Intraspecific variation in body size and sexual size dimorphism, and a test of Rensch's rule in bats

Abstract

Ulian, C.M.V. and Rossi, M.N. 2017. Intraspecific variation in body size and sexual size dimorphism, and a test of Rensch's rule in bats. -Acta Zoologica (Stockholm) 98: 377-386.The magnitude and direction of sexual size dimorphism (SSD) may vary considerably within and among taxa, and the primary causes of such variation have not been thoroughly elucidated. For example, the effect of abiotic factors is frequently attributed to explain intra-and interspecific variation in SSD. Rensch's rule, which states that males vary more in size than females when body size increases, has rarely been tested in bats. Therefore, whether bats follow Rensch's rule remains unclear, particularly when females are larger than males. We investigated whether four bat species presented SSD, as well as whether their body sizes varied within each sex across localities, testing the hypothesis that intraspecific SSD varies substantially depending of sampling localities. We finally examined whether bats followed Rensch's rule by simultaneously using intraspecific and interspecific approaches. Although SSD was not observed for most bat species within each locality, the females of three of the four captured species exhibited differences in body size between particular localities. Usually the females varied more in size than did males across localities, mostly exhibiting a female-biased SSD. Significant differences in SSD were observed (i.e. mean values of the sexual dimorphism index), even though Rensch's rule was not followed.

High Duty Cycle Echolocation May Constrain the Evolution of Diversity within Horseshoe Bats (Family: Rhinolophidae)

“…However, in both studies on the Rhinolophidae, female body size was only slightly larger than male body size and Rensch's rule was not supported after controlling for phylogeny. Similarly, in four species of Phyllostomidae, another bat family, SSD was evident among three of the four species across localities but only significant in one species (Anoura caudifer; [71]). Although sexual selection upon which SSD is based, may be evident in bat populations, particularly on traits like echolocation frequency which has been implicated in mate choice [72], the traits on which the general patterns of Rensch's rule are usually based (e.g., body size) may be subject to only weak selection [70].…”

Not playing by the rules: mixed support of ecogeographic rules in an arid‐adapted African ground squirrel

“…In mammals, males are more often the larger sex, known as male‐biased sexual dimorphism (Shine, 1988). Most commonly, male‐biased sexual dimorphism is accredited to sexual selection, wherein males compete for mating opportunities with females (Darwin, 1871; Ulian & Rossi, 2017). Alternatively, female‐biased sexual dimorphism, when females are the larger sex, is often attributable to fecundity selection (Ulian & Rossi, 2017).…”

“…Most commonly, male‐biased sexual dimorphism is accredited to sexual selection, wherein males compete for mating opportunities with females (Darwin, 1871; Ulian & Rossi, 2017). Alternatively, female‐biased sexual dimorphism, when females are the larger sex, is often attributable to fecundity selection (Ulian & Rossi, 2017). Rensch's rule is an allometric rule that predicts that if there is male‐biased sexual dimorphism, sexual size dimorphism will increase with increasing body size and the opposite is predicted if sexual dimorphism is female‐biased (Rensch, 1950; Bubadué et al ., 2018).…”