Inverse of Rensch’s rule of allometry for sexual size dimorphism in Bufo andrewsi

Difference in body size between males and females (sexual size dimorphism: SSD) and its variation are a common phenomenon in animal kingdom. Rensch’s rule predicts that the degree of SSD variation increases with the enlarged mean body size when males are larger than females and decreases when females are larger than males. Here, whether the patterns of variations in SSD in the Andrew’s toad (Bufo andrewsi) follow Rensch’s rule was tested using unpublished data from 14 populations and published data from 17 populations. Results show the reduced major axis regression of log10 (male size) on log10 (female size) across all populations displayed a significant hyperallometric relationship, which was consistent with inverse Rensch’s rule (the degree of SSD increased with enlarged mean body size). SSD could also be explained by sexual age difference (SAD) due to a positive SSD–SAD relationship among all populations. The findings suggest that the occurrence of inverse Rensch’s rule in B. andrewsi is likely to be a result of fecundity selection on increased reproductive investments in larger females.

This table is descriptive information about the study sites of Andrew’s toad (B. andrewsi), together with mean (± SD) body size and age of males and females.