Variation in reproductive surpluses of the agile antechinus (Antechinus agilis) at different teat-number locations

Abstract

The teat number of Antechinus agilis can vary from 6 to 10 depending on geographical location. Previous studies have found that there are more eggs ovulated and embryos produced than the number of teats available; however, the full range of teat numbers has not been examined. The aim of this study was to determine how pre- and post-embryonic loss varies between females from different populations characterised by differences in the number of teats. In the current study females from 6-, 8- and 10-teat populations across Victoria were trapped during gestation. Reproductive tracts of females were removed and the number of embryos and corpora lutea counted. Evaluation of the reproductive surpluses in these three populations indicate that females from the 8-teat population have the lowest level of reproductive surplus, from both oocyte to embryo and embryo to teat. Females from the 6-teat population had few losses from the oocyte to embryo stage; however, a maximum of only ~60% of these embryos could result in pouch young because of the reduced number of teats. A similar pattern of high embryo loss occurred in the 10-teat populations, despite an increased number of teats being available, because of the excessive numbers of embryos produced.