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

The teat number of Antechinus agilis can vary from 6 to 10 depending on geo graphical location. Previous studies have found that there are more eggs ov ulated and embryos produced than the number of teats available; however, th e full range of teat numbers has not been examined. The aim of this study w as to determine how pre- and post-embryonic loss varies between females fro m different populations characterised by differences in the number of teats . In the current study females from 6-, 8- and 10-teat populations across V ictoria 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 po pulation had few losses from the oocyte to embryo stage; however, a maximum of only similar to 60% of these embryos could result in pouch young becaus e of the reduced number of teats. A similar pattern of high embryo loss occ urred in the 10-teat populations, despite an increased number of teats bein g available, because of the excessive numbers of embryos produced.