Factors influencing pre-natal fertility in the brown marsupial mouse, Antechinus stuartii.

The number of eggs ovulated per ovary, estimated as the number of corpora lutea in histological sections, was 6.1 +/- 1.4 (s.d.) in 100 sides of the reproductive tract in 53 female Antechinus stuartii during 5 breeding seasons. Post-ovulatory fertility, estimated as the number of normal embryos divided by the number of corpora lutea, was 74 +/- 25% (s.d.). By analysis of variance the number of corpora lutea per ovary did not vary significantly with the year of breeding or the origin of the female but did decline significantly (P less than 0.05) with increasing age of the female to 5.4 +/- 1.1 (s.d.) in females in their second breeding season. Analysis of variance showed that the mean percentage of surviving embryos did not vary significantly with the year of breeding, origin or age of the female, the stage of development or whether the female had been mated 1, 2 or 3 times. Failure of development was most marked during fertilization and cleavage to the unilaminar blastocyst and only 79 +/- 21% (s.d.) of embryos reached the latter stage. Additional mortality occurred mainly during implantation.