EUSOCIALITY HAS EVOLVED INDEPENDENTLY IN 2 GENERA OF BATHYERGID MOLE-RATS - BUT OCCURS IN NO OTHER SUBTERRANEAN MAMMAL

Extensive field and laboratory studies show that Damaraland mole-rats, like naked mole-rats, have an extreme form of vertebrate sociality. C olonies usually contain 2 reproductives and up to 39 non-breeding sibl ings, 90% of whom live a socially-induced lifetime of sterility; they remain in the natal colony, forage for food, defend the colony and car e for successive litters. Although there is heightened dispersal follo wing good rainfall, the majority of adult non-reproductives remain in their natal colony and failure to disperse is not directly attributabl e to habitat saturation or unfavourable soil conditions. A major dispe rsal event follows the death of a reproductive. Differences in colony cohesion, ethology and the hormonal profiles of non-reproductive anima ls suggests that eusociality evolved along different pathways in these two phylogenetically divergent genera of the Bathyergidae.