DEFERRED SEASONAL INCREASE IN TESTES WEIGHT UNDER POOR NUTRITIONAL CONDITIONS IN A SUB-ANTARCTIC POPULATION OF RABBITS (ORYCTOLAGUS-CUNICULUS)

The annual cycle of testes weight of adult male rabbits (Oryctolagus c uniculus) was studied in three populations on the sub-Antarctic Kergue len archipelago during 1984-85. This study was completed in April 1987 with an analysis of differences in diet quality between populations, assessed by the proportion of nitrogen and lignin in stomach contents. A marked annual cycle of testes weight was observed in all population s, with a rapid fall in testes weight from February to March. As in mo st rabbit populations studied elsewhere, testes growth resumed immedia tely in two populations (called Morne and Molloy). In contrast, testes growth was deferred by five to six months in the third population (Ar mor), subject to harsher environmental conditions. Moreover, a larger proportion of the Armor males had inactive testes during the reproduct ive season. The diet of the Armor population was characterized by low nitrogen and high lignin content, suggesting poor-quality diet as an i mmediate cause of deferred testes growth. We propose that reduced test es size during adverse conditions might be adaptive by increasing surv ival probability through reduction of basal metabolism and limitation of agonistic and reproductive activities, behaviours which are costly in terms of high energetic expenditure. However, at the population lev el, the timing of the breeding season was not related to the cycle of male testes weight and thus seems to depend on females' condition.