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Morphological correlates of river velocity and reproductive development in an ornamented stream fish
Abstract
Adaptive phenotypic divergence can arise when environments vary in ways favoring alternative phenotypic optima. In aquatic habitats, the costs of locomotion are expected to increase with water velocity, generally favoring a more streamlined body and the reduction of traits that produce drag. However, because streamlining in fish may come at the cost of maneuverability, the net benefits of drag reduction can differ not only among habitats, but also among individuals (or classes of individuals) that rely on locomotion for different uses (e.g., males vs. females or adults vs. juveniles). We tested these predictions by exploring relationships among river velocity, body streamlining, ornamental fin size, and male reproductive condition in the steelcolor shiner (Cyprinella whipplei), a small-bodied North American cyprinid. Overall, males in peak reproductive condition (defined by the development of sexually dimorphic tubercles) had less streamlined bodies and larger ornamental fins than males in lower reproductive condition or individuals lacking these secondary sexual characters (females and immature males). There was a relationship between river velocity and body streamlining only for males in peak reproductive condition, but it was in the opposite direction of our predictions: these males were less streamlined in faster rivers. We found only weak support for the prediction that ornamental fin size would be negatively associated with river velocity. Overall, these results suggest either that drag is not an important selective pressure in these habitats, or that the sexual selection advantages of a deep body and large fin compensate any natural selection costs for C. whipplei males. This study highlights the often overlooked diversity of selective pressures acting on streamlining in fishes, and can offer novel insights and predictions allowing a more nuanced understanding of fish ecomorphology.
Supplementary resource (1)
Data
August 2015
... In addition, the observed morphological distinctions among C. alburnus populations, particularly the larger head length and body height in the northern (XKL) population compared with southern populations, likely reflect adaptations to local environmental conditions, such as resource availability and temperature gradients, influencing growth patterns (Fig. 1, Fig. S1) (Rutterford et al., 2023). The distinct morphological traits observed in the southern populations of C. alburnus, including a streamlined body contour and a broadened caudal peduncle (Fig. 1G), could be adaptations shaped by swift water currents (Dugas et al., 2016). Differences between lotic and lentic habitats, such as faster growth and higher fecundity in lotic environments, indicate that adaptations in C. alburnus populations may also be influenced by environmental conditions (Harimana et al., 2018;Dunn et al., 2020). ...
Geographically separated populations of Culter alburnus in China exhibit marked physiological and behavioral characteristics, particularly between populations inhabiting the northern and southern part of Huai River (HR), indicating their adaptation to local environments. In this study, the morphological characteristics of C. alburnus were measured, and restriction site associated DNA (RAD) sequencing was used for C. alburnus to investigate the genomic features of the Xingkai Lake (XKL) population from the northern part and HR, Yangtze River (YR), and Dianshan Lake (DSL) populations from the southern part of China. Analyses results revealed significant morphological differences and population genetic structure among these populations, with pronounced genetic differentiation between the northern and the southern part. Notably, the northern (XKL) population exhibited significantly lower genetic diversity than the other three southern populations. Furthermore, genes involved in synaptic vesicle transmission regulation, androgen receptor signaling, and behavior regulation pathways, including oligophrenin 1, ch25h13, androgen receptor, and Rho kinase genes, showed selection signals with high genetic differentiation indices (Fst), significant nucleotide diversity (Pi) differences, and significantly differential expression values in the northern (XKL) population compared with southern populations. These findings indicate that these genes may influence the different adaptive reflex behavioral responses of northern and southern C. alburnus populations. This study highlights the genetic structure and adaptations of C. alburnus, providing important resources for its management and aquaculture.
... The seasonal change in gonad weight is most remarkable in females but, in many species, it is also observed in males (e.g., Awaji and Hanyu 1987). Moreover, males often express sexual characters that act as mating signals only in the reproductive season; for example, nuptial coloration (Kodric-Brown 1998), muscle mass for vocalization (Nguyen et al. 2008), elongation of fins (Torricelli et al. 2000), and breeding tubercles of Cyprinidae (Dugas et al. 2016). ...
Many animals are sexually dimorphic, whereby males may display brighter body coloration and more distinctive ornamentation than females. Fishes in temperate regions markedly change their energy allocation toward reproduction in response to the seasonal environment. Seasonal change in reproductive investment affects the expression of sexually dimorphic traits in males through gonadal weight change. Here, we report seasonal changes in body size, testis weight and sexual dimorphism of the fins (anal fin length and dorsal fin length) in the northern medaka Oryzias sakaizumii. Fish were collected periodically from a wild population (Aomori). Gonad weight increased from May to July in both males and females, corresponding to the reproductive season. Moreover, during this period, the degree of sexual dimorphism in fin length increased. To investigate the relationship between testis weight and individual differences in male fin length, we analyzed relationships among morphological traits using structural equation modeling. In the reproductive season, increased testis weight was associated with longer fin length in males, but the relationship disappeared after the reproductive season. These observations suggest that the sexually dimorphic fin in this fish is a mating signal. Results from a mating experiment also support this view. Males with larger size and/or longer fin attracted more mates than those with smaller fins, suggesting that sexual selection operates through females choosing to mate with males having longer fins.
... Similarly, Haas et al. [16] found that deeper-bodied Cyprinella (Cyprinidae) are indicative of reservoir compared to riverine habitats. More recently, Dugas et al. [17] studied body streamlining (fusiform) with river velocity in Cyprinella whipplei males and did not find positive correlations but did suggest that deeper body shape may provide increased maneuverability during male-male interactions during combat and that this may be of greater importance than increased streamlining. Regardless, while these field documented effects of local habitats influence on morphology are varied they have been reproduced and manipulated in laboratory experiments [18]. ...
Background
Aquatic habitats have been altered over the past century due to a variety of anthropogenic influences. Ecomorphology is an area of aquatic ecology that can both directly and indirectly assess the effects of habitat alterations on organisms. However, few studies have explored long term trends in morphological variation. Long term changes in morphology can potentially impact niche and ultimately contribute to organismal success and the ecosystem. Therefore, in this study we assessed long term morphological variation with body size, sex, time, and hydrology using museum collections of five species of Cyprinidae (Minnows) from lentic and lotic systems over the past 100 years to gain insight into long term patterns in morphology. ResultsVariation in Cyprinidae morphology tended to relate to: body size—indicating strong allometric growth patterns with robustness of larger individuals; sex—indicating a level of fecundity selection for deeper bodies in females compared with males; and year—indirectly suggesting responses to habitat changes over the past century. In lotic ecosystems, Cyprinidae morphology tended to be more fusiform in conjunction with lower mean annual discharge or higher variation in discharge. In lentic ecosystems, change in morphology was observed but no historic habitat variables were available to discern potential mechanisms. Interestingly, not all species responded in the same magnitude or directionality. Conclusions
Long term changes in morphological variation provide a link to exploring functional relationships between taxa and their environment and have implications for understanding ecosystem attributes, community assembly patterns, and conservation.
Performance-related variation in fitness can manifest as morphological responses to ecological and evolutionary pressures. Eco-morphological studies often utilize stark binary comparisons, such as lentic to lotic populations of freshwater fishes, to characterize relationships between form and function despite possible complications from confounding factors. In the present study, we compared body shape variation among lotic populations of a stream fish (Cyprinella venusta Girard) to disentangle the influence of ecological and evolutionary drivers of phenotypic change. We assessed the extent to which body shape corresponded to three key environmental factors (mean channel velocity, mean discharge, and mean annual run-off), phylogeny (mitochondrial DNA divergence), and body size (centroid size). We also examined relationships between these parameters and a fineness index, which is a measure of streamlining and morphological optimization for steady swimming performance. All three environmental variables had some explanatory power, although morphological characteristics were predominantly associated with variation in mean annual run-off. Phylogeny was also a strong predictor of morphological variation, whereas body size had little predictive power. Populations experiencing higher mean annual run-off exhibited a shorter base of the dorsal fin, a more slender body and caudal peduncle, a smaller head in both horizontal and vertical dimensions, and a more anterior placement of the eye. With some exceptions, such as variation in jaw length, differences in body shape associated with phylogenetic history were similar to those associated with run-off. Notably, all clades exhibited parallel responses to variation in run-off. Populations experiencing high mean annual run-off approached a hydrodynamic optimum, suggesting a morphology optimized for steady swimming performance. In contrast to previous studies that emphasize the importance of average water velocity, the findings of the present study indicate that morphological variation among populations of stream fishes is tightly linked to more complex aspects of hydrology and evolutionary history. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, ●●, ●●–●●.
The costs and benefits of investing in expensive sensory systems are shaped by environments that vary in the ease with which sensory information can be accessed. Fish provide an excellent model system in which to address questions of sensory evolution; while fishes rely heavily on vision, their visual environment is far more diverse and challenging than that of terrestrial animals. Turbidity, for example, alters the quantity of ambient light, its color, and the ability of animals to resolve borders of objects. Several comparative studies suggest that turbidity is associated with a reduction in the resources devoted to vision. Using these as a guide, we tested the prediction that turbidity and eye size would be negatively associated in populations of red shiners (Cyprinella lutrensis (Baird and Girard, 1853)), a small-bodied cyprinid that is common and abundant in habitats spanning nearly the entire range of turbidity found in the Great Plains of the United States. We found that eye size was positively associated with turbidity, perhaps surprising given previous comparative work, but consistent with the finding that red shiners from turbid habitats display more intense nuptial coloration. This result highlights the need for further investigations of among-population variation to fully understand the mechanisms underlying sensory system diversity in animals.
In teleost fishes, 11-ketotestosterone (11KT) is a critical androgen regulating primary and secondary sex characteristics. In the sexually dimorphic Lythrurus fasciolaris (Cyprinidae), dominant nuptial males display heavy tuberculation on the head and nape, dark dorsolateral vertical bars, and dramatic red coloration in the fins, venter, and operculum area. This study aimed to quantify 11KT circulating levels in males and females, and determine any correlation with key male reproductive status indicators such as nuptial coloration, size, and gonadosomatic index (GSI). Thirty-one wild-caught L. fasciolaris were divided into three groups according to reproductive status: dominant males (D), non-dominant males (ND), and females (F). Physical measurements, digital imaging, and blood samples were used to quantify body size, GSI, nuptial coloration, and 11KT circulating levels. Dominant males had higher 11KT levels and nuptial coloration traits compared to ND males and females (red area, hue, saturation), and a higher GSI than ND males. Non-dominant males had more 11KT and coloration than females. Increased 11KT levels corresponded to increased coloration, size and GSI.
Environmental niche modeling is a valuable tool but it often fails to identify causal links between environmental gradients and individual-or population-level performance that drive species' distributions. Correlation between the abundances of stream fish species and longitudinal position in stream networks is well documented and is hypothesized to occur through differential environmental filtering of trophic traits. Still, trophically similar congeners often exhibit complementary distributions along stream size gradients, suggesting that other mechanisms are important. We present niche models to test the hypothesis that four congeneric pairs (Teleostei: Cyprinidae) exhibit complementary distributions along a gradient of stream size in the central Great Plains of Kansas, USA. Stream size was the strongest predictor of abundance compared to five other environmental variables tested and three of the four species pairs exhibited complementary distributions along a stream size gradient. We carried out field experiments to quantify potentially causal environmental gradients (food resources, temperature, and turbidity) and four measures of individual performance (adult spawning success and juvenile survival, condition, and growth) along a stream size gradient for one congeneric pair: Pimephales notatus, a tributary species and P. vigilax, a river mainstem species. These experiments revealed an increase in temperature and food resources with stream size, along with a corresponding increase in adult spawning success, juvenile condition, and juvenile growth for both species. We conclude that these congeners respond similarly to abiotic gradients associated with the river continuum and that complementary distributions are a consequence of biotic interactions, differential environmental filtering evident in an unmeasured performance metric, or differential environmental filtering by a direct environmental gradient operating at longer timescales.
Males and females often differ from one another in phenotypic traits due to differential investment in traits relevant to the fitness of each sex. However, how differences in sexually dimorphic traits affect ecologically relevant performance traits and whether these are correlated with variation in ecology remains poorly understood.
Here, we test the co‐evolution of head shape, bite force capacity and diet in male and female lizards ( G allotia ) from the Canary Islands, known to be sexually dimorphic. We collected data on bite force and head size and shape for both sexes of all seven extant species on all seven islands of the archipelago (ten evolutionary‐independent lineages). Moreover, we collected diet data for five out of the seven species (eight lineages).
Our results show that the evolution of head morphology is associated with the evolution of bite force in both sexes. However, only in females is the evolution of head morphology and bite force associated with the evolution of diet. In males, head morphology and bite force are decoupled from the evolution of diet. In conjunction with the male head shape characterized by a broad rostrum, this suggests that head shape and bite force may be evolving principally under sexual selection in males.
Our data thus suggest that head morphology and associated functional traits may evolve under different selective pressures in the two sexes.
Recent evidence indicates that evolution can occur on a contemporary time scale. However, the precise timing and patterns of phenotypic change are not well known. Reservoir construction severely alters selective regimes in aquatic habitats due to abrupt cessation of water flow. We examined the spatial and temporal patterns of evolution of a widespread North American stream fish (Pimephales vigilax) in response to stream impoundment. Gross morphological changes occurred in P. vigilax populations following dam construction in each of seven different rivers. Significant changes in body depth, head shape and fin placement were observed relative to fish populations that occupied the rivers prior to dam construction. These changes occurred over a very small number of generations and independent populations exhibited common responses to similar selective pressures. The magnitude of change was observed to be greatest in the first 15 generations post-impoundment, followed by continued but more gradual change thereafter. This pattern suggests early directional selection facilitated by phenotypic plasticity in the first 10–20 years, followed by potential stabilizing selection as populations reached a new adaptive peak (or variation became exhausted). This study provides evidence for rapid, apparently adaptive, phenotypic divergence of natural populations due to major environmental perturbations in a changing world.
Understanding population-level responses to human-induced changes to habitats can elucidate the evolutionary consequences of rapid habitat alteration. Reservoirs constructed on streams expose stream fishes to novel selective pressures in these habitats. Assessing the drivers of trait divergence facilitated by these habitats will help identify evolutionary and ecological consequences of reservoir habitats. We tested for morphological divergence in a stream fish that occupies both stream and reservoir habitats. To assess contributions of genetic-level differences and phenotypic plasticity induced by flow variation, we spawned and reared individuals from both habitats types in flow and no flow conditions. Body shape significantly and consistently diverged in reservoir habitats compared with streams; individuals from reservoirs were shallower bodied with smaller heads compared with individuals from streams. Significant population-level differences in morphology persisted in offspring but morphological variation compared with field-collected individuals was limited to the head region. Populations demonstrated dissimilar flow-induced phenotypic plasticity when reared under flow, but phenotypic plasticity in response to flow variation was an unlikely explanation for observed phenotypic divergence in the field. Our results, together with previous investigations, suggest the environmental conditions currently thought to drive morphological change in reservoirs (i.e., predation and flow regimes) may not be the sole drivers of phenotypic change.
Flow regimes are believed to be of major evolutionary significance in fish. The flow regimes inhabited by cyprinids vary extensively from still flow regimes to riptide flow regimes. To test (i) whether flow-driven swimming performance and relevant morphological differentiation are present among fish species and (ii) whether evolutionary shifts between high-flow and low-flow habitats in cyprinids are associated with evolutionary trade-offs in locomotor performance, we obtained data on both steady and unsteady swimming performance and external body shape for 19 species of cyprinids that typically occur in different flow regimes (still, intermediate and riptide). We also measured the routine energy expenditure (RMR) and maximum metabolic rate (MMR) and calculated the optimal swimming speed. Our results showed that fish species from riptide groups tend to have a higher critical swimming speed (Ucrit ), maximum linear velocity (Vmax ) and fineness ratio (FR) than fish from the other two groups. However, there was no correlation between the reconstructed changes in the steady and unsteady swimming performance of the 19 species. According to the phylogenetically independent contrast (PIC) method, the Ucrit was actively correlated with the MMR. These results indicated that selection will favour both higher steady and unsteady swimming performance and a more streamlined body shape in environments with high water velocities. The results suggested that steady swimming performance was more sensitive to the flow regime and that for this reason, changes in body shape resulted more from selective pressure on steady swimming performance than on unsteady swimming performance. No evolutionary trade-off was observed between steady and unsteady swimming performance, although Ucrit and MMR were found to have coevolved. However, a further analysis within each typically occurring habitat group suggested that the trade-off that may exist between steady and unsteady swimming performance may be concealed by the effect of habitat.
While the importance of competition in adaptive divergence has recently been demonstrated in a number of systems, its interaction with other ecological factors has been neglected. We attempt a more pluralistic approach in this comparative study of divergence in pumpkinseed sunfish (Lepomis gibbosus) from the Adirondack region of New York. In some lakes, pumpkinseed forms that use shallow- and open-water environments coexist. We tested four predictions relating to an hypothesis of character release: (1) Pumpkinseed divergence is favored in the absence of the closely related bluegill sunfish (L. macrochirus), a known competitor elsewhere, (2) divergence is favored when the combined effects of other planktivorous fish taxa that may impose diffuse competition is reduced, (3) divergence is positively related to lake size because larger lakes provide more distinct and diverse environments, and (4) divergence is favored in lakes dominated by open-water habitat. In two lakes with introduced bluegill (sympatry), bluegill appear to limit pumpkinseed divergence, as they do elsewhere. Pumpkinseeds were neither found in the open-water habitat, nor did they eat significant amounts of open-water prey. In nine allopatric lakes selected for their similarity to the sympatric lakes, pumpkinseeds were ecologically and morphologically divergent, consistent with a character release hypothesis. Morphological divergence followed functional expectations. Open-water pumpkinseeds generally had longer caudal peduncles, shorter heads, thinner bodies, and smaller paired fins compared to shallow-water pumpkinseeds (heritable variation in body shape has been demonstrated elsewhere). Among 26 allopatric lakes, other planktivores had a negative effect on intrapopulation divergence as if they collectively imposed diffuse competition. Surprisingly, lake size was unrelated to divergence, and the amount of open-water habitat had an unexpected negative effect. Mean body size was also negatively related to divergence. Our findings illustrate that a variety of ecological factors, in addition to competition, may influence the divergence of pumpkinseeds, and possibly other fishes in postglacial north temperate lakes.
The aerodynamic properties of a bird's tail, and the forces produced by it, can be predicted by using slender lifting surface theory. The results of the model show that unlike conventional wings, which generate lift proportional to their area, the lift generated by the tail is proportional to the square of its maximum continuous span. Lift is unaffected by substantial variations in tail shape provided that the tail initially expands in width along the direction of flow. Behind the point of maximum width of the tail the flow is dominated by the wake of the forward section. Any area behind this point therefore causes only drag, not lift. The centre of lift is at the centre of area of the part of the tail in front of the point of maximum width. The moment arm of the tail, about its apex, is therefore more than twice the moment arm of a conventional wing about its leading edge. The drag of the tail is a combination of induced drag proportional to lift, and profile drag proportional to surface area. Induced drag can be halved by drooping the outer tail feathers to generate leading edge suction. This may be used for control, particularly in slow flight when both wings and tail are generating maximum lift. The slender lifting surface model is very accurate at angles of attack below about 15-degrees. At higher angles of attack vortex formation at the leading edge can stabilize the flow over the tail and thereby generate increased lift by a detached vortex mechanism. Asymmetry in the orientation of the leading edges with relation to the freestream (either in roll, yaw or caused by asymmetry in the planform) is amplified in the flow field and leads to large rolling and yawing forces that could be used for control in turning manoeuvres. The slender lifting surface model can be used to examine the effect of variations in tail shape and tail spread on the aerodynamic performance of the tail. A forked tail that has a triangular planform when spread to just over 120-degrees gives the best aerodynamic performance and this may be close to a universal optimum, in terms of aerodynamic efficiency, for a means to control pitch and yaw. However, natural selection may act to optimise the performance of the tail when it is not widely spread. The tail is normally only widely spread during manoeuvres, or at low speeds, selection may act to improve the efficiency of the tail when it is spread to only a relatively narrow angle - for example to maximize the bird's overall lift to drag ratio - the optimum shape at any angle of spread is that which gives a straight trailing edge to the tail. This will always give a slightly forked planform, but depth will depend on how widely the tail is spread when selection acts, and this depends on the criteria for optimization under natural selection. A forked tail is more sensitive to changes in angle of attack and angle of spread, than other tail types. Forked tails are more susceptible to damage than other tail morphologies, and suffer a greater loss of performance following damage. Forked tails also confer less inherent stability than any other type of tail. Aerodynamic performance may not be an important optimization criterion for birds that fly in a cluttered environment, or do not fly very much. Natural selection, under these conditions, may favour tails of other shapes. The aerodynamic costs of sexually selected elongated tails can be predicted from the model. These predictions can be used to distinguish between the various models for the evolution of elongated tails. Elongated graduated tails and pintails could have evolved either through a Fisherian or Handicap mechanism. The evolution of long forked tails can be initially favoured by natural selection, the pattern of feather elongation seen in sexually selected forked tails is predicted by the Fisher hypothesis (Fisher 1930) but not by any of the other theories of sexual selection.
Correction for ‘Exposure to pesticides impairs the expression of fish ornaments reducing the availability of attractive males’ by Omar Arellano-Aguilar and Constantino Macias Garcia (Proc. R. Soc. B 274 , 2925–2933. (doi: [10.1098/rspb.2008.0163][1])).
On p. 1346, the caption for figure 2 was presented incorrectly.
[1]: /lookup/doi/10.1098/rspb.2008.0163
Understanding population-level responses to novel selective pressures can elucidate evolutionary consequences of human-altered habitats. Stream impoundments (reservoirs) alter riverine ecosystems worldwide, exposing stream fishes to uncommon selective pressures. Assessing phenotypic trait divergence in reservoir habitats will be a first step in identifying the potential evolutionary and ecological consequences of stream impoundments. We tested for body shape divergence in four stream-adapted fishes found in both habitats within three separate basins. Shape variation among fishes was partitioned into shared (exhibited by all species) and unique (species-specific) responses to reservoir habitats. All fishes demonstrated consistent significant shared and unique morphological responses to reservoir habitats. Shared responses were linked to fin positioning, decreased body depths and larger caudal areas; traits likely related to locomotion. Unique responses were linked to head shape, suggesting species-specific responses to abiotic conditions or changes to their trophic ecology in reservoirs. Our results highlight how human-altered habitats can simultaneously drive similar and unique trait divergence in native populations.
Endocrine disrupting chemicals (EDCs) have been detected in surface waters worldwide and can lead to developmental and reproductive disruption in exposed fishes. In the US Great Plains, EDCs are impacting streams and rivers and may be causing adverse reproductive effects. To examine how estrogenic EDCs might affect reproductive success of plains fishes, we experimentally exposed male red shiners (Cyprinella lutrensis) to exogenous 17-estradiol. We characterized the effects of estradiol on male gonadal histology and secondary sexual characteristics, determined whether exposure reduced reproductive success, and examined the effects of depuration. Adults were exposed to a mean concentration of 70ngL¹ estradiol, a solvent control, or a water control for at least 83days. Male exposure to estradiol resulted in elevated plasma vitellogenin concentrations, changes in spermatogenesis, reduced mating coloration and tubercles, altered mating behaviors, and reduced reproductive success with no viable progeny produced. Reproductive endpoints improved upon depuration (28days). Exposure to estradiol had significant adverse effects on red shiners, indicating that wild populations may face developmental and reproductive difficulties if they are chronically exposed to estradiol.
Close correlations between social dominance and levels of some hormones modulated mainly by agonistic behavior have been reported in mammals. The hormone changes which accompany agonistic interactions appear to be more dramatic and longer lasting than those associated, for example, with sexual interactions (Harding 1981). Clearly, dominant animals generally have lower pituitary/adrenocortical activities than submissive animals living with them. Thus, the dominant -+position usually based on aggressive behavior often tends to be related to elevated androgen level, while subordinate status seems to be associated with lower androgen secretion and increasing levels of glucocorticoids (Brain 1980; Leshner 1980). Increased chronic ACTH/glucocorticoid production in subordinate animals suppresses androgens (Brain 1980). In Cervidae the evidence for these relationships has been obtained in white-tailed deer (Bubenik, A. & Bubenik, G. 1976b; Forand et al. 1985), red deer (Short 1979), and reindeer (Stokkan et al. 1980).
Phenotypic plasticity in morphology is often considered adaptive. Stream-living fish encounter considerable spatial and temporal
environmental variation in their native habitats, and the ability to adapt to this variation is of utmost importance. We studied
experimentally whether water velocity affects the body shape of juvenile Atlantic salmon (Salmo salar m. sebago Girard) and brown trout (Salmo trutta m. lacustris L.). The fish were reared in slow and fast water flow, and their morphology was studied by measuring a number of morphometric
characters. We studied which characters differed between the environments in each species, and found that water velocity caused
morphological differentiation in both salmon and brown trout. The differences occurred especially in body height as well as
in fin sizes, characters that are very likely to be of functional importance for life in the stream environment. Salmon in
fast flow became more robust, whereas brown trout in fast flow became slightly more streamlined. The observed variation in
body morphology of salmon and brown trout indicates phenotypic plasticity, but the species differed in their response to environmental
variation, which may be due to different energetics and cost reduction strategies. Morphological differentiation caused by
water flow occurred very rapidly, within 1-month exposure to the different water flows.
Delayed plumage maturation is the delayed acquisition of a definitive colour and pattern of plumage until after the first potential breeding period in birds. Here we provide a comprehensive overview of the numerous studies of delayed plumage maturation and a revised theoretical framework for understanding the function of delayed plumage maturation in all birds. We first distinguish between hypotheses that delayed plumage maturation is attributable to a moult constraint with no adaptive function and hypotheses that propose that delayed plumage maturation is a component of an adaptive life-history strategy associated with delayed reproductive investment. We then recognize three potential benefits of delayed plumage maturation: crypsis, mimicry and status signaling. Evidence suggests that delayed plumage maturation is not a consequence of developmental constraints and instead represents a strategy to maximize reproductive success in circumstances where young adults cannot effectively compete with older adults for limited resources, particularly breeding opportunities. A multi-factorial explanation that takes into account lifespan and the degree of competition for limited breeding resources and that combines the benefits of an inconspicuous appearance with the benefits of honest signaling of reduced competitiveness provides a general explanation for the function of delayed plumage maturation in most bird species. Delayed plumage maturation should be viewed as a component of alternative reproductive strategies that can include delay in both plumage and sexual development. Such strategies are frequently facultative, with individuals breeding prior to the acquisition of definitive plumages when conditions are favourable. Presumably, the benefits of delayed plumage maturation ultimately enhance lifetime reproductive success, and studying delayed plumage maturation within the context of lifetime reproductive success should be a goal of future studies.
Measurements of eight body parts were made on individuals of the red shiner, Notropis lutrensis, that were collected from the Salt River, Maricopa County, Arizona, March through August, 1964. Changes in relative proportions of these characters in relation to body length are shown. Sexual dimorphism was present in certain characters.
Tuberculation of the red shiner, Notropis lutrensis, was studied throughout the reproductive period of the year. Head tuberculation of N. lutrensis follows a definite developmental sequence from an intermediate linear pattern to a terminal profuse or scattered pattern. Tuberculation on the body is relatively constant in its distribution and appears closely associated functionally with the breeding activities.
The reproductive behavior of Notropis spilopterus and Notropis whipplii was studied concurrently in several central Ohio streams. During the warmer months of the year, they were found in pools and eddies near riffles with a moderate current. The spawning season lasted from early June to late August. Eggs were deposited beneath loose bark or in the crevices of submerged logs and tree roots. Breeding adults exhibited a high degree of sexual dimorphism, and males of the 2 species differed in fin and snout coloration, size and shape of the dorsal fin, and size of nape tubercles. Most sexually mature individuals of both species were in their third summer, but a few males and females spawned in their second summer. The species hybridized readily in aquaria but natural hybrids appear to be rare. Female hybrids were fertile, and backcrosses with N. spilopterus were produced. Male F1 hybrids appeared to be sterile, but both sexes of the backcross were fertile. Segregation of the species while spawning appeared to be the principal isolating mechanism.
Environmental variation drives ecological and phenotypic change. How predictable is differentiation in response to environmental change? Answering this question requires the development and testing of multifarious a priori predictions in natural systems. We employ this approach using Gobiomorus dormitor populations that have colonized inland blue holes differing in the availability of fish prey. We evaluated predictions of differences in demographics, habitat use, diet, locomotor and trophic morphology, and feeding kinematics and performance between G. dormitor populations inhabiting blue holes with and without fish prey. Populations of G. dormitor independently diverged between prey regimes, with broad agreement between observed differences and a priori predictions. For example, in populations lacking fish prey, we observed male-biased sex ratios, a greater use of shallow-water habitat, and larger population diet breadths as a result of greater individual diet specialization. Furthermore, we found predictable differences in body shape, mouth morphology, suction generation capacity, strike kinematics, and feeding performance on different prey types, consistent with the adaptation of G. dormitor to piscivory when coexisting with fish prey and to feeding on small invertebrates in their absence. The results of the present study suggest great potential in our ability to predict population responses to changing environments, which is an increasingly important capability in a human-dominated, ever-changing world. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, ●●, ●●–●●.
The crevice spawning behavior of Dionda dichroma is described for the first time, and compared to spawning behavior in the genus Cyprinella. The evolution of crevice spawning with respect to other spawning behaviors of North American shiners is examined using explicitly phylogenetic hypotheses for this group. We present evidence that broadcast spawning is plesiomorphic and all other spawning behaviors are independently derived. There is evidence that crevice spawning has evolved independently at least three times within the shiner clade. There is no support for an evolutionary transition between egg clustering and crevice spawning. Nest association, spawning on habitat prepared by other species, has also evolved multiple times within this clade. Evolution of spawning in shiners is best described by phylogenetic stasis with several independent origins of specialized spawning stragegies.
In many animal species, male armature has evolved through sexual selection. This male weaponry can increase reproductive success, but only if the owner overcomes the associated costs.
Male stag beetles bear one of the most extreme examples of male weaponry: their mandibles can be almost as long as their own body. We question whether the armature of male Cyclommatus metallifer negatively affects terrestrial locomotion (stability and cost). If so, we investigate whether these effects are potentially compensated by morphological and/or behavioural features, as seen in other specialized insect species. Conspecific females are used to represent the non‐dimorphed condition.
The presence of the huge male mandibular apparatus shifts the body centre of mass ( bCOM ) anteriorly. Concomitantly, the male fore limbs are 28% longer and are systematically positioned in a more anterior angular sector than in females. Thus, the rostral border of the support area of the leg tripod also moves forward. This suggests a stability enhancing mechanism. However, in contrast to load‐carrying ants, the anteriorly placed bCOM still creates two pronounced statically instable periods each locomotor cycle.
Due to the static instability, males must adjust their locomotor behaviour: they walk at higher cycle frequencies when compared to females of the same size, to ensure they proceed to the next stance before bumping to the ground with their heavy heads.
Contrary to other specialized load‐carrying insect species, the (muscle) mass specific mechanical cost of transport of males exceeds that of females by 40%.
Since neither stability nor cost of transport benefit from the male forelimb size and positioning, their role in guaranteeing adequate terrestrial locomotion while carrying an enlarged mandibular apparatus seems doubtful. Instead, the long limbs are themselves functional in fights, by pitching the body upwards in order to throw opponents backwards.
The oversized male stag beetle armature comes at high ecological costs: locomotion economics as well as stability clearly suffer from the large mandibles. The observed limb length dimorphism does not prevent this, but should probably be considered part of sexual selection, rather than a compensation for its consequences.
The red shiner Cyprinella lutrensis is the most widespread and abundant minnow (Cyprinidae family) in central and southwestern North America, occurring at very high local densities in streams from northern Mexico to Nebraska and Iowa. The streams in which red shiners occur are typically harsh, unpredictable environments with temperature extremes and episodes of low oxygen, floods, and drought. In outdoor experimental streams, red shiners stocked at densities typical of natural streams showed moderate density effects on overwinter survival and strong effects on growth from October to May. At lower densities a higher percentage (>70% on average) of individuals survived winter, and most grew to adult size the next spring. At higher densities survival and average growth were lower, and the distribution of final body size was highly skewed, with a few individuals reaching sexual maturity and most remaining at the juvenile stage. The apparent growth of the cohort in the Washita River, Oklahoma, from which experimental fish were taken, was similar to that of red shiners at high densities in the experimental streams, suggesting that red shiner population parameters are density dependent in the wild despite the strong potential for the influence of abiotic factors in their typical habitats.
The spawning behaviour and sexual dimorphism of the little known North American cyprinid fish, Notropis leedsi, is described based on observations made in laboratory aquaria. Notropis leedsi is a crevice spawning species, a trait characteristic of members of the subgenus Cyprinella. Males establish breeding territories through ‘mock battles’ and defend them by chasing away intruding males or, at times, through threat displays or ‘mock battles’. Although wild-caught males are significantly larger than females, sexual dimorphism is more pronounced in the colour pattern and fin size, especially the dorsal and anal fins.The modes of spawning behaviour in the genus Notropis are reviewed. The relationship between the promiscuous mating system (polybrachygamy), the crevice spawning mode, and sexual dimorphism in N. leedsi are discussed in relation to current notions regarding sexual selection.
We quantified body morphology in individuals from 49 collections of spotfin shiner (Cyprinella spiloptera) in the Wabash River watershed. Ten morphological measurements were used to produce principal component (PC) axes that were examined for relationships with watershed area. Analyses of males and females resulted in sexual dimorphism for one PC axis that represented caudal fin length and head depth; both have increased size in males. An analysis of body shape with watershed area resulted in different relationships for males and females. Caudal peduncle length increased with stream size for males and decreased with stream size for females. No significant relationships were found for sexual size dimorphism (SSD) with stream size. Allometry for SSD supported Rensch's rule—male body size increased more rapidly than female body size with increased SSD. Morphology in spotfin shiners is constrained by a combination of sexual selection and the hydrologic regime of the watershed.
In the Fond du Lac River, adult male Arctic grayling defend territories on the spawning ground for up to 7 days. Females do not defend territories and do not exhibit agonistic behaviour during the breeding season.
The behaviour patterns exhibited by Arctic grayling during spawning are virtually identical to those exhibited by European grayling. The characteristic large dorsal fin of the grayling is of major importance during the spawning act.
Less than 50% of all spawning attempts proceed to completion. Interference by other fish or the improper orientation of one fish may result in one member of the spawning pair moving away. Most often however, incomplete acts are the result of the female moving away for no apparent reason. Females may initially ‘test’ males or may simply not be ready to spawn when approached by males. Homosexual spawning attempts were rarely observed.
We examined intra- and interspecific variability in shape of three topminnow species (Funduluidae: Fundulus notatus, F. olivaceus, and F. euryzonus) across ten drainages. Within each drainage, five or more adult male topminnows were digitized at multiple sites (83 total sites) along the river continuum representing a range of stream sizes (cumulative drainage area) and hydrological conditions. Nine of the ten drainages contained two Fundulus species that were longitudinally separated along the river continuum with narrow areas of coexistence. Upstream–downstream distribution patterns were variable by drainage, allowing us to examine patterns repeated across ecologically similar species. More variability in shape was explained by drainage (19.7%) than by species (7.4%) differences. Populations of F. notatus from headwaters (three drainages) converged on a deep-bodied form similar to F. olivaceus which was typically sampled in headwaters. Fundulus notatus shape was more closely related to stream size than in the other two species. Headwater populations of F. notatus and F. olivaceus had fineness ratios near the hydrodynamic optima of 4.5 whereas downstream populations of F. notatus had shallower bodies. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103, 612–621.
Male predation risk due to ornaments seldom reduces female mating opportunities because males escape costs through alternative mating strategies and/or females cease to select for highly ornamented males. Males of the Amarillo fish Girardinichthys multiradiatus (Goodeidae) have large sexually selected fins that impair attack-avoidance manoeuvres. This fish was used to seek evidence that intersexual selection for handicapping traits can result in a deficit of acceptable mating partners. Also it was examined whether, under male scarcity, females remain choosy to the point of missing mating opportunities, and that they can exert effective control over matings, which is a pre-condition of effective female choice. It was found that snakes prey disproportionately on males, that it leads to female-biased sex ratios, and that highly ornamented males are more scarce after predation than males with small ornaments. Females can avoid being fertilized by unattractive males, and that missing one reproductive period can lead to infertility. Thus it appears that females have promoted the exaggeration of a male trait that increases predation risk, remain choosy even when acceptable males are scarce, and pay a large cost when missing mating opportunities. A prediction from these results is that females enjoy substantial fitness benefits from mating with highly ornamented males, which override the occasional fatal costs of refusing to mate with sub–optimal males. One potential consequence of female selectivity and control over matings when males are scarce may be a reduced capability to colonize new habitats.
Anthropogenic habitat alteration creates novel environments that can alter selection pressures. Construction of reservoirs worldwide has disturbed riverine ecosystems by altering biotic and abiotic environments of impounded streams. Changes to fish communities in impoundments are well documented, but effects of those changes on native species persisting in reservoirs, which are presumably subjected to novel selective pressures, are largely unexplored. I assessed body shape variation of a native stream fish in reservoir habitats and streams from seven reservoir basins in the Central Plains of the USA. Body shape significantly and consistently diverged in reservoirs compared with stream habitats within reservoir basins; individuals from reservoir populations were deeper-bodied and had smaller heads compared with stream populations. Individuals from reservoir habitats also exhibited lower overall shape variation compared with stream individuals. I assessed the contribution of genotypic divergence and predator-induced phenotypic plasticity on body shape variation by rearing offspring from a reservoir and a stream population with or without a piscivorous fish. Significant population-level differences in body shape persisted in offspring, and both populations demonstrated similar predator-induced phenotypic plasticity. My results suggest that, although components of body shape are plastic, anthropogenic habitat modification may drive trait divergence in native fish populations in reservoir-altered habitats.
A considerable literature has been devoted to documenting differences between the sexes. However, relatively little attention has hitherto been directed towards those differences that arise as an indirect consequence of mating system even though they can have profound implications for the daily lives of the animals involved. In this review we focus on differences in the non-reproductive behaviour of fish and relate these to sexual dimorphism in size and morphology, and to variance in fitness between the sexes. In line with our expectation, differences in distributional ecology, schooling, aggression, predator avoidance and foraging are exaggerated in sexually dimorphic species and polygamous mating systems. Nonetheless, the behaviour of males and females may also differ in sexually monomorphic and monogamous species. We conclude by highlighting promising directions for further research.
We tested the mating preference of female sailfin mollies (Poecilia latipinna) by presenting them with pairs of dummy males differing in: (I) sailfin and body size together (holding sailfin : body size ratio constant); (II) body size alone (holding sailfin size constant); (III) sailfin size alone (holding body size constant); and (IV) sailfin : body size ratio (holding total lateral projection area constant). Females spent more time near dummies of greater sailfin or greater body size. The preference functions based on the first three sets of stimuli showed a similar pattern: the preference between any two simultaneously presented dummies increased with the magnitude of the discrepancy in lateral projection area (LPA) between them. However, when LPA was held constant in expt (IV), neither body size, sailfin size, nor any particular dummy (i.e. any particular sailfin + body size combination) was preferred. These findings suggest that increased LPA is more stimulating to sexually receptive females and that females consequently prefer larger males. The sailfin may therefore have evolved as a way for males to exploit this sensory bias and appear larger to prospective mates.
How ornaments that are used during mate choice and rival assessment remain reliable has been a source of contention for many years. Such signals are hypothesized to be costly (i.e., 'handicaps'), but empirical studies testing for costs of sexually selected ornaments are equiv-ocal at best, contradictory at worst. We review recent studies finding compensation for sex-ually selected ornaments, in both intra-and inter-specific studies, suggesting that other traits evolve to mitigate costs of ornaments. We synthesize these studies to elucidate the role of compensatory traits in the evolution of reliable ornaments and explain how selection to re-duce ornament costs may influence aspects of the phenotype that are not subjected to direct sexual selection and may obscure our ability to directly measure ornament costs. Both intra-specific studies and comparative studies in a phylogenetic framework are important for our understanding of how the costs of signals may be reduced by compensation, but each ap-proach answers different questions about ornament evolution. We also elaborate on a general theoretical model that can be useful when testing for costs of ornaments in correlational and experimental studies. We recommend that future investigators should consider compensatory traits when testing for ornament costs, especially when manipulating ornamentation.
Metabolic scaling laws predict a variety of emergent properties of biological systems based on relationships among temperature, body size, and rates of physiological processes. These models have been criticized as being overly simplistic and not accounting for directional variability arising from evolutionary tradeoffs. I measured hatch success and egg development time at six temperatures for 12 populations throughout the latitudinal range of two broadly distributed topminnows (Fundulus). I asked if hatch success and development time differed between the species and northern and southern populations. Hatch success reaction norms suggested that the more broadly (and northern) distributed Fundulus notatus was more eurythermic with a lower optima and broader performance breadth than Fundulus olivaceus. Temperature explained most variability in mass-corrected development time. Development time differed between the species, but not northern and southern populations. Deviations from predictions of universal scaling laws were most pronounced away from specie's thermal optima.
The objective of this study was to determine if three male ornaments in the guppy (Poecilia reticulata) were reliable indicators of swimming performance. Tail shape and dorsal fin length were chosen because they are ornaments that are of primary importance in swimming, which is a major survival component of fitness in fish. The carotenoid pigments and especially their density are ornaments that are hypothesized to be long term indicators of male vigor. Carotenoid pigment density and swimming performance were significantly positively correlated, but there was no relationship between swimming performance and tail shape or dorsal fin length. These results indicate that density of carotenoid pigmentation may function as a male vigor indicator during mate choice. Tail shape and dorsal fin length are not related to swimming performance, and females probably could not use them as vigor indicators during mate choice. The results are discussed in terms of ornament function and adaptive and Fisherian hypotheses of female choice.
Handicap models of sexual selection predict that ornaments must be costly to produce and/or to wear and maintain; only then can they evolve as reliable signals of genetic quality. We investigated in the laboratory one potential cost of possessing ornaments, using the viviparous fish Girardinichthys multiradiatus and its natural predator, the snake Thamnophis melanogaster. We found that female G. multiradiatus show preferences for males with larger fins, as measured from body correlates. Males with a morphology attractive to females, however, were more likely to be captured by snakes than were other males (Fig. 5). Greater vulnerability to snakes cannot be explained as a result of snake visual preferences, because snakes responded similarly to males and females (Fig. 6). Finally, males, particularly dominant ones, were more likely to inspect foraging snakes than were females (Fig. 7). We conclude that male Girardinichthys multiradiatus experience a sexually-selected handicap due to reduced mobility resulting from having enlarged fins.
Abstract. Factors associated with the evolution of sexual dimorphism in sockeye salmon were examined by relating individual behavioural correlates of reproductive success with morphological measurements in both sexes. Adult salmon were captured, measured and tagged, then released and observed in Iliamna Lake, Alaska. Males were generally larger than females (447 versus 428 mm) and had larger dorsal humps and more elongated jaws for their length. Indices of male reproductive success varied considerably among individuals (e.g. 0-12 observations in dominant status). Male social status was positively associated with both length and dorsal hump size, independent of length. All resident females completed spawning and only nine of 82 had their nests dug up by other females. However, size-related variation in spawning-site location was observed; larger females tended to spawn in shallower water than did smaller females. Thus reproductive success apparently varied much more in males than in females. Consistent with the theory regarding the evolution of sexual dimorphism, the greater variability in male reproduction was directly associated with the greater average size and exaggerated shape of males.
Evolutionary trajectories under hard and soft selection can differ: in hard selection, the environments with the highest initial mean fitness contribute most individuals to the mating pool. In both hard and soft selection, evolution toward the optimum in a rare environment is much slower than it is in a common one. A subdivided population model reveals that migration restriction can facilitate local adaptation. However, unless there is no migration or one of the special cases discussed for panmictic populations holds, no geographical variation in the norm of reaction will be maintained at equilibrium. Implications of these results for the interpretation of spatial patterns of phenotypic variation in natural populations are discussed. -from Authors Dept. of Biol., Iowa Univ., Iowa City, IA 52242, USA.