Body size, age, growth and alternative mating tactics in toads: satellite males are smaller but not younger than calling males

摘要

Body size-age relationships may have important implications for the evolution and maintenance of alternative mating tactics, but these relationships remain largely unexplored in anuran amphibians (frogs and toads). In a single territorial anuran species, smaller noncalling 'satellite' males are younger than calling males. These results have led to the general assumption that such an age difference also holds for other anuran species with body size differences among behavioural phenotypes. However, individuals of many organisms show different developmental and/or growth trajectories that correspond to variation in adult morphology and behaviour. To test the generality of smaller satellite males being younger than larger calling males in anurans, we examined body size-age-behaviour relationships in Woodhouse's toads, Bufo woodhousii, and Great Plains toads, B. cognatus. Age estimates, based on skeletochronologic analysis of lines of arrested growth (LAGs) from phalanges, indicated that males sampled while adopting a noncalling satellite tactic were smaller, but not younger, than males sampled while adopting a calling tactic. Furthermore, examination of inter-LAG areas of bone deposition indicated that smaller satellite male B. woodhousii showed lower growth rates relative to calling males. A similar trend occurred for B. cogriatus. We discuss our results in the context of developmental patterns associated with alternative mating tactics in other species and endocrine regulation of behavioural tactics in anurans.