The repeated evolution of multiple traits between forest and prairie ecotypes of the deer mouse
Authors: Brock Wooldridge; Sade McFadden; Chris Kirby; Kemi Ashing-Giwa; Hopi Hoesktra
Affiliation: Department of Organismic and Evolutionary Biology, Harvard, Cambridge, MA; Department of Molecular and Cellular Biology, Harvard, Cambridge, MA; Museum of Comparative Zoology, Harvard, Cambridge, MA; Howard Hughes Medical Institute, Harvard, Cambridge, MA
Keywords: Phylogenetics, Macroevolution, and Biogeography
Local adaptation often involves changes in more than one trait. One classic example is the evolution of forest and prairie ecotypes within a single species of deer mouse (Peromyscus maniculatus), which have evolved striking morphological differences. First reported over a century ago, some populations of forest-dwelling mice were described as having longer tails, larger feet, bigger ears, and elongated whiskers relative to prairie populations. However, the extent to which these morphological differences are correlated with habitat across their range and if these multi-trait differences have evolved multiple times independently remains largely unknown. To answer these questions, we measured both phenotypic and genetic variation in deer mice from across North America. Using satellite-based land cover estimates and museum specimens, we found widespread and significant correlation between habitat type and morphological variation, suggesting these morphological traits broadly represent adaptation to local environments. Next, whole-genome sequencing of 177 mice from 44 of those populations reveals two contrasting patterns. First, we find a significant effect of genetic isolation-by-environment (IBE): more closely related populations are more likely to be phenotypically similar given the same geographic distance. Nonetheless, we were still able to identify several independent gains and losses of ecotype-specific morphological adaptations. Together, these data point towards a set of independently evolved forest-prairie population pairs, which consistently differ in morphology, yet have high levels of gene flow, thus representing an exciting system to study the repeated co-evolution of multiple adaptive traits in a single widespread species.