ON THE POTENTIAL FOR ESTIMATING THE EFFECTIVE NUMBER OF BREEDERS FROMHETEROZYGOTE-EXCESS IN PROGENY

The important parameter of effective population size is rarely estimab le directly from demographic data. Indirect estimates of effective pop ulation size may be made from genetic data such as temporal variation of allelic frequencies or linkage disequilibrium in cohorts. We sugges t here that an indirect estimate of the effective number of breeders m ight be based on the excess of heterozygosity expected in a cohort of progeny produced by a limited number of males and females. In computer simulations, heterozygote excesses for 30 unlinked loci having variou s numbers of alleles and allele-frequency profiles were obtained for c ohorts produced by samples of breeders drawn from an age-structured po pulation and having known variance in reproductive success and effecti ve number. The 95% confidence limits around the estimate contained the true effective population size in 70 of 72 trials and the Spearman ra nk correlation of estimated and actual values was 0.991. An estimate b ased on heterozygote excess might have certain advantages over the pre vious estimates, requiring only single-locus and single-cohort data, b ut the sampling error among individuals and the effect of departures f rom random union of gametes still need to be explored.