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Beavers and muskrats are semi-aquatic, generalist herbivorous rodents regarded as invasive in southern South America, with high impacts on the ecosystem. They share some morphological characters of the skull, but different body sizes and phylogenetic history, showing evident shape differences in young and adult skulls during the development in both species. Considering their similar ecological specializations, skull shape could be achieved through different or similar patterns of allometric growth during ontogeny. We analyzed quantitatively the ontogenetic series including 94 specimens of beavers and muskrats and performed multivariate and bivariate analyses considering 20 linear measurements. Our main results from the different approaches suggest high differences in the ontogenetic trajectories of beavers and muskrats, implying disparity in the muscular, functional, and structural conditions of the skull of both species. These differences reflect that although skulls might undergo similar mechanical stress, it is possible to reach a cranial morphology compatible with the similar behavioral and ecological specializations between both species from patterns of skull development that are markedly different. [Display omitted] [ABSTRACT FROM AUTHOR]

The oryzomyine rodent Euryzoryzomys russatus is endemic to the Atlantic Forest of South America, where it inhabits mostly pristine humid forests. Previous phylogeographical studies performed with limited sample sizes indicated that rivers and climatic oscillations might have driven the diversification of this species. Here, we used a more comprehensive database to revisit the phylogeography and demographic history of E. russatus. Our phylogenetic inferences and haplotype network recovered four groups within E. russatus , each of which diversified between 0.33 and 0.60 Mya. These groups are mostly allopatric and are structured latitudinally along the Atlantic Forest. We did not detect any genetic break related to the major river drainages. Species distribution models recovered similar suitable areas for E. russatus in the present and past times, suggesting stability in the geographical range during the Pleistocene. The most pronounced change was the expansion of suitable areas onto the emerged continental shelf during the Last Glacial Maximum. Demographic analyses showed evidence of population expansion during periods of lowered seal levels, especially for the haplogroup associated with the Serra do Mar forest refuge. Therefore, our results failed to support the hypothesis of riverine barriers and suggest that the diversification of E. russatus is explained better by forest refugial processes. [ABSTRACT FROM AUTHOR]

As currently understood, the subgenus Abrothrix (Angelomys) Teta et al. (33:153–182, 2017) includes four species of small (< 25 g), short-tailed mice (< 65% of the length of the head plus body), widely distributed from southern Peru to southernmost Argentina and Chile. At least four nominal forms of this subgenus (i.e., canescens Waterhouse 2:109–27, 1837, hershkovitzi Patterson et al. (23:1–16, 1984), llanoi Pine (40:63–68, 1976), and xanthorhina Waterhouse 2:109–27, 1837), reach the southernmost portion of South America, being their taxonomy largely discussed during the last century. In this contribution we reviewed all these nominal forms, which were alternatively considered as valid at the species level or as subspecies of A. olivacea, (Waterhouse 2:109–27, 1837) based both on molecular (D-loop) and morphological (qualitative and quantitative) evidence. Phylogenetic and phylogeographic analysis of molecular data depicts a main break between north (= olivacea) and south (= xanthorhina) population of the Magellan Strait, which is moderately reflected in multivariate analysis of morphological cranial traits. Based on these results, the lack of qualitative craniodental differences among samples, plus additional genetic evidences (SNPs), we discuss some alternative taxonomic scenarios (i.e., if xanthorhina is a valid species or a subspecies of olivacea). Within this context, we advocated for the recognition at the subspecies level of the nominal forms hershkovitzi and llanoi, based on their large phenotypic distinctiveness and geographical isolation. We consider these data to be of utmost importance for the conservation of the biodiversity of the delicate island ecosystems of southernmost South America. [ABSTRACT FROM AUTHOR]

Sigmodontine rodents colonized South America in Late Miocene or earlier, leading to the clade Oryzomyalia, which rapidly radiated in distinct lineages and occupied almost all continental habitats, in a pattern classically interpreted as an adaptive radiation. Nevertheless, no evidence of strong influence of niche diversification on the evolution of cranial and mandibular morphology, or of deceleration in rates of phenotypic evolution in these structures over time following niche saturation, as expected according to the Ecological Opportunity model, has been detected. Here, we investigated morphometric variation among 59 oryzomyalian species using phylogenetically informed comparative analyses for testing (1) if the diversification of locomotor habits played an important role in shaping the morphology of the appendicular skeleton, and (2) if the disparification of appendicular skeleton showed high rates at the early diversification of Oryzomyalia and then has deaccelerated. Results showed that the different locomotor habits are associated with different shapes in both the forelimb and hindlimb, and selection of evolutionary models suggested that each locomotor habit was associated with their own adaptive optima. Moreover, the most extreme and specialized phenotypes, found in the semifossorial species Geoxus valdivianus, Blarinomys breviceps, and Paynomys macronyx, seem to have appeared after events of acceleration in the rates of morphological evolution. On the other hand, no evidence of a reduction in the rate of evolution over time was detected. The results suggest that the acquisition of different locomotor habits in oryzomyalians was associated with morphological specializations in the appendicular skeleton guided by natural selection and that, especially in the case of the evolution of fossoriality, there was a marked change in evolutionary regimes, generating highly modified phenotypes after acceleration of the pace of morphological changes. Despite the strong association between diversification of locomotor niches and evolution of the appendicular skeleton, the diversification of oryzomyalians does not seem to have experienced niche saturation, as noted in some other adaptive radiation events on Neotropics. [ABSTRACT FROM AUTHOR]

Sigmodontines comprise one of the most diverse radiations of mammals. The cranial ontogeny has been studied in several mammals, but remains poorly studied in the group. We quantified the ontogenetic pattern for 22 sigmodontine species and 8 outgroups, generating partial reconstructions of ancestral allometric growth patterns, and testing the role of evolutionary history on cranial ontogeny. Sigmodontines were conservative in growth pattern, without unique patterns defining tribes. The allometric growth of the cranium was mostly negative, with Akodontini being the most isometric and Phyllotini the most allometric tribes. Allometry of variables associated with the neurocranium was mostly negative, while those linked to trophic functions showed positive allometry or isometry. A general cranial lengthening was detected, but variables associated with cranial width or height grew at lower rates. Cranial growth and development were associated with changes in the musculature functionally involved in bite and mastication. Most changes occurred in earlier postnatal stages, achieving an early morphological optimum. Few changes in the rate of growth at internal nodes were detected, and the stasis along the backbone was recurrent. Cranial elongation was a pattern widespread in the sample and likely a plesiomorphic condition. The few synapomorphies defining the ancestor of Sigmodontinae conform to a pattern with zygomatic arches little expanded laterally and globose braincases. The conservative pattern may be attributed to the biomechanically optimal morphology for omnivorous diets, suggesting that the generalized morphology allows the exploitation of multiple types of food with minor morphological adjustments. [ABSTRACT FROM AUTHOR]

Sigmodontine rodents (Cricetidae, Sigmodontinae) represent the second largest muroid subfamily and the most species-rich group of New World mammals, encompassing above 410 living species and ca. 87 genera. Even with advances on the clarification of sigmodontine phylogenetic relationships that have been made recently, the phylogenetic relationships among the 12 main groups of genera (i.e. tribes) remain poorly resolved, in particular among those forming the large clade Oryzomyalia. This pattern has been interpreted as consequence of a rapid radiation upon the group entrance into South America. Here, we attempted to resolve phylogenetic relationships within Sigmodontinae using target capture and high-throughput sequencing of ultraconserved elements (UCEs). We enriched and sequenced UCEs for 56 individuals and collected data from four already available genomes. Analyses of distinct data sets, based on the capture of 4634 loci, resulted in a highly resolved phylogeny consistent across different methods. Coalescent species-tree-based approaches, concatenated matrices, and Bayesian analyses recovered similar topologies that were congruent at the resolution of difficult nodes. We recovered good support for the intertribal relationships within Oryzomyalia; for instance, the tribe Oryzomyini appears as the sister taxa of the remaining oryzomyalid tribes. The estimates of divergence times agree with the results of previous studies. We inferred the crown age of the sigmodontine rodents at the end of the Middle Miocene, while the main lineages of Oryzomyalia appear to have radiated in a short interval during the Late Miocene. Thus, the collection of a genomic-scale data set with a wide taxonomic sampling provided resolution for the first time of the relationships among the main lineages of Sigmodontinae. We expect the phylogeny presented here will become the backbone for future systematic and evolutionary studies of the group.[Coalescent; Muroidea; Oryzomyalia; phylogenomics; polytomy; Rodentia; Sigmodontalia; species tree; UCEs.] [ABSTRACT FROM AUTHOR]

The Amazonian marsh rat, Holochilus sciureus, is a member of the subfamily Sigmodontinae, the second-largest subfamily of muroid rodents, with 410 species and ca. 84 genera in 12 tribes. This semiaquatic rodent is distributed in South America and is of great economic and epidemiological importance. In this study, we obtained the first mitochondrial genome of the genus Holochilus obtained from a tissue sample associated with a museum voucher specimen. The generated mitogenome sequence of H. sciureus is 16,358 bp length. It comprises a control region and a conserved set of 37 genes encoding for 2 rRNA genes, 22 tRNA genes and 13 protein-coding genes. We conducted a phylogenetic analysis that included H. sciureus and the only five other published mitochondrial genomes of this poorly studied subfamily of rodents. [ABSTRACT FROM AUTHOR]

Nectomys is a cricetid genus of medium-large sized oryzomyines broadly distributed in creeks and rivers of lowland South America. It has been mentioned in two localities, one in Bolivia and another in Argentina in Pleistocene assemblages. After revising the fossils that supported both records we conclude that they are not Nectomys. The record from Bolivia is Reigomys primigenus. The record from Argentina is attributable to Scapteromys. In conclusion, past occurrences of Nectomys are restricted to those of undifferentiated Quaternary age from Brazilian caves. The unexpected connections between fossils described here are discussed to explore the rationality behind detected misidentifications. [ABSTRACT FROM AUTHOR]

Kunsia tomentosus (Lichtenstein, 1830), the woolly giant rat, is a semifossorial cricetid typically associated with the Cerrado and Beni domains in central South America. Kunsia was recently revised and includes only 1 species. It is the largest extant sigmondontine and is readily distinguishable by its size, a body covered with dark-gray fur that is coarse and dense, moderately short tail, short limbs, bicolored manus and pes, and long, powerful claws. It inhabits primarily open grasslands and savannas from central and southwestern Brazil and northern Bolivia. K. tomentosus presently is not considered threatened; however, westernmost populations have presumably been extirpated in the past 2 centuries. [ABSTRACT FROM AUTHOR]

Aim To infer areas of endemism for the tribe Oryzomyini in South America by employing a database of species richness and geographical distribution, and to compare these results with areas of endemism and species richness proposed in the literature for other taxa. Location We analysed specimens of the tribe Oryzomyini distributed throughout South and Central America, which are housed in European, North and South American museums and collections. Methods We analysed 2768 occurrence records for 102 species of the tribe Oryzomyini using the ndm/vndm algorithm and three different grid sizes to assess the possible effects of grid cell area on the results. Results Using the overlap of consensus areas in South America, we identified three generalized areas of endemism for the Oryzomyini: north-western South America (NWSA), eastern South American (ESA), and northern South America (NSA); we also identified the Galápagos archipelago (GA) as an area of endemism. Main conclusions Areas of endemism detected in the continental portion of South America include its three main mountain chains: the Andes Cordillera, the Guyanan Shields, and an area east of the Brazilian Shield named Serra do Mar. Each of these regions encompasses many different types of vegetation, and the species richness and composition of the areas of endemism of the tribe are directly related to this environmental diversity. Different grid sizes affected the distributional heterogeneity of the consensus areas. The smallest grid cell size identified mainly Andean areas, which contain a higher number of more exclusive species in a small area along a steep elevational gradient. In contrast, the largest grid size identified areas of endemism along an environmental gradient that co-varied with latitude and longitude. The identified areas of endemism are corroborated by previous studies on other taxa. [ABSTRACT FROM AUTHOR]

Sooretamys is a monotypic genus of the family Cricetidae, subfamily Sigmodontinae, that is distributed throughout eastern South America in the Atlantic Forest Biome, including Argentina, Brazil, and Paraguay. The taxonomic history of the forms associated with this genus is long and relatively complex, and few studies have evaluated the taxonomic problems of this genus. To this end, our goal was to describe the degree and geographical pattern of morphological and molecular variation in this genus to test the current hypothesis that the genus is monotypic, and, as a consequence, to determine the status of the nominal forms associated with Sooretamys. Accordingly, we employed morphometric, morphological, and molecular tools, according to an integrative taxonomy approach. The results show that some level of morphometric discontinuity is present between the individuals from Paraguay and those from adjacent localities in Brazil and Argentina; sharp discontinuities were not observed in qualitative traits. Molecular analyses of the mitochondrial cytochrome b gene showed that the Paraguayan populations have some degree of genetic differentiation, but the haplotypic variants do not form a monophyletic group. Thus, the evidence so far suggests a difference in the genes and morphology of the Paraguayan population, but there is no consistent resolution (e.g. lack of monophyly) to show that specimens from Paraguay represent a distinct population that would merit taxonomic recognition. Thus, we recognize a single species within the genus Sooretamys, named Sooretamys angouya. The pattern of morphological and genetic differentiation of Sooretamys could be the result of divergence with gene flow. However, our data also correspond in some aspects with the model advanced by Carnaval & Moritz, which claims the existence of stable Atlantic Forest areas where the forest biota persisted during the Quaternary climatic fluctuations. Whatever process has occurred, S. angouya represents one species with a complex evolutionary history, and the analysis of additional samples would be welcome to further elucidate the process of diversification of this taxon. © 2014 The Linnean Society of London [ABSTRACT FROM AUTHOR]

Six species of 3 genera belonging to the fur mite family Listrophoridae were recorded on skins of South American rodents of the cricetid subfamily Sigmodontinae housed in the Bavarian State Collection of Zoology (Munich, Germany). Among them, Amlistrophorus geoxus sp. nov. from Geoxus valdivianus from Chile is described as a new for science, and males of Prolistrophorus amazonicus amazonicus Fain, 1971 are recorded for the first time. The full generic status for the subgenus Amlistrophorus of the genus Prolistrophorus proposed by Fain et al. (1996) is not supported, and Prolistrophorus musculinus Fain, 1973 stat. nov. (formerly a subspecies of P. amazonicus) from Mus musculus (Rodentia: Muridae) from Suriname is raised to species status. New hosts are recorded for the following species: Prolistrophorus argentinus (Hirst, 1921) from Holochilus brasiliensis and H. chacarius from Argentina, P. amazonicus from Calomys callosus from Argentina and Bolivia, C. laucha and C. musculinus from Argentina, P. akodon Fain and Lukoschus, 1982 from Akodon montensis from Argentina, P. nectomys Fain, 1971 from Nectomys palmipes from Peru and Melanomys caliginosus from Panama, and Sclerolistrophorus oxymycteris Fain, 1976 from Oryzomys laticeps from Brazil. [ABSTRACT FROM AUTHOR]

Abstract: In a recent paper (Verzi, D.H., Montalvo, C.I., 2008. The oldest South American Cricetidae (Rodentia) and Mustelidae (Carnivora): late Miocene faunal turnover in central Argentina and the Great American Biotic Interchange. Palaeogeography, Palaeoclimatology, Palaeoecology 267, 284–291) the potentially oldest South American Cricetidae (Rodentia) and Mustelidae (Carnivora) have been reported from a Late Miocene (Huayquerian) assemblage located in central Argentina (Caleufú site, La Pampa province). These findings expand the biochron of these important families in South America 3–4Ma earlier than previous records. However, several observations prevent us from accepting the validity of these assumptions. In this paper we discuss the age of the Caleufú assemblage, and the assignment of the GHUNLPam 21722 to Mustelidae. The Caleufú assemblage contains a mixture of Pliocene and Late Miocene faunal elements, and has been assigned to the Huayquerian only due to the “stage of evolution” of some rodents. The lack of isotopic or paleomagnetic data coupled with the isolation of this locality and the absence of a local stratigraphic succession inhibit its correlation with other palaeontological comparable sites and a robust inference about its chronology. The “stage of evolution” of a taxon is not a biostratigraphic tool, thus we cannot rule out the possibility that the Caleufú assemblage has an Early Pliocene (Montehermosan) age. The GHUNLPam 21722, a poorly preserved specimen, shows several characters (e.g., 4 lower incisors, mental foramina below the incisors absent, third lower incisor smaller than the first and second ones) that do not match with Mustelidae (or Carnivora) but instead strongly resemble those observed in didelphimorphian marsupials. The discussed caveats regarding Caleufu assemblage chronology and taxonomy indicate that new and detailed studies are needed before the hypotheses advanced by Verzi and Montalvo can be accepted. [Copyright &y& Elsevier]

Abstract: The discovery of a rich fauna from the late Miocene Cerro Azul Formation in Caleufú, central Argentina, is reported. This fauna includes vertebrate Holarctic immigrants, among which are the oldest South American records of mammals of the families Cricetidae (Rodentia) and Mustelidae (Carnivora). Stratigraphic, biochronological and taphonomic evidence indicates that the faunal assemblage from Caleufú is confidently synchronous and represents the late Huayquerian (Zone of Xenodontomys elongatus; late Miocene). Thus, this fauna supports hypotheses of the arrival of cricetids and mustelids prior to the Pliocene completion of the Panamanian isthmus. However, the new records do not permit inferences to be made about precise moments of entry of these groups into South America. Representation of the GABI in the fossil record is here interpreted as a major event integrated by a nested pattern of events, including geographically more restricted turnovers (implying particular taphonomic and geographic biases) and associated environmental changes. In such a hierarchical context, the record of Caleufú represents a local turnover different from those occurring with arrivals of these taxa, or their ancestors, into the continent. In accordance with biochronological data, the turnover recorded in Caleufú could be coeval with the global-scale glacial event detected for the late Miocene (ca. 5.7–5.8 Ma). In southern South America, this arid and cold pulse would have triggered the distribution drift to central Argentina of fauna previously restricted to western peri-Andean areas. Local turnovers such as the one reported here, and associated physical changes, have to be analyzed in detail as individual events in order to interpret the chronology, dynamics and paleoenvironmental context of hierarchically greater episodes such as the GABI. [Copyright &y& Elsevier]

We present the most comprehensive systematic study to date of Necromys, a rodent genus distributed in open areas north and south of Amazonia and in Andean grasslands. The study is based on sequences of the cytochrome-b gene that were analyzed by parsimony and Bayesian approaches. The analyses include sequences of 62 specimens from 51 localities from Argentina, Bolivia, Brazil, Colombia, Paraguay, Peru, Uruguay, and Venezuela, representing all but 1 of the species currently recognized in the genus. Necromys was recovered as a monophyletic group and we found a large polytomy at its base that involves 3 lineages. One, represented by the Andean N. lactens, shows a marked phylogeographic pattern. The 2nd clade is formed by N. urichi from the northern grasslands of South America and N. amoenus from the central Andes. Results suggest that each of these taxa may represent more than 1 biological species. The 3rd clade is formed by lowland species found south of Amazonia. Within this clade N. obscurus is sister to the remaining species. Haplotypes recovered from specimens assigned to N. benefactus, N. temchuki, and N. lasiurus form a clade, but these taxa do not form reciprocally monophyletic groups, nor does this large clade possess geographic structure. These genealogical results, discussed in the context of genetic variation, are the basis of taxonomic (e.g., N. benefactus and N. temchuki are regarded as junior synonyms of N. lasiurus) and biogeographic considerations. [ABSTRACT FROM AUTHOR]

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., Competing Interests: The authors declare there are no competing interests., (©2022 Di-Nizo et al.)