A comparison of testes size and sperm length between Polypedates megacephalus populations at different altitudes

Variation in temperature and breeding season length caused by altitude has long been considered a major influence on the evolution of life-history traits in amphibians. Here, we examined differences in reproductive investment (testes mass and sperm length) of male spot-legged treefrog (Polypedates megacephalus) from two altitudes (680 m and 1300 m above sea level) in Guizhou Province, western China. Relative testes size from the high-altitude population was larger than that of the low-altitude population, whereas sperm length exhibited a converse cline. Testes mass but not sperm length increased with body size at both altitudes. Our findings suggest that differences in reproductive traits between populations might result from differences in the level of sperm competition.