Peculiar processes Delayed fertilization and delayed implantation

The opportunity to find a suitable mate is essential for reproduction, but because gestation is fixed in duration, timing of mating has direct implications on the timing of parturition. However, mammals have evolved two strategies to separate

Barred Bandicoot Nest
A western barred bandicoot (Perameles bougainville) joey suckling in mother's pouch. (Photo by © Jiri Lochman/Lochman Transparencies. Reproduced by permission.)

marsupials, rodents, roe deer, and bats, but probably is best known in carnivores. In the Carnivora, not all species exhibit delayed implantation, but the best examples probably are in the Mustelidae, Ursidae, and pinnipeds (Odobenidae, Phoci-dae, Otariidae). Examples of species that have delayed implantation include American marten (Martes americana), wolverine (Gulo gulo), black bear (Ursus americanus), giant panda (Ailuropoda melanoleuca), and northern fur seal (Cal-lorhinus ursinus). In bears, mating occurs after den emergence in the spring, but birth of offspring does not occur until late winter of next year, a full 9-10 months later. Delayed implantation likely evolved to uncouple the tight relationship between mating and birth, and because it is most prevalent in northern species, would provide an advantage to allow parturition at the time of greatest food availability and possibly mating to occur at the time of greatest mate availability. Possibly, mating systems may influence delayed implantation and at least two species in North America show variable delay, the American mink (Mustela vison) and the striped skunk (Mephitis mephitis), where the delay varies from 0-14 days. In the pinnipeds, delayed implantation would allow females to mate when conditions are favorable to maximize male competition and availability, thus allowing females to breed at a time when seals are aggregated, thus facilitating mate choice.

in time mating and parturition: delayed fertilization and delayed implantation.

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