Ultrastructural changes in testes of the snapping turtle, Chelydra serpentina in relation to plasma testosterone,...

Ultrastructural changes in the testes of the common snapping turtle, Chelydra serpentina, were observed throughout the year. Plasma testosterone levels were measured and compared with the occurrence of delta 5-3 beta-hydroxysteroid dehydrogenase (3 beta-HSD), cholesterol, and steroidogenic ultrastructural features (smooth endoplasmic reticulum (SER), mitochondria with tubular cristae) in Sertoli and Leydig cells. The testosterone level is highest in May and October (mating) and relatively low during the rest of the year. Fluctuations in 3 beta-HSD and cholesterol are consistent with the interpretation that the Leydig cells are potentially active throughout the year. They undergo very little ultrastructural change, (tubular SER to vesiculate and loss of golgi during spermatogenesis and in the winter). Sertoli cells are active only during spermatogenesis from May through October and become inactive until the next cycle; 3 beta-HSD, cholesterol and ultrastructural features change more drastically in the Sertoli cells than in the Leydig cells. These results are discussed with reference to the hypothesis that testosterone of Leydig origin is concerned mainly with mating behavior and that of Sertoli origin with spermatogenesis and maturation of sperm.