A multiyear comparison of the male reproductive biology of the brown treesnake (Boiga irregularis) from Guam and the native range

Abstract

Previous studies have suggested that reproduction in the brown treesnake (Boiga irregularis) is reduced on Guam because of elevated stress hormones caused by limited food availability. This study examined the reproductive anatomy of male brown treesnakes on Guam over a 15-year period (1985–99) to determine whether the size at maturity and development of the testis and sexual segment of the kidney varied between years and to compare these data to those for snakes collected from the native range. On Guam, the average snout–vent length and body mass of B. irregularis has decreased from its high in 1985 and remained stable from 1989 to 1999. The snout–vent length at maturity was similar between years. Mean diameters of the seminiferous tubule and the sexual segment of the kidney were not significantly different between years. However, the number of sexual segment tubules hypertrophied per snake varied greatly. Snakes from the native range matured at smaller snout–vent lengths and had significantly more hypertrophied sexual segment tubules per kidney than populations on Guam. These data suggest that elevated plasma levels of corticosterone, potentially due to an increase in male–male interactions as a result the explosive population growth experienced on Guam, may be negatively influencing male reproduction.