Effects of Body Size, Operational Sex Ratio, and Age on Pairing by the Asian Toad, Bufo stejnegeri

摘要

Male and female Bufo stejnegeri pair within a stream and overwinter together in the stream for 3 mo before spawning in early spring. To investigate whether body size, the operational sex ratio (OSR; the ratio of sexually active males to females), or age affects pairing of B. stejnegeri during the long pairing period, we surveyed 2 study sites on 2 separate occasions between 2005 and 2007. In total, 684 toads were sampled, consisting of single males, amplectant males, and amplexed females. No single females were found. When the OSR was slightly male-biased (e.g., 1.85 or 1.96), amplectant males were larger than single males, but when the OSR was highly male-biased (e.g. 2.75 or 4.1), size-assortative pairing occurred. The forelimbs and hindlimbs of amplectant males were thicker than those of single males. At a study site, the frequency distributions of amplectant and single males across different ages were significantly biased, such that most of the single males were 1 (16.7%) and 2 yr old (76.3%).These results suggest that competition occurs between males during the long pairing period of B. stejnegeri, and that body size and age affect pairing of male toads; these effects may differ with variable OSRs. http://zoolstud.sinica.edu.tw/Journals/48.3/334.pdf