INTERSPECIFIC COMPETITION AND THE EVOLUTION OF COMMUNAL BREEDING IN BURYING BEETLES

Size of breeding groups and resource quality (carcass mass) were varie d independently in experiments using the burying beetle, Nicrophorus d efodiens, to examine reproductive output of beetles using carcasses ex posed to carrion competitors. Male-female pairs experienced the same r ate of brood failure as groups of four beetles (two males and two fema les). Groups of four produced more total larvae and a greater brood ma ss than pairs on large but not small carcasses, whereas reproductive o utput per female was lower for groups. Carcasses prepared by groups of two males and two females attracted similar numbers of free-flying co ngeners as carcasses prepared by pairs. The ability of more than two i ndividuals to produce a larger brood than that of pairs may decrease t he costs of communal breeding on larger carcasses, but by itself, is n ot sufficient to explain the evolution of breeding associations consis ting of multiple females.