The annual reproductive cycle of the Smooth newt (Triturus vulgaris) in England

Abstract

Newts were collected throughout the year from both breeding ponds and terrestrial sites and were weighed, measured and dissected; in males, the testes were examined histologically. Smooth newts show post‐nuptial gametogenesis such that, during late summer and autumn they are producing mature gametes for the following year's breeding season. In males, the testes are at their smallest size during the spring, when they consist mostly of immature sperm cysts and evacuated tissue, mature sperm having been evacuated into the vasa deferentia during the newts' migration to water. Evacuated testicular tissue is glandular in function and there is evidence that secretions from this tissue control the development of secondary sexual characters: the dorsal crest, fringes of skin on the toes and the dorsal cloacal gland. In both sexes, fat body and liver weights are lowest in the spring and increase in the autumn. In females, oocytes vary in size, depending on the amount of yolk they contain. Only the larger oocytes are laid in a current breeding season, the smaller ones being retained and yolked in late summer and autumn. In both sexes, measures of fecundity (testis size in males, oocyte number in females) are strongly correlated with body size. The finding that male newts have a finite supply of sperm during the breeding season leads to an interpretation of various aspects of male courtship behaviour. These are adaptations for conserving sperm and allocating it to courtship encounters in a way likely to promote male reproductive success.