Article

Deferred agonistic behavior in a long-lived scincid lizard Eumeces laticeps

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Abstract

A laboratory experiment with the broad-headed skink (Eumeces laticeps) involving staged agonistic encounters demonstrates that larger males have an advantage over smaller ones in agonistic bouts. Field data on head wounds produced by intraspecific fighting during the breeding season show a much higher frequency of new wounds among males over 100 mm in snout-vent-length than in smaller males. The significant difference in new-wound frequency strongly suggests avoidance of fights by the small males, which is corroborated by laboratory and field observations. Access by males to reproductively active females depends on the ability to defeat other males in aggressive contests virtually always involving head biting if the males are of nearly equal size. Because the probability of winning agonistic encounters increases with size, young males avoid fights with older males. Aggressive contests with larger males and reproductive attempts other than courtship in the absence of larger males are deferred. Aggressive behavior in E. laticeps may be employed in direct defense of females, but might also be expressed in defense of specific sites and/or territories. In the laboratory, males in their home cages were significantly more likely to win encounters with males of similar size than were males fighting in the home cages of opponents. This suggests that encounter site could be important in determining encounter outcome and that field study of possible site defense or territoriality is needed.

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... Among North American skink species, Plestiodon laticeps, the Broad-headed Skink, is probably the best studied. It has been shown to exhibit pronounced intrasexual aggression such as fighting and biting during the breeding season (Cooper and Vitt 1987;1997). These studies focused on the behavior of adult males; the behavior of adult females was not specifically addressed. ...
... Our research showed that size is critical in determining dominance in female S. lateralis: in 9 of 10 trials, the larger of the two females was dominant. This result agrees with what has been found for both female (Akin 1998) and male (Myers and Paulissen 2017) S. lateralis and for skinks in general (Zwickel and Allison 1986;Cooper and Vitt 1987;Whittier and Martin 1992;Torr and Shine 1996;Paulissen and Moran 2017;Baines et al. 2020). Larger size in lizards is typically associated with superior capacity to threaten or to fight (Cooper and Vitt 1987;López and Martín 2001). ...
... This result agrees with what has been found for both female (Akin 1998) and male (Myers and Paulissen 2017) S. lateralis and for skinks in general (Zwickel and Allison 1986;Cooper and Vitt 1987;Whittier and Martin 1992;Torr and Shine 1996;Paulissen and Moran 2017;Baines et al. 2020). Larger size in lizards is typically associated with superior capacity to threaten or to fight (Cooper and Vitt 1987;López and Martín 2001). In female S. lateralis, however, threat displays and fighting were not observed and aggressive behavior was extremely rare (Table 1). ...
Article
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Studies of aggression and space use are essential to understanding resource use by reptiles, particularly lizards. Research in this area, however, exhibits bias in that the seminal work has been done on (1) species that are highly visible in their habitats (e.g. Iguanians); and (2) males. Studies of secretive species such as skinks and of females are less common. Here, we present results of a lab study of dyadic encounters of adult females of a common North American skink: Scincella lateralis (Little Brown Skink), and compare them to results obtained from an earlier study of adult males of the same species. Female S. lateralis never interacted unless they were within one body length of each other. The most common behavior exhibited was avoidance of one lizard (the subordinate) away from the other lizard (the dominant). As a result, the two lizards spent more time apart than close together and rarely shared the retreat. The larger of the two females was dominant in 9 of 10 trials. Compared to adult males, adult females showed far fewer aggressive behaviors such as lunging or chasing, and never bit each other. Unlike males, however, subordinate female S. lateralis exhibited tail twitching significantly more often than did dominants, suggesting this behavior may be a social signal for females, though the data suggest there may be other possible functions. Despite differences in the frequency of behaviors exhibited, patterns of space use and retreat use were the same in females as they were in males.
... Specific site defense is probably the ancestral condition in skinks (Martins 1994;Vitt and Caldwell 2014), though a few species exhibit true territoriality (e.g., Jennings and Thompson 1999;Stapley and Keogh 2004). Aggressive behaviors of various types have been documented in many species of skinks (Torr and Shine 1996;Jennings and Thompson 1999;Stapley 2006), including North American species in the genus Plestiodon (formerly Eumeces) (Fitch 1954;Perrill 1980;Cooper and Vitt 1987). But little is known about how such behaviors affect use of resources by the contestants. ...
... Dominant male Little Brown Skinks also bit their opponents much more often than they were bitten by their opponents, though the difference fails to reach statistical significance because the subordinate skinks sometimes bit back (Table 2). Biting is also a common behavior exhibited by skinks; it has been documented previously in Little Brown Skinks (Akin 1998) and many other skink species (Cooper and Vitt 1987;Torr and Shine 1996;Jennings and Thompson 1999;Stapley 2006;Fenner and Bull 2010;Sanchez-Hernandez et al. 2012). Though chases, lunges, and biting are the most dramatic aggressive behaviors exhibited by adult male Little Brown Skinks, by far the most common behavior exhibited was avoidance of the dominant male by the subordinate male. ...
... If both males were moving when they approached each other, the subordinate male either abruptly changed direction and ran off or darted around the dominant male; in either case, the subordinate male often ran to the side of the observation chamber opposite the side occupied by the dominant male. This behavior is again commonly seen in skinks (Perrill 1980;Zwickel and Allison 1986;Cooper and Vitt 1987;Whittier and Martin 1992;Sanchez-Hernandez et al. 2012), including Little Brown Skinks (Akin 1998). The behaviors chase/lunge, bite, and avoid are probably common to skinks in general and play an important role in establishing and maintaining dominance relationships. ...
Article
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The aggressive behaviors of adult male Little Brown Skinks, Scincella lateralis, and their effects on access to an important resource (a single retreat) were the subject of a study consisting of 10 laboratory trials in which the behavioral interactions between a pair of individuals was recorded. Analysis of these interactions made it possible to identify a dominant and a subordinate male in each trial; the male with the greater bulk was dominant in 9 of the 10 trials. Aggressive behaviors recorded include lunging, chasing, and biting; the dominant male performed lunging significantly more often than the subordinate male and was the only individual to exhibit chasing. The most common behavior recorded was avoidance which was shown almost exclusively by the subordinate male. Both dominant and subordinate males exhibited tail twitching which we hypothesize to be a sign of agitation. The two males spent significantly more time on opposite sides of the observation chamber than on the same side and almost never occupied the single retreat simultaneously because the subordinate male repeatedly moved to avoid the dominant male. The implications of these results on spacing patterns and resource use of Scincella lateralis in the wild are discussed.
... One characteristic of lizards' social relationships is that dominance may be based on differences in body size per se (Cooper and Vitt, 1987;Olsson, 1992;Tokarz, 1985). Therefore, when there is a conflict between the color badge signal and body size, lizards may rely primarily on body size and ignore the presence or absence of a badge. ...
... To avoid the effect of prior residence advantage (Cooper and Vitt, 1987;Olsson, 1992), we performed all the experiments in a neutral, previously unoccupied arena, consisting of a 1.5ϫ1.5 m enclosure that could be divided into two equal compartments by the use of a plywood partition. Males were placed in separate compartments and given 15 min to habituate to the new environment before the partition was removed. ...
... Behavioral observations of P. algirus lizards in the field and in seminatural enclosures have revealed that fights between males are frequent, with social status being correlated with mating success (Salvador et al., 1995). Body size has been found to be an important determinant of dominance in numerous lizards, with larger males usually being dominant in contests with smaller males (Cooper and Vitt, 1987;Olsson, 1992;Tokarz, 1985). In free-ranging P. algirus, interactions between large and small males are always initiated by the large male, which chases the smaller male whenever it approaches a female or the large male too closely (Salvador et al., 1995). ...
... They generally agree in pointing size as the first determinant of combat outcomes (e.g. Tokarz, 1985;Carpenter, 1995), as larger males are usually dominant over smaller ones (Cooper & Vitt, 1987;Olsson, 1992; Molina-Borja, Andron-Fumer & Alfonso-Martin, 1998;Sacchi et al., 2009). By avoiding fights with a larger male that presumably is the owner of a territory, an intruding small male may reduce the costs of aggressive interactions (Marler & Moore, 1988, 1989Marler et al., 1995). ...
... This is because a specific area has a greater value to residents than to intruders because of residents' familiarity with the physical and social environment (Stamps & Krishnan, 1994;Stamps, 1995). In this way, size and residency (or site familiarity) may strictly interact in determining the outcomes of social contests, for example, in lizards (Cooper & Vitt, 1987;Stamps & Krishnan, 1994;L opez & Mart ın, 2001;Sacchi et al., 2009). ...
Article
Territoriality evolves when the benefits gained from exclusive access to limited resources exceed the costs of defence. Sometimes animals evolve distinct morphs, that may reflect different capability, and in some territorial species of lizards the polymorphism is associated to alternative strategies, both for reproductive efficiency and territorial dominance. It is known that normally larger males are more aggressive and are able to defend a larger area and for longer than small males; in fact this dynamic is widespread in many animal species including the genus Podarcis. The aim of our study was to test which factors determine the outcome of fighting in the strongly territorial Italian ruin lizard, Podarcis siculus, using two types of contests: (1) resident versus intruder and (2) in a neutral arena. Furthermore, because these lizards are characterized by strong ventral colour variability, usually restricted to jaws and throat, we wanted to investigate if coloured lizards have higher chances at winning than white lizards. The results showed that the fight's result was significantly influenced by the state of residence, while the colour had no effect; instead, the snout to vent length difference between opponents had significant influence on the outcome in the neutral arena. Our results suggest that, in this lizard, both the size and the state of residency, no matter of colour, play an important role to determine the outcome of a fight, however, highly depending on the contest. We think that P. siculus should be object of future studies, focusing on behavioural and ecological aspects, even considering the occurrence of different colours within and among populations.
... Part of the reason skinks have been understudied relative to their diversity is that many species are secretive and do not use conspicuous visual displays to the extent of Iguania (Johnson et al., 2019). However, many skinks have been shown to exhibit intraspecific aggression, at least as adults (Cooper and Vitt, 1987;Akin, 1998;Stapley, 2006; Sá nchez-Herná ndez and Molina-Borja, 2019). As with lizards in general, however, intraspecific aggression in immature, juvenile, or neonate skinks has received little study (but see Jennings and Thompson [1999]; Paulissen and Moran [2017]). ...
... Part of the reason skinks have been understudied relative to their diversity is that many species are secretive and do not use conspicuous visual displays to the extent of Iguania (Johnson et al., 2019). However, many skinks have been shown to exhibit intraspecific aggression, at least as adults (Cooper and Vitt, 1987;Akin, 1998;Stapley, 2006; Sá nchez-Herná ndez and Molina-Borja, 2019). As with lizards in general, however, intraspecific aggression in immature, juvenile, or neonate skinks has received little study (but see Jennings and Thompson [1999]; Paulissen and Moran [2017]). ...
Article
Neonate Little Brown Skinks do NOT display aggression toward each other
... Studies on the courtship behaviour or social behaviour of lizards are not very common and many of them are in fact carried out as part of larger ecological studies. A few ethograms and several other studies on the courtship behaviour have been published for lizards, but these are mainly focused either on iguanids (Cooper, 1979;Greenberg, 1977a,b;Jenssen, 1975;Jenssen & Feely, 1991) or on scincids (Cooper & Vitt, 1987a;Done & Heatwole, 1977;Langkilde et al., 2003;Torr & Shine, 1994). Studies describing the sequential events in courtship and mating behaviour in agamids are rare (Brattstrom, 1971;Carpenter et al., 1970;Pandav et al., 2007). ...
Article
The current study describes and interprets the courtship behaviour exhibited by Sitana cf. ponticeriana. An ethogram comprised of 20 behavioural acts was compiled. Though complex communications were lacking in Sitana cf. ponticeriana, other acts were by and large similar (and perhaps evolutionarily homologous) to other agamids. The courtship behaviour was divided into three distinct patterns – orientation, persuasion and copulation. Gular flap extensions by the males of Sitana cf. ponticeriana was a peculiar display but not unique to this species. Head bobbing, which is a common feature to many agamids, was rare and functioned to enhance the visual acuity rather than to serve as a social signal. Neck grip was also a very short event performed rapidly by the male to subdue the female. Rest events of the courtship were more or less similar to other types of lizards. Tail twitching and tail twisting seemed to express high levels of arousal rather than ritualized social signals.
... In lizards, the chemical and visuals signals are the most studied; however, there are some studies that focus on auditory signals (Pough et al. 2001;Labra 2008). Chemical signals (pheromones), dependent on the vomeronasal organ (Labra et al. 2005;Labra 2008;Mason and Parker 2010), play a fundamental role in many aspects of reptile biology, sexual recognition (Cooper 1994;Labra and Niemeyer 1999), territory marking (Halloy and Robles 2002;Fox and Shipman 2003), avoidance of agonistic encounters (Cooper and Vitt 1987;Halloy and Halloy 1997;Labra 2006), aiding in the location of shelter, detection of predators, selection of microhabitat, foraging, communication, and recognition of conspecifics (Labra et al. 2001b;Font et al. 2010;Vitt and Caldwell 2013). Different organs, femoral, precloacal, or urodaeal glands, can produce pheromones (Cooper and Trauth 1992;Cooper 1994;Sánchez-Martínez et al. 2007;Labra 2008). ...
Chapter
The reproductive cycle of Galapagos giant tortoises has primarily been studied in captive individuals via noninvasive methodologies, including hormonal studies, radiographs, and ultrasound. During the annual reproductive cycle, mating peaks occur during the hot season months (December–June), followed by nesting during the cool season (June–December). Females dig flask-shaped holes in the soil typically in flat areas at lower elevations where soil suitable for digging accumulates. Females deposit 1–26 eggs and close nests with a mixture of urine, feces, and soil, which then dries into a hard cap, which seals in moisture and provides a protective layer for developing embryos. Rate of development and sex of the embryos depend on the temperature of the nest: when incubation temperatures are high (above 29.5°C) embryos become female and when temperatures are low (below 28°C) male. Eggs hatch after between 90 and 270 days of incubation. Young remain in the nest for up to 1 month until all eggs have hatched and consumed their yolk reserves. Hatchlings then dig an exit hole and emerge from the nest.
... L'importance de la taille du corps dans la vie des lézards a été démontrée par plusieurs études, notamment sur le succès reproducteur chez les mâles. Il a été démontré que la taille du corps est déterminante dans la compétition entre les mâles(Trillmich, 1983;Ruby, 1984;Vitt et Cooper, 1985 ;Cooper et Vitt, 1987;Olsson, 1992), et ceci affecte le succès Les résultats de Salvador et Veiga (2001) sur Psammodromus algirus montrent que les variables morphologiques affectent le succès d'accouplement chez les mâles. Les mâles les plus grands et les plus ornés ont plus de femelles (Salvador et Veiga, 2001). ...
Thesis
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Approche fonctionnelle de l’écologie de deux espèces de Reptiles Lace rtidés insectivores (Psammodromus algirus et Acanthodactylus erythrurus) et d’un reptile chélonien phytophage (Testudo graca graeca), dans un maquis dunaire du parc national d’El-Kala (Wilaya d’El-Tarf
... In lizards, the chemical and visuals signals are the most studied; however, there are some studies that focus on auditory signals (Pough et al. 2001;Labra 2008). Chemical signals (pheromones), dependent on the vomeronasal organ (Labra et al. 2005;Labra 2008;Mason and Parker 2010), play a fundamental role in many aspects of reptile biology, sexual recognition (Cooper 1994;Labra and Niemeyer 1999), territory marking (Halloy and Robles 2002;Fox and Shipman 2003), avoidance of agonistic encounters (Cooper and Vitt 1987;Halloy and Halloy 1997;Labra 2006), aiding in the location of shelter, detection of predators, selection of microhabitat, foraging, communication, and recognition of conspecifics (Labra et al. 2001b;Font et al. 2010;Vitt and Caldwell 2013). Different organs, femoral, precloacal, or urodaeal glands, can produce pheromones (Cooper and Trauth 1992;Cooper 1994;Sánchez-Martínez et al. 2007;Labra 2008). ...
Chapter
Reptiles have physiological, morphological, and behavioral adaptations that allow them to survive in desert environments, at high altitudes and in cold climates, such as the Patagonia region in southern Argentina. Knowledge of the ecology of Patagonian lizards is limited and fragmentary. The objective of this chapter is to present a synthesis of the current state of knowledge of the ecology of Patagonian lizards with regard to the use of (1) spatial resources (home range, use of microhabitats), (2) temporal resources (daily and seasonal patterns of activity), and (3) trophic resources (diet and nutrition strategies). We also discuss inter- and intra-species interactions, including predation, seed dispersal, parasitism, behavior, and resource partitioning. Keywords: Diet. Habitat. Use time. Behavior. Predation. Parasitism. Seed dispersal. Competition. Resource partitioning. Teiidae. Liolaemidae. Phyllodactylidae. Leiosauridae.
... In lizards, the chemical and visuals signals are the most studied; however, there are some studies that focus on auditory signals (Pough et al. 2001;Labra 2008). Chemical signals (pheromones), dependent on the vomeronasal organ (Labra et al. 2005;Labra 2008;Mason and Parker 2010), play a fundamental role in many aspects of reptile biology, sexual recognition (Cooper 1994;Labra and Niemeyer 1999), territory marking (Halloy and Robles 2002;Fox and Shipman 2003), avoidance of agonistic encounters (Cooper and Vitt 1987;Halloy and Halloy 1997;Labra 2006), aiding in the location of shelter, detection of predators, selection of microhabitat, foraging, communication, and recognition of conspecifics (Labra et al. 2001b;Font et al. 2010;Vitt and Caldwell 2013). Different organs, femoral, precloacal, or urodaeal glands, can produce pheromones (Cooper and Trauth 1992;Cooper 1994;Sánchez-Martínez et al. 2007;Labra 2008). ...
Chapter
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Understanding how human beings perceive and interact with the local herpetofauna is fundamental for its conservation. In this chapter, we propose looking forward to the local ecological knowledge (LEK) of the Patagonian lizards, especially the “matuasto”. The preliminary analysis of ethnohistorical sources points out the relevant role of “matuastos” in the cosmologies of the original people from Patagonia, often considered as immortal, selfish and harmful beings. Field reports agree on the warning not to disturb these territorial lizards; otherwise, they would react aggressively with bites. The recorded stories account for frequent biting events on sheep. The local perception on “matuastos” as harmful beings would provoke an attitude of caution and rejection towards them. This work provides a first overview on the relationship of lizards and the people from Patagonia while constituting an initial step for future research.
... Hasegawa, 1990;Webb & Shine, 1993). Finally, greater size confers a competitive advantage, with larger-bodied individuals more likely to win agonistic interactions (Tokarz, 1985;Cooper & Vitt, 1987;Sacchi et al., 2009), thereby maximizing their ability to secure key resources, such as territories (Sacchi et al., 2009), favourable perching sites (Tokarz, 1985), food (Stamps, 1977) and optimal basking and refuge sites (Carothers, 1981). ...
Article
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Islands are biodiversity hotspots, but their native inhabitants are vulnerable to predation from exotic predators. Conservation of island endemics has often involved translocating captive‐reared populations to predator‐free refugia. However, the long‐term success of these translocations has rarely been assessed. We investigated the traits that maximize post‐translocation survival in a cohort of captive‐reared Suter's skinks Oligosoma suteri and compared traits normally associated with survival and persistence of lizards (body condition, speed and overall size) to that of wild‐born skinks 6 years after release onto a predator‐free island in the north‐east of New Zealand. Our models showed that larger lizards, and lizards with lower body condition, had improved survival. While sprint speed of captive‐reared lizards did not differ significantly to that of wild skinks, diving ability of captive‐reared skinks was poor, with only female captive‐reared lizards diving during trials. Our results indicate that the traits associated with higher survival after release are not necessarily obvious and may be influenced by adaptation to captive conditions. Long‐term monitoring post‐translocation is therefore vital to determine the success of the translocation.
... Additionally, crypsis may be more effective for small snakes because they are less conspicuous. Previous studies on a variety of taxa have shown that conspecific agonistic encounters are typically won by larger individuals (Caldwell and Dingle, 1979;O'Neill, 1983;Tokarz, 1985;Schuett, 1997) and small individuals avoid confrontation (Cooper and Vitt, 1987;Van Buskirk, 1992;Schuett, 1997). Similar relationships may exist between snakes and their predators. ...
Article
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The use of defensive behaviors to avoid predation increases the likelihood of survival. Snake species have evolved numerous and diverse antipredatory behaviors to fit a variety of natural histories. Understanding how snakes react to simulated predation events can help us understand their ecology. I conducted behavioral trials on 11 colubrid and dipsadid species (n = 16 individuals) in the Republic of Panama to examine patterns of antipredation behavior. The level of aggression and number of antipredatory behaviors exhibited during simulated predation was positively correlated with body size. To complement these results, data from previously published studies were used to assess these patterns with a larger sample of Neotropical colubrids and dipsadids (n = 44 species). Indeed, the level of aggression and number of antipredatory behaviors known for each species was positively correlated with body size. However, the positive association between the number of antipredatory behaviors known for a species and body size was driven largely by colubrids and not dipsadids. Larger snakes may be more intimidating to potential predators, therefore making aggressive defensive behaviors more likely to be successful. Larger snakes also may encounter a higher diversity of predators and may benefit from the ability to choose from a suite of defensive behaviors specific to certain contexts. Although this study suggests two interesting patterns in the defensive behaviors of Neotropical colubrids and dipsadids, comparative studies of the interactions between snakes and their predators are needed to better understand the pressures driving variation in snake antipredation behavior.
... Most of what is known of lizard behaviour has come from the study of New World iguanids and teiids and Old World agamids (Carpenter and Ferguson 1977;Stamps 1977Stamps , 1983. A few behavioural studies of scincid lizards have focused on chemosensory behaviour in secretive fossorial New World species (Mount 1963;Vitt and Cooper 1985;Cooper and Vitt 1987a, 1987b, 1988. In Australia, the family Scincidae has undergone extensive radiation, with members of this family occupying ecological niches typical of those filled by iguanids and teiids elsewhere. ...
... Male lizards are much more aggressive against their peers compared to females (Kwiatkowski and Sullivan, 2002;Lailvaux and Irschick, 2007;McEvoy et al., 2013). Ergo, agonistic encounters between males are more common and may end up to tail loss (Cooper and Vitt, 1987;Bateman and Fleming, 2009;Cooper et al., 2015). Nonetheless, a byproduct of this increased intraspecific competition could be a higher propensity of males to hold on to tails more strongly. ...
Article
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Caudal autotomy is one of the most effective and widespread defensive mechanisms among lizards. When predators grasp the tail, lizards are able to shed it from the point of the attack and further. Numerous factors have been reported to affect tail-shedding performance such as temperature, age, predation pressure, intraspecific competition etc. Interestingly, the impact of sex on tail loss remains greatly understudied. Here, we analyzed tail autotomy performance, simulated in the lab, in 12 species of lacertid lizards belonging to five genera (Algyroides, Anatololacerta, Hellenolacerta, Ophisops, Podarcis). Our aim was to investigate whether sex affects caudal autotomy and/or the duration of post-autotomic tail movement. We failed to detect any effect of sex on tail loss in the species examined. Also, we did not find any sexual impact on the duration of tail movement after autotomy, with a single exception. Our findings suggest that autotomy serves as a defensive tactic equally in both sexes and is used in the same extent.
... Another plausible explanation is that small juveniles perceive adults as a greater threat than large juveniles and thus shift to less preferred substrates. These interpretations are supported by previous studies that demonstrate that agonistic encounters are typically won by larger individuals (Caldwell & Dingle 1979;O'Neill 1983;Tokarz 1985;Schuett 1997) and that small individuals avoid confrontation (Cooper & Vitt 1987;Van Buskirk 1992;Schuett 1997). Competition between size and age classes can be complex with competition occurring not just between adults and juveniles, but also between juveniles of different sizes (Van Buskirk 1992; Claessen et al. 2000). ...
Article
Habitat choice often has strong effects on performance and fitness. For many animals, optimal habitats differ across age or size classes, and individuals shift habitat use through ontogeny. Although many studies document ontogenetic habitat shifts for various taxa, most are observational and do not identify the causal factor of size-specific habitat variation. Field observations of the brown anole lizard (Anolis sagrei) show that juveniles perch on shorter and thinner vegetation than adults. We hypothesized that this variation is due to adult males forcing smaller juveniles to less preferred habitat. To test this assertion, we manipulated adult male densities in mesh enclosures with artificial trees to examine the response of juvenile microhabitat choice. We found that adult male density had strong effects on juvenile perch height, perch width, and substrate use, suggesting that age-class competition contributes to the observed ontogenetic differences in habitat choice. We also found that time of day significantly affected juvenile perch height and substrate use. In many cases, our results suggest that juveniles distance themselves from adults using different microhabitats from those used in our control ‘no-adult’ treatment. However, these findings were often body size dependent and varied depending upon time of day. This study highlights the complexity of juvenile perching behavior and demonstrates the role of intraspecific interactions in shaping habitat use by juvenile animals. For full article, visit - http://onlinelibrary.wiley.com/doi/10.1111/eth.12586/full
... There are few examples of gecko intersexual aggregations, but these are usually composed of only one male and one or more females (Chapple, 2003;Mouton, 2011;Barry, Shanas & Brunton, 2014). The most probable explanation of an intersexual aggregation, still to be experimentally tested, might be to avoid agonistic interactions that potentially might result in fatal or debilitating conse- quences for reptiles (Cooper & Vitt, 1987). Intraspecific agonistic behaviour is common in geckos, with a high level of intraspecific territoriality and associated male-male aggression (Stamps, 1977). ...
Article
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Background The extent of social behaviour among reptiles is underappreciated. Two types of aggregations are recognized in lizards: ecological and social, i.e., related to the attraction to a site or to animals of the same species, respectively. As most lizards are territorial, aggregations increase the probability of aggressive interactions among individuals, a density-dependent behaviour. Methods After some spurious observations of aggregation behaviour in the endemic Cabo Verde nocturnal gecko Tarentola substituta, we conducted a field-based study in order to thoroughly characterize it. We sampled 48 transects and 40 10 × 10 m quadrats on São Vicente Island to describe the incidence, size and composition of aggregations and to study the effect of gecko and refuge density, plus refuge quality, on refuge sharing. We hypothesize that when density of animals and scarcity of high-quality refuges is higher, lizards have increased probability of aggregating. We also predict a consistent pattern of size and composition of groups (male–female pairs, only one adult male per group) throughout the year if there is a selected behaviour to avoid agonistic interactions, and low thermal advantage to aggregating individuals. Results We present one of the first evidences of aggregation for Phyllodactylidae geckos. We found that T. substituta forms aggregations around 30–40% of the time, and that refuges are almost always shared by a female-male pair, sometimes with a juvenile, probably a mechanism to avoid aggressive interactions. We also observed that refuge sharing is dependent on refuge quality, as medium–large (thermally more stable and positively selected) rocks are shared much more frequently than small ones, but independent of adult sizes. Refuge sharing is also directly related to the density of geckos and inversely related to the density of high-quality refuges. We found no relation between body temperatures of geckos and refuge sharing when controlling the effect of rock/air temperature, suggesting that huddling does not improve thermoregulation. Discussion Our results suggest that in this harsh environment (rocks reach 46 °C) aggregation incidence is mainly driven by an ecological factor (scarcity of high-quality refuges) and its intersexual composition by social factors (avoidance of agonistic interactions by males, and possible increased reproductive success of the pair). This study sheds some light on the little explored gecko aggregation behaviour and other studies should follow.
... In regard to more physical aspects of fighting, a growing literature demonstrates that whole-organism performance abilities (i.e., the capacity of an organism to conduct ecologically relevant tasks, such as running, jumping, or biting; Bennett and Huey 1990;Garland and Losos 1994;Irschick and Garland 2001) can influence male-male contests in various taxa, independent of body size, such that good performers typically win fights against poor performers (Lailvaux and Irschick 2006a). Male lizards, for example, will bite each other during fights, often causing severe injuries (Cooper and Vitt 1987;Jennings and Thompson 1999), and the ability to acquire or defend territories appears to be positively related to both relative bite force (Huyghe et al. 2005;Lappin and Husak 2005) and relative head size (correlated with bite force ;Hews 1990;Herrel et al. 2001aHerrel et al. , 2001bPerry et al. 2004; but see Lappin and Husak 2005) in lizards. Furthermore, performance capacities important to fighting ability, such as bite force or endurance, are positively correlated, independent of body size, with the expression of male secondary sexual characters used during fights in several highly sexually dimorphic animal species (Lailvaux et al. 2005;Vanhooydonck et al. 2005aVanhooydonck et al. , 2005b, suggesting that male signals or displays may act as size-free indexes of important physiological components of fighting ability to rival males (Maynard Smith and Harper 2003). ...
Article
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Despite the empirical and theoretical attention paid to the role of sexual signals in resolving agonistic interactions between conspecific males, few studies have applied a comparative perspective, particularly across species that vary in combat intensity. We investigated the relative roles of a male sexual signal (dewlap size) and whole‐organism performance capacity (bite force) on male combat outcomes in nine species of Caribbean Anolis lizards that differ markedly in territoriality, as indicated by sexual size dimorphism. We found that (1) dewlap size was generally an honest signal of bite force in dimorphic but not less dimorphic species; (2) maximum bite force consistently predicted male combat success in dimorphic but not less dimorphic species; (3) in contrast to a priori predictions, dewlap size significantly predicted male combat success in less dimorphic but not dimorphic species; and (4) the incidence of biting but not dewlapping increases as species become more dimorphic. These findings suggest that more dimorphic (and hence more territorial) species escalate to biting during fights more readily compared with less territorial species. The ecological and behavioral qualities of species may therefore modify both the shape and the size of sexually selected traits as well as the nature of the information those traits convey.
... Within the context of sexual selection, two such advantages are usually advanced to explain differences in body size in lizards (Shine 1989;Anderson & Vitt 1990). The first hypothesis predicts an advantage for large adult males in male-male aggressive encounters, with resulting greater access to females (Cooper 1977;Ruby 1978;Carothers 1984;Cooper & Vitt 1987). Shine (1978) and Fitch (1981), for example, pointed out that larger males are common among species that exhibit combat behaviour. ...
Article
The extent of sexual selection in two girdled lizard species was evaluated by measuring sexual dimorphism in those characters normally affected by sexual selection. Neither Cordylus niger, a cool-adapted species, nor C. cordylus, a warm-adapted species, displayed any notable sexual differences in asymptotic body sizes, but both species displayed slight dimorphism in head size measurements. The C. niger sample contained more large males than large females, which may be attributed to a lower growth rate in females. In the cool Saldanha area, females of both species lack generation glands. In the warmer Gansbaai area, these glands are present in females of C. cordylus, but in lower numbers than in males. Sex ratios favouring females, have been recorded for both species. The observed sexual dimorphism in the two species seems to be mainly the result of differential energy allocation by females, and not of sexual selection perse.
... We videotaped (JVC GZ-MG680 camera) encounters, each lasting 30 min, between lizard pairs (one adult and one juvenile) in a neutral trial terrarium (77 Â 55 cm and 43 cm high) with a thin layer of sand on the bottom and no shelter (see Ethical Note). Both lizards were placed in the trial terrarium at the same time to avoid the effects of prior residency on the outcome of encounters (Cooper & Vitt, 1987;Olsson & Shine, 2000). Trials were performed from 1000 to 1700 hours local time, within the species' period of activity (Busack, 1976). ...
Article
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In many animal taxa, coloration is a visual signal used for communication among conspecifics, for example between age classes. Juvenile coloration has been hypothesized to reduce aggression from adults in some species, in what is called the aggression avoidance hypothesis. Spiny-footed lizards are good subjects for testing this hypothesis, as juveniles develop conspicuous red coloration on their hind limbs and tails that fades in adulthood. To test the influence of juvenile coloration on adult aggressiveness, we conducted videotaped encounters in captivity between adults of both sexes and juveniles with their natural red coloration, or experimentally painted either red or white on their natural red parts. Then we recorded the number of times juveniles were bitten and attacked. In unpainted juveniles, no significant relationship was found between juvenile coloration (brightness, red chroma or hue) and adult aggressiveness. However, juveniles painted red were bitten less than those painted white when number of times bitten was controlled for number of times attacked. This result supports the aggression avoidance hypothesis, as an escalation from low-intensity (attacking) to high-intensity aggression (biting) was less probable towards red juveniles. The presence of red coloration in juveniles caused the reduction in adult aggression, while small natural variations in this red colour did not seem to have any further effect. Juvenile red coloration in this species might indicate age or sexual immaturity to adults.
... The high percentages of aggressive behavior between males reflect their intrasexual competition for territory, food, and mates (Yasui 1998;Lailvaux & Irschick 2007;McEvoy et al. 2012). Intrasexual competition in male lizards often leads to fighting, which may inflict injury because the larger heads of males exert high bite force (Cooper & Vitt 1987;Husak et al. 2009;Herrel et al. 2010). Weaker intrasexual competition and inability to exert such high bite forces may limit the motivation of females for aggression and ability to be cannibals. ...
Article
Island populations may evolve distinct behavioral repertoires as a response to the conditions of insular life. Strong intraspecific competition is typical in insular lizards and may include cannibalism. In this study, we investigated sexual and age patterns of aggression in two populations of the Skyros wall lizard (Podarcis gaigeae), one from the main island of Skyros (Aegean Sea, Greece) and another from the satellite islet Diavates. The latter is terrestrial predator-free biotope, hosting a dense population of large-bodied lizards that have been reported to exert cannibalism. In staged encounters, we examined the aggressive propensities of adult male and female lizards against their age-peers and juveniles. Males from both populations were much more aggressive than females toward juveniles and other adults. Males from Diavates were more frequently aggressive to juveniles and other male lizards than males from Skyros. Diavates cannibals also captured their targets at shorter latency. We ascribe this distinct behavioral pattern to the high population density. Infanticide and intramale aggressiveness confer two great advantages to cannibals: food and elimination of future rivals.
... In the past, I have observed free-living White's Skinks Liopholis whitii and Eastern Blue-tongued Skinks Tiliqua scincoides persisting in the wild despite missing scales. In addition, head wounds are frequently sustained in male Broad-headed Skinks Eumeces laticeps during intraspecific fighting (Cooper & Vitt, 1987). ...
... Head size was a better predictor of contest success, although our study did not specifically address the role of head size in determining dominance. Nevertheless, it is likely that larger heads offer an advantage during male-male contests (Cooper & Vitt 1987b), especially in Platysaurus, where escalated contests often include biting. ...
Article
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Mistaken identity and competitive exclusion are two alternative hypotheses proposed to explain interspecific aggression between males. We examined agonistic behaviour in males of two lizard species: Platysaurus minor and P. monotropis. In each of nine outdoor field enclosures, we maintained a male and a female of both species (i.e., four total) and observed the dominance relationship between the males. Interspecific aggression was intense and P. monotropis was dominant in eight of nine enclosures. Furthermore, P. minor males received significantly more bite marks than P. monotropis males during the course of the experiment. To distinguish among the two hypotheses for interspecific aggression (mistaken identity and competitive exclusion), we presented P. minor males from sympatry and allopatry with model lizards of both taxa and measured aggressive responses. All trials with models were conducted in field enclosures where males were kept alone for the duration of the experiment. The model experiment revealed that compared to P. minor from sympatry, allopatric P. minor males were no less aggressive towards the heterospecific model than the conspecific model, a finding that supports the mistaken identity hypothesis. Finally, in the same experiment, we included a supernormal stimulus (pink Platysaurus model) to test if males were simply responding to a brightly coloured male lizard. Males showed some aggression towards the supernormal model, but significantly less than towards the two models (P. minor and P. monotropis) combined.
... Sexual size dimorphism in C. lineatissimus may result from sexual selection in which larger males are at an advantage over smaller males in acquiring mates. Sexual selection can maintain large body size in male lizards when large males mate more frequently than smaller ones, such as in C. tigris (Anderson, 1986), Anolis garmani (Trivers, 1976), A. carolinensis (Ruby, 1984), Sceloporus jarrovi (Ruby, 1981), and Iguana iguana (Dugan, 1982), or when larger males win in intrasexual agonistic encounters (Ruby, 1984;Vitt and Cooper, 1985;Cooper and Vitt, 1987). We have no direct evidence for this in C. lineatissimus, but observations on other teiid lizards suggest that this may occur in most or all species (e.g., Anderson and Vitt, 1990;Censky, 1996). ...
Article
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We studied the reproductive ecology of the teiid lizard Cnemidophorus lineatissimus during 1993 and 1994 near Chamela, Jalisco, Mexico. We estimate that males reached sexual maturity at a snout-vent length (SVL) of 51 mm and an age of five months, and females reached sexual maturity at a SVL of 62 mm and an age of seven months. Testicular mass increased from April to July, reaching maximal size between August and December, and decreased in January of the next year. Gonads of females began to increase in mass during June when vitellogenesis occurred. They reached maximum mass from July to November when most egg production occurred. Some egg production occurred in January as well. The reproductive season for males and females is extended, similar to many other tropical lizards. Mean clutch size was 4.1 ± 0.2 eggs. Clutch size was correlated with female size, but egg size and relative clutch mass remained constant among females and between years. Mean clutch size and female body condition were lower in 1993 compared to 1994, presumably reflecting the effects of annual variation in resource availability on females. Proximal climatic factors influence the timing and intensity of reproduction in C. lineatissimus, but the historical effect of foraging mode on teiid lizard morphology constrains relative clutch mass. Sexual dimorphism is evident with males reaching larger size than females, and seasonal variation in mean SVL in both sexes suggests that much of the population is replaced annually.
... Although we have not observed agonistic interactions between males of T. umbra, they are common in other Tropidurus species. Such interactions usually occur in species exhibiting dimorphism in relative head size (e.g., Cooper and Vitt 1987). Maintenance of sexual dimorphism in relative head size cannot be attributed to sexually mediated resource partitioning (e.g., Schoener 1967) because there is no relationship between lizard head size and prey size, and prey size relative to head size is very small. ...
Article
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The tropidurid lizard Tropidurus umbra lives on medium-sized trees in lowland tropical forest of the Amazon region. Individuals may be active on tree trunks in sun or shade, with most activity occurring from 11:00 to 13:00. Body temperatures average 29.1 degrees C. The diet consists nearly exclusively of ants and there is no relationship between prey size and lizard size. Females reach sexual maturity at 79 mm snout-vent length (SVL) and males at 78 mm SVL. Although there appears to be no sexual dimorphism in SVL, males have relatively larger heads than females. Clutch size is usually two eggs and females appear to produce more than one clutch per season. Comparisons with other studied tropidurid lizards suggest that dietary specialization on ants, reduced sexual dimorphism, and reduced clutch size are derived characters.
... Most information on lizard behaviour has come from the study of New World iguanids and teids and Old World agamids (Carpenter and Ferguson 1977;Stamps 1977Stamps , 1983. Study of social behaviour in scincid lizards has been limited mainly to secretive fossorial members of New World species (Mount 1963;Stamps 1977; Vitt and Cooper 1985; Cooper and Vitt 1987a, 1987b, 1988. The study of Emoia physicae in New Guinea suggests that the social behaviour of Australasian scincids may be different from that of North American species (Zwickel and Allison 1986). ...
Article
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A laboratory study was conducted to observe patterns of social behaviour of males of the sexually dimorphic rainbow skink, Carlia rostralis. Animals were observed alone or in matched pairs, both as residents and non-residents of the testing cage. Behavioural patterns observed included active, aggressive, submissive, assertive, exploratory and escape categories of acts. These patterns of behaviour varied in social contexts. Active behaviour increased significantly when males were paired. Of the paired encounters, 60% had neutral outcomes in which no dominant/subordinate individual could be determined. When dominance/subordinance interactions occurred they were found to be expressed in a linear hierarchy. Dominance was positively correlated with male snout-vent length. Dominance of males was absolute and did not depend on residence status. These observations of social behaviour in the laboratory, together with preliminary observations of behaviour of this species in the field, suggest that Carlia rostralis exhibits different patterns of social behaviour from that observed in other scincid lizards.
... Large overall size and large relative head size, characteristic of most macroteiids studied (Fitch 198 1 ; Anderson and Vitt 1990 ), presumably reflect the advantages of hypertrophy in characteristics that affect male mating success, and consequently, fitness. Large overall size as well as large relative head size have been shown to be related to success in intrasexual encounters (Cooper and Vitt 1987) and mate choice (Cooper and Vitt 1993) in other lizard species. Greater hind-leg length in males may reflect a combination of advantages associated with speed and agility in social interactions with other males (intrasexual selection), including the mobility required to court females (intersexual selection), and the mobility required to patrol large home ranges (Anderson and Vitt 1990). ...
Article
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The whiptail lizard Cnemidophorus deppii was studied during late dry season on a tropical beach on the Pacific coast of Nicaragua. Most aspects of the ecology of this species are similar to those of other active foraging lizard species studied. Individual C. deppii spend most of a typical daily activity period on sand moving from vegetation patch to vegetation patch, presumably in search of food. The amount of time spent in the sun is greatest in early morning and at its lowest level at midday. The average rate of movement was 0.048 ± 0.004 m/s. Body temperatures of active lizards averaged 40.0 ± 0.25 °C, and most activity occurred during morning and late afternoon. Body temperatures were significantly lower in whiptails active during the morning than later in the day. Forty-two types of prey were identified in stomachs, with termites, spiders, and various orthopterans accounting for most of the diet volumetrically. There was no correlation between lizard size and prey size. There was a significant negative relationship between prey width and the number of prey in stomachs. Snout–vent length (SVL) at sexual maturity was 60 mm for females and 58 mm for males. Mature females averaged 63.8 ± 0.7 mm SVL and produced clutches varying from 1 to 3 eggs (). Oviductal eggs averaged 13.6 ± 0.64 × 7.7 ± 0.21 mm in size. There was no significant relationship between female SVL and clutch size. Relative clutch mass was similar to that for other active foraging lizard species. Sexual dimorphism was apparent in coloration (males brightly colored), body size (males larger), and relative head size (male heads larger independent of body size differences). These differences presumably are due to sexual selection.
... Studies on the courtship behaviour or social behaviour of lizards are not very common and many of them are in fact carried out as part of larger ecological studies. A few ethograms and several other studies on the courtship behaviour have been published for lizards, but these are mainly focused either on iguanids (Cooper, 1979; Greenberg, 1977a,b; Jenssen, 1975; Jenssen & Feely, 1991) or on scincids (Cooper & Vitt, 1987a; Done & Heatwole, 1977; Langkilde et al., 2003; Torr & Shine, 1994). Studies describing the sequential events in courtship and mating behaviour in agamids are rare (Brattstrom, 1971; Carpenter et al., 1970; Pandav et al., 2007). ...
Article
The current study describes and interprets the courtship behaviour exhibited by Sitana cf. ponticeriana. An ethogram comprised of 20 behavioural acts was compiled. Though complex communications were lacking in S. cf. ponticeriana, other acts were by and large similar (and perhaps evolutionarily homologous) to other agamids. The courtship behaviour was divided into three distinct patterns – orientation, persuasion and copulation. Gular flap extensions by the males of S. cf. ponticeriana was a peculiar display but not unique to this species. Head bobbing, which is a common feature to many agamids, was rare and functioned to enhance the visual acuity rather than to serve as a social signal. Neck grip was also a very short event performed rapidly by the male to subdue the female. Rest events of the courtship were more or less similar to other types of lizards. Tail twitching and tail twisting seemed to express high levels of arousal rather than ritualized social signals.
Chapter
Contests are an important aspect of the lives of diverse animals, from sea anemones competing for space on a rocky shore to fallow deer stags contending for access to females. Why do animals fight? What determines when fights stop and which contestant wins? Addressing fundamental questions on contest behaviour, this volume presents theoretical and empirical perspectives across a range of species. The historical development of contest research, the evolutionary theory of both dyadic and multiparty contests, and approaches to experimental design and data analysis are discussed in the first chapters. This is followed by reviews of research in key animal taxa, from the use of aerial displays and assessment rules in butterflies and the developmental biology of weapons in beetles, through to interstate warfare in humans. The final chapter considers future directions and applications of contest research, making this a comprehensive resource for both graduate students and researchers in the field.
Article
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Cranial morphology in lepidosaurs is highly disparate and characterized by the frequent loss or reduction of bony elements. In varanids and geckos, the loss of the postorbital bar is associated with changes in skull shape, but the mechanical principles underlying this variation remain poorly understood. Here, we seek to determine how the overall cranial architecture and the presence of the postorbital bar relate to the loading and deformation of the cranial bones during biting in lepidosaurs. Using computer-based simulation techniques, we compare cranial biomechanics in the varanid Varanus niloticus and the teiid Salvator merianae , two large, active foragers. The overall strain magnitudes and distribution across the cranium is similar in both species, despite lower strain gradients in Varanus niloticus . In Salvator merianae , the postorbital bar is important for the resistance of the cranium to feeding loads. The postorbital ligament, which partially replaces the postorbital bar in varanids, does not affect bone strain. Our results suggest that the reduction of the postorbital bar impaired neither biting performance nor the structural resistance of the cranium to feeding loads in Varanus niloticus . Differences in bone strain between the two species might reflect demands imposed by feeding and non-feeding functions on cranial shape. Beyond variation in cranial bone strain related to species-specific morphological differences, our results reveal that similar mechanical behaviour is shared by lizards with distinct cranial shapes. Contrary to mammals, the morphology of the circumorbital region, calvaria and palate appears to be important for withstanding high feeding loads in these lizards.
Preprint
There is uncertainty regarding the timing and fossil species in which mammalian endothermy arose, with few studies of stem-mammals on key aspects of endothermy such as basal or maximum metabolic rates, or placing them in the context of living vertebrate metabolic ranges. Synchrotron X-ray imaging of incremental tooth cementum shows two Early Jurassic stem-mammals, Morganucodon and Kuehneotherium , had lifespans (a basal metabolic rate proxy) considerably longer than comparably sized living mammals, but similar to reptiles. Morganucodon also had femoral blood flow rates (a maximum metabolic rate proxy) intermediate between living mammals and reptiles. This shows maximum metabolic rates increased evolutionarily before basal rates, and that contrary to previous suggestions of a Triassic origin, Early Jurassic stem-mammals lacked the endothermic metabolism of living mammals. One Sentence Summary Surprisingly long lifespans and low femoral blood flow suggest reptile-like physiology in key Early Jurassic stem-mammals.
Article
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.
Thesis
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All organisms have specific habitat requirements that allow them to properly function in the environment. However, optimal habitats often differ across age classes, and accordingly, juveniles shift habitat choice as they age. Field observations of the brown anole lizard (Anolis sagrei) suggest that juveniles perch in open-canopy areas on low vegetation whereas adults reside in forest edges on higher vegetation. I hypothesized that this age-specific habitat variation is because adults force juveniles to less preferred habitat. To address these issues, I conducted a series of experiments to examine the role of inter-age class competition in driving variation in perch use behaviors. In Chapter 1, I provide a background of relevant literature and briefly discuss the justification and design of the experiments. In Chapter 2, I altered the density of adult males in mesh enclosures in the laboratory to examine the response of microhabitat choice by juveniles. I found that juveniles decreased perch height and had complex density-dependent effects on perch width and substrate use in the presence of adult males. In Chapter 3, I conducted two simultaneous field experiments. The first experiment examined how adult male and female (independently) density affect juvenile microhabitat choice and survival. The second experiment examined how juvenile presence influences adult microhabitat choice. I found that high adult male density reduced juvenile survival, yet juveniles did not vary microhabitat choice in response to either adult male or female density. In addition, adults did not select against juveniles in a way that would contribute to the observed age-class habitat variation. Neither adult male or female microhabitat choice was influenced by the presence of juveniles. Overall, we show that adults have a sex- and density-dependent effect on juvenile populations. In the lab, we found that juveniles modify microhabitat choice in response to adult males, but we find no evidence for this in the field. This inconsistency in laboratory versus field studies may be explained by the differences of juvenile body size used between experiments (i.e., juveniles in the field experiment were much smaller than those used in the laboratory experiment). Thus, I suggest that the selective pressure from adults and/or other predators is strong enough that hatchlings innately stay low to the ground, whereas larger juveniles are able to shift microhabitat choice plastically depending on environmental context. In addition, juvenile macrohabitat dispersal from areas of high adult male density may contribute to the variation in age-class habitat use.
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Alternative mating tactics in males of various taxa are associated with body color, body size, and social status. Chameleons are known for their ability to change body color following immediate environmental or social stimuli. In this study, we examined whether the differential appearance of male common chameleon during the breeding season is indeed an expression of alternative mating tactics. We documented body color of males and used computer vision techniques to classify images of individuals into discrete color patterns associated with seasons, individual characteristics, and social contexts. Our findings revealed no differences in body color and color patterns among males during the non-breeding season. However, during the breeding season males appeared in several color displays, which reflected body size, social status, and behavioral patterns. Furthermore, smaller and younger males resembled the appearance of small females. Consequently, we suggest that long-term color change in males during the breeding season reflects male alternative mating tactics. Upon encounter with a receptive female, males rapidly alter their appearance to that of a specific brief courtship display, which reflects their social status. The females, however, copulated indiscriminately in respect to male color patterns. Thus, we suggest that the differential color patterns displayed by males during the breeding season are largely aimed at inter-male signaling.
Article
Significant sexual dimorphism in overall size occurs in the rock agama, Agama atra (Sauria; Agamidae), with males growing larger than females. Geographic variation in the degree of sexual size dimorphism also exists, males growing significantly larger than females in Namaqualand and Namibia compared to populations in other areas. Sexual differences in scaling of head, limb and tail dimensions were mainly the result of differential asymptotic sizes reached by the sexes. Head size was also influenced by a faster increase in head dimensions with increasing snout to vent length in males compared to females, probably as a result of sexual selection. In females, scaling of limb and tail dimensions was decreased compared to males, possibly a result of differential energy allocation to reproduction.
Article
Previous studies of lizard mating systems have provided morphological and ecological hypotheses that may explain variation in male reproductive success. We present the results of a field study of factors associated with pairing success in males and females of the lacertid lizard Psammodromus algirus. Operational sex ratio was male biased and varied during the mating season. Early in the season, large females frequently paired sequentially with two males. However, late in the season, small females tended to pair with only one male. This suggests that male-male competition was stronger for larger females at the beginning of the mating season or there were fewer fertile females available. Pairs were observed together for 1-4 days, suggesting pre- or postcopulatory mate guarding behavior. Male pairing success was primarily influenced by morphological traits; males with larger heads, larger snout-vent lengths, and more ornamentation paired with more females. Male home range size and number of females overlaped did not affect male pairing success. More active males, which may have selectively moved within home ranges of paired females, had higher pairing success than less active males. The temporal distribution of receptive females seemed to favor polygyny. However, only the largest males were successful in competition for females throughout the mating season.
Article
Full-text available
Contests are an important aspect of the lives of diverse animals, from sea anemones competing for space on a rocky shore to fallow deer stags contending for access to females. Why do animals fight? What determines when fights stop and which contestant wins? Addressing fundamental questions on contest behaviour, this volume presents theoretical and empirical perspectives across a range of species. The historical development of contest research, the evolutionary theory of both dyadic and multiparty contests, and approaches to experimental design and data analysis are discussed in the first chapters. This is followed by reviews of research in key animal taxa, from the use of aerial displays and assessment rules in butterflies and the developmental biology of weapons in beetles, through to interstate warfare in humans. The final chapter considers future directions and applications of contest research, making this a comprehensive resource for both graduate students and researchers in the field.
Article
Many animals face the task of locating and settling on a territory where they can produce offspring. Over the past 36 years, theoretical and empirical studies have provided growing support for the 'foothold hypothesis', which attempts to explain territorial settlement of long-lived animals. The hypothesis maintains that a young prebreeder lives within or intrudes into a cluster of breeding territories, accumulates site-dependent dominance there, then outcompetes other prebreeders for a territory within the cluster when it becomes available. We examined patterns in territorial intrusion and settlement among prebreeders of known age and natal origin to test the foothold hypothesis in the common loon, Gavia immer. We tested two other hypotheses for territory settlement: the maturation hypothesis, which posits that animals await physical and/or behavioural maturity before territory acquisition; and the assessment hypothesis, which maintains that prebreeders intrude into territories to assess fighting ability of territory owners, one of which they ultimately evict. We found no evidence for footholds in loons: prebreeders focused their intrusions within roughly 10 clustered territories, but intruded infrequently into the lake on which they later settled. Furthermore, prebreeders that waited years to usurp a territory had reproductive success no different from those that settled more rapidly on a vacant territory. The maturation hypothesis, in contrast, was supported in both sexes: prebreeders showed a sharp increase in fighting ability with age, and males exhibited age-related increases in mass and tendency to confront territory owners. The assessment hypothesis also gained support because intruders interacted extensively with owners and intruded frequently after territorial turnovers. Our study adds to a small but growing number of studies that fail to support the foothold hypothesis for territory settlement and support the conclusion that modes of territory acquisition might be more varied than previously thought.
Article
The heterochronic basis of evolution of size and sexual dimorphism within the American members of the fasciatus group of Eumecces was investigated. All Asian and American fasciatus group species are sexually dimorphic in size and shape. Males are larger with relatively larger heads. In most species adult male snout-vent length is between 70 and 90 mm. However, the southeastern U.S. species E. laticeps is much larger, attaining up to 143 mm SVL, and shows greater sexual dimorphism in size and relative head proportions. The greater sexual dimorphism in SVL in E. laticeps is a result of a type of peramorphic heterochrony known as rate hypermorphosis. Sexual dimorphism in E. laticeps can be viewed as a result of two adaptive events. The first is the evolution of distinct sexual dimorphism in size and shape which occurred in the common ancestor of the entire group, presumably as a result of sexual selection. The second is the evolution of significantly higher dimorphism in E. laticeps, which is correlated with a general increase in body size. Increased body size may be an adaptation to increased territoriality. Rate hypermorphosis is seen as a means of increasing size without altering a plesiomorphic ontogenetic pattern and seasonal breeding system.
Article
Natural-history studies represent the observational stage of the scientific method, and the single greatest discovery in biological sciences, evolution by natural selection, was based largely on a vast amount of natural-history information collected by Charles Darwin. I briefly review natural-history observations that I have made during my career that led to discoveries in life-history theory, placentation in New World Mabuya that rivals that of eutherian mammals, social behavior in the North American clade of five-lined skinks, and the relationship of ecological traits of lizards globally to their evolutionary history (phylogeny). Gifted collaborators provided the intellectual interplay that led to these discoveries, and they certainly deserve as much credit as I do. I briefly comment on what I consider to be frontiers in herpetology that involve combining phylogenetic hypotheses with natural-history data. In a final comment, I encourage those among us who are able to spend extended time periods in the field to collect as much natural-history data as possible, because these data describe reality, and, as theories and phylogenies evolve, the kinds of basic data that led to Darwin's theory of evolution by natural selection can be applied again and again.
Article
Among iguanian lizards, males are often larger than females. As a result, much attention has been directed toward understanding the evolution of sexual size dimorphism (SSD) in this group. SSD can result from a number of developmental, physiological, and demographic processes, which may cause sex differences in growth trajectories, timing of maturity, and adult age distributions. Knowledge of these proximate mechanisms can improve our understanding of the evolution of SSD. Only recently, however, have efforts been directed toward understanding proximate mechanisms. I examined the proximate causes of SSD in a population of a South American iguanian lizard, Microlophus occipitalis. The majority of the SSD in this population resulted from continued postmaturity growth in males and reduced postmaturity growth in females. Additionally, adult males tended to live longer than females, which affected adult age and size distributions. The proportion of young individuals in samples had strong effects on temporal fluctuations in SSD in the population. I discuss the importance of studying proximate mechanisms for evolutionary analyses of SSD in organisms that continue to grow after reaching maturity.
Article
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Little information on the behavioral ecology and social organization of New Zealand's diplodactylid geckos is available. At least two species may be gregarious and share shelters, but data on the extent and possible function of this behavior are lacking. We examined the spatial distribution patterns of Duvaucel's Geckos in diurnal retreats over the four seasons. We tested whether geckos formed aggregations more often than expected by chance, and investigated whether or not the thermal properties of used shelters, gecko body temperatures and group composition affected aggregation patterns. Duvaucel's Geckos utilized a range of natural structures as diurnal shelters and showed a tendency to aggregate throughout the year (47–71% of individuals). Mixed-sex groups of up to eight individuals, including juveniles, occurred year round. Aggregations never contained more than one adult male and typically consisted of a male–female pair. Shelter-sharing adult males were larger than solitary males. Juveniles sheltered in close association with adults of either sex throughout the study. Shelter thermal properties did not appear to influence aggregative behavior. Aggregation patterns fluctuated seasonally, but the factors affecting these distribution patterns remain unclear. The occurrence of year-round shelter aggregations and frequent male–female and adult–juvenile associations indicate that this species might possess a complex social system. Further research examining the social and genetic relationships between group members, juvenile dispersal rates, and the temporal stability of aggregations is required to confirm the degree of complexity.
Article
Boldness and aggressiveness are two behavioural traits that have received extensive attention in the field of animal behaviour. However, relatively little is known about how these traits are maintained in populations and the fitness of individuals that exhibit them. We tested the effect of boldness and aggressiveness on the reproductive success of zebrafish, Danio rerio. Using behavioural tests, we established groups of males that varied consistently in their boldness (bold, middling and shy) as well as groups of males that differed in their aggressiveness (aggressive, middling and nonaggressive) and paired them with randomly selected females. We found no difference in the total number of eggs laid by females mated to bold or aggressive males. However, the number of fertilized eggs differed, with the boldest and the most aggressive males fertilizing more eggs than the other groups. Furthermore, the proportion of fertilized eggs differed between groups. These results show that an individual's reproductive fitness can be associated with behavioural variations in boldness and aggressiveness.
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Two main explanations, intraspecific niche divergence and sexual selection, have been proposed to explain the origin of sexual size dimorphism. To test these competing hypotheses I studied the ecology, feeding behavior, and diet of the lizard Anolis polylepis in a Costa Rican rain forest. Male A. polylepis were significantly larger and heavier than females but ate smaller food items and had lower stomach volumes, despite possessing longer and wider heads. Males were more sedentary than females or juveniles, chose higher perches, and were more likely to be involved in agonistic interactions. Diets of males, females, and juveniles were also significantly different taxonomically. These data are consistent with the sexual selection origin theory but not with an ecological one. Thus, observed dietary differences probably evolved once dimorphism had been attained through sexual selection.
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A model similar to the single-species source-sink models developed by Pulliam and by Pulliam and Danielson is described for species that have "distinct" habitat preferences and preemptive occupation of sites within habitats. The model shows that the interactions between two species do not result solely from the intrinsic properties of the species involved. They are also functions of the landscape in which the species occur. One species may cause an increase (facilitation) in the equilibrium population size of another species if the high-quality source habitat for the second species is rare relative to the abundance of low-quality sink habitat. A species may inhibit another if the second species' source habitat is abundant. Combinations of facilitation and inhibition effects describe the interactions between two species. There are two sets of possible interactions for any landscape of two habitat types. These are [(-, +), (-, -), (+, -)} and {(-, +), (+, +), (+, -)}. Species for which individuals can sample a large number of sites are likely to exhibit one of the interactions in the first set. Species for which individuals sample only a few sites are likely to exhibit interactions from the second. Within each set of interactions, the relative abundances of each habitat will determine which interaction will occur in the landscape.
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Kentropyx pelviceps was studied in lowland tropical forest of eastern Ecuador. Most individuals were first observed in leaf litter of treefall gaps or forest, approximately 30% being first observed above ground on trunks or branches of fallen trees. Activity occurred from 10:00 to 16:00 in microhabitats receiving maximum insolation. Body temperatures of active lizards averaged 34.1 +/- 0.4 degrees C. Lizards active when sun was available had higher body temperatures than lizards active when sun was not available. When sun was available, lizards spent more time moving and moved farther than when sun was not available. When sun was hidden behind clouds, lizards typically ceased foraging, pressed their bodies against the substrate, and basked, receiving direct exposure. Most time active was allocated to basking, presumably as a result of limited availability of sunlight. Prey consisted primarily of roaches, orthopterans, and spiders, and prey size was determined to a large extent (69.6% of variation) by lizard body size. Males and females reached sexual maturity at 80 mm snout-vent length. Males reached a larger maximum size than females, and sexual dimorphism was apparent in nearly all morphological characteristics of adults when the effect of size was removed. Clutch size averaged 6.5 +/- 0.3 eggs, and there was no relationship between clutch size and female size. Evidence suggests that the breeding season is extended. Comparisons with other studied species of Kentropyx suggest that many aspects of the ecology of K. pelviceps in eastern Ecuador are affected by the reduced time available for activity resulting from reduced sun availability.
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We measured body dimensions and coloration and quantified the behavior of females and males of two color phases in the Bonaire whiptail, Cnemidophorus murinus, to begin addressing the ultimate causation for sexual dimorphism in this species. Examination of size-adjusted body dimensions revealed that males have wider, longer, and deeper heads as well as somewhat longer forelegs and hind legs. Males were characterized by two distinct coloration patterns. Blue males displayed purple–blue dewlaps, blue–gray background coloration on the head and anterior torso, numerous light blue spots on the flanks, brown–orange coloration on the posterior torso, and a turquoise section on the proximal portion of the tail. By contrast, brown males were uniform olive–green to yellow–brown, with the exception of light blue spots on the lateral torso. Females were colored like brown males but lacked the blue spots. Testis length scaled with body size. Testes of only 26% of brown males were active, whereas all blue males had active testes. Blue males initiated aggressive encounters involving chases and displays directed toward other males much more frequently than females were aggressive with consexuals or with either type of male. Brown males were not observed to initiate aggression. Most blue male aggression was directed toward other blue males (70.6% of encounters), whereas 29.4% of encounters were with brown males. Blue males initiated 85.7% of the courtship encounters observed compared with only 7.1% initiated by brown males and 7.2% by females. Male-biased dimorphism in head and leg dimensions as well as coloration, together with higher rates of intrasexual aggression and courtship activity by blue males, are consistent with the hypothesis that sexual selection explains the evolution of sexual dimorphism in C. murinus.
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Not all individual lizards in a population are simultaneously active even when thermal conditions are suitable for activity. We examined inter-individual variability in activity levels of male Iberian rock lizards (Lacerta monticola) in a seminatural enclosure during the mating season, and analyzed whether social status affects their activity levels, time budgets, and body-mass changes. Activity levels of lizards varied significantly with time of day. However, activity levels of individual males were significantly correlated with their rank in the social hierarchy. When the males were active, their status did not influence the time spent basking, resting, or moving, but males with a higher status spent more time in social activities. Higher activity levels were costly, causing males to lose more body mass, although this could have been mainly due to the costs of maintaining a higher social status. We conclude that because attaining a higher status may require a male to be more active and more involved in agonistic encounters, subordinate individuals decrease their activity in order to decrease the costs of social behavior.
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1. The social behavior of A. garmani was studied for a total of eight months during seven separate visits to a study area of nine acres in Jamaica. 2. Adult males are 2.25 times larger by weight than adult females. At all times of the year and at all sizes for which there are data males grow faster than females. Growth rates for the same individuals in different four month periods are positively correlated. 3. By measuring reproductive success as frequency of copulation, it was discovered that in adults of both sexes increasing size increases reproductive success, but that this tendency is significantly stronger in males than in females. There is no evidence that age makes an independent contribution to a male's frequency of copulation. 4. The steep slope of the function relating reproductive success to adult male size results apparently from sexual selection: males compete aggressively to occupy exclusive territories containing females. There is a strong tendency for large males to occupy correspondingly large territories which in turn contain large numbers of females. About 90% of copulations were performed by a territorial male within his territory. 5. As young males mature they tend to be found less frequently within the territories of large males. Males 105 mm and larger are almost never seen within the territories of other males in this category. Males 100-104 mm must disperse if they are still within a large male's territory and males within this size range show a significantly lower frequency of copulation than would be expected from the function relating size to reproductive success for other adult males. 6. Two homosexual copulations were observed and are described. 7. The adult sex ratio is biased in favor of females. 8. Recapture data appear to show that females survive better with increasing size up to 90 mm. Males appear to survive better up to 110 mm but probably not at larger sizes.
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The spacing behavior, displays and aggression of hatchling and juvenile lizards (Anolis aeneus) were compared to the behavior of the adults. Tn adults these behaviors are sexually dimorphic, but juveniles of both sexes show similar behavior. Hatchling lizards a few days old have nonoverlapping home ranges or participate in dominance hierarchies of up to six steps. Status in dominance hierarchies is almost entirely size dependent. The particular type of social system shown varies with microhabitat. Juvenile home ranges are smaller than those of adults and enlarge with age. Home ranges of juveniles are more variable in size than those of adults. Temporal elements of the species specific bob pattern are very stereotyped in both juveniles and adults. Intraindividual variation in display element duration is low and interindividual variation high in all age and size groups. However, mean duraton of elements is longer for larger lizards. Two other displays are significantly more variable in juveniles than in adults. Most of this variation is due to added interindividual variance in juvenile display elements. Juveniles and adults of both sexes are able to give all displays except courtship displays. The frequency with which certain displays are given is significantly different for juveniles, adult females and adult males. Juveniles are more apt to give certain aggressive displays than are adults of either sex. Longterm ontogenetic studies of individual females indicates that initially they give the aggressive displays characteristic of juveniles in general, but that the frequency of these displays decrease when they become sexually mature. When territorial resident lizards of any age are exposed to tethered intruders they react aggressively. Aggressive responses were ranked and aggression computed for certain size ratios of intruder and resident juveniles (I/R ratio). This aggression was compared to that predicted on the basis of food competition between different lizard size ratios. At both large and small lizard size ratios (I/R) juvenile Anolis aeneus are more aggressive than are either adult males or adult females at the same size ratios. This added aggressiveness to very large and very small intruders cannot be explained in terms of food competition between juvenile lizards of different sizes.
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Agonistic behaviour in male lizards belonging to the fasciatus group of Eumeces (Scincidae) is directed primarily and perhaps almost exclusively to conspecific males. Heterospecific males, although visually quite similar to conspecific males, are usually ignored following chemosensory investigation by tongue-flicking. Male E. inexpectatus did not behave aggressively toward male E. fasciatus except when cloacal and skin odors of male E. inexpectatus had been transferred to them. Male E. inexpectatus therefore recognize conspecific males by a species-identifying odor. Eumeces fasciatus and E. laticeps may or may not possess similar abilities. -from Authors
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Eumeces egregius, a small fossorial skink of the southeastern Coastal Plain was studied in the laboratory and in the field to obtain information on its ecology, life history, behavior, and geographic range. Most of the specimens used in the study were obtained by raking through mounds of sand pushed up by the pocket gopher, Geomys pinetis; and by certain geotrupine scarab beetles. The mounds apparently serve as basking sites for the skinks and for certain other fossorial animals. The preferred temperature range for E. egregius lies between 26 and 34 C. Food studies indicate seasonal variation in food habits and reveal peculiarities in the diets of certain populations. Courtship and mating occur mostly during the fall and winter. Males recognize females chiefly by odor. The stereotyped courtship ends with the assumption of a mating position in which the male seizes the female on the side and directs his body first over then under hers. Copulation usually lasts from 15 to 30 minutes. In captivity males are inclined to fight among themselves. Homosexual behavior was noted among captive female lizards. The females undergo a 3- to 4-week period of relative inactivity following mating, after which they feed voraciously and develop fat stores. Nesting activity is greatest from April through June. Usually, from 3 to 7 eggs are laid in nest cavities constructed in the soil at depths varying from several inches to 6 feet. The females remain in their nests constantly from the time they construct them until the young have dispersed. In the laboratory young lizards of Florida parents grew rapidly and attained sexual maturity and mated during the first fall. Those of Georgia and Alabama parents grew more slowly and were still immature at almost 1 year of age. Red-tailed skinks appear to be gregarious. There is no evidence of territoriality among males. Known predators are the snakes, Masticophis flagellum, Coluber constrictor, Lampropeltis doliata, and Sistrurus miliarius. One per cent of the specimens collected were parasitized by trombiculid mites; 3.5% by nematodes; and 0.5% by cestodes.
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An ethogram comprised of 27 behavioral acts is described for Eumeces inexpectatus. Tail-wag, raised-tail-wag, move-away and flee are submissive acts. Cloacal-fan (raising the base of the tail, placing the hind feet under the cloaca, rubbing the feet together and usually passing feces or liquid) is displayed predominantly by males and may be associated with chemical marking. Mating of E. inexpectatus is described.
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A population of the rock-inhabiting lizard, Sceloporus undulatus erythrocheilus, was studied over two activity seasons in the eastern Colorado foothills. The convex polygon method was used to determine home range and figures were adjusted to eliminate sample size bias. Ninety-seven lizards (53 ♂ and 44 ♀) were captured. On the basis of ten or more observations, resident adults (= 50 mm snout-vent length) had an average home-range size of 826 m2 for 12 males and 363 m2 for 9 females. Male home-range size decreased significantly after the breeding season. The large degree of male home-range overlap (52%) suggests that home range is not equal to territory in this population. A promiscuous mating system is implied from the overlap of male and female home ranges and from behavioral notes.
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Male Eumeces laticeps develop bright orange head coloration during the spring breeding season, when they fight with other males and engage in sexual behavior with females. Outside the breeding season the head color fades and the sexual and agonistic behaviors cease. Intraperitoneal implantation of testosterone propionate in Silastic capsules restores the bright orange head coloration and activates courtship and agonistic behaviors in castrated males.
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This paper analyzes how cumulative injury data in age-structured populations can be used to determine some properties of the injury-producing process, such as predation. If the injury-producing process is the only source of mortality or injury, raw frequencies of animals free from injury (e.g., tail breaks) are shown in a theoretical analysis to equal the efficiency of the injury-producing process (e.g., the fraction of predation attempts that result in death of the prey); they are not affected by the intensity of the injury-producing process. If alternate sources of mortality exist, this conclusion may still be approximately true unless those sources are large. If there exists alternative sources of injury that never result in death, raw frequencies of uninjured animals actually increase with increasing intensity of the process that produces both injury and death (e.g., predation). To estimate the intensity of the injury-producing and the per-unit-time rate of accumulating injuries in the simplest case, one needs both injury and survival frequencies. Formulae for these estimations are provided.
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Territorial behavior of Sceloporus jarrovi was observed in Arizona during 3 years. Male aggression, activity and home range size increased and overlap between home ranges decreased as the fall breeding season approached. Most animals defended the entire home range. Males shifted their positions to maximize overlap with females in the fall. Females were less aggressive, occupied smaller areas and shifted positions less.
Article
The morphology and reproductive biology of Eumeces fasciatus and E. inexpectatus were studied in the southeastern United States. Eumeces inexpectatus are slightly larger in body size than E. fasciatus. Males are larger than females in E. inexpectatus but not in E. fasciatus. In both species there is sexual dimorphism in head size (males larger) independent of body size among sexually mature adults, apparently as a consequence of sexual selection. Individuals of both species reach sexual maturity in their second spring at an age of 21 months. Females of E. fasciatus lay eggs in nests constructed in hardwood logs, trees, and stumps, often in proximity to nests of other females. Eggs deposited in late May and early June are brooded by females and hatch in late July or early August. Clutches brooded in the laboratory revealed that eggs increase in mass considerably during development, but offspring hatch at a size much smaller than eggs at deposition. In addition, significant differences were found in hatchling size among clutches. Brooding behavior and the potential significance of variable offspring size are discussed.
Article
The diet of Eumeces laticeps consists of a variety of insects and their larvae, snails, isopods, spiders, Anolis lizards, and juvenile Eumeces. Many of the prey species occur only in leaf litter or under surface objects ("hidden prey') during the predator's activity period. Various measures of prey size correlate with size of the lizards' trophic structures. Prey types and sizes vary seasonally. Both visual and chemical cues are important in locating prey. Hidden prey may also be flushed from diurnal retreats.-from Authors
Article
Conflicts between animals of the same species usually are of ``limited war'' type, not causing serious injury. This is often explained as due to group or species selection for behaviour benefiting the species rather than individuals. Game theory and computer simulation analyses show, however, that a ``limited war'' strategy benefits individual animals as well as the species.
Article
Adults of the skink Eumeces laticeps are sexually dimorphic in coloration, body size, head size, and relative head size. Males have larger heads at a given body size than females and the divergence in relative head size is coincident with the size at which sexual maturity is reached. Although there were no differences between sexes in tail loss frequencies, there were substantial differences in frequencies of body and head scars, a consequence of aggressive male–male interactions. Prey size was correlated with body and head size and males tended to eat larger prey items than females. However, both sexes are capable of eating prey much larger than the mean or maximum size of prey found in stomachs, suggesting that resource partitioning is a consequence of sexual size differences rather than a cause. The heads of males at a given body size increase during the breeding season, and a combination of head and body size apparently determines the outcome of intrasexual aggressive encounters. Moreover, small males were never observed with females during the breeding season, and those males observed "guarding" females were significantly larger than males observed in the absence of females. We conclude that sexual selection accounts for many of the differences in morphological traits between sexes of E. laticeps.
Article
Blue tail coloration in hatchling skinks ( Eumeces fasciatus and E. laticeps ) appears to be an antipredatory adaptation that distracts attention away from the body to the tail. The tail itself serves as a decoy that may be autotomized as a final defense against capture. The effectiveness of intact tails in deflecting attacks from the body was 50% against scarlet kingsnakes in the experimental conditions used. Brightness rather than hue presumably accounts for the higher attack frequency on blue than black tails in this study, but the blue color may have evolved in response to avian predation. Repeated predation without ill effects by several predators allows rejection of the hypothesis that the blue tail is aposematic for the predators tested. The hypothesis that blue tails provide stimuli inhibiting aggression or predation by adult male conspecifics is untenable for E. laticeps because adult males readily eat intact hatchlings. Although this study provides no statistical evidence that blue tail coloration inhibits attack by female E. laticeps on hatchlings, the trend of predation rates on blue‐ and black‐tailed hatchlings is in the direction predicted for inhibition.
Article
Olfactory stimuli are sufficient for detection and discrimination of sex of conspecific lizards by the male broad-headed skink, Eumeces laticeps, a member of a large group of lizards with pronounced chemosensory abilities, the Autarchoglossa. The capacity of male broad-headed skinks to detect conspecific odors was assessed by measuring tongue extrusion rates in response to odor stimuli presented on moist cotton applicators. Tongue-flick rates of postreproductive males were siginificantly higher for clocal odors of postreproductive conspecif-ics of both sexes than to distilled water and higher to female than male odors over the initial 20- and 60-sec intervals. In a second experiment using testosterone-treated males and estrogen-injected females, testosterone-treated males emitted significantly more tongue flicks to female cloacal odors than to the other stimuli, and two males bit applicators bearing male odors. Testosterone did not affect reaction to male cloacal odors, but markedly increased tongue flick rates in response to cloacal odors of estrogen-treated females. Post reproductive males also responded to female, but not male, skin odors at a significantly higher rate than to water. Possible sources and presumed adaptive significance of conspecific odors are discussed.
Article
Wall lizards occupied overlapping territories, the size of which seemed to vary directly with the dominance level of the individual. Average territories of both males and females encompassed about 25 square meters. The overlap in territories among males was about 8 percent, and among females, about 18 percent. When both sexes were considered, overlap was 100 percent. This spacing mechanism appeared to be effective in governing the number of resident males but less so in governing number of resident females. In each of three years, females outnumbered males by 3.5 to one, probably because, among non-resident individuals, males were forced to move about more than females in order to avoid resident males, and as a consequence were subjected to greater predation pressure. Of 47 lizards marked on the study area, 60 percent were resident; the remainder were apparently wandering in search of unoccupied habitat. The number of resident lizards increased over the 5-year period of study from 10 to 21 individuals. Over the same period the average snout-to-vent length of this population decreased from 70.7 mm to 68.2 mm among males and 63.2 mm to 57.3 mm among females, probably reflecting a younger age structure. Correlated with these changes in population size was an increase in predation pressure from feral cats as reflected in the incidence of caudal autotomy among lizards.
Article
The results of staged agonistic encounters between males indicate that body size is an important determinant of dominance in male brown anoles (Anolis sagrei). Larger males defended their perch sites more successfully than did smaller males, perched higher than smaller males, and were most often the first male to enter the other male's territory. Larger males also exhibited more challenge displays than did smaller males. Head-nods, a display given by subordinate individuals, were observed only in smaller males.
Article
Thesis (Ph. D.)--University of Kansas, Zoology, 1969. Includes bibliographical references.
Article
Manuscript copy. Thesis--University of Florida. Vita. Bibliography: leaves 84-85.
Article
A field study of Tropidurus delanonis was carried out on an uninhabited island (Hood) of the Galapagos Archipelago over 18 months. The purpose of the study is to show the interrelation between social structure, behaviour and ecological aspects of the iguanid lizard Tropidurus delanonis. Five lizard categories are distinguished and the interrelation between colouration type and behaviour is shown. Data are given on population structure, composition and flexibility, reproductive cycle, clutch size, ontogeny and changes in colouration and behaviour. Detailed maps show the distribution of female and male territories and the area occupied by those male male that attempt to acquire a territory. The biomass is calculated for all categories in resect to total area available and to favorable and unfavorable areas within the observation area. The significance of various colouration types was tested experimentally.
Article
The view is examined that the adaptive value of conventional aspects of fighting behaviour is for assessment of relative RHP (resource holding power) of the combatants. Outcomes of aggressive disputes should be decided by each individual's fitness budget available for expenditure during a fight (determined by the fitness difference between adoption of alternative strategies, escalation or withdrawal without escalation) and on the rate of expenditure of the fitness budget if escalation occurs (determined by the RHPs of the combatants). Thus response thresholds for alternative strategies (“assessments”) will be determined by natural selection on a basis of which opponent is likely to expend its fitness budget first, should escalation occur. This “loser” should retreat (before escalation) and the winner should stay in possession of the resource. Many aggressive decisions depend on whether one is a resource holder, or an attacker. Assuming the RHP of the combatants to be equal, there are many instances of fitness pay-off imbalances between holder and attacker which should weight the dispute outcome in favour of one or other opponent by allowing it a greater expendable fitness budget. Usually the weighting favours the holder; the attacker therefore needs a correspondingly higher RHP before it may be expected to win. This is not invariably the case, and much observed data fits the predictions of this sort of model. If assessments are perfect and budget expenditure rates exactly predictable, then there would never seem to be any case for escalation. Escalation can be explained in terms of injury inflictions (expenditures) occurring as discrete events; i.e. as “bouts” won or lost during fighting. Assessment can give only a probabilistic prediction of the outcome of a bout. A simple model is developed to investigate escalation situations. Each combatant assesses relative RHP; this correlates with an absolute probability of winning the next bout (cabs). The stake played for is infliction of loss of RHP and is determined by the fitness budgets of the opponents. (Each individual plays for the withdrawal of its opponent.) This defines a critical probability of winning (ccrit) for each combatant, above which escalation is the favourable strategy (cabs > ccrit) and below which withdrawal is favourable (cabs < ccrit). Escalation should occur only where cabs-ccrit is positive for both combatants. This model gives predictions compatible with the observations, indicating that RHP loss alone can be adequate to explain withdrawal: escalation behaviour. Withdrawal tendency will be increased by low searching costs. Escalations should be restricted to closely matched RHP opponents if RHP disparity is the major imbalance. Outside the “escalation range” of a given individual, the higher RHP individual wins and the lower one loses (i.e. it should withdraw after conventional display). RHP disparity and holder: attacker imbalance should both interact to shape the observed pattern, though their relative importances will depend on species and situation. In some instances selection may favour immediate withdrawal from an occupied territory even without assessment of RHP.
Article
MALE BLUEGILL SUNFISH ARE SHOWN TO HAVE TWO ALTERNATIVE MATING STRATEGIES: cuckoldry or parental care. Cuckolder males first mature at age 2. They follow a developmental sequence of sneaking and then mimicking female behavior to deceptively gain access to spawnings. Males who become parentals (construct nests, attract females, provide brood care) delay maturation until age 7. The parental investment of these males is parasitized by the cuckolders. This system is an example of a truly parasitically dependent mating strategy in vertebrates. A natural selection model is developed to predict the equilibrium frequencies of the two male types. A preliminary test of the model provides qualitative agreement.
Article
Noncalling adult male tree frogs were found in close association with about 16 percent of the calling males in a pond in Georgia. In 13 of 30 field experiments a noncalling satellite male intercepted and achieved amplexus with a gravid female moving toward the calling male. This mating strategy, which conserves energy required for calling, resembles the strategy employed by other vertebrates.
Spatial relationships among members of a popula-tion of wall lizards The relation of rank to physiological state in Cnemidophorus sexlineatus hierarchies
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Boag DA (1973) Spatial relationships among members of a popula-tion of wall lizards. Oecologia (Berlin) 12:1 13 Brackin MF (1978) The relation of rank to physiological state in Cnemidophorus sexlineatus hierarchies. Herpetologica 34:185-191
Home-range size and overlap in Sceloporus undu-latus erythrocheilus (Reptilia: Iguanidae) Life history and ecology of the five-lined skink Eumecesfasciatus
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Ferner JW (1974) Home-range size and overlap in Sceloporus undu-latus erythrocheilus (Reptilia: Iguanidae). Copeia 1974:332-337 Fitch HS (1954) Life history and ecology of the five-lined skink Eumecesfasciatus. Univ Kans Publ Mus Nat Hist 8:1-156
Lizard sexual behavior and phero-mones: Ethological isolating mechanisms in the fasciatus group of the scincid genus Eumeces Natural nest sites and brooding behavior of Eumeeesfasciatus
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Cooper WE Jr, Vitt LJ (1987c) Lizard sexual behavior and phero-mones: Ethological isolating mechanisms in the fasciatus group of the scincid genus Eumeces. Ethology Cooper WE Jr, Vitt LJ, Vangilder LD, Gibbons JW (1983) Natural nest sites and brooding behavior of Eumeeesfasciatus. Herpetol Rev 14:65-66
Induction of orange head colora-tion and activation of courtship and aggression by testosterone in the male broad-headed skink (Eumeees laticeps) Intraspecific and interspecific ag-gression in lizards of the scincid genus Eumeces: Pheromonal recognition of conspecific sexual competitors
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Cooper WE Jr, Vitt LJ (1987a) Induction of orange head colora-tion and activation of courtship and aggression by testosterone in the male broad-headed skink (Eumeees laticeps). J Herpetol (in press) Cooper WE Jr, Vitt LJ (1987b) Intraspecific and interspecific ag-gression in lizards of the scincid genus Eumeces: Pheromonal recognition of conspecific sexual competitors. Herpetologica 43 : 7-14
Phenotypic correlates of male reproductive suc-cess in the lizard, Seeloporus jarrovi Natural selection and social behavior Inferring the properties of predation and other injury-producing agents from injury frequencies
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Ruby DE (1981) Phenotypic correlates of male reproductive suc-cess in the lizard, Seeloporus jarrovi. In: Alexander RD, Tinkle DW (eds). Natural selection and social behavior. Chiron Press, pp 96-107 Schoener TW (1979) Inferring the properties of predation and other injury-producing agents from injury frequencies. Ecology 60:1110 1115
Natural nest sites and brooding behavior of Eumeces fasciatus
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Notes on the natural history of the lizard Eumeces laticeps in northern Florida
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Ecology of a population of great plains skink (Eumeces obsoletus)
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