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ABSTRACT Animal coloration is a complex phenotype that may be affected by genetics, evolution, ecology, and environment. Disentangling the impact of environment on phenotype can often be done in laboratory studies, but the results do not necessarily correspond to the natural variation present in the wild. Painted turtles are a brightly colored freshwater species that inhabit a variety of environments in North America. There is known to be plasticity in the melanin coloration of the shell of painted turtles in a lab setting, but this has not been measured in the wild. The bright skin coloration that gives painted turtles their name is caused by carotenoids, which can only be obtained from an organism's diet in vertebrates. Though the availability of carotenoids likely varies between environments, and there is evidence that some of the carotenoid‐based coloration in this species is a visual signal, it is unknown if or how environmental variation impacts coloration in the wild. To address this, we measured the effect of the environment on turtle coloration by assessing multiple populations of painted turtles in northern Wisconsin. We measured water clarity and aquatic plant density at each site where turtles were caught. We found that females had brighter carapaces than males, and that plastron brightness varied with water clarity and plant density, despite its ventral orientation. We also found that neither water clarity nor plant density predicted carotenoid chroma, despite reason to believe that light environment and carotenoid availability should impact a visual signal. These findings suggest that colorful phenotypic traits in this turtle species are complex and their potential role as visual signals requires more research. It is crucial to understand the different phenotypes of painted turtles since coloration may influence fitness in this species, and since laboratory studies are unable to represent natural variation. 

Color signals in animals are often honest, containing information about the individual for potential mates or predators. Both males and females may have honest color signals, though female signals are less often assessed for honesty. Different colorimetric traits, such as overall brightness, hue, ultraviolet brightness, or carotenoid chroma, may be assessed by receivers for information. Painted Turtles, Chrysemys picta (Schneider, 1783), are a brightly colored and widely distributed freshwater turtle species with no visible sexual dichromatism, but the function of their coloration is unknown. We assess two populations of Painted Turtles to compare colorimetric traits across and within populations, and to determine whether any color traits correlate with innate immune function. We find that there is greater carotenoid chroma on areas of the shell not typically associated with courtship than on the neck stripes that are thought to have a role in mate choice. We also find that only one measure of coloration in one color patch, the carotenoid chroma of the neck stripes, is correlated with bactericidal capacity, and in only one population. This system provides an example of a common species having vibrant but understudied coloration that may provide insights into unknown functions of color or uncommon sexual selection variation. 

Abstract Animal coloration serves a variety of visually related functions in nature (e.g. mate choice, aposematism and camouflage) but the pigments in integumentary tissues such as skin, scales and feathers may also serve functions unrelated to the visual environment (e.g. temperature regulation, detoxification and pollutant protection). Our understanding of the significance of the non‐visual functions of animal integumentary pigments, as well as how they interact with the visually related functions to shape animal visual systems, remains limited.Furthermore, due to their important roles in shaping species interactions and mediating interactions in the environment, animal colour traits are likely to be impacted by global change (e.g. increased temperatures, altered habitat quality and quantity, increased environmental stochasticity, pollutants and novel species assemblages).Considering the effects of global change on both visual and non‐visual functions is important for understanding whether the selection is acting directly on the pigment or on coloration. Since changing the trait distributions can then lead to changes in visual systems, we advocate for studies to consider all potential functions of integumentary pigments, both visual and non‐visual functions and their interaction.Towards this goal, we first highlight common functions of pigments with a focus on non‐visual functions across animal systems. Then we synthesize our current understanding of how global change can impact pigmentation and discuss factors that can modify the interactions between climate change and pigment function. Lastly, we discuss how changes in colour traits can impact visual systems and provide an example using amphibians and their responses to climate change as a model. Read the freePlain Language Summaryfor this article on the Journal blog. 

Sex-related differences in mortality are widespread in the animal kingdom. Although studies have shown that sex determination systems might drive lifespan evolution, sex chromosome influence on aging rates have not been investigated so far, likely due to an apparent lack of demographic data from clades including both XY (with heterogametic males) and ZW (heterogametic females) systems. Taking advantage of a unique collection of capture–recapture datasets in amphibians, a vertebrate group where XY and ZW systems have repeatedly evolved over the past 200 million years, we examined whether sex heterogamy can predict sex differences in aging rates and lifespans. We showed that the strength and direction of sex differences in aging rates (and not lifespan) differ between XY and ZW systems. Sex-specific variation in aging rates was moderate within each system, but aging rates tended to be consistently higher in the heterogametic sex. This led to small but detectable effects of sex chromosome system on sex differences in aging rates in our models. Although preliminary, our results suggest that exposed recessive deleterious mutations on the X/Z chromosome (the “unguarded X/Z effect”) or repeat-rich Y/W chromosome (the “toxic Y/W effect”) could accelerate aging in the heterogametic sex in some vertebrate clades.