Long-term stress level in a small mammal species undergoing range expansion

Climate changes are currently altering species distribution ranges. In the cases of disease reservoir species, the impacts of these range shitfs may cause major health issues by promoting the emergence of diseases in naïve regions. Evalutating the long term stress level endured by wild animals constitutes a promising challenge that would enable biologist to better understand how species cope with this changing environment. These methods, as opposed to the short term stress level evaluation methods, are less sensible to capture, handling, or to any daily fluctuation and are therefore better suited for larger temporal scale studies. Here, we focused on Peromyscus leucopus, a small rodent considered as the main reservoir for Lyme disease in North-America and whose distribution area is currently shifting northward because of the warming occuring in the region. We applied four methods of long term stress level evaluation to several populations of P. leucopus in Quebec (Canada), from the very edge of the species distribution to more central populations. First, we tried to figure out if any difference in the stress levels could be detected between populations installed for several years and the ones recently installed on the very edge of the shifting species distribution. Second, we compared the four long term stress measures in order to evidence congruence between their results. Our results did not evidence any heterogeneity between the populations, regardless the used method. Moreover, no correlation between the four tested methods could be evidenced, underlying the possibility that these methods would mesure stress having occurred at different time periods.