Correlates of melanization in multiple high- and low-elevation populations of the lizard,Sceloporus occidentalis: Behavior, hormones, and parasites

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.

Assessing the Association Between Animal Color and Behavior: A Meta-Analysis of Experimental Studies

Color varies in pattern and degree across the tree of life. In animals, genetic variation in color is hypothesized to have pleiotropic effects on a variety of behaviors due to shared dependence on underlying biochemical pathways. Such pleiotropy can constrain the independent evolution of color and behavior. Although associations between color and behavior have been reported, this relationship has not yet been addressed across a broad taxonomic scale with a formal meta-analysis. We used a phylogenetic meta-analytic approach to examine the relationship between individual variation in aggressive behavior and variation in multiple colors. Seventy-four studies met our inclusion criteria (vertebrates = 70; invertebrates = 4). After accounting for phylogeny and correcting for publication bias, there was a positive association between measures of aggression and degree or area of coloration (mean = 0.248, 95% CI = (0.044, 0.477)). Because this positive association was not restricted to melanin-based coloration, we conclude that this pattern does not strongly support the melanin pleiotropy hypothesis. Because the association was also not affected by moderators accounting for individual condition, social rank, or age, the results do not strongly support hypotheses that condition dependence accounts for relationships between color and aggressive behavior. The badge of status hypothesis predicts that arbitrary traits can evolve to signal aggression or social dominance. We propose that this is the most parsimonious explanation for the patterns we observe. Because of the lack of evidence for condition dependence in the association between color and aggression, we further propose that the genetic covariation between traits contributes to the evolution of the badges of status.

You're Just My Type: Mate Choice and Behavioral Types

Consistent individual differences in behavior [i.e., behavioral types (BTs)], are common across the animal kingdom. Consistency can make behavior an adaptive trait for mate choice decisions. Here, we present a conceptual framework to explain how and why females might evaluate a male's BT before mating. Because BTs are consistent across time or context, a male's BT can be a reliable indicator of his potential to provide direct benefits. Heritable BTs can enable informed mate choice via indirect benefits. Many key issues regarding patterns of mate choice, including sensory biases, context dependence, and assortative mating apply to BT-dependent mate choice. Understanding the relationship between BTs and mate choice may offer insights into patterns of variation and consistency common in behavioral traits.

Melanism, body size, and sex ratio in snakes-new data on the grass snake (Natrix natrix) and synthesis

It is postulated that melanism in ectotherms is adaptive by enhancing thermoregulation, subsequent resource acquisition, and growth. Such effects may differ between the sexes as a result of the differential costs of self-maintenance and reproduction, but empirical support for the sex-specific consequences of melanism remains inconsistent. We studied the effects of melanism on body size and sex ratio in a population of the European grass snake (Natrix natrix) in SE Poland and also carried out a systematic review of the literature on the consequences of melanism in terrestrial snakes. Melanistic grass snakes of both sexes appeared to be smaller than the typical phenotype, which indicates higher predation pressure and minimal thermal benefits for black individuals. A female-biased sex ratio was observed in the typical phenotype, but not in melanistic snakes, suggesting that the costs for females and/or benefits for males are higher in melanistic individuals. In conjunction with earlier studies, our data indicate that the consequences of melanism may be related to the reproductive mode of species. In viviparous species, melanism tends to improve growth and/or body size and is more frequent in females, whereas the opposite holds for oviparous snakes. Further studies on melanism should examine a wider array of species with different reproductive strategies and traits beyond the usual thermal benefits.

Melanization, α-melanocyte stimulating hormone and steroid hormones in male western fence lizards from nine populations

Hormones can mediate suites of correlated traits. Melanocortins regulate melanin synthesis and elements of the melanocortin system can directly, and indirectly, affect a number of other traits, such as stress reactivity. Trait correlations within the melanocortin system have been studied mainly in birds and mammals but less so in reptiles. We examined adult male western fence lizards (Sceloporus occidentalis) and if melanization was correlated with plasma levels of three hormones, including peptide hormone α-melanocyte stimulating hormone (α-MSH), testosterone and corticosterone, and ectoparasite loads. This lizard is darker at higher elevations in California, and we compared five high-elevation and four low-elevation populations during comparable periods of the breeding season at each site. We first validated use of an α-MSH assay kit with lizard plasma. Since Anolis carolinensis is one of the few species with published values for α-MSH plasma levels, we assayed both Anolis and Sceloporus plasma and compared hormone values to those we generated for Anolis to the publish values. We also evaluated effects of different methods of storing spiked plasma pools on resulting α-MSH concentrations. Plasma levels of α-MSH did not differ significantly, but some populations differed significantly in mean corticosterone and mean testosterone. Combining all individuals from the nine populations, we found that individual variation in α-MSH was not associated with individual variation in melanization, but levels of α-MSH were positively associated with plasma testosterone and negatively associated with corticosterone. The lack of association between individual levels of melanization and expression of most other traits differs from a growing number of within-population studies of melanization, and we discuss what differences in physiological mechanisms could produce different hypothetical patterns. Circulating levels of -MSH are only one element of the melanocortin system; in situ synthesis of α-MSH by the skin and the diversity of melanocortin receptors could also contribute to variation in traits mediated by the melanocortin system and should be examined.