Latitudinal genetic diversity gradients steepen toward the poles

Anne-Céline Granjon , Michael Gerth , Chloé Schmidt 

Latitudinal biodiversity gradients are among the best-described biogeographic patterns. However, there is little agreement on whether genetic diversity, the most fundamental level of biodiversity, is also latitudinally distributed. The confusion about the distribution of genetic diversity at biogeographic scales stems in part from the fact that genetic diversity gradients have been described for multiple types of genetic diversity, with good reasons to expect patterns to vary with the component of genetic diversity examined. Genome-wide diversity varies both within and across species. Thus, nuclear genetic diversity gradients might arise due to the existence of parallel latitudinal gradients within species, or due to species turnover and differences in species-level genetic diversity across latitudes. We used a compilation of nuclear genetic data from 100 mammal species across 1,426 locations to test for latitudinal genetic diversity gradients using Bayesian hierarchical regressions. We detected no general latitudinal genetic diversity gradients within or across species. However, the direction of within-species genetic diversity gradients was associated with species attributes. Notably, the slopes of intraspecific latitudinal gradients became increasingly positive for species distributed at higher latitudes. Interactions between species-level and population-level processes appear to shape the biogeography of genetic diversity.