Constraints of pregnancy and evolution of sociality in mole-rats With special reference to reproductive and social patterns in Cryptomys hottentotus (Bathyergidae, Rodentia)1

Abstract

Described: basic characteristics of reproduction and pre- and postnatal growth rate and development in Zambian mole-rats, Crypromys hottentotus (Bathyergidae), and compared with the available data on other small subterranean hystricognathous rodents. It is demonstrated that C. hottentotus from relatively rnesic habitats are monoamous and eusocial. The animals in each colony may be divided into several cateories according to their body size and pelage colouration (polymorhim) and prevailing beiavioural pattern (polyethism). Particularly breeding animals are sexually dimorphic. Freuent sexual interactions can be noted in the breeding pair even outside the female's estrus. Growth and sexual behaviour are pheromonally suppressed in the offspring (subordinate animals by their mutual contact and, particularly, by the parents (dominant animals). Most eflicient supression of growth is accomplished by a lactating female. It is arued that eusociality of the naked mole-rat, Heterocephalus glaber, is not qualitatively unique and has not evolved as an immediate response to aridity and dispersed food resources as generally considered. Evidence is presented that eusociality may have evolved as a direct consequence of decreasing the body size combined with retention of a long developmental time (phylogenetic constraint), limitations to store fat reserves, reduction of female's activit and consequent constraints of prenancy. Gestation had to be shortened at the cost of bearing altricial young and prolongation of tie postnatal development. Monogamy and establishment of a caste of helpers may be understood as energy-saving mechanisms of breeding females. Eusociality may be useful for survival in arid habitats, yet reasons for origin should te distinguished from the current (manifold) utility.