Ecological Process Explains the Rensch's Rule in Penaeidae (Decapoda, Dendrobranchiata)

The evolution of body size and its association with sexual size dimorphism (SSD) in species is a subject of significant debate in evolutionary ecology. Rensch's rule predicts that SSD tends to decrease with body size in species where females are the larger sex. However, to comprehend the underlying causes of SSD emergence, it is necessary to understand how ecological and evolutionary processes differentially influence males and females. In this study, we quantified the effects of geographic, biotic, and abiotic factors on body size and evaluated Rensch's rule in penaeid shrimps by examining how ecological and evolutionary processes—such as sexual selection and resource competition—affect males and females differently. We reconstructed the phylogenetic relationships within the group and analyzed the evolution of male and female body sizes in 65 species of the family Penaeidae using phylogenetic comparative models. Our findings revealed that the sexual dimorphism detected in the family follows Rensch's rule. Male size is primarily influenced by female size, with males becoming larger as females increase in size, suggesting a role for sexual selection. Our results demonstrate how multiple ecological and evolutionary forces act differentially on males and females, shaping the emergence and evolution of SSD. These findings offer new insights into the ecological and evolutionary dynamics shaping sexual size dimorphism in marine organisms, with broader implications for understanding patterns of body size evolution.