Geographic variation in life-history traits: growth season affects age structure, egg size and clutch size in Andrew's toad (Bufo andrewsi)

Background: Environmental variation associated with season length is likely to promote differentiation in lifehistory 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.