Effective population size: the effects of sex, genotype, and density on the mean and variance of offspring numbers in the flour beetle,Tribolium castaneum

Abstract

SUMMARY: In this paper I present the results of an experimental study of the effects of genotype and density on the mean and variance of offspring numbers in both sexes of the flour beetle,Tribolium castaneum. From the observed variance in offspring numbers the effective population size at several different densities is estimated using the methods of Crow & Morton (1955).I found that both the mean and variance of offspring numbers varied with genotype and density. In general, males were more variable in offspring numbers than females and this variability increased with density. Individuals homozygous for the black body colour mutant,b/b, were less variable in offspring numbers than + / + individuals, but the latter produced more offspring at most densities. As density increased, + / + individuals became more variable in offspring numbers whereasb/bindividuals were less sensitive in this regard. These findings are discussed in relation to the ecology of selection at the black and closely linked loci.