Microevolutionary Responses to Seasonality Contribute to the Latitudinal Biodiversity Gradient

Anne-Céline Granjon , Michael Gerth , Jean-Philippe Lessard , Colin Garroway, Chloé Schmidt 

The latitudinal gradient in species richness is one of ecology’s oldest observed patterns, yet the mechanisms maintaining it remain debated. One prominent explanation links seasonality to the evolution of broad physiological tolerances, creating evolutionary conditions that impede population divergence and speciation. We tested whether seasonality leaves detectable signatures in the genetic composition of natural populations by estimating genome-wide diversity, genetic differentiation, and effective population size across 100 mammal species at 1,426 local populations worldwide. Within species, genetic diversity was higher and genetic differentiation lower in the most seasonal parts of the range. In wide-ranging species occurring at higher latitudes, genetic diversity increased in populations toward the poleward range edge. Our results suggest that the population genetic conditions generally associated with the promotion of speciation vary systematically across latitudes in parallel with the latitudinal species diversity gradient.