Changing Peromyscus distributions in the upper Midwest and consequences for tick-borne pathogens

In the United States, mice are the most abundant small mammal reservoir of the Lyme disease spirochete and consequently are responsible for infecting a high proportion of blacklegged ticks, Ixodes scapularis Say. Long-term observations in the Midwest suggest warming temperatures are promoting poleward expansion of the white-footed mouse, Peromyscus leucopus Rafinesque, as well as replacement of the woodland deer mouse, Peromyscus maniculatus gracilis Wagner. We used species distribution modeling (SDM) and joint species distribution modeling (JSDM) approaches to identify the role of abiotic and biotic factors in shaping the distributions of two sympatric tick-borne pathogen reservoirs, Peromyscus maniculatus and P. leucopus, in Minnesota and Wisconsin. Additionally, we predicted the future distributions for P. leucopus based on climate projections. Finally, we conducted small mammal trapping in north-central Wisconsin, where both species occur, to compare tick infestations and Borrelia burgdorferi prevalence. We found no evidence that these Peromyscus species co-occurred less than expected given their shared responses to environmental variables. The number of frost-free days was the most important variable describing distributions for both mice and future projections suggest that the northernmost areas of Wisconsin and Minnesota will become more suitable for P. leucopus. Although P. maniculatus were more likely to be infected with Borrelia burgdorferi compared to its congener, P. leucopus were more infested with both larval and nymphal I. scapularis. Collectively, results suggest that shorter-milder winters could promote further expansion of P. leucopus, a more competent reservoir of tick-borne pathogens, in the Midwest.