Genomic analysis of inbreeding depression in the wild.
General Genetics and Functional Genome Biology
Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions
Final Report Abstract
Inbreeding depression is a phenomenon where the offspring of related parents have decreased fitness. It is a major theme in evolutionary biology since Darwin and we know now that inbreeding depression occurs in virtually all animal and plant species. A deeper understanding of the genetic mechanisms behind inbreeding depression will help to shed light on the genetic architecture of traits and patterns of selection against deleterious alleles and could even contribute to the management of endangered populations. Here, we used a highly detailed dataset consisting of both fine-scale genetic data and long-term fitness data to explore the genomics of inbreeding depression in wild Soay sheep on the Scottish St. Kilda archipelago. The offspring of matings between relatives have a higher proportion of their genome in a homozygous state, which can be measured through runs of homozygosity. Such homozygosity can lead to the unmasking of rare, deleterious mutations and hence lower the fitness of an individual. In the Soay sheep, we found that inbreeding dramatically reduces the chances of survival in a given year, with offspring of first cousins being four times more likely to die than an average individual. This pattern is so strong, that even mildly inbred individuals rarely survive to older ages. Looking a bit deeper into the patterns within the genome, we find that there is little selection in against these deleterious recessive genetic variants. This is not too surprising, as population genetic theory predicts that, genetically speaking, small population have more random genetic fluctuations across the generations, which allows even deleterious alleles to spread across the population. Lastly, we find that these deleterious alleles or genetic variants are not spread randomly across the genome. In contrast, we find a few spots where being homozygous as a consequence of inbreeding is particularly detrimental for a sheep’s chance of survival. Looking deeper into the affected genes and their function will be part of the future analysis of this project.
