SPERM PRODUCTION, STORAGE, AND THE SYNCHRONIZATION OF MALE AND FEMALEREPRODUCTIVE-CYCLES IN THE ITEROPAROUS, STRIPE-FACED DUNNART (SMINTHOPSIS-MACROURA, MARSUPIALIA) - RELATIONSHIP TO REPRODUCTIVE STRATEGIES WITHIN THE DASYURIDAE

Seasonal changes in the number and distribution of spermatozoa in male s, and annual changes in the distribution of liners and embryos in fem ales were examined in the iteroparous dasyurid marsupial, Sminthopsis macroura, in captivity. Total number of sperm in the testis (0.53 x 10 (6) sperm/testis) and epididymidis (0.54 x 10(6) sperm/epididymidis) w ere extremely low when compared with those in other marsupials and eut herian mammals. Testicular sperm production and epididymal sperm reser ves were high between May and October and declined to a minimum in Mar ch. These changes reflected monthly changes in testicular and epididym al weight and testis morphology. Data on changing epididymal sperm dis tribution suggest that sperm storage in the cauda epididymidis is limi ted and that few sperm are required for successful insemination. Litte rs were born between June and January, with most litters occurring bet ween July and October. Second pregnancies occurred between October and January, with a peak in December. The data indicate that the timing o f mating activity and litter production by S. macroura correspond very closely with the period of maximum sperm production by males. The syn chrony of these events contrasts dramatically with that of similar-siz ed semelparous dasyurid species. It is hypothesized that testicular fa ilure prior to the mating season, copulatory behaviour, and possibly m ale die-off in dasyurid marsupials are related to the degree of compet ition between males for mates and, hence, population density and envir onmental predictability. These data suggest that intermale sperm compe tition is affected by the periods of female receptivity and the length of sperm storage in the female reproductive tract. Fundamental differ ences in the reproductive strategies of iteroparous and semelparous da syurid marsupials are discussed.