Male size, sperm transfer, and colony fitness in the western harvester ant, Pogonomyrmex occidentalis

Mating success in the western harvester ant, Pogonomyrmex occidentalis, inc reases with male size. We tested the hypothesis that increased mating succe ss increases male fitness and the fitness of colonies that make large males by comparing the sperm content of males prior to and at the conclusion of the mating swarm. The number of sperm a male initially possesses is a funct ion of male size, and large males transfer a greater proportion of their sp erm than do small males. For colonies, the payoff per unit of investment is an increasing function of male size, and investment in large males is not equivalent to investing in a larger number of small males. Allocation ratio s in species that show size variation in reproductives may need to be modif ied by the individual fitness functions.