Optimizing reproduction in the Tasmanian echidna Tachyglossus aculeatus setosus: the influence of an obligatory hibernation period and intense sexual conflict

The echidna is a solitary, seasonally breeding monotreme mammal with a mating system characterized by high levels of intra-male competition for access to receptive females. Throughout Australia the breeding season follows a period of inactivity which ranges from shallow bouts of torpor to prolonged deep hibernation. In this thesis I investigated how the Tasmanian echidna optimizes its reproduction around an obligatory hibernation period and in the presence of intense sexual conflict. The bradymetabolic (slowing of metabolism) effect of hibernation was exploited by both sexes to optimize their reproduction. I found that testes recrudescence (defined as an increase in testes volume and density) was initiated prior to males entering hibernation, a strategy not seen in any other hibernating mammal. This strategy can be linked to the low energy and density diet and requirement to hibernate to maximise energy-savings, and to the large relative size of echidna testes reflecting a mating system with intense levels of intra-male competition. It took approximately two months at euthermic body temperatures from the initiation of recrudescence in December for echidna testes to reach 75% of peak size. Therefore if testes recrudescence did not occur prior to entering hibernation, hibernation would be restricted to a one and a half month period to allow mating in June. Male echidnas initiated mating activity by locating hibernating females and entering their hibernacula. This strategy was common in my study population and males that remained with a female in her hibernaculum for 13 hours or more gained a copulation opportunity. However, all females that mated or were disturbed by males prior to July 27 re-entered hibernation. This indicates that mating often occurred earlier than optimal for female reproductive success. Many of the females that re-entered hibernation after mating were pregnant. Pregnant females entered hibernation only in early pregnancy: hibernation extended the gestation period and hence allowed females to delay egg-laying. Females timed their reproduction so that they emerged from their 37 day period of nursery burrow confinement as ecosystem productivity increased. Hibernation therefore allows successful reproduction in a population where there is asynchronous timing of optimal mating between males and females. This thesis explores the influence of hibernation on sexual conflict, demonstrates the numerous interactions that can occur between hibernation and reproduction and shows that the bradymetabolic property of hibernation is exploited by both male and female echidnas to optimize reproductive fitness.