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

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.

Background Environmental variation associated with season length is likely to promote differentiation in life-history traits, but has been little studied in natural populations of ectotherms. We investigated patterns of variation in egg size, clutch size, age at sexual maturity, maximum age, mean age, growth rate and adult body size in relation to growth season length among 17 populations of Andrew’s toad (Bufo andrewsi) at different latitudes and altitudes in the Hengduan Mountains, western China. Results We found that egg size, age at sexual maturity, and mean age increased with decreasing length of the growth season, whereas clutch size showed a converse cline. Body size did not increase with decreasing length of the growth season, but was tightly linked to lifetime activity (i.e. the estimated number of active days during lifetime). Males and females differed in their patterns of geographic variation in growth rates, which may be the result of forces shaping the trade-off between growth and reproduction in different environments. Conclusions Our findings suggest that growth season plays an important role in shaping variation in life-history traits in B. andrewsi across geographical gradients. Electronic supplementary material The online version of this article (doi:10.1186/s12983-016-0138-0) contains supplementary material, which is available to authorized users.