Reproductive Correlates of a Perineal Gland in the Hispid Cotton Rat

During studies of the annual cycle of reproduction in the hispid cotton rat (Sigmodon hispidus) in southeastern Virginia, we discovered an anal (more specifically, perineal) gland that is present only in males during the breeding season. The perineal gland encircles the lower end of the rectum and has ductal connections to the urethra, through which its secretions probably are delivered. This fatty gland is highly developed in breeding males but, like the testes and seminal vesicles, regresses during the winter non-breeding season. The prominence and cyclicity of the perineal gland suggests that it somehow facilitates normal reproduction. The combined mass of testes, seminal vesicles, and perineal gland constitutes only about 0.01 percent of the body mass of large males during the non-breeding season, but as much as 4.8 percent of body mass during the breeding season. Thus, males devote a large amount of energy to growing and maintaining these glands in anticipation of and during the breeding season. Despite two field trials, the function of the perineal gland and the nature of its secretion are unknown.