Ovulation in a social ground squirrel

The timing of ovulation, whether an animal is a spontaneous or induced ovulator, plays an important role in the understanding of the evolution of reproductive strategies and social systems within a given species. The Cape ground squirrel, Xerus inauris, is a highly social, non-hibernating ground squirrel found in southern Africa. To determine the method of ovulation in this species, ten males and 15 females were brought into captivity for a period of 15 weeks. Female urine was initially collected in the absence of male stimuli and then in either chemical and visual contact or physical contact with males. The urine was then analyzed for progesterone content using a [sup.125]I radioimmunoassay. The ovaries of six females were also sectioned and mounted to look at follicular development. Hormonal and histological evidence supports the prediction that the Cape ground squirrel is a spontaneous ovulator. This is the first evidence of spontaneous ovulation in a ground-dwelling squirrel.