Abstract The Madrean sky islands have been studied for decades due to their high biodiversity, which results from the intersection of biomes and their role as refugia for populations isolated on mountain tops during the last ice age. There has been controversy and confusion about the identification of Peromyscus sp . found in the montane forests on these sky islands, which is often assumed to be the widespread and ubiquitous P. maniculatus . Here, we provide mitochondrial phylogenetic data suggesting that all individuals of Peromyscus captured on three isolated mountains in southern Arizona are Peromyscus melanotis , a species previously thought endemic to Mexico. Furthermore, with molecular clock analyses on two mitochondrial loci we show these populations have been isolated from each other for ∼11,000-50,000 years, corresponding to the transition from the last ice age. These isolated populations represent important conservation targets due to habitat loss. In addition, we suggest that future genomic and ecological research is warranted to better understand these unique populations.

Isolation and Divergence of Peromyscus melanotis Populations Across the Madrean Sky Islands in Arizona