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

Abstract

AbstractMarginal 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’s marginality, estimated across entire species’ ranges. Using 10,185 SNPs across 82 populations ofPinus pinasterAit., 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.