MAMMALIAN EUSOCIALITY - A FAMILY AFFAIR

Comparative studies of two species of mole-rat are helping to clarify the ecological correlates of mammalian eusociality. Both species live in social groups composed of close kin, within which breeding is restr icted to one female and one to three males. They inhabit xeric areas w ith dispersed, patchy food and unpredictable rainfall. During droughts , they can neither expand their tunnel systems nor disperse. In brief periods after rain the animals must cooperate and dig furiously to loc ate rich food patches. By living in groups, arid-zone mole-rats can ta ke full advantage of windows of opportunity when conditions are right for burrowing. Thus, ecological factors and kin selection have apparen tly interacted in the evolution of eusociality in these species.