Seasonal Testicular Development and Sperm Storage in Tropical and Subtropical Populations of the Brown Tree Snake (Boiga irregularis)

Abstract

The seasonal pattern of testicular development of tropical and subtropical brown tree snakes, Boiga irregularis, was investigated. We also examined sperm storage in the reproductive tracts of both sexes. Males in south-eastern Queensland had a testicular cycle that was strongly seasonal, with testicular regression during the wet summer. Males from Papua New Guinea had a continuous testicular cycle, in which sperm was present in some animals every month.

Females from south-eastern Queensland had no stored sperm or sperm storage receptacles in their oviducts. Sperm was found in only one of 28 female reproductive tracts. The sperm was located in the lumen, suggesting recent insemination. In contrast, the presence of sperm in the ductus deferens of most males in both populations indicated that males store sperm. This facilitates the apparent dissociation between the male and female reproductive cycles that has been reported previously in south-eastern Queensland populations. Male B. irregularis must store sperm for at least six months, from the time of maximal testicular development in autumn, until ovulation occurs in spring and early summer. This pattern of reproduction in B. irregularis fits neither a postnuptial nor a prenuptial pattern, as has been observed in a few other tropical snakes.