A new species of Thomasomys Coues, 1884 (Rodentia: Sigmodontinae) from the montane forests of northern Peru with comments on the “aureus” group

Abstract

We describe a new species of the cricetid rodent Thomasomys (Sigmodontinae) of the "aureus" group based on four specimens collected from Carmen de la Frontera, Piura Department, Peru. This new species has a very long and white tail, very long mystacial vibrissae that extend posteriorly beyond the pinnae, and a distinctive cranial and dental morphology that differ from any other known species of Thomasomys. It is also one of the largest species of Thomasomys, exceeded in size only by T. apeco. A phylogenetic analysis using sequences of Cytb recovered this species within a non-monophyletic "aureus" group with a genetic distance between 5.47% (with T. auricularis) to 10.17% (with Thomasomys sp. 1). In addition to this finding, the phylogenetic position of T. apeco, T. praetor, and T. pyrrhonotus are presented for the first time, prompting a discussion on the nature of the "aureus" group.

Historical biogeography of a rapid and geographically wide diversification in Neotropical mammals

“…In a period of ~2.64 Mya, Oligoryzomys diversified reaching approximately 32 living species and colonized almost all Neotropical biomes. There are two sigmodontine genera, Akodon and Thomasomys , which have more species than Oligoryzomys (see Hurtado and D'Elía, 2019a; for Akodon and Thomasomys , see Mammal Diversity Database, 2020; Brandão et al, 2021; Brito et al, 2021; Ruelas & Pacheco, 2021) but have smaller distributions than Oligoryzomys (Patton et al, 2015). Akodon , which is absent from Central America and most of northern South America, southern Patagonia and most of Chile, has 41 recognized living species and a crown age of ~3.80 Mya (Parada et al, 2015).…”

“…The rates of Akodon and Oligoryzomys get much closer (0.52 and 0.49 respectively), but also above that of Thomasomys (0.38) if crown ages estimated by Steppan and Schenk (2017) are used. Additionally, it is worth noting that species boundaries in Thomasomys and Akodon (in particular for the former) are not as well understood as in Oligoryzomys (see generic accounts in Patton et al, 2015 and the recent discussions on species limits for Akodon and Thomasomys in Brandão et al, 2021 and Ruelas & Pacheco, 2021 respectively). It is also relevant to note that in a study of the diversification of the whole sigmodontine subfamily, a MEDUSA analysis detected shifts to higher rates at the nodes leading to Akodon and Thomasomys , but not with Oligoryzomys (Parada et al, 2015).…”

“…However, it allows the comparing of groups that, as said, are not included with their whole species richness in each phylogeny. The number of living species of each genus was taken from Mammal Diversity Database (2020) and subsequent publications (Brandão et al, 2021; Brito et al, 2021; Ruelas & Pacheco, 2021). Three dating schemes were used to obtain the crown ages of the three genera of interest—Parada et al (2015), Maestri et al (2017) and Steppan and Schenk (2017).…”

“…A lineage through time (LTT) analysis was completed by plotting the MCC tree with 95% confidence interval, using the package ‘ape’ (Paradis et al, 2004) in R 3.5.3 (R Core Team, 2019). As a method of comparing the speciation rate of Oligoryzomys with that of Akodon and Thomasomys , the only two sigmodontine genera that are more diverse than Oligoryzomys (Brito et al, 2021; Hurtado & D'Elía, 2019a; Mammal Diversity Database, 2020; Ruelas & Pacheco, 2021), and considering that no dating analysis has included the entire species richness of the three genera (e.g. Maestri et al, 2017; Parada et al, 2015; Steppan & Schenk, 2017), we followed Magallon and Sanderson (2001) as a first approximation to estimate speciation rates of these three genera.…”

“…Based on unilocus species delimitation methods, we recently recognized 30 living species of Oligoryzomys (Hurtado & D'Elía, 2019a); however, as the forms O. magellanicus and O. griseolus were not included in our study, the species count may rise to 32. As such, Oligoryzomys is the most diverse genus of the tribe Oryzomyini (followed by Oecomys with 22 species and Nephelomys with 14 species; Patton et al, 2015; Ruelas et al, 2021) and the third most of Sigmodontinae (after Thomasomys with 47 species and Akodon with 41 species; Brito et al, 2021; Patton et al, 2015; Ruelas & Pacheco, 2021). Oligoryzomys has been recovered monophyletic in multiple studies based on one gene (e.g.…”