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  1. Abstract Coloration and body size are among the many morphological traits that vary among fish lineages. Elaborate coloration and body size covary in other animal groups, but relationships between these two morphological characteristics have not been rigorously examined in fishes. We formally test for correlations between coloration and body size in darters (Percidae: Etheostomatinae), a group of North American freshwater fishes that vary in the presence of male coloration and maximum body size. Although uncorrected analyses indicate a significant correlation between colour traits and body size in darters, phylogenetically corrected logistic regression models and ANOVAs revealed no significant correlations, suggesting body size does not act as a constraint on elaborate coloration or vice versa. These results are discussed in an ecological and behavioural context. 
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  2. Taking an evolutionary approach to the question of beauty, we discuss the expression and perception of sexual beauty across the animal kingdom. Animals experience beauty in their brains, and animal brains are tuned to features of the environment most relevant to their survival. Over evolutionary time, sexually reproducing animals have exploited that tuning to maximize their attractiveness to the opposite sex, often leading to extreme courtship traits and behaviors. These are the traits of sexual beauty. Combining modern principles of neuroscience and neuroaesthetics with established principles of evolutionary biology, we aim to understand the biological basis and evolution of beauty in all animals, including ourselves. 
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  4. Abstract

    Recent studies show that epigenetic variation in the form ofDNAmethylation may serve as a substrate for selection. Theory suggests that heritable epigenetic marks that increase fitness should increase in frequency in a population, and these changes may result in novel morphology, behaviour, or physiology, and ultimately reproductive isolation. Therefore, epigenetic variation might provide the first substrate for selection during the course of evolutionary divergence. This hypothesis predicts that populations in the earliest stages of divergence will differentiate in their methylome prior to any genetic differentiation. While several studies have investigated natural epigenetic variation, empirical studies that test predictions about its role in speciation are surprisingly scarce. Here, we investigateDNAmethylation variation using an isoschizomeric digest method, Methyl‐Sensitive Amplified Polymorphism, across multiple stages of evolutionary divergence in natural populations of North American stream fishes. We show that epigenetic differentiation between methylomes is greater than genetic divergence among closely related populations across two river drainages. Additionally, we demonstrate that epigenetic divergence is a stronger predictor of the strength of behavioural reproductive isolation and suggest that changes in the methylome could influence the evolution of reproductive isolation between species. Our findings suggest a role for epigenetics not only in the initiation of divergence, but also in the maintenance of species boundaries over greater evolutionary timescales.

     
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