Ovarian activity and early embryonic development in the rusty bat, Pipistrellus rusticus

The reproductive pattern of the female rusty bat, Pipistrellus rusticus, was investigated by means of a histological examination of the ovarian follicles as well as early embryonic development. Bats were collected from two localities in Limpopo Province. Female rusty bats are seasonal monestrous breeders, initiating copulation in mid-autumn (April), storing sperm until the time of ovulation in late winter (August), and giving birth to twins in late spring (November). The period April until mid-August was characterized by sperm storage and increased follicular development. During mid-August the females ovulated and excess sperm were discarded. Females released between three and five ova, while a maximum of two embryos implanted successfully. Only a single embryo implanted per uterine horn. Embryo movement through the Fallopian tubes appeared to be a rapid process. Redundant embryos were resorbed before implantation. The period from the end of August until mid-November was marked by pregnancy. Females invariably carried twins (one foetus in each uterine horn). Large-scale follicle atresion, and very low levels of follicle development, characterized the period end of August until March. High incidences of polyovular follicles were recorded for all months of the year. No obvious form of reproductive asymmetry was recorded in the rusty bat.Keywords: vespertilionid bat, ovarian cycle, embryogenesis, blastocys