Information out of the blue: phenotypic correlates of abdominal color patches in Sceloporus lizards

The integrative biology of decoy coloration in lizards

Anti-predator coloration is a widespread phenomenon that includes such tactics as aposematism, crypsis and mimicry. Most research on colorful anti-predator traits has focused on these well-known and well-studied tactics. One anti-predator trait that is found in diverse taxa yet is still poorly understood is anti-predator decoys. New advances in phylogenetics, genomics and molecular biology have allowed for an enriched understanding of the integrative biology of this type of anti-predator trait, particularly in lizards. While anti-predator decoy coloration is present in multiple taxa across the animal tree of life, it is particularly prevalent among lizards, which use both color and behavior to attract predator attention to the tail, which is often autotomizable and can regrow. In this Review, we discuss the integrative biology of decoy coloration in lizards, including the role of color, ontogenetic variation, gene expression and genomics. We begin by reviewing the mechanisms of the production of decoy coloration in lizards then discuss the function and macroevolution of decoy coloration. Finally, we suggest potentially fruitful avenues for future research on anti-predator decoys in lizards and other animal taxa.

Effects of Urbanization on Ventral Patch Size and Phenotypic Correlates of Patch Expression in Male Western Fence Lizards (Sceloporus occidentalis)

In some animals, males use colorful ornaments or badges to visually communicate with conspecifics. These traits can be condition-dependent, suggesting that environmental changes could impact the intensity of male sexual signals. Drastic habitat changes caused by urbanization can act as physiological stressors, potentially affecting male signaling traits through changes to condition or immune function. Here, we quantified the effects of urbanization on ventral patch size and correlates of patch expression, namely body size, body condition, corticosterone concentrations, and ectoparasites in male Western Fence Lizards (Sceloporus occidentalis). We compared three aspects of male ventral color patches between urban and natural populations: area of the throat patch, total area of the paired belly patches, and total area of the black borders of the belly patches. All three area measurements across both habitat types were positively related to body size, and total belly patch area was positively related to body condition, indicating that these traits may signal male competitive ability and/or quality. Males from urban populations had larger throat patches than those from natural populations after controlling for body size. This difference in patch size was associated with a difference in probability of ectoparasite infection, but not with differences in corticosterone concentrations or body condition between urban and natural populations. Our results may indicate an effect of urbanization on immune function affecting male patch expression, although this idea remains untested. Overall, we show that urbanization can impact male sexual traits, which may have repercussions for visual communication in urban environments.

Natural parasites in conjunction with behavioral and color traits explain male agonistic behaviors in a lizard

Male competition conforms to a cost-benefit model, because while aggression may increase reproductive prospects, it can also increase the risk of injury. We hypothesize that an additional cost in aggressive males would be an increase in parasite load associated with a high energy investment into sexual competition. Some of these infections, in turn, may downmodulate the level of host aggression via energetic trade-offs. We staged dyadic male contests in the lab to investigate the relationships of multiple parasites with the agonistic behavior of lizard hosts, Sceloporus occidentalis. We also included both color and behavioral traits from opponents in the analyses because (1) color patches of lizards may serve as intraspecific signals used by conspecifics to assess the quality of opponents, and (2) contests between male lizards fit classical models of escalated aggression, where lizards increase aggression displays in response to an opponent's behavior. The results conform to our hypothesis because male lizards displayed more pushups when they had more ticks. Moreover, some parasites may modulate the levels of aggression because lizards infected by hematic coccidians performed fewer pushups. Interestingly, lizards also displayed fewer pushups when both the chroma and size of the opponent's blue patch were greater. The results thus also supported the role of the blue patch of S. occidentalis as a sexual armament, because it contributed to the deterrence of aggression from opponent lizards. We revealed that natural parasitic infections in lizard hosts can contribute to their agonistic behavior. We encourage future studies to account for parasites in behavioral tests with lizards.

Identifying and locating carotenoids in supra-orbital combs of male black grouse (Lyurus tetrix) using Raman and transmission electron microscopy: A histological study using rehydrated tissue samples

Colourful signals have long been implicated as indicators of individual quality in animals. Bare-skin signals are an understudied aspect of avian colouration compared with plumage studies, despite displaying rapid changes in size and colour in response to different environmental or physiological stressors. Even fewer studies have focused on the underlying histology of these structures and the importance this plays in the resulting skin colour. Using the Black Grouse (Lyrurus tetrix), we identified the underlying structure of individual dermal spikes, which make up the red supra-orbital comb (a known integumentary signal of male quality), and highlight visual structural differences between combs of different sizes. In addition, we used Raman spectroscopy to indicate the presence of carotenoids within the tissue, something that had previously only been inferred through characteristic reflectance patterns. An increased understanding of the structural basis of colour of featherless parts of the skin opens up exciting new avenues for interpreting the information content of integumentary signals.