Growth, Reproduction, and Sexual Dimorphism in Thomomys bottae Pocket Gophers

Genetic and demographic characteristics of a population of Thomomys bottae pocket gophers were studied in the central coastal ranges of California from 1976-1983, using both kill-trapping and live-trapping techniques. The widely accepted view that male pocket gophers continue to grow throughout their life does not account for the large variation in male body size observed in this, and other, populations. In particular, heavier adult males were not necessarily older than lighter adult males, and some juveniles reached weights by four months of age that were greater than 35 percent of all adult males. A prime component of the variation in adult male body size probably stems from differential individual growth rates. The degree of closure of sutures of the postero-basal cranium is used to distinguish age classes, the calendar ages of which are based on known-age individuals. Although it was common for females to breed within the season of their birth (within three months of age), males did not breed until the following season, at a minimal age of six to nine months.