Abstract

In the highly punctuated monsoonal climate of the Alligator Rivers area of Australia, Pseudomys nanus and Pseudomys delicatulus breed in the latter part of the monsoon season and can extend their breeding activity into spring. P. nanus may reproduce virtually year-round, presumably when environmental conditions are favourable. In both species, the predominance of young non-breeding adults and juveniles in the spring signals a new infusion of animals into the population and a large population turnover at the expense of older members. The young survivors of the seasonal transition from extremely dry to intensely wet conditions then become the primary contributors to the next major breeding episode. This study is based on histological evidence from the reproductive systems of both sexes.