Data from: Genetic drift outweighs natural selection at toll-like receptor (TLR) immunity loci in a reintroduced population of a threatened species

During population establishment, genetic drift can be the key driver of
changes in genetic diversity, particularly while the population is small.
However, natural selection can also play a role in shaping diversity at
functionally important loci. We used a well-studied, re-introduced
population of the threatened Stewart Island robin (N = 722 pedigreed
individuals) to determine whether selection shaped genetic diversity at
innate immunity toll-like receptor (TLR) genes, over a 9-year period of
population growth following establishment with 12 genetic founders. We
found no evidence for selection operating with respect to TLR diversity on
first-year overwinter survival for the majority of loci, genotypes and
alleles studied. However, survival of individuals with TLR4BE genotype was
significantly improved: these birds were less than half as likely to die
prior to maturity compared with all other TLR4 genotypes. Furthermore, the
population frequency of this genotype, at a two-fold excess over
Hardy–Weinberg expectation, was increased by nonrandom mating.
Near-complete sampling and full pedigree and reproductive data enabled us
to eliminate other potential causes of these patterns including
inbreeding, year effects, density dependence, selection on animals at
earlier life history stages or genome-level association of the TLR4E
allele with ‘good genes’. However, comparison of observed levels of gene
diversity to predictions under simulated genetic drift revealed results
consistent with neutral expectations for all loci, including TLR4.
Although selection favoured TLR4BE heterozygotes in this population, these
effects were insufficient to outweigh genetic drift. This is the first
empirical study to show that genetic drift can overwhelm natural selection
in a wild population immediately following establishment.