Migration and sexual selection in Ambystoma jeffersonianum

Initiation of reproductive migration, structure of the breeding population, and length of the breeding season in Ambystoma jeffersonianum were studied for two consecutive winters at a small, sylvan pond in Kentucky. Early response to cues of temperature and precipitation, and continued movement under declining nocturnal temperatures enabled males to arrive at the pond sooner and in greater numbers than females, who frequently moved later and under prolonged periods of favorable conditions. During 1973, movement conditions were favorable, and males arrived in greater numbers and stayed significantly longer at the pond than in 1974 when male movement periods were reduced, males were fewer in number, and their length of stay was shorter. The number of females and their mean duration of stay were virtually identical in each season. Breeding congregations that become increasingly skewed toward males are known to precipitate intense male–male competition and male sexual interference. Hence the intensity of sexual selection was believed to have been greater in 1973 than in 1974.Although the mating system of A. jeffersonianum adapts quickly to changes in the environmental potential for polygamy, ecological constraints of temperature and precipitation apparently limit the degree to which sexual selection can operate within local populations of this species.