Effects of fine-scale population structure on the distribution of heterozygosity in a long-term study ofAntirrhinum majus

Abstract

Inbreeding depression can be estimated by correlating heterozygosity with fitness components, but such heterozygosity-fitness correlations are typically weak. For over ten years, we studied a population of the self-incompatible plant, Antirrhinummajus, measuring heterozygosity and fitness proxies from 22,353 plants. Using a panel of 91 SNPs, we find that relatedness declines rapidly over short spatial scales. Individual heterozygosity varies more between individuals than expected, reflecting identity disequilibrium (g2) due to variation in inbreeding − a prerequisite for detecting inbreeding depression. We use two types of simulations to ask whether the heterozygosity distribution is consistent with spatially structured mating. First, we simulate offspring from matings with fathers at different distances and find that the distribution of heterozygosity in the field data is consistent with the measured pollen dispersal kernel. Second, we simulate a 1000-generation pedigree using the known spatial distribution, and find that identity disequilibrium, though highly variable between simulations, is consistent with that observed. Finally, we estimate inbreeding depression through the relationships between heterozygosity and six fitness proxies. Only the number of flowering stems is predicted by heterozygosity. Our approach provides a novel example of how long-term studies can elucidate population structure and fitness variation in the wild.