Sex-specific Shift in Age and Morphological Traits of a Non-native Toad Introduced to Beijing About 100 Years Ago

Successful non-native species can exhibit rapid divergence of key phenotypic traits to facilitate population persistence and further range expansion. Such phenotypic shifts can be sex-dependent as males and females usually have distinct reproductive and dispersal modes responding to relevant selective forces. Here, we showed significant phenotypic divergence in a set of fitness-related traits among males but not among females in the introduced oriental fire-bellied toads (Bombina orientalis), which established a non-native population in Beijing after being introduced in 1927. Specifically, compared with the native counterparts, introduced males displayed younger age and reduced body size, but increased hindlimb length and eye size after controlling the age effect. As the toads have male-biased sex ratio and male-biased dispersal during breeding season, the observed shifts may suggest that the male-biased selective forces have induced increased energy allocation to dispersal and foraging, and thus decreased allocation to maintain longevity in males. Overall, our study provides evidence for the modification of fitness-related phenotypic traits in a non-native anuran population compared with native populations and extends our understanding of key trait divergence in established non-native amphibian under sexual-unbalanced selective forces.