Abstract
The Andean cloud forests of western Colombia and Ecuador are home to several endemic mammals; members of the Oryzomyini, the largest Sigmodontinae tribe, are extensively represented in the region. However, our knowledge about this diversity is still incomplete, as evidenced by several new taxa that have been described in recent years. Extensive field work in two protected areas enclosing remnants of Chocó montane forest recovered a high diversity of small mammals. Among them, a medium-sized oryzomyine is here described as a new genus having at least three new species, two of them are named and diagnosed. Although externally similar to members of the genera Nephelomys and Tanyuromys, the new genus has a unique molar pattern within the tribe, being characterized by a noticeable degree of hypsodonty, simplification, lamination, and third molar compression. A phylogeny based on a combination of molecular markers, including nuclear and mitochondrial genes, and morphological data recovered the new genus as sister to Mindomys, and sequentially to Nephelomys. The new genus seems to be another example of a sigmodontine rodent unique to the Chocó biogeographic region. Its type species inhabits cloud forest between 1,600 and 2,300 m in northernmost Ecuador (Carchi Province); a second species is restricted to lower montane forest, 1,200 m, in northern Ecuador (Imbabura Province); a third putative species, here highlighted exclusively by molecular evidence from one immature specimen, is recorded in the montane forest of Reserva Otonga, northern Ecuador (Cotopaxi Province). Finally, the new genus is also recorded in southernmost Colombia (Nariño Department), probably represented there also by a new species. These species are spatially separated by deep river canyons through Andean forests, resulting in marked environmental discontinuities. Unfortunately, Colombian and Ecuadorian Pacific cloud forests are under rapid anthropic transformation. Although the populations of the type species are moderately abundant and occur in protected areas, the other two persist in threatened forest fragments.
Highlights
The Oryzomyini is the largest tribe among the 56 extant sigmodontine rodent clades, and according to current counts, it comprises about 152 living species distributed in 33 genera (Weksler, 2015; Pardiñas et al, 2017)
Phylogenetic trees produced by maximum likelihood and Bayesian analyses of this supermatrix were similar (Fig. 1), with high proportions of nodes with high support, that is, bootstrap support (BS) > 85% and posterior probability (PP) > 0.95
The topological base of Oryzomyini remains unchanged from previous analyses, with clade C (Oreoryzomys, Neacomys, Microryzomys, and Oligoryzomys) representing the sister group to clade D (Holochilus, Pseudoryzomys, Oryzomys, Nectomys, Amphinectomys, Aegialomys, Nesoryzomys, Melanomys, Sigmodontomys, Tanyuromys, Eremoryzomys, Drymoreomys, Cerradomys, Sooretamys, and Lundomys) with high nodal support (BS = 98%, PP = 1)
Summary
The Oryzomyini is the largest tribe among the 56 extant sigmodontine rodent clades, and according to current counts, it comprises about 152 living (including 57 historical extinct) species distributed in 33 genera (Weksler, 2015; Pardiñas et al, 2017). The Chocó biogeographic region is one of the zones with the greatest biodiversity and endemism on the planet (Myers et al, 2000) For this reason, and because of its high degree of threats to biodiversity, it is considered as one of the 25 Priority Terrestrial Ecoregions of the World and an endemism hotspot (Mittermeier et al, 1999; Myers et al, 2000). Hunting is a problem for several species of birds and mammals (Mittermeier et al, 1999; Brooks et al, 2002)
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