Species limits and recent diversification of Cerradomys (Sigmodontinae: Oryzomyini) during the Pleistocene

Cerradomys is a genus of the tribe Oryzomyini with eight species currently recognized, and a controversial taxonomy. These species are mainly distributed in the South America dry diagonal, but some species extend into Atlantic Forest, reaching the coastal sandy plains known as Restingas. This study aimed to address species limits and patterns of diversification of Cerradomys species. For this purpose, we performed cytogenetic and molecular analyses (phylogeny, coalescent species delimitation, barcoding, and divergence times estimation) using multiple mitochondrial and nuclear markers on a comprehensive sampling, representing all nominal taxa reported so far. Chromosomal information was a robust marker recognizing eight Cerradomys species. Reciprocal monophyly was recovered for all the species, except for C. subflavus. These results together with coalescent analyses recovered eight species as the most congruent species delimitation scenario for the genus (mean C _tax : 0.72). Divergence time estimates revealed that Cerradomys' diversification occurred about 1.32 million years ago (Mya) during the Pleistocene. Although our results conservatively support the eight Cerradomys species described so far, different lines of evidence suggest that C. langguthi and C. subflavus could potentially be species-complexes. We discussed this scenario in the light of multiple evolutionary processes within and between species and populations, since Cerradomys comprises a species group with recent diversification affected by Pleistocene climatic changes and by the complex biogeographic history of South America dry diagonal. This work supports that the diversity of Cerradomys is underestimated and reiterates that interdisciplinary approaches are mandatory to identify small rodent species properly, and to unhide cryptic species.

Systematics of the rodent genus Neacomys Thomas (Cricetidae: Sigmodontinae): two new species and a discussion on carotid patterns

The taxonomy of the oryzomyine genus Neacomys currently is in a state of flux: systematic studies in the last 20 years increased its diversity from four to 16 species, with an additional several undescribed phylogenetic lineages. Despite this progress, morphological variation and species limits remain poorly known for several species groups and complexes within the genus, such as N. tenuipes, N. musseri, and N. dubosti. Here we analyze the variation of morphological characters and morphometric patterns of two new candidate species of Neacomys for northern Venezuela and Pará state, Brazil, that are characterized by the presence of derived carotid circulation, a rare character state for the genus. Analyzed material included holotypes, type series, and/or topotypes of almost all described species of Neacomys, including type series of N. musseri, the holotype of N. tenuipes, and sequenced specimens of N. xingu. Qualitative comparison showed that 25 characters are informative for the distinction of the two new forms, and morphometric analyses corroborated the morphological separation of the new species. Results also point that N. tenuipes might represent a species complex. The new forms are sympatric with other species, including N. tenuipes and N. xingu, and can be identified by a suite of morphological characters, including the presence of a derived carotid pattern and, for the Pará form, by a unique morphology of the first upper molar. We review the occurrence of carotid circulation patterns within Sigmodontinae and discuss its use for the systematics of the subfamily. Further studies involving the new Neacomys species will contribute to understanding the biogeographic patterns and evolutionary trends within this distinct and diverse genus.

The mammalian faunas endemic to the Cerrado and the Caatinga

We undertook a comprehensive, critical review of literature concerning the distribution, conservation status, and taxonomy of species of mammals endemic to the Cerrado and the Caatinga, the two largest biomes of the South American Dry-Diagonal. We present species accounts and lists of species, which we built with criteria that, in our opinion, yielded results with increased scientific rigor relative to previously published lists - e.g., excluding nominal taxa whose statuses as species have been claimed only on the basis of unpublished data, incomplete taxonomic work, or weak evidence. For various taxa, we provided arguments regarding species distributions, conservation and taxonomic statuses previously lacking in the literature. Two major findings are worth highlighting. First, we unveil the existence of a group of species endemic to both the Cerrado and the Caatinga (i.e., present in both biomes and absent in all other biomes). From the biogeographic point of view, this group, herein referred to as Caatinga-Cerrado endemics, deserves attention as a unit - just as in case of the Caatinga-only and the Cerrado-only endemics. We present preliminary hypotheses on the origin of these three endemic faunas (Cerrado-only, Caatinga-only, and Caatinga-Cerrado endemics). Secondly, we discovered that a substantial portion of the endemic mammalian faunas of the Caatinga and the Cerrado faces risks of extinction that are unrecognized in the highly influential Red List of Threatened Species published by the International Union for Conservation of Nature (IUCN). "Data deficient" is a category that misrepresents the real risks of extinction of these species considering that (a) some of these species are known only from a handful of specimens collected in a single or a few localities long ago; (b) the Cerrado and the Caatinga have been sufficiently sampled to guarantee collection of additional specimens of these species if they were abundant; (c) natural habitats of the Cerrado and the Caatinga have been substantially altered or lost in recent decades. Failures either in the design of the IUCN criteria or in their application to assign categories of extinction risks represent an additional important threat to these endemic faunas because their real risks of extinctions become hidden. It is imperative to correct this situation, particularly considering that these species are associated to habitats that are experiencing fast transformation into areas for agriculture, at an unbearable cost for biodiversity.