Taxonomy and conservation of the critically endangered shrew Cryptotis nelsoni (Eulipotyphla: Soricidae), endemic to Los Tuxtlas, Veracruz, Mexico

The Nelson's small-eared shrew (Cryptotis nelsoni) is a mammal at high risk of extinction and endemic to the cloud forest in the mountains of Los Tuxtlas, an isolated volcanic field in eastern Mexico. It is a little-known species that remained unrecorded for over a century. However, recent works have increased the number of museum specimens and tissue samples of C. nelsoni, which we studied here to improve our knowledge of their taxonomy and conservation status. We compared the morphology and DNA barcode sequences of C. nelsoni against its three most closely related species. We also evaluated the possible effect of anthropogenic climate change on this mountain species according to three general circulation models and two scenarios proposed for the year 2050. The results showed that the skull and postcranial variables could easily discriminate C. nelsoni from the other species in terms of body size, to which some distinctive qualitative characteristics related to the width of the snout and the curvature of the humerus also contribute. DNA barcoding also helped identify the shrew species accurately, with a genetic distance of more than 6% from its closest species. The morphological and genetic characteristics highlight the evolutionary distinctiveness of C. nelsoni. Unfortunately, warmer extremes and higher rainfall than today could pose a severe threat to the survival of this shrew for decades to come, even in the most optimistic scenarios.