The behavior and demographics of the naked mole-rat, Heterocephalus glaber.

Abstract

The question of how eusociality evolved in insects has been a major question for evolutionary biology since Darwin. Recently, a mammal, the naked mole-rat, was discovered also to have queens and functionally sterile workers. From 1986 to 1990 I trapped, marked, and studied the demography and behavior of a wild population of over 2000 naked mole-rats in Meru National Park, Kenya. Sex ratios in wild colonies were male biased. However, higher mortality among small males resulted in female biased sex ratios among the larger members of the colony. Few phenotypic differences were found between the sexes and the reasons for higher mortality among small males were not discovered. Despite unusually high life spans reported for naked mole-rats in captivity (16 years or greater), attrition in wild colonies sometimes exceeded 60 percent in a single year. Such mortality is compensated at the colony level by extremely high reproductive rates. Mortality of queens was much lower than that of workers. Attrition in wild colonies may be due in large part to mortality, during colony maintenance and defense or failed attempts to disperse. Although others have argued that naked mole-rats only form new colonies by fissioning of existing colonies, I present evidence that pairs of mole-rats can found new colonies. Individual naked mole-rats also move about on the soil surface at times, perhaps in efforts to disperse. Discovery of eusociality in two new animal taxa in the past 15 years (Homoptera and Rodentia), suggests that the selective forces which have led to the evolution of eusociality in animals may have led to similar division of reproductive labor in the plant kingdom. Suggestions are made as to where to look for analogues of social behavior in the plant kingdom.