Reproductive biology

In solitary species, courtship and mating are brief encounters and the animals then resume their solitary existence. When pups are about two months old, they disperse to es tablish their own burrow systems. Colonies of all social molerats have reproductive division of labor, whereby reproduction is restricted to a single female and a few males. The remaining members are closely related to the breeders, but are reproductively quiescent while in the colony. Colony formation and the mechanisms of suppression differ in the species. Thus, there is strong inhibition to incest in Cryptomys, whose colonies are founded by a female and her unrelated consorts. Initially, their offspring remain as non-breeding helpers, only risking dispersing if environmental conditions are favorable. Colonies break up completely when a breeder dies. Mechanisms of reproductive suppression within this genus range from incest avoidance to physiological mechanisms that inhibit ovulation in the females but not sperm production in the males. Colonies of naked mole-rats, on the other hand, are inbred. The aggressive behavior of the breeding female induces neuroendocrine changes in the pituitary that affect the functioning of the gonads of both non-breeding males and females. When the breeding female dies, some of the oldest females in the colony become sexually active (this can occur within a week of the death of the breeder), and they often fight viciously for the vacated position.

Bathyergus, Georychus, C. hottentotus, and possibly Heliopho-bius breed seasonally, whereas Heterocephalus, C. damarensis, C.

darlingi, and C. mechowi breed throughout the year. Gestation lengths range from about 44 days in Georychus to 100 days in C. amatus. Mean litter sizes are less than four, except Georychus, which have up to six, and Heterocephalus, which can have up to 13. A breeding female Heterocephalus can bear huge litters (up to 28 pups). During her first few pregnancies, her lumbar vertebrae elongate, thereby increasing the size of her abdominal cavity and her capacity to bear these large litters. She thus becomes morphologically distinct from the rest of the colony, a unique feature amongst mammals. This phenomenon, together with having a monopoly of reproduction, large litters, and presiding over colonies of up to 300 animals, makes naked mole-rats the closest mammalian equivalent to social insects such as termites.

0 0

Post a comment