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Sexual size dimorphism (SSD), the difference in body size between males and females, is a widespread phenomenon and commonly attributed to variation in sex-specific patterns of selection. Using data from three populations of Polypedates megacephalus, we tested the hypotheses that sexual selection favoured large male body size and that fecundity selection favoured large female size. Females had a larger body size than males in all populations and thus exhibited a female-biased sexual size dimorphism. Standardized selection gradients showed that sexual selection for large male size was weak at best and hence unlikely to be an important driving force for SSD. As fecundity selection favouring large females was weak as well, it could not explain the female-biased SSD patterns found. However, a faster growth rate in females favoured a larger size, providing an explanation for female-biased SSD. Our findings suggest that female-biased SSD does not result from a phenotypic selection of female by size in P. megacephalus. [ABSTRACT FROM AUTHOR]

Sexual size dimorphism (SSD) is a widespread phenomenon commonly attributed to sex-specific patterns of selection on body size. Using data from Dengchigou population of the Omei treefrog (Rhacophorus omeimontis) in Fengtongzhai National Nature Reserve, southwestern China, we evaluated the hypothesis that direct phenotypic selection on both males and females can produce SSD. Female biased-SSD was generally driven by selection on females due to fecundity advantage of large body size rather than sexual selection favouring large male body size. Furthermore, differences in life-history traits (i.e. growth rate and/or time available for growth) between the sexes also resulted in female biased-SSD. Our findings suggest that the relationship between female size and fecundity supports the prediction that selection for fecundity drives female biased-SSD. [ABSTRACT FROM AUTHOR]

Rensch's rule describes that sexual size dimorphism (SSD) increases with body size (hyperallome-try) when males are larger, and decreases with body size (hypoallometry) when males are smaller. In this paper, on the basis of mean adult body size resulting from 18 populations of the common frog Rana temporaria and 24 populations of the Tibetan frog Nanorana parkeri, we tested the consistency of allometric relationships between males and females with Rensch's rule. Our results show that the variation in degree of female-biased SSD increased with increasing mean size at intraspecific levels in two species, which is consistent with the inverse of Rensch's rule. Furthermore, we tested the hypoth-esis that the degree of SSD decreased with increasing altitudes. Inconsistent with the predications of our hypothesis, we found no relationships between the degree of SSD and altitude for the two species investigated. These findings suggest that females living in adverse climates in high altitudes cannot adjust their body size as plastically as males. [ABSTRACT FROM AUTHOR]

Background Sexual size dimorphism (SSD) is widespread and variable among animals. Sexual selection, fecundity selection and ecological divergence between males and females are the major evolutionary forces of SSD. However, the influences of mating system and habitat types on SSD have received little attention. Here, using phylogenetic comparative methods, we at first examine the hypotheses to that mating system (intensity of sexual selection) and habitat types affect significantly variation in SSD in anurans (39 species and 18 genera). Results Our data set encompass 39 species with female-biased SSD. We provide evidence that the effects of mating system and habitat types on SSD were non-significant across species, also when the analyses were phylogenetically corrected. Conclusions Contrast to the hypotheses, our findings suggest that mating system and habitat types do not play an important role in shaping macro-evolutionary patterns of SSD in anurans. Mating system and habitat types cannot explain the variation in SSD when correcting for phylogenetic effects. [ABSTRACT FROM AUTHOR]

Background: Sexual size dimorphism (SSD) is related to ecology, behaviour and life history of organisms. Rensch's rule states that SSD increases with overall body size in species where males are the larger sex, while decreasing with body size when females are larger. To test this rule, we analysed literature as well as own data on male and female body size in anurans (39 species and 17 genera). We also tested the hypothesis that SSD is largely a function of age difference between the sexes. Results: Our data set encompassed 36 species with female-biased SSD, and three species with male-biased SSD. All considered species failed to support Rensch's rule, also when the analyses were phylogenetically corrected. However, SSD was significantly correlated with Sexual Age Difference (SAD) across species. We also found a significant correlation between SSD contrasts and SAD contrasts. Conclusions: Our study suggests that Rensch's rule does not accurately describe macroevolutionary patterns of SSD in anurans. That SAD can explain most of the variation in SSD among species when controlling for phylogenetic effects suggests that phylogeny is not responsible for the broad relationship between age and size across the sexes. [ABSTRACT FROM AUTHOR]

Age determination in amphibians is crucial to investigation of life-history traits. In this context, we studied age structure of the Guenther's frog, Hylarana guentheri, population from southwestern China located at an altitude of 300 m using skeletochronological method. Our results showed that age in adult males ranged from 1 to 4 years, and from 2 to 6 years in adult females. Average age in females was significantly older than males in 2008 and 2009. Also, females had significantly larger average body size than males in both years. A significant relationship between age and body size within each sex was found in this species for both years. The ANCOVA analysis revealed that there was significant difference in body size between sexes when the effect of age was removed. The von Bertalanffy's model showed that females had larger [ABSTRACT FROM AUTHOR]