Reproductive biology of the brush-tailed phascogale, Phascogale tapoatafa (Marsupialia : Dasyuridae)

This study investigated the reproductive biology of a captive population of brush-tailed phascogales Phascogale tapoatafa. A 'round robin' mating syst em was established in which seven adult male animals were rotated through s even adult females. Changes in vaginal cytology and peripheral plasma proge sterone and oestradiol levels were monitored to determine features of the f emale reproductive cycle. Regular measurement of scrotal diameter, collecti on of testicular biopsies and monitoring of plasma testosterone levels was used to assess male reproductive activity. Oestrous cycle length was estima ted as 40 +/- 5 days (n = 7) and gestation length as 27+/-5 days (n = 7). P lasma progesterone levels showed no significant variation. This negative re sult is attributed to the small sample size (n = 4). Plasma oestradiol leve ls however, followed the predicted pattern, with an increase in peripheral concentration occurring prior to the breeding season. Oestradiol concentrat ion peaked at 246.9 +/- 169.2 pg ml(-1) (mean +/- se) just before mating an d declined to 24.3 +/- 12.0 Fg ml(-1) after mating. Histological studies of testicular biopsies revealed that spermatogenesis does not cease until aft er the breeding season has begun, in contrast to Antechinus species, in whi ch spermatogenesis ceases before breeding. Plasma testosterone levels incre ased at the onset of the breeding season, peaking at 6.3 +/- 0.60 ng ml(-). Testosterone concentrations remained high until approximately 3 weeks afte r breeding, followed by a decline to pre-breeding levels. Litter size and s ex ratio did not vary significantly between first- and second-year females. Females did not undergo a second oestrous cycle when pouch young were remo ved 15 and 17 days after parturition.