Female reproductive patterns in hibernating bats

Abstract

Summary. Hibernation exerts a profound influence on the physiology of reproduction in two families of bats, Vespertilionidae and Rhinolophidae. The imposition of a period of hibernation on the female reproductive cycle appears to arrest the progress of reproductive events begun in the autumn and to postpone their completion until spring. The sequence of reproductive events in hibernating bats follows one of two basic patterns. In the Type I pattern, oestrus and copulations are initiated in late summer and early autumn and the bats typically enter hibernation soon thereafter. Intermittent arousal and additional copulations may occur throughout the hibernation period. Spermatozoa are then stored in the female reproductive tract until after permanent arousal in the spring when ovulation, fertilization and gestation take place. In the Type II pattern, copulation in autumn is followed immediately by ovulation, fertilization and initial embryogenesis, and females enter hibernation in a pregnant condition. During hibernation, implantation is delayed and does not occur until after permanent arousal in the spring. The significant features that are of special interest in the reproductive processes of hibernating bats are the delay of ovulation and storage of sperm following autumn copulation in Type I or, alternatively, the delay of implantation following autumn fertilization in Type II. Morphological, physiological and experimental analyses of gamete and steroid production by the ovary and of pituitary control of these processes with respect to hibernation are reviewed in this paper. The evidence indicates that hibernation and the external factors regulating it act to suppress endocrine activity of the pituitary and ovary, resulting in the protraction of certain stages of the reproductive cycle. Although this argument is especially persuasive with respect to ovarian function, a comprehensive understanding of the mechanisms controlling the progress of reproductive events and their delay in these bats is lacking. Accordingly, areas that require elucidation are discussed.