Circannual testicular rhythm in the green frog, Rana esculenta

Abstract

We followed testis weight, seminiferous tubule diameter, spermatogenetic activity, pituitary gonadotropa secretory activity and spermiation response in Rana esculenta, under day length 12:12. On this lighting schedule, groups of frogs were studied at 4°C, 15°C and 24°C. A group of frogs reared in the laboratory under natural temperature and lighting conditions served as captive controls, whereas freshly captured frogs were used as wild controls. In frogs exposed to 24°C the testicular growth was greatly speeded up compared to other groups, but long-term exposure to this temperature apparently caused regression of pituitary gonadotropic activity and testicular growth. Circannual testicular rhythm was evident in frogs reared at constant 15°C. In the 4°C group the testicular cycle proceeded for 120 days and then apparently “ stopped” at a specific phase associated with winter stasis. The rhythm, in fact, was reinitiated by an appropriate environmental input (15°C). In summary, it was demonstrated that a circannual testicular rhythm occurs in Rana esculenta and that it can take place only within a certain temperature range. However, this by no means suggests that the temperature is the only trigger or timer - or whatever we call it-of this rhythm in the frog. © 1981, Taylor & Francis Group, LLC.