Long-Day Inhibition of Reproduction and Circadian Photogonadosensitivity in Zembra Island Wild Rabbits (Oryctolagus cuniculus)

We investigated the effects of photoperiod on testicular ac-tivity in wild rabbits (Oryctolagus cuniculus) captured on Zem-bra Island (North Tunisia) and maintained in experimental pho-toperiodic conditions. Sexually inactive animals were subjected to alternate 3-mo periods of short days (8L:16D) and long days (16L:8D) for 1 yr. Testicular activity increased significantly and then decreased to levels equivalent to or lower than those mea-sured during sexual quiescence after 1 mo of 8L:16D or 16L: 8D, respectively. Eight groups of sexually active animals were also exposed to 8L:16D for 60 days. The light phase was divided into two photofractions (7.5 and 0.5 h). The short photofraction interrupted the dark phase 9.5–18.5 h after the beginning of the main photofraction. Testicular activity was inhibited if the short photofraction interrupted the dark phase 12.5 h or more after the beginning of the main photofraction. These results clearly confirm that photoperiod affects reproduction in this species: Short days stimulate reproduction, whereas long days inhibit it. The asymmetric pattern of skeleton photoperiods used demon-strated the existence of a circadian rhythm for photogonadosen-sitivity, with the photosensitive phase beginning 12.5 h after dawn. In this species, photoperiod length controls both the be-ginning and the end of the reproductive period. These results differ from those obtained with continental populations of wild rabbits, in which reproduction is inhibited by short day length. This difference may reflect genetic drift linked to the geographic isolation of this population, which is known to have been pre-sent on this small island for more than 2000 yr. environment, male sexual function, seasonal reproduction, ste-roid hormones, testis, testosteron