The tammar wallaby, Macropus eugenii is a seasonally breeding macropodid marsupial. The seasonality observed in males is known to be driven by the reproductive state of the females. There is a significant increase in male prostate and Cowper's gland weights and testosterone concentration during the breeding season in January/February and again in October when the young females leave their i;nothers pouches and enter puberty. The dynamics of sperm production in the male tammar wallaby was assessed using changes in ejaculatory and sperm characteristics in and out of the breeding season in order to determine more accurately true seasonality in the male. Semen was collected from wild-caught adult males by electro-ejaculation at four times during the year (January, February, June/July and October). Ejaculates were assessed for semen volume, plug formation, sperm index, percentage and rating of motility, sperm and motile sperm concentration, and total sperm count. Increases were observed during the two breeding seasons in all traits assessed. Semen volume showed a steady increase from June/July (0.7 ml) to reach a peak in February (10.25 ml). In conclusion, we found a significant decrease in the size and coagulation properties of the ejaculate, and in sperm quality out of season. Implications for captive and assisted breeding programs are discussed
