Andrew meets Rensch: sexual size dimorphism and the inverse of Rensch’s rule in Andrew’s toad (Bufo andrewsi)

Abstract

Variation in sexual size dimorphism (SSD) is a widespread phenomenon and is commonly attributed to variation in sex-specific patterns of selection. According to Rensch's rule, SSD increases with increasing body size when males are the larger sex, and decreases when females are the larger sex. Using data from 17 populations of Andrew's toad (Bufo andrewsi), we tested whether the patterns of SSD conform to Rensch's rule. Using field experiments, we also evaluated the hypothesis that sexual selection favours large male body size and that fecundity selection favours large female body size. The results revealed that the degree of SSD increased with increasing mean size in females, consistent with the inverse of Rensch's rule. Although experiments revealed evidence for a large-male mating advantage, selection for large male size was weak at best, and hence unlikely to be an important source of variation in SSD. However, fecundity selection favouring large females was evident, and likely to explain the observed inverse of Rensch's rule. After correcting male and female body size for age differences, the patterns of SSD remained the same, suggesting that the intra- and interpopulational variation in SSD is not driven by sex differences in age structure. Hence, these findings suggest that the strong fecundity selection favouring large females drives the evolution of female-biased SSD in B. andrewsi, providing an explanation for the inverse of Rensch's rule. As such, the study provides an important addition to the small body of literature that uses an intraspecific approach to demonstrate the inverse of Rensch's rule.

Re-assessment of rensch’s rule in Centrobolus

“…The regression of SSD on body size (Figure 1) of the data for SSD and body size (Table 1) indicates a positive regression to reject Rensch's rule in Centrobolus. Although the null hypothesis is accepted and the rule rejected the inverse relationship is true [26][27][28][29][30][31][32] . This was seen in the SSD increases with body size.…”

Seasonality and Age is Positively Related to Brain Size in Andrew’s Toad (Bufo andrewsi)

“…The activity and growth period of B. andrewsi is markedly shaped by the length of the activity period, which in turn is determined by altitude as well as latitude. Towards high altitudes, where the activity period is shorter, B. andrewsi attain a larger size at metamorphism, a higher longevity, and a larger body size at slower growth rates (Liao and Lu 2012;Liao et al 2015). At low altitude, on the other hand, males have more time for food acquisition and reproduction, and food is also more abundant (Liao andLu 2009, 2012;Liao et al 2014).…”

Modulation of Gene Expression in Liver of Hibernating Asiatic Toads (Bufo gargarizans)

“…The species is an explosive breeder with a relatively short spawning period (6–24 days) [20], with typical breeding habitats concentrated along the vegetated edges of large, still water bodies. Competition for mating is fierce among males [19,21], and the species experiences a period of hibernation from early-December to mid-February and the mating behaviour occurs as soon as the hibernation period ends. Hence, B. gargarizans is a suitable model for investigating the physiological and molecular mechanisms underlying metabolic suppression during the hibernating period.…”