Phylogenetic, morphological and niche differentiation unveil new species limits for the big brown bat ( Eptesicus fuscus ).

Phylogeographic accounts of mammals across fragmented landscapes show high levels of genetic, morphological and ecological variation. The big brown bat ( Eptesicus fuscus ) widely spans mainland landmasses from Canada to Ecuador and Colombia, and the insular Caribbean through The Bahamas and Greater and Lesser Antilles. Given the distribution of E. fuscus , we hypothesized that insular lineages could represent a different species aided by isolation. We assessed species limits by capitalizing on available mitochondrial and genomic data. Novel morphological and spatial datasets were produced to examine limits phenotypically and whether ecological niches could be associated with differences between groups. Phylogenetics strongly supported the Caribbean as unique compared to the mainland. Genomic data indicated high levels of genetic structure within the Caribbean and no detectable admixture of the Caribbean with continental lineages. Similarly, the Caribbean group shows high phenotypic disparity, and niche models revealed differences in habitat suitability between groups, concordant with the phylogenetic results. This study uncovered signals of divergence supporting the Caribbean clade of E. fuscus as unique through an integrative framework. We endorse re-evaluating the taxonomic status of Caribbean big brown bats as Eptesicus dutertreus . This recognition can help promote local conservation plans for insular lineages of big brown bats.