Abstract:
In the monovular macropodid marsupial, the tammar wallaby (Macropus eugenii), the cervices are the primary selective barrier to spermatozoa, resulting in differential transport to the non-gravid uterus where a sperm reservoir is established (Tyndale-Biscoe CH and Rodger JC 1978 J. Reprod. Fertil. 52, 37?43). However, due to limited sample size, the dynamics of sperm transport could not be thoroughly examined. In this study, the distribution of spermatozoa, the size of the copulatory plug in the reproductive tract at various times after mating, and the timing of ovulation were characterized in 28 naturally mated female tammars. After the first postpartum (p.p.) mating, adult females were isolated and their reproductive tracts dissected at 0.5, 6, 18, 36, and 40 h post-coitum (p.c.). Each tract was ligated into 13 major anatomical sections, and spermatozoa and eggs were recovered by flushing. Mating occurred 21.7 � 2.5 h p.p. (mean � SEM; n = 20) in these animals that were checked frequently and lasted 7.8 � 0.7 min (n = 15). Within 0.5 h after a single mating (n = 5) the tract contained 2.6 � 1.0 _ 107 spermatozoa and 21.6 � 8.8 g of copulatory plug, 96 and 70% of which was lost within 6 h p.c., respectively. Spermatozoa reached the uterus, isthmus, and ampulla of the oviduct ipsilateral to the developing follicle within 0.5, 6, and 18 h p.c. respectively, and a uterine population of 2.6 � 1.2 _ 104 spermatozoa (n = 24) was maintained for over 40 h (ANOVA, P > 0.05). Sperm numbers were reduced at the cervix (up to 57-fold) and utero-tubule junction (8-fold), and only 1 in ?7600 ejaculated spermatozoa (3.4 � 0.9 _ 103; n = 14) reached the oviduct on the side of ovulation. Although sperm numbers were reduced in the gravid uterus (n = 24), differential transport of spermatozoa was not observed (ANOVA, P > 0.05). Ovulation and recovery of sperm-covered eggs from the isthmus of the oviduct occurred 36?41 h p.c. (49?72 h p.p.) (n = 8). Like many eutherian mammals, but in contrast to polyovular dasyurid and didelphid marsupials, the tammar ejaculates large numbers of spermatozoa, but transport is relatively inefficient and sperm storage in the tract before ovulation is limited. Research was supported by the Australian Research Council (grant No. C09930004) and the University of Melbourne.