When and where animals breed can shape the genetic structure and diversity of animal populations. The importance of drivers of genetic diversity is amplified in island populations that tend to have more delineated gene pools compared to continental populations. Studies of relatedness as a function of the spatial distribution of individuals have demonstrated the importance of spatial organisation for individual fitness with outcomes that are conditional on the overall genetic diversity of the population. However, few studies have investigated the impact of breeding timing on genetic structure. We characterise the fine-scale genetic structure of a geographically-isolated population of seabirds. Microsatellite markers provide evidence for largely transient within-breeding season temporal processes and limited spatial processes, affecting genetic structure in an otherwise panmictic population of sooty terns Onychoprion fuscatus. Earliest breeders had significantly different genetic structure from the latest breeders. Limited evidence was found for localised spatial structure, with a small number of individuals being more related to their nearest neighbours than the rest of the population. Therefore, population genetic structure is shaped by heterogeneities in collective movement in time and to a lesser extent space, that result in low levels of spatio-temporal genetic structure and the maintenance of genetic diversity.
Bibliographical noteFunding Information:
Data collection was aided and assisted by Katherine Mullin, the Ascension Island Government Conservation and Fisheries Department (AIGCFD) and the UK Army Ornithological Society (AOS). We thank Gavin Horsburgh and Natalie dos Remedios for providing laboratory support and Terry Burke for providing advice on genetic analyses. This study was funded by the UK Natural Environment Research Council (NERC) as part of a Central England NERC Training Alliance (CENTA) PhD studentship awarded to LJHG (NE/L002493/1) and through the Ascension Island Government (AIG) as a CASE partner. Logistical support was provided by the AIG. Laboratory work was funded by the NERC through a Scientific Facilities & Technology Grant (NBAF944) and performed at the NERC Bimolecular Analysis Facility at the University of Sheffield, Sheffield, UK.
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