Effective number of breeders from sibship reconstruction: empirical evaluations using hatchery steelhead

Effective population size ( N e ) is among the most important metrics in evolutionary biology. In natural populations, it is often difficult to collect adequate demographic data to calculate N e directly. Consequently, genetic methods to estimate N e have been developed. Two N e estimators based on sibship reconstruction using multilocus genotype data have been developed in recent years: sibship assignment and parentage analysis without parents. In this study, we evaluated the accuracy of sibship reconstruction using a large empirical dataset from five hatchery steelhead populations with known pedigrees and using 95 single nucleotide polymorphism ( SNP ) markers. We challenged the software COLONY with 2,599,961 known relationships and demonstrated that reconstruction of full‐sib and unrelated pairs was greater than 95% and 99% accurate, respectively. However, reconstruction of half‐sib pairs was poor (<5% accurate). Despite poor half‐sib reconstruction, both estimators provided accurate estimates of the effective number of breeders ( N b ) when sample sizes were near or greater than the true N b and when assuming a monogamous mating system. We further demonstrated that both methods provide roughly equivalent estimates of N b . Our results indicate that sibship reconstruction and current SNP panels provide promise for estimating N b in steelhead populations in the region.