SOCIAL MODIFICATIONS RELATED TO RARENESS IN ANT SPECIES

Abstract

In the evolution of true sociality in insects, one potentially disadvantageous side effect is the reduction of the effective population size. As a result of sociality, the reproductive individuals are longer lived and the populations more stable, but these features have been achieved by converting most of the adult population into the sterile supporting worker caste. In the case of the social Hymenoptera, the effective size of a discrete population is clearly not the same as the number of adult individuals. It must be derived in relation to the existing nest queens and the males (mostly no longer living) that contributed, during the nuptial flights, to the sperm now living in the spermathecae of the queens. In population genetics the effective population size, N, is defined (cf. Li, 1955, p. 320) as the equivalent "ideal" population containing N breeding individuals, half of them females and half males, mating at random. The variance of the random deviation of gene frequencies is therefore p (1 p) /2N; and the rate of loss of heterozygosis 1/2N. When the N breeding individuals are not evenly divided between the sexes, N is less than N. Where No and N1 are the numbers of female and male parents respectively,