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

Abstract

Timing of mating, sperm transport and storage, and ovulation were examined in a wild population of agile Antechinus (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 the mated females caught that had not yet ovulated were captured on 19-20 August. This corresponded with a peak (67%) in the ovulation date determined for pregnant females. Approximately 25.9 x 103 spermatozoa per side were recovered from the reproductive tract of each mated female captured (range: 1.7 x 103-75.5 x 103 spermatozoa per side). Spermatozoa were consistently found in greater numbers in the lower isthmus (19.7 x 103 ± 19.9 x 103 spermatozoa per side) of the oviduct (~ 67% of all sperm found in the female tract; range 17-94%) than elsewhere in the reproductive tract. Few spermatozoa were found in the upper isthmus, and none were detected in the ampulla. Sperm number in the female reproductive tract supports the hypothesis that females will mate several times within the one estrus. At the conclusion of the rut, ~ 80.0 x 103 spermatozoa remained in each testis and ~ 630 x 103 spermatozoa in each epididymis. Most epididymal spermatozoa were restricted to the distal corpus/proximal cauda regions of the duct. This study shows that both field and laboratory reproductive data correlate well in the agile Antechinus and that successful breeding is indeed an exercise in reproductive brinkmanship.