Martin J. Whiting

Ultraviolet signals ultra-aggression in a lizard

Understanding the role of multiple colour signals during sexual signalling is a central theme in animal communication. We quantified the role of multiple colour signals (including ultraviolet, UV), measures of body size and testosterone levels in settling disputes between male rivals in an elaborately ornamented, African lizard, played out in a large ‘tournament’ in the wild. The hue and brightness (total reflectance) of the UV throat in Augrabies flat lizards, Platysaurus broadleyi, as well as body size, were consistent and strong predictors of ‘fighting ability’. Males with high fighting ability were larger and displayed a UV throat with low total reflectance. In contrast, males with low fighting ability were smaller and had violet throats with broader spectral reflectance curves (higher total reflectance). As fighting ability is associated with alternative reproductive tactics in this system (territorial versus floater), we also examined the role of colour signals in predicting male reproductive tactic. Territorial males had UV throats with higher chroma but had poorer body condition than floater males, probably because of the energetic costs of maintaining a territory. Although testosterone was not a significant predictor of fighting ability or reproductive tactic, it was correlated with the hue of the UV throat, suggesting that testosterone may impose some constraint on signal expression. Lastly, we show that within the context of the natural signalling environment, UV-reflective throats constitute a conspicuous, effective signal that male Augrabies flat lizards use to advertise their status honestly to rivals.

An Integrative Framework for the Appraisal of Coloration in Nature

The world in color presents a dazzling dimension of phenotypic variation. Biological interest in this variation has burgeoned, due to both increased means for quantifying spectral information and heightened appreciation for how animals view the world differently than humans. Effective study of color traits is challenged by how to best quantify visual perception in nonhuman species. This requires consideration of at least visual physiology but ultimately also the neural processes underlying perception. Our knowledge of color perception is founded largely on the principles gained from human psychophysics that have proven generalizable based on comparative studies in select animal models. Appreciation of these principles, their empirical foundation, and the reasonable limits to their applicability is crucial to reaching informed conclusions in color research. In this article, we seek a common intellectual basis for the study of color in nature. We first discuss the key perceptual principles, namely, retinal photoreception, sensory channels, opponent processing, color constancy, and receptor noise. We then draw on this basis to inform an analytical framework driven by the research question in relation to identifiable viewers and visual tasks of interest. Consideration of the limits to perceptual inference guides two primary decisions: first, whether a sensory-based approach is necessary and justified and, second, whether the visual task refers to perceptual distance or discriminability. We outline informed approaches in each situation and discuss key challenges for future progress, focusing particularly on how animals perceive color. Given that animal behavior serves as both the basic unit of psychophysics and the ultimate driver of color ecology/evolution, behavioral data are critical to reconciling knowledge across the schools of color research.

Predator-specific camouflage in chameleons

A crucial problem for most animals is how to deal with multiple types of predator, which differ in their sensory capabilities and methods of prey detection. For animals capable of rapid colour change, one potential strategy is to change their appearance in relation to the threat posed by different predators. Here, we show that the dwarf chameleon, Bradypodion taeniabronchum, exhibits different colour responses to two predators that differ in their visual capabilities. Using a model of animal colour perception to gain a ‘predators eye view’, we show that chameleons showed better background colour matching in response to birds than snakes, yet they appear significantly more camouflaged to the snake visual system because snakes have poorer colour discrimination.

Natural Selection on Social Signals: Signal Efficacy and the Evolution of Chameleon Display Coloration

Whether general patterns of signal evolution can be explained by selection for signal efficacy (detectability) has yet to be established. To establish the importance of signal efficacy requires evidence that both signals and their detectability to receivers have evolved in response to habitat shifts in a predictable fashion. Here, we test whether habitat structure has predictable effects on the evolution of male and female display coloration in 21 lineages of African dwarf chameleon (Bradypodion), based on a phylogenetic comparative analysis. We used quantitative measures of display coloration and estimated signal detectability as the contrast of those colors among body regions or against the background vegetation as perceived by the chameleon visual system. Both male and female display colors varied predictably with different aspects of habitat structure. In several (but not all) instances, habitat‐associated shifts in display coloration resulted in habitat‐associated variation in detectability. While males exhibit a remarkable variety of colors and patterns, female display coloration is highly conserved, consisting in all populations of contrasting dark and light elements. This color pattern may maximize detectability across all habitat types, potentially explaining female conservatism. Overall, our results support the view that selection for signal efficacy plays an important role in the evolution of animal signals.

Sex‐Based Differences and Similarities in Locomotor Performance, Thermal Preferences, and Escape Behaviour in the Lizard Platysaurus intermedius wilhelmi

Differences between sexes in physiological performance have received little attention in animals. We tested for sex differences in maximum sprint speed and maximal exertion over a range of temperatures in a population of Platysaurus intermedius wilhelmi lizards. We also examined sex‐based differences in selected temperature range, mean field body temperatures (Tb), and thermal activity limits. Finally, we conducted field studies to quantify male and female responses to a potential predator, which may be affected by their respective performance capabilities. Males were faster than females at all temperatures, and body size had no significant effect on sprint speeds. Males and females also selected similar Tbs when placed in a thermal gradient, but in the field, male lizards’ Tbs were different from those of the females. However, predicted sprint speeds for males and females at their field Tbs are similar. No significant differences were found between males and females with regard to maximal exertion. When approached in the field, adult male lizards took refuge significantly earlier than did adult females and also fled over shorter distances, suggesting that females rely on crypsis as an escape strategy.

When to be neighbourly: differential agonistic responses in the lizard Platysaurus broadleyi

Abstract Differential treatment of neighbours and strangers (the dear enemy phenomenon) can reduce the costly effects of territory defence. Individual recognition, and by extension the dear enemy phenomenon, was examined in the cordylid lizard Platysaurus broadleyi. I had no knowledge of familiarity between individuals and therefore classed intruders as neighbours or non-neighbours and tested for differences in agonistic response consistent with the dear enemy phenomenon. In the dear enemy phenomenon, levels of aggression are inversely related to degree of familiarity such that residents are more tolerant of immediate neighbours than distant territory holders. A manipulative field experiment in conjunction with field observations of known territory holders revealed that resident males allowed neighbours to approach more closely than non-neighbours before challenging them, residents were more aggressive towards non-neighbours than neighbours, contests between neighbours were significantly longer than between neighbours and non-neighbours and contests between residents and non-neighbours were likely to result in a win for the resident, while neighbours frequently drew contests. These results suggest a level of recognition consistent with the dear enemy phenomenon. I also manipulated front leg colour to test the hypothesis that it alone could serve as a cue for individual recognition. I found no support for this hypothesis and suggest that multiple cues operate in individual recognition.

Multiple signals in chameleon contests : designing and analysing animal contests as a tournament

Traditionally, studies of intrasexual selection have focused on single traits that are more exaggerated in males. Relatively little is known about systems in which traits are larger in females or the role of multiple traits in male contests. We used a tournament design in which each male encounters a series of different opponents, in conjunction with the structured Bradley–Terry model, to examine the role of multiple male traits in contests between male Cape dwarf chameleons, Bradypodion pumilum. Females are larger but males have relatively longer tails, larger and more ornamented heads and a larger central flank patch, all of which are emphasized during agonistic displays. We found no evidence that larger body size confers an advantage in male contests, despite high levels of aggression and escalated encounters. However, both the height of the casque (head ornament) and relative area of the flank patch were positively associated with fighting ability, and not correlated with each other, suggesting that they may represent independent sources of information about an opponents ability. We discuss these results in relation to the role of male contest competition in the evolution of multiple male signals and sexual dimorphism in dwarf chameleons. In addition, we show that the use of tournament designs, in conjunction with the structured Bradley–Terry model, has important advantages over traditional designs and methods of analysing animal contests.

Ultraviolet signals fighting ability in a lizard

Ultraviolet (UV) signals are used in female mate choice in numerous taxa; however, the role of UV signals in male contests remains relatively unexplored. We experimentally reduced throat UV of free-ranging lizards (Platysaurus broadleyi) to test whether UV acts as a signal of fighting ability during male contests. We found that UV-reduced males were more likely to be challenged than control males. However, contest outcome was not influenced by UV-reduction, and this was despite other obvious asymmetries between opponents, such as body size and residency. Throat UV was confirmed as a signal of fighting ability because contests were more likely to escalate when one contestant had reduced UV. Therefore, throat UV, not body size or residency, was used during the initial stage of opponent assessment, but this did not influence contest outcome. The results suggest that UV overrides other traits that could function as signals during rival assessment.

Foraging modes of cordyliform lizards

The first quantitative data on foraging mode in the cordyliform lizards reveal different foraging behaviours between and within families. All species of cordylids studied (four Cordylus, two Pseudocordylus. and one Platysaurus) are ambush foragers. However, the species of Cordylus and Pseudocordylus microlepidotus are the most extreme ambushers. These species spent a significantly lower per cent time moving than did all of the other species studied and made significantly fewer movements per minute than Platysaurus capensis and gerrhosaurids. In addition, P. microlepidotus made significantly fewer movements per minute than did its congener Pseudocordylus capensis. Possible reasons for the high number of movements per minute in Platysaurus capensis are discussed. Very limited observations of two gerrhosaurid species show that Cordylosaurus subtessellatus is an active forager and Gerrhosaurus validus forages actively at least some of the time. A tentative hypothesis of the evolution of cordyliform foraging behaviour based on very limited data hints that active foraging is plesiomorphic in the Gerrhosaurini and further that gerrhosaurids may have retained active foraging from the common ancestor of Scincidae and Cordyliformes. Somewhat stronger data suggest that ambush foraging arose in the common ancestor of Cordylidae or Cordylinae. Further study is needed to trace inter- and intrageneric changes in foraging mode in cordylids.

Sex and boldness explain individual differences in spatial learning in a lizard

Understanding individual differences in cognitive performance is a major challenge to animal behaviour and cognition studies. We used the Eastern water skink (Eulamprus quoyii) to examine associations between exploration, boldness and individual variability in spatial learning, a dimension of lizard cognition with important bearing on fitness. We show that males perform better than females in a biologically relevant spatial learning task. This is the first evidence for sex differences in learning in a reptile, and we argue that it is probably owing to sex-specific selective pressures that may be widespread in lizards. Across the sexes, we found a clear association between boldness after a simulated predatory attack and the probability of learning the spatial task. In contrast to previous studies, we found a nonlinear association between boldness and learning: both ‘bold’ and ‘shy’ behavioural types were more successful learners than intermediate males. Our results do not fit with recent predictions suggesting that individual differences in learning may be linked with behavioural types via high–low-risk/reward trade-offs. We suggest the possibility that differences in spatial cognitive performance may arise in lizards as a consequence of the distinct environmental variability and complexity experienced by individuals as a result of their sex and social tactics.