Reproductive Cycles of Male Snakes and Their Relationships with Climate and Female Reproductive Cycles

• Published in: Herpetologica 1982-01, Vol.38 (1), p.5-16
• Main Author: Girons, H S
• Format: Article
• Language: English
• Subjects: Animal reproduction; Dry seasons; Herpetology; Ovulation; Serpentes; Sexual reproduction; Snakes; Spermatogenesis; Spermatozoa; Spermiogenesis; Temperate regions
• ISSN: 0018-0831; 1938-5099

Reproductive cycles of male snakes may be classified into four major types: (1) Aestival (summer) and postnuptial, which is found only in temperate and subtropical regions. Spermatogenesis occurs in the warm season and spermatozoa are stored throughout the winter in the vas deferens of the males, or occasionally in the oviducts of the females. The latter occurs when there is both a spring and fall mating. The sexual segment of the kidney has only one brief period of partial regression in July. (2) Mixed type, which is found only in temperate and subtropical regions, and is characterized by spermatogenesis beginning in late spring and being completed one year later. Two sub-types may be distinguished. In the first, there are two periods of spermiogenesis and mating (fall and spring), and the sexual segment of the kidney undergoes a brief period of partial regression in July. In the second sub-type, there is only one period of spermiogenesis and mating (spring), and the sexual segment of the kidney reaches full development only in April. (3) Prenuptial type, which is found everywhere except in cool and cold temperate regions. Spermatogenesis is completed towards the end of the mating period, and always occurs in the spring in temperate and subtropical regions but at any time in intertropical zones. The sexual segment of the kidney is usually completely regressed during the periods of sexual rest. In polyestrous species, male sexual activity may last through most of the year. (4) Continuous reproductive activity, found only in polyestrous species from intertropical regions without a very marked dry season. Of the climatic factors likely to influence reproduction, only temperatures low enough to require prolonged hibernation play any part in the determination of the reproductive cycle of the males, which then have a spermatogenesis of the aestival or mixed type. In regions where there is no prolonged hibernation, male sexual activity may occur at any time of the year, depending on the reproductive cycle of the females. The latter, however, is always dependent upon the climate. Storage of sperm in the vas deferens of males may be indispensable in the reproductive cycles of aestival type, but prolonged retention of sperm in the oviducts, while permitting fertilization in the absence of males, plays only a very minor role in the harmonization of the reproductive cycles of both sexes in the snakes.