species, are the characters supporting the monophyly of the genus. © 1996 Wiley-Liss, Inc.

The role of exaggerated male chelicerae in male–male contests in New Zealand sheet-web spiders

Article

May 2018

Animal weaponry has long captured the imagination of researchers and these weapons are frequently exaggerated in size. Large weapons are particularly common in species in which males defend females from potential rivals and sexual selection is generally credited with driving this pattern of exaggeration. Male New Zealand sheet-web spiders, Cambridgea foliata (Araneae: Desidae), possess chelicerae (jaws) that are substantially larger than those of female conspecifics. To investigate whether chelicerae exaggeration is selected for in the context of male–male competition, we staged contests between males and analysed how different components of resource-holding potential influenced the outcomes and durations of contests. We found that while males with large chelicerae were more likely to win contests, body condition and body size were better predictors of contest outcome. While contest durations were highly variable, there is some evidence that males make decisions about when to retreat from contests using self-assessment. As a result, only very large males are likely to reach the most escalated phase of fighting in which they lock chelicerae with their opponent. In this way, regardless of whether extra-long chelicerae impart any advantage over similarly sized opponents, exaggerated chelicerae are only used by especially large males and are therefore of little use to small males.

A new Bolivian species of the genus Telmatobius (Anura: Leptodactylidae) with a humeral spine

Article

Feb 1999

Redescription of Dekeyseria picta (Siluriformes; Loricariidae), a poorly known ancistrin from the Amazon and Orinoco Basins: redescription of dekeyseria picta

Article

Mar 2018

A re‐evaluation of Dekeyseria brachyura and D. pulchra found them to be junior synonyms of D. picta, the oldest species among these congeners, based on continuous intraspecific variation in morphometrics and colour pattern. Examination of material deposited at Brazilian and Venezuelan collections, including the original type specimens of Ancistrus brachyurus and A. pictus, plus samples recently collected in the Rio Negro, Amazonas, Brazil, allowed re‐evaluation of the taxonomic status of D. picta and provides additional information on its distribution, habitats and reproductive strategies.

Global patterns of sexual dimorphism in Amblypgyi

Article

Feb 2018

Sexual dimorphism is a common feature of life. Researchers have noted that some species of Amblypygi (Class Arachnida) exhibit male-biased sexual dimorphism, but a broad overview of the prevalence of sexual dimorphism in the order does not exist. In order to provide such an overview, we imaged and measured morphological characteristics of 390 amblypygids from 36 species. Our aim was to gain insight into general patterns of sexual dimorphism across the order. We found that, generally, males have larger pedipalps, longer antenniform legs, but smaller carapace widths relative to conspecific females for nearly all species studied. Species ranged from no sexual dimorphism (Phrynus exsul and Charinus insularis) to male pedipalps almost double the length of females in some species (Charon grayi, Euphrynichus amanica). Phylogenetic patterns remain unclear in Amblypygi and our data better match geographic patterns than evolutionary history. We thus suggest that sexual dimorphism is ancestral for the order, but has been reduced or lost in some species.

Horns, Pronghorns, and Antlers: Evolution, Morphology, Physiology, and Social Significance

Book

Jan 1990

Since the first drawings left on walls of ancient caves, human beings have been fascinated with that unique phenomenon of the animal kingdom, the presence of horns and antlers. From the mythical ''unicorn'' exercising the power over life and death to the perceived aphrodisiacal and other medical properties of rhinoceros horns and growing antlers, these conspicuous protuberances have had a significant place in the history of mankind. Part of that ancient interest in antlers and horns was due to their value as sym bols of masculinity; this interest persists today in trophy hunting, an honorable tradition carried on for centuries in many countries of the world. This book, which deals with evolution, morphology, physiology, and behavior, has not been devised as a comprehensive review of the subject of horns, prong horns, and antlers; rather, it is a series of chapters stimulating thoughts, discus sions, and initiation of new studies. As editors, we did not interfere with the content of articles nor with the opin ions and interpretations of our contributors, and we left them to decide whether to accept the suggestions of our reviewers. Despite the fact that various aspects of cranial appendages have been studied since the end of the eighteenth century, many controversial views still exist, as witnessed in various chapters of this book.

Size and Scaling in Primate Biology

Book

Jan 1985

William Jungers

In very general terms, "scaling" can be defined as the structural and func tional consequences of differences in size (or scale) among organisms of more or less similar design. Interest in certain aspects of body size and scaling in primate biology (e. g. , relative brain size) dates to the turn of the century, and scientific debate and dialogue on numerous aspects of this general subject have continued to be a primary concern of primatologists, physical an thropologists, and other vertebrate biologists up to the present. Indeed, the intensity and scope of such research on primates have grown enormously in the past decade or so. Information continues to accumulate rapidly from many different sources, and the task of synthesizing the available data and theories on any given topic is becoming increasingly formidable. In addition to the formal exchange of new ideas and information among scientific experts in specific areas of scaling research, two of the major goals of this volume are an assessment of our progress toward understanding various size-related phe nomena in primates and the identification of future prospects for continuing advances in this realm. Although the subject matter and specific details of the issues considered in the 20 chapters that follow are very diversified, all topics share the same fundamental and unifying biological theme: body size variation in primates and its implications for behavior and ecology, anatomy and physiology, and evolution.

Evolutionary Trade-Off between Secondary Sexual Traits and Ejaculates

Article

Nov 2017
TRENDS ECOL EVOL

Recent theoretical models predict that the evolutionary diversification of the weapons and ornaments of pre-mating sexual selection should be influenced by trade-offs with male expenditure on ejaculates. However, the patterns of association between secondary sexual traits and ejaculate expenditure are frequently inconsistent in their support of this prediction. We show why consideration of additional life-history, ecological, and mating-system variables is crucial for the interpretation of associations between secondary sexual traits and ejaculate production. Incorporation of these 'missing variables' provides evidence that interactions between pre- and post-mating sexual selection can underlie broad patterns of diversification in male weapons and ornaments. We call for more experimental and genetic approaches to uncover trade-offs, as well as for studies that consider the costs of mate-searching.

First insights into the function of the sawshark rostrum through examination of rostral tooth microwear: rostral tooth microwear in sawsharks

Article

Oct 2017

Potential roles of the rostrum of sawsharks (Pristiophoridae), including predation and self-defence, were assessed through a variety of inferential methods. Comparison of microwear on the surface of the rostral teeth of sawsharks and sawfishes (Pristidae) show that microwear patterns are alike and suggest that the elongate rostra in these two elasmobranch families are used for a similar purpose (predation). Raman spectroscopy indicates that the rostral teeth of both sawsharks and sawfishes are composed of hydroxyapatite, but differ in their collagen content. Sawfishes possess collagen throughout their rostral teeth whereas collagen is present only in the centre of the rostral teeth of sawsharks, which may relate to differences in ecological use. The ratio of rostrum length to total length in the common sawshark Pristiophorus cirratus was found to be similar to the largetooth sawfish Pristis pristis but not the knifetooth sawfish Anoxypristis cuspidata. Analysis of the stomach contents of P. cirratus indicates that the diet consists of demersal fishes and crustaceans, with shrimp from the family Pandalidae being the most important dietary component. No prey item showed evidence of wounds inflicted by the rostral teeth. In light of the similarities in microwear patterns, rostral tooth chemistry and diet with sawfishes, it is hypothesised that sawsharks use their rostrum in a similar manner for predation (sensing and capturing prey) and possibly for self-defence.

Intrasexually selected weapons

Abstract

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