Reproductive biology of the Tasmanian Bettong (Bettongia Gaimardi)

The Tasmanian bettong is a rat-kangaroo found only in Tasmania. Information on this macropodid is extremely scant and the thesis presents a detailed study of the species' reproductive biology. Techniques for accurately estimating the age of the pouch young are reported, together with their application to the analysis of breeding season and growth rates. The bettong is able to breed throughout the year. The growth rate of pouch young is faster than that of other kangaroo species and this mirrors the findings that prenatal growth is also so rapid that the bettong has the shortest gestation of any macropodid. The reproductive biology of the bettong conforms to the pattern found in most kangaroos. Gestation and the oestrous cycle are of similar duration (21-22 days), and a post-partum oestrus may result in the formation of a blastocyst that remains quiescent (embryonic diapause) throughout most of the pouch life. Oestrous cycles including a gestation are shorter (by 1.5 days) than those cycles without a pregnancy. The presence of a fetus also has morphological effects upon the uterus. The uterine glands in the pregnant uterus remain enlarged for a longer period than do those of the non-pregnant uterus. Pouch life is always terminated when a new young is born. In the absence of birth, final pouch emergence is associated with oestrus. Pouch vacation is apparently a consequence of a dramatic tightening of the pouch musculature. Data are presented to support the conclusion that, contrary to expectations b~seu on previous work, it is the physiology of the mother that is most important in the determination of the duration of pouch life. It appears that the duration of pouch life, in effect, may be a compromise between the wellbeing of the existing pouch young and the mother's capacity to maximise reproductive output during her life span. The bettong displays a circadian rhythm in body temperature. The daily fluctuations in body temperature of females vary according to the phases of the reproductive cycle. This is a consequence of a relatively stable daily maximum temperature but a more labile basal body temperature (BBT). Computer analysis of the variations in the BBT demonstrate a cyclical variation whose period corresponded closely with the duration of the oestrous cycle. A profile of the fluctuations in the sex hormone progesterone appears to mirror the changes in basal body temperature.