Oxford biologists explore ability for some females to conceive during pregnancy

In a fascinating new study forthcoming from The Quarterly Review of Biology, biologists from the University of Oxford explore a rare tactic employed by females badgers to maximize their reproductive success. The authors argue that conception during pregnancy, known as superfetation, benefits female reproductive fitness by reducing the risk of infanticide, extending the female’s window of opportunity for conception, and increasing the genetic diversity of the litter.

“Natural selection and sexual selection act on both sexes. However, emphasis on sexual selection as a direct evolutionary force acting on males has diverted attention away from the selective process acting on females, whose discrete mating tactics may have masked the extent of reproductive conflict between the sexes,” write Nobuyuki Yamaguchi, Hannah L. Dugdale, and David W. Macdonald, all of the Wildlife Conservation Unit at the University of Oxford.

One of only two known species that exhibit or are presumed to exhibit both superfetation and embryonic diapause – during which the newly fertilized egg temporarily ceases development and remains free in the uterus cavity instead of implanting directly into the uterus – the female European badger first ovulates and is fertilized in late winter-early spring (January-March). However, implantation does not occur until December or January of the following year, a gestation period of nearly eleven months.

“The combination of embryonic diapause and superfetation may… benefit females, regardless of their social system, by enabling cryptic polyandry [mating with more than one male],” write the authors.

The European badger (Meles meles) is unique among badgers in exhibiting large variation in social organization, from large, multi-male, multi-female groups in southern England to small group and paired coexistence. All other species of badgers are primarily solitary.