Effect of Female Reproduction and Mate Choice on Sexual Size Dimorphism in the Northeast Treefrog Hyla ussuriensis (Anura:Hylidae) in China

Sexual size dimorphism(SSD) plays a significant role in understanding the evolution of life history and mating behavior. In this study,we analyzed the morphological data from a treefrog,Hyla ussuriensis,in northeastern China and found that there are significant differences between males and females. Females that are larger in body size increase fecundity as the total number of eggs is positively correlated to female body size. Males are smaller in body size due to the mate choice by females based on the size dimorphism index(SVL mean of female divided by that of male) for the population,which may be an evolutionary stable strategy(ESS). SSD can be influenced not only through mate choice,but also reproductive behavior by analyzing the female reproduction output in the field. Our data are consistent with many previous studies,indicating that fecundity selection and sexual selection may be the common cause for sexual dimorphism in this species. Furthermore,there are no significant morphological differences between mated and unmated frogs of both sexes,which suggests that any frog can obtain a breeding chance when it matures. It further indicates that males may not affect female choice except by their snout-vent length(SVL) and body mass. It is,of course,possible that females adopt a mating strategy to mate with males whose SVL and body mass are smaller than paired females. Our research provides unequivocal evidence for effective female choice and information on the evolution of SSD in the production of anuran pairing patterns.

Sexual size dimorphism in lizards:Rensch’s rule,reproductive mode,clutch size,and line fitting method effects

Rensch’s rule relates to a pattern whereby sexual size dimorphism is more female-biased in small-sized species and more male-biased in large-sized ones.We collected literature and museum data on the body size of males and females belonging to 4032 lizard species,as well as data on their reproductive modes and clutch sizes.We used phylogenetic comparative analyses,and general linear mixed models,to test Rensch’s rule and examined how re-productive mode and clutch size affect sexual size dimorphism.Sexual size dimorphism was independent of clutch size in lizard species with variable clutch sizes and in oviparous lizards.Large litters were associated with female-biased sexual dimorphism in viviparous and in scincomorph lizards.Inference regarding Rensch’s rule depended on the analytical method used to identify it.The widely used,but less conservative,reduced major axis regression usually support Rensch’s rule while ordinary least squares regressions mostly show isometric relationships.The rule tended to apply more to oviparous than to viviparous lizards.We infer that Rensch’s rule is,at best,a weak pattern in lizards.This is especially true in viviparous lineages where females reproduce infrequently and therefore evolve large sizes to maximise fecundity,resulting in female-biased dimorphism.