Reproductive costs of migration for males in a partially migrating, pond-breeding amphibian

Abstract

Migratory animals face costs and benefits related to traveling to another habitat and the timing of the journey. These trade-offs can be sex-specific, with male reproductive success expected to be influenced by arrival time at the breeding habitat. In this study, we examined mating success in a population of partially migrating Red-Spotted Newts ( Notophthalmus viridescens viridescens (Rafinesque, 1820)). We tested the hypothesis that migrant males are at a disadvantage for spring mating opportunities compared with resident males owing to (i) later arrival time at the breeding pond and (ii) delay in developing the aquatic tail fin, which reduces their competitiveness. We measured the tail heights of successfully courting males compared with the general male population, as well as the time required for migrating males to develop tail fins. Temporally, migrant males arrived at the breeding pond before the majority of mating activity. However, we found that the time required for migrating males to acquire tail-fin heights necessary to be competitive for mating opportunities places them at a significant reproductive disadvantage compared with resident males. For partial migration to be maintained in the population, a reproductive cost for migrants could either trade off with another life-history trait or migration could be condition-dependent.