Quantifying the heritability of migration behaviours in a facultatively migrating ungulate

Background/Question/Methods

Migration behaviour in ungulates is declining globally in the face of rapid human-mediated environmental change. Ungulate populations experiencing fluctuating environments can adapt to novel conditions through behavioural plasticity and short-term evolution where selection acts on repeatable behavioural phenotypes that confer a greater fitness benefit. Predicting how environmental change affects ungulate migration behaviour requires partitioning the effects of behavioural repeatability and plasticity of migratory traits and quantifying the extent to which repeatable behavioural variation is heritable. Using GPS collar data from 412 facultatively migrating female mule deer we quantified repeatability of migration timing, duration, and direction. Advances in high-throughput sequencing technologies make it possible to directly estimate pairwise genetic relatedness from genomic data in wild populations without the need for a multigenerational pedigree. We used a double-digest RAD sequencing approach to generate genomic data for each individual and compute a Genomic Relatedness Matrix (GRM) for the population using identity-by-state SNP relationships. We combined the GRM with the “animal model” approach and partitioned the phenotypic variance for migration timing, duration, and direction into among- and within-individual variation, and then partitioned among-individual variation into its genetic and non-genetic (environmental) components. From this we estimated narrow sense heritability for migratory traits.

Results/Conclusions

Migration timing, duration, and direction were all found to be repeatable, and a component of the among-individual variation in these traits was due to additive genetic variance. Behavioural variation in migration timing and duration have been linked to fitness components such as timing of reproduction and foraging success in other ungulate systems. This, combined with moderate heritability in migratory traits suggests that consistent directional selection on those traits could lead to marked changes in population means of migration timing, and duration in a relatively short period of time (a few hundred generations). Understanding the relationship between heritability and repeatability is of critical interest in behavioural ecology, and it is necessary to investigate both the genetic and environmental mechanisms underpinning observed repeatability, particularly for migration behaviours that are being affected by global climate change.