Timing of mating, sperm dynamics, and ovulation in a wild population of agile Antechinus (Marsupialia : Dasyuridae)

Timing of mating, sperm transport and storage, and ovulation were examined in a wild population of agile Antechinos (Marsupialia: Dasyuridae) in order to ascertain the validity of direct comparisons between captive and field- based mating studies in this species. Mating commenced in early August, and all females had ovulated by the 27th of the month. Fifty-five percent of t he mated females caught that had not yet ovulated were captured on 19-20 Au gust. This corresponded with a peak (67%) in the ovulation date determined for pregnant females. Approximately 25.9 x 10(3) spermatozoa per side were recovered from the reproductive tract of each mated female captured (range: 1.7 x 10(3)-75.5 x 10(3) spermatozoa per side). Spermatozoa were consisten tly found in greater numbers in the lower isthmus (19.7 x 10(3) +/- 19.9 x 10(3) spermatozoa per side) of the oviduct (similar to 67% of all sperm fou nd in the female tract; range 17-94%) than elsewhere in the reproductive tr act. Few spermatozoa were found in the upper isthmus, and none were detecte d in the ampulla. Sperm number in the female reproductive tract supports th e hypothesis that females will mate several times within the one estrus. At the conclusion of the rut, similar to 80.0 x 10(3) spermatozoa remained in each testis and similar to 630 x 10(3) spermatozoa in each epididymis. Mos t epididymal spermatozoa were restricted to the distal corpus/proximal caud a regions of the duct. This study shows that both field and laboratory repr oductive data correlate well in the agile Antechinos and that successful br eeding is indeed an exercise in reproductive brinkmanship.