Evolutionary allometry of sexual dimorphism of jumping performance in anurans

Abstract

Sexual dimorphism is a common feature in animals, yet the degree of sexual dimorphism is not constant across taxa. Sometimes the magnitude of sexual dimorphism varies systematically with body size, resulting in evolutionary allometry of sexual dimorphism. While such patterns are commonly investigated for traits such as overall size, allometric variation in sexual dimorphism of other traits remains underexplored. Here, we characterize the evolutionary allometry of sexual dimorphism in a functional phenotypic trait (jumping performance) in anurans. Using morphology and anatomical approximations of jumping performance across 146 species, we test for evidence of the correlated selection model of sexual dimorphism evolution. We analyze patterns of evolutionary allometry of sexual dimorphism in key phenotypic traits, including: body size (snout-vent length and mass), relative leg length, relative leg muscle volume, mass-specific peak jumping energy, and peak jumping velocity. We find that as previously reported, sexual size dimorphism scales isometrically between species and is independent of sexual dimorphism in jumping performance. Notably, however, we found significant trends in the evolutionary allometry of sexual dimorphism in relative limb length, and in two components of jumping performance. Additionally, we found greater rates of evolution for females versus males in relative limb length, but not jumping performance. We also observed that the allometric trends in limb length dimorphism were related to performance allometry. Sexual dimorphism in jumping performance increased in species with high performance while females in high performance species displayed increased relative limb length. Thus, we hypothesize that selection acting on functional performance explains allometric patterns of sexual dimorphism in morphology. We discuss biological implications of our findings in relation to natural and sexual selection. This study highlights the types of insights one may gain by studying the allometry of sexual dimorphism from a functional perspective to learn about both patterns and processes in evolution.

Ecology, sexual dimorphism, and jumping evolution in anurans

“…Instead, we interpret this result to signify that fecundity selection and female‐biased SSD are common in anurans, but the average degree of SSD is small. This interpretation agrees with previous findings of fecundity selection and female‐biased SSD in the literature on anurans (De Lisle & Rowe, 2013; Han & Fu, 2013; Juarez & Adams, 2021; Nali et al, 2014). Our novel finding is that fecundity selection has impacted the evolution of jumping velocity in female anurans.…”

“…This is not surprising, given our findings that anatomical approximations of jumping outperform single anatomical variables in predicting in vivo jumping performance (see SI). Our findings reinforce previous work describing how jumping performance is highly correlated to the combined biomechanical effects of multiple components within the musculoskeletal system (James et al, 2007; Juarez & Adams, 2021; Juarez et al, 2020; Marsh, 1994; Moen, 2019).…”

“…We estimated jumping performance via anatomy‐based approximations of peak velocity and energy at take‐off, as described in detail by Juarez et al (2020) and Juarez and Adams (2021). Briefly, these methods use body mass, leg muscle volume and L com (0.67 times the distance from the sacral joint to the tip of the toes; Peplowski & Marsh, 1997) to approximate peak jumping performance.…”

“…Briefly, these methods use body mass, leg muscle volume and L com (0.67 times the distance from the sacral joint to the tip of the toes; Peplowski & Marsh, 1997) to approximate peak jumping performance. Total muscle volumes (the sum of thigh and calf muscle volume) were estimated using the geometric equation for the volume of a bicone, as described in Juarez and Adams (2021). See Appendix S2 for a comparison of using leg muscle volume instead of muscle mass to approximate jumping performance.…”

“…Female jumping performance may be reduced if females increase in body mass (e.g., due to increased clutch mass) without changing another aspect of their anatomy (e.g., leg muscle mass or leg length) to compensate (i.e., a trade‐off; Jagnandan & Higham, 2018; Kuo et al, 2011; Marsh, 1994; Moen et al, 2013). For example, Juarez and Adams (2021) found that females have evolved longer legs at a given body length, possibly to compensate for decreased jumping performance associated with heavier bodies for carrying eggs. Thus, in species that compensate for fecundity‐related decreases in jumping performance, we can expect (1) females to be larger than males (female‐biased SSD), (2) no SD of jumping performance, and (3) a correlation between SSD and SD of jumping‐related morphology.…”