Relatedness between Individuals in General Populations with a Focus on Their Use in Conservation Programs

3 ABSTRACT Relatedness estimators are widely used in genetic studies, but effects of population structure on performance of estimators, criteria to evaluate estimators, and benefits of using such estimators in conservation programs, have to date received little attention. In this paper we present new estimators, based on the relationship between coancestry and molecular similarity between individuals, and compare them with existing estimators using Monte-Carlo simulation of populations, either panmictic or structured. Estimators were evaluated using statistical criteria and a diversity criterion that minimized relatedness. Results show that ranking of estimators depends on the population structure. An existing estimator based on two-gene and four-gene coefficients of identity performs best in panmictic populations, whereas a new estimator based on coancestry performs best in structured populations. Number of marker alleles and loci did not affect ranking of estimators. Statistical criteria were insufficient to evaluate estimators for their use in conservation programs. The regression coefficient of pedigree relatedness on estimated relatedness (ß2) was substantially lower than unity for all estimators, causing overestimation of the diversity conserved. A simple correction to achieve ß2 = 1, improves both existing and new estimators. Using relatedness estimates with correction, considerably increased diversity in structured populations, but did not do so or even decreased diversity in panmictic populations. 4 Additive genetic relatedness between individuals plays an important role in many fields of genetics. In genetic analyses, knowledge of relatedness is used to estimate genetic parameters such as heritabilities and genetic correlations (FALCONER and MACKAY 1996). In artificial selection, estimation of breeding values relies on knowledge of relatedness of individuals (HENDERSON 1984; LYNCH and WALSH 1998), and relatedness between individuals affects optimum designs of selection programs (e.g NICHOLAS and SMITH 1983). In evolutionary biology, knowledge of relatedness between interacting individuals is required to predict evolutionary consequences of social interaction (HAMILTON 1964). In conservation genetics, knowledge of relatedness is required to optimize conservation strategies. In the present article we focus on estimating relatedness for use in conservation strategies, but results are equally relevant for other fields in genetics. Throughout, we consider the traditional population-genetic definition of relatedness for diploid individuals, which equals twice the coefficient of When pedigrees of populations are known, additive genetic relatedness between individuals can be calculated from the pedigree (EMIK and TERRILL 1949), and can be used to estimate additive genetic variance. Pedigree data is, however, often lacking or incomplete, especially between subpopulations of a species. In …