Measuring genetic relatedness in natural populations: Methodology

Abstract

The estimation of relatedness within social groups, such as the colonies of a population of social insects, is an important field for evaluating hypotheses concerning the evolution and maintenance of social behaviour. The methodology of this estimation from genetic data in the absence of pedigree information has been poorly understood; we develop this methodology for b, the regression coefficient of relatedness, and discuss its applications. Both b and G (the pedigree coefficient of relatedness) are potentially asymmetric coefficients, whereas φ, r, and F ST are necessarily symmetric. We develop an estimator for b suitable for small samples, and also one for standard deviation, and examine the properties of both using sampling simulations. The b estimator returns values slightly below E( b), and the standard deviation estimator yields conservative confidence intervals. A comparative study of b and F ST shows that, given the same set of data, b is estimated with greater reliability than is F ST . As is the case for F ST , b can be used to examine population structure at various levels, and b possesses the advantage of an estimator for its standard error, which can also be used to test for heterogeneity among the loci surveyed. The actual numbers of identical genes held in common by interacting individuals, and not simply their proportions, need to be considered in using coefficients of relatedness in inclusive fitness calculations. This necessity is handled by the weighted coefficients of relatedness, G′ and b′, which have been referred to in the literature as r (as have most relatedness measures).