Genetic diversity in caribou linked to past and future climate change

Climate-driven range fluctuations during the Pleistocene have continuously reshaped species distribution leading to populations of contrasting genetic diversity. Contemporary climate change is similarly influencing species distribution and population structure, with important consequences for patterns of genetic diversity and species’ evolutionary potential1. Yet few studies assess the impacts of global climatic changes on intraspecific genetic variation2–5. Here, combining analyses of molecular data with time series of predicted species distributions and a model of diffusion through time over the past 21 kyr, we unravel caribou response to past and future climate changes across its entire Holarctic distribution. We found that genetic diversity is geographically structured with two main caribou lineages, one originating from and confined to Northeastern America, the other originating from Euro-Beringia but also currently distributed in western North America. Regions that remained climatically stable over the past 21 kyr maintained a high genetic diversity and are also predicted to experience higher climatic stability under future climate change scenarios. Our interdisciplinary approach, combining genetic data and spatial analyses of climatic stability (applicable to virtually any taxon), represents a significant advance in inferring how climate shapes genetic diversity and impacts genetic structure. When looking at impacts of climate change on biodiversity, numerous studies treat ecosystem and species as a unit and thus ignore intraspecific genetic diversity2,5. Intraspecific genetic variation is the most fundamental level of biodiversity, provides the basis for any evolutionary change and is crucial for maintaining the ability of species to adapt to new environmental conditions6. Species may respond to climate change by local adaptation, shifting or reducing range or a combination of these1. In many cases, these changes will reduce genetic diversity in populations and species, in extreme situations to the point where genetic impoverishment will contribute to reduce population viability6. In the light of present global climate change, it is necessary to study the effects of past climatic changes on intraspecific genetic diversity to decipher the evolutionary consequences of climate change and its effects on biodiversity. Phylogeographic studies that disentangle population history during the Pleistocene and through the Holocene warming implicitly reconstruct the fate of genetic diversity during a major climate change and then can provide important insights into species’ reactions to present and future climate change5. Here we applied a multidisciplinary approach to quantitatively estimate climate-related past and future changes of genetic diversity in the iconic northern species Rangifer tarandus, commonly named reindeer in Eurasia and caribou inNorth America (hereafter termed caribou for simplicity). This is particularly relevant because climate