Sexual Size Dimorphism in Multiple Traits: An Integrative Perspective in Several Anuran Species
Sexual dimorphism is a fascinating phenomenon that showcases the wide variation of characteristics related to life strategies in organisms. It is driven by two key evolutionary processes: sexual selection and natural selection. Anurans provide an excellent opportunity to study the origin and diversification of sexual dimorphism due to their variation in size and secondary sexual characters, as well as their diverse life histories. Here, we compared the morphology of males and females in six anuran species (Ceratophrys cranwelli, Boana pulchella, Leptodactylus luctator, Odontophrynus americanus, Physalaemus biligonigerus, and Rhinella arenarum) inhabiting the same breeding site. Additionally, we employed an allometric approach to assess changes in magnitude of sexually dimorphic traits relative to body size. No common pattern of sexual size dimorphism emerged, with species exhibiting dissimilar combinations of dimorphic and monomorphic traits. These differences in sexual dimorphism could only be partially attributed to specific behaviors or life histories in certain cases. Discordant patterns of allometry between sexes in most species further contributed to observed diversity. Overall, selective forces shaping morphologies of both sexes appear complex, related not solely to trait function, but also to life history differences between sexes. To fully understand mechanisms driving sexual dimorphism, it is crucial to consider multiple factors such as behavior, reproductive strategies, and environmental conditions. Lack of a common pattern and presence of diverse morphological variations among species underscore the complexity of selection on body size.ABSTRACT
Overview of sexually size dimorphic traits of six syntopic neotropical anurans. Relative sizes of frogs and toads indicate the number of dimorphic traits for each species, independent of the average SVL of each species.
Size dimorphism index across 10 measured traits (not adjusted to SVL) in six syntopic neotropical anurans. Species exhibit dissimilar combinations of di- and monomorphic traits. Positive values indicate female-biased dimorphism whereas negative values indicate male-biased dimorphism.
Boxplots showing sexual dimorphism of six syntopic neotropical anurans. The first column of panels (SVL) show raw data, and other plots are residuals extracted from linear models between the target variable and SVL covariate (see Table 1) to exclude effects of size. All variables were log-transformed.
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