The Genetic Basis for Dispersal in a House Sparrow Metapopulation

Dispersal is an ecologically important trait that shows phenotypic variation in many populations, and which may play an increasingly important role in population dynamics as the climate changes. Dispersal and traits associated with dispersal, have been shown to be highly heritable in many species, including some bird species. For these reasons, dispersal is a suitable and interesting trait for investigating genetic architecture. Knowledge of the underlying genetic architecture is required to understand the mechanisms driving phenotypic change in dispersal and to interpret their involvement in eco-evolutionary cycles. Previous studies have revealed several genes which may influence dispersal, but studies on dispersal as a phenotypic trait in itself, rather than traits associated with dispersal, are few, and the number of causal loci and their locations in the genome is largely unknown. In this study, phenotypic, pedigree and genome wide SNP data, from an insular house sparrow metapopulation off the coast of northern Norway, was used to explore the genetic basis of dispersal. Rather than investigating specific traits that may be associated with dispersal in the house sparrow, the dispersal phenotype was defined as an individual that left their natal island, and successfully established on a new island. Heritability for dispersal was estimated using animal models in MCMCglmm, and dispersal was found to be a highly heritable trait. Genome partitioning analyses did not find a significant, positive relationship between chromosome size and proportion of variance explained. In addition, chromosome 12 explained a disproportionate amount of the variance in dispersal. GWA analysis was used to search for causal loci and revealed one locus of significant effect. No genes that have been associated with dispersal were found near significant or suggestive loci. This work illustrates both the difficulties and advantages of performing association studies in natural populations and investigates the genetic architecture of dispersal in house sparrows

The genetic basis of dispersal in a vertebrate metapopulation

Dispersal affects evolutionary processes by changing population size and genetic composition, influencing the viability and persistence of populations. Investigating which mechanisms underlie variation in dispersal phenotypes and whether populations harbour adaptive potential for dispersal is crucial to understanding the eco-evolutionary dynamics of this important trait. Here, we investigate the genetic architecture of dispersal among successfully recruited individuals in an insular metapopulation of house sparrows. We use an extensive long-term individual-based ecological data set and high-density single-nucleotide polymorphism (SNP) genotypes for over 2500 individuals. We conducted a genome-wide association study (GWAS), and found a relationship between dispersal probability and a SNP located near genes known to regulate circadian rhythm, glycogenesis and exercise performance, among other functions. However, this SNP only explained 3.8% of variance, suggesting that dispersal is a polygenic trait. We then used an animal model to estimate heritable genetic variation (σA2), which composes 10% of the total variation in dispersal probability. Finally, we investigated differences in σA2 across populations occupying ecologically relevant habitat types (farm vs. non-farm) using a genetic groups animal model. We found different adaptive potentials across habitats, with higher mean breeding value, σA2, and heritability for the habitat presenting lower dispersal rates, suggesting also different roles of environmental variation. Our results suggest a complex genetic architecture of dispersal and demonstrate that adaptive potential may be environment dependent in key eco-evolutionary traits. The eco-evolutionary implications of such environment dependence and consequent spatial variation are likely to become ever more important with the increased fragmentation and loss of suitable habitats for many natural populations