Estimation of effective number of breeders from molecular coancestry of single cohort sample

The effective population size, N(e), is an important parameter in population genetics and conservation biology. It is, however, difficult to directly estimate N(e) from demographic data in many wild species. Alternatively, the use of genetic data has received much attention in recent years. In the present study, I propose a new method for estimating the effective number of breeders N(eb) from a parameter of allele sharing (molecular coancestry) among sampled progeny. The bias and confidence interval of the new estimator are compared with those from a published method, i.e. the heterozygote-excess method, using computer simulation. Two population models are simulated; the noninbred population that consists of noninbred and nonrelated parents and the inbred population that is composed of inbred and related parents. Both methods give essentially unbiased estimates of N(eb) when applied to the noninbred population. In the inbred population, the proposed method gives a downward biased estimate, but the confidence interval is remarkably narrowed compared with that in the noninbred population. Estimate from the heterozygote-excess method is nearly unbiased in the inbred population, but suffers from a larger confidence interval. By combining the estimates from the two methods as a harmonic mean, the reliability is remarkably improved.