PUBERTY IN THE FEMALE TAMMAR WALLABY

The growth and timing of female puberty in a seasonally breeding marsu pial, the tammar wallaby, was examined in wild and captive animals. Pu berty, defined as the time of first estrus and ovulation, can occur at any time of the year. Sixty percent of young wild females went throug h puberty in late October-November, 3 mo before the normal adult matin g season in late January-February, but puberty was delayed in captive animals kept with a low ratio of males to females. During initial cycl es, 19% of these captive animals were infertile as judged by failure t o conceive. In the wild, puberty occurred well before the animals were fully grown (body weight 2.0 +/- 0.3 kg [mean +/- SD], n = 23; adult females, 4.7 +/- 0.6 kg; n = 34). Only 3% of animals with a body weigh t below 1.5 kg had ovulated. Thus, attainment of a minimum body weight was a key prerequisite associated with puberty. Progesterone concentr ations in the peripheral plasma of prepubertal females were not signif icantly different from those of adult females during the nonbreeding s eason (prepubertal, 142 +/- 121 pg/ml, n = 34; adult, 194 +/- 105 pg/m l, n = 32, p > 0.05). However, there was a significant increase in pro gesterone (322 +/- 242 pg/ml, n = 32, p < 0.05) in the postpubertal fe males (ovulating but still < 3.5 kg body weight) even though the corpu s luteum was quiescent after its formation. There was no increase in p lasma progesterone before the first estrus. These data confirm that es trus does not require a change in the progesterone:estradiol ratio, an d that a ''silent'' ovulation does not precede the first estrus in thi s species, so that the onset of puberty coincides with the first behav ioral estrus and ovulation, when the animals have reached a body weigh t of 2 kg. Although adult female tammars are strict seasonal breeders, with 6 mo of seasonal quiescence from the winter to the summer solsti ce, young females can go through puberty at any time of the year. The unique feature of the female tammar wallaby is that it does not become a seasonally breeding mammal until after puberty, when it has acquire d a corpus luteum.