The genetic consequences of population marginality: a case study in maritime pine

Marginal tree populations, either those located at the edges of the species range or in suboptimal environments, are often a valuable genetic resource for biological conservation. However, there is a lack of knowledge about the genetic consequences of population marginality, estimated across entire species ranges. Using 10,185 SNPs across 82 populations of Pinus pinaster Ait., a widespread and economically important conifer characterised by a fragmented range, we modelled the relationship of five genetic indicators potentially related to ecological resilience, population vulnerability and adaptability (genetic diversity, inbreeding, genetic differentiation, recessive genetic load and genomic offset) with population geographical, demo-historical and ecological marginality (as estimated by nine quantitative indices). Models were constructed for both regional (gene pool) and range-wide spatial scales. We showed an overall trend towards decreasing genetic diversity and increasing differentiation with geographic marginality, supporting the centre-periphery hypothesis. Moreover, we found no correlation between population inbreeding and marginality, while geographically marginal populations had a lower recessive genetic load (only models without the gene pool effect) and ecologically marginal populations had a higher genomic offset. Overall, our results suggest that marginal populations of maritime pine could be more vulnerable to climate change than core populations, despite reduced levels of genetic load, a risk that is exacerbated by typically small effective population sizes and increasing human impact. ### Competing Interest Statement The authors have declared no competing interest.