Season-specific genetic variation underlies early-life migration in a partially migratory bird

Eco-evolutionary responses to environmentally-induced selection fundamentally depend on magnitudes of genetic variation underlying traits that facilitate population persistence. Additive genetic variances and associated heritabilities can vary across environmental conditions, especially for labile phenotypic traits expressed through early life. However, short-term seasonal dynamics of genetic variances are rarely quantified in wild populations, precluding inference on eco-evolutionary outcomes in seasonally dynamic systems. This limitation applies to seasonal migration versus residence, constituting one key trait where rapid micro-evolution could rescue partially migratory populations from changing seasonal environments. We fitted novel quantitative genetic ‘capture-recapture animal models’ to multi-generational pedigree and year-round resighting data from 11 cohorts of European shags (Gulosus aristotelis), to estimate season-specific additive genetic variances in liabilities to migrate..., We utilised a pedigreed partially migratory population of European shags (Gulosus aristotelis) breeding on Isle of May National Nature Reserve (hereafter ‘IoM’), Scotland (56°11′N, 2°33′W).
Data Collection
Each breeding season (April-July) since 1997, all breeding attempts on IoM were systematically monitored (223-1068 per year). Chicks reaching approximately 3 weeks old were individually marked with uniquely coded metal and colour rings readable from ≤150m with a telescope (559-1143 chicks ringed per year, mean 863, recently comprising >95% of fledglings). Ringed breeding adults were identified, or caught and colour-ringed if initially unringed, with sexes inferred through behaviour, vocalizations and/or genotyping.
During 2010-2022, we undertook large-scale non-breeding season (August-March) resighting surveys to locate colour-ringed individuals, and thereby assign juveniles as seasonal migrant or resident. Regular (approximately biweekly) surveys were undertaken on IoM and adjacen..., , # Season-specific genetic variation underlies early-life migration in a partially migratory bird

[https://doi.org/10.5061/dryad.j6q573nnr](https://doi.org/10.5061/dryad.j6q573nnr)

In our study, capture-recapture data and pedigree data were analysed using a Bayesian statistical model coded in Stan language and run in R using package rstan.

The model outputs, i.e. posterior samples of the model parameters and derived parameters, are the primary results of our analyses.

NB: Full understanding of these files requires careful reading of the paper and electronic supplementary materials.

## Description of the data and file structure

The following files represent the data used for the analysis:

\- Data file with capture-recapture histories for all individuals

crh_clean.txt

\** Contains the following columns

\# BirdID - identity of the individual

\# Column 2 to 7 (X1 to X6) - resighting history of the individual across six defined occasions, with cell values 1 to 4 representing the fo...