Darren Hunter and Jon Slate

PNAS February 5, 2019 116 (6) 1834-1836

Figure: A Florida Scrub-Jay from the Archbold Biological Station study site. Image courtesy of Reed Bowman (Archbold Biological Station, Venus, FL).

Virtually the first thing a young population genetics student will learn is that changes in gene frequency can be caused by genetic drift, natural selection, and migration. However, quantifying the relative importance of these mechanisms on changes in a population’s genetic composition is a major challenge in any study system. In PNAS, Chen et al. (1) meet this challenge and describe a framework in which genetic change within a population can be tracked and understood. They did so with the help of two vital ingredients. First, they recognized that any investigation of allele frequency change requires an accurate family tree (or pedigree), along with detailed knowledge of gene flow into and out of the study population. Long-term monitoring of a wild population of Florida Scrub-Jays (Aphelocoma coerulescens) (Fig. 1) since 1969 has allowed an observational pedigree spanning many generations to be constructed for their study system. The extensive dataset produced by painstaking field work has been augmented by the collection of high-quality DNA genotype data for most birds alive since 1990 (2), meaning that the pedigree is confirmed with molecular tools and is therefore highly accurate. The second ingredient, which requires an accurate pedigree, is the estimation of every individual bird’s genetic contribution (Box 1) to the population, something which is rarely measured in real populations. The expected genetic contribution estimated using this approach is closely related to the theoretical idea of an individual’s reproductive value (Box 1), a concept that was first defined almost a century ago by Ronald Fisher (3). Genetic contributions and reproductive value have been shown to be comparable when estimated for a population’s descendants far enough in the future (4). Thus, by estimating an ancestral individual’s genetic contribution to the pedigree, the contribution that it makes to the future population can be estimated. This individual reproductive value has been shown to be the target of selection (5).

See: https://www.pnas.org/content/116/6/1834