The tammar wallaby (Macropus eugenii) is a small, promiscuous, macropodid marsupial. Females usually produce a single young each year and there is a clear dominance hierarchy between adult males. The dominant male usually mates first and then guards the female to prevent access to her by other males. In this study, agonistic encounters and mating behaviour were observed to determine male dominance hierarchies in six groups of captive tammars consisting of a total of 23 males and 50 females. Mating behaviour was observed immediately post-partum when females were in oestrus and was correlated with plasma testosterone concentrations. Male mating sequences were recorded, and the paternity of offspring was determined by using seven macropodid marsupial microsatellites. Rates of sexual checking and aggression by males housed with females in oestrus in the non-breeding season were lower than in the breeding season. These males also had lower concentrations of testosterone, but were still able to sire young. High testosterone concentrations neither ensured dominance nor appeared to control directly the level of sexual activity. Females usually mated with more than one male. The dominant male most often secured the initial copulation (60%), but the first-mating male did not always secure parentage, with second and third matings resulting in as many young as first matings. Using these data, we were unable to discount first sire, last sire or equal chance models of paternity in this species. Half the young (50%) were sired by the dominant alpha male, but of the remaining progeny, the beta male sired more (35%) than gamma and delta males (15%). Dominance therefore is only a moderately effective predictor of paternity in the tammar. Although the dominant males gained most first matings and individually sired half of the offspring, the subdominant males still contributed significantly to the population, at least in captivity.

The surge of LH that induces ovulation in mammals showing spontaneous ovulation is precipitated by the positive feedback of increasing oestrogens from the developing follicles in the ovary. In eutherians, exogenous oestrogens can mimic this effect by eliciting an LH surge in females, but not usually in males. The absence of a positive LH response to eutherian males is either due to an acute suppression by the secretory products of the testes during adulthood or the permanent disabling of the system by testosterone during early development. This phenomenon is examined in tammar wallabies, Macropus eugenii. The results show that the oestradiol-LH positive feedback response is sexually dimorphic in this marsupial. A surge in plasma LH occurred between 15 and 28 h after injection of 2.5 micrograms oestradiol benzoate kg-1 in 13 of 16 intact females and 4 of 4 ovariectomized females, but in none of 11 intact males. Five females each implanted with a 100 mg testosterone pellet 3 months earlier failed to produce an LH surge. Four males castrated in adulthood and three adult males castrated before puberty also failed to show an LH surge. However, three males castrated 24-26 days after birth showed an unambiguous LH surge when challenged with oestradiol benzoate during adulthood. Thus, in tammar wallabies, the ability to generate an LH surge to oestradiol is a sexually dimorphic response that is suppressed in the male by the organizational effects of the testes in early life and presumably supplemented by an inhibitory effect of circulating testosterone in adulthood.

Tammar wallaby (Macropus eugenii) luteinizing hormone (LH) was purified from pituitaries collected from wild and captive populations by salt sequential precipitation, ion exchange chromatography and gel filtration. Pituitary tissue (5 g) yielded 1.8 mg of purified wallaby luteinizing hormone (ME-14B), as verified by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). A heterologous radioimmunoassay has been developed for measurement of LH in plasma of marsupials using a monoclonal antibody raised against bovine LH (518B7). This assay system was able to measure basal LH concentrations in male and female tammars and detected a significant rise in plasma LH in response to oestradiol benzoate in female tammars and luteinizing hormone-releasing hormone (LHRH) in males. Parallel dose-response curves were also obtained from pituitary extracts from four other species of marsupial (brushtail possum, Trichosurus vulpecula; brown antechinus, Antechinus stuartii; kowari, Dasyuroides byrnei; and Eastern pygmy possum, Cercartetus nanus) in this assay, which suggests its usefulness in the measurement of LH in other marsupial species.

In the tammar wallaby, Macropus eugenii, the expression of male-type sexual behavior is apparently determined by the activating effects of testicular hormones in adulthood. The incidence of male-type copulatory behavior and sexual checking behavior was compared in intact (control) males, control females, testosterone-treated females, and three groups of males castrated either postnatally (24-26 days of age), prepubertally (14.5 months of age), or in adulthood. All three groups of castrated male wallabies showed a very low incidence of male sexual behavior in adult life, comparable to that shown by the untreated females. Adult female wallabies with 100-mg testosterone implants showed a high incidence of male sexual behavior which was indistinguishable from that shown by intact males. The results suggest that sex differences in male-type behavior in the tammar wallaby are due to short-term inductive effects of testosterone acting on a sexually indifferent brain. There is no evidence of any long-term organizational effects of testosterone acting in fetal or neonatal life on the neural pathways controlling male-type sex behavior in this marsupial mammal.

This study describes the sexual behaviour of the adult male and female tammar wallaby from the time a female gives birth to the end of post‐partum oestrus. Eleven females were continuously observed from around the time of birth until up to 3 h after the last observed mating attempt. Males began to associate with females from around the time of birth, thus females appear to be attractive to males at, but not prior to parturition. Females subsequently allowed males to mate with them from 1.3±0.8h (mean±S.D.) post‐partum, although the first ejaculation was delayed until 1.8±0.8h after birth owing to intense intermale aggression directed towards any male which attempted to mate with an oestrous female. Mating chases, in which a post‐partum female was pursued by several males, were observed from 1.3±0.8h post‐partum. All of this mating activity usually occurred within the first 6h after birth.