Abstract Species delimitation in recently evolving taxa presents unique challenges. Such taxa may not have accumulated enough genetic or morphological differences to be easily distinguished using traditional methods, while processes such as incomplete lineage sorting or gene flow may obscure these distinctions. One paradigmatic recently evolved taxon is the Corrientes group of the subterranean genus Ctenomys (Rodentia, Ctenomyidae), a set of populations with different chromosomal forms occurring in the homonymous province of Argentina. Previously, three nominal species and several independently evolving lineages had been proposed; however, a comprehensive integrative approach—including qualitative and quantitative morphological analyses, as well as additional molecular proxies for lineage delimitation—was still lacking, and these results had not been evaluated in a taxonomic context. In this study, we added new lines of evidence, including Bayesian phylogenetics and divergence time estimation, haplotype networks, and genetic distances. We integrated this information with karyotypic and microsatellite data to discuss previously proposed lineages, as well as to analyze the evolutionary processes that shaped the history of this group. Finally, we analyzed the qualitative and quantitative morphology of individuals from the nominal species and a chromosomally derived lineage, and we propose a revised species-level and infraspecific classification for this complex group of rodents. This resulted in the delimitation of two species, C. roigi and C. perrensi, the latter being subdivided into three subspecies: Ctenomys perrensi perrensi, C. perrensi dorbignyi, and C. perrensi iberaensis subsp. nov. In addition, other identified lineages, such as Sarandicito, Manantiales, and Santa Rosa, deserve future taxonomic investigation.

Hantaviruses infect a wide range of vertebrate hosts. In the Americas, Orthohantavirus species pose a major public health concern due to their ability to cause Hantavirus Cardiopulmonary Syndrome (HCPS). Given the lack of approved vaccines and specific treatments for HCPS, identifying circulating orthohantavirus genotypes and their hosts, along with estimating prevalence, is essential for designing effective preventive strategies. The objectives of this study were: (1) to identify the orthohantavirus hosts, (2) to determine the circulating orthohantavirus genotypes, (3) to assess the population structure and dynamics of Akodon montensis, (4) to characterize the rodent communities, and (5) to evaluate associations between A. montensis abundance and environmental variables in two protected natural areas of Misiones Province, Argentina. A total of 12 rodent trapping sessions were conducted from April 2021 to February 2023 in Urugua-í and Cruce Caballero Provincial Parks. Orthohantavirus antibodies were detected in four A. montensis and three Oligoryzomys nigripes from both Provincial Parks. Molecular analyses provided evidence of the co-circulation of Jaborá and Juquitiba orthohantavirus genotypes. Both areas exhibited similar rodent community compositions, with A. montensis as the numerically dominant species and O. nigripes occurring at low abundance. In Urugua-í, A. montensis abundance varied in relation to precipitation and vegetation productivity, whereas no such associations were observed in Cruce Caballero. Further studies are needed to effectively monitor these communities and to gain a better understanding of potential fluctuations in seroprevalence, changes in genotype pathogenicity, and the possible detection of unknown genotypes.

Akodon montensis is widely distributed throughout the Atlantic Forest (AF) hotspot biodiversity, encompassing Brazil and reaching its southern limit in eastern Paraguay and northeastern Argentina. Here, we combined analysis of molecular data and ecological niche modelling to contribute to elucidating its evolutionary history. At a local scale, we studied the genetic variability in microsatellite loci in populations from the remaining AF in Misiones province, Argentina. The moderate genetic differentiation observed in some populations suggests that limited gene flow may result from habitat fragmentation at the south of the AF. At a wide geographic range, the ecological niche modelling identified areas of high environmental suitability for A. montensis during the last glacial maximum (LGM) on the coast of Brazil, where the forested habitats expanded onto the continental shelf. This could explain the high diversity in the cytochrome b in this region and contiguous areas, agreeing with the Atlantis Forest hypothesis. Additionally, we observed an extended area of high habitat suitability during the LGM and at present in southwestern Brazil, eastern Paraguay and northeastern Argentina. The evolutionary history of A. montensis seems to have been influenced by demographic processes that occurred at different times and regions, shaping its genetic variability and structure.

The Andes are known to be one of the most species-rich regions on Earth, with their origination promoting formation of new habitats and acting as climatic barriers. This orogenic event was structured latitudinally with 3 major segments having different formation times and with different environmental and historical conditions. The Andean region has been historically important in the evolutionary history of small mammals and is considered the region of Earth with the highest values of rodent species richness and turnover. Therefore, the region provides an excellent opportunity to evaluate mechanisms involved in structuring rodent assemblages and beta diversity patterns. Here, we assessed spatial patterns of rodent beta diversity along the Andes Mountains, with specific goals of examining patterns of turnover and nestedness as 2 recognized processes that drive species composition. We explored the role of spatial, climate, and historical factors on beta diversity patterns using geographic range maps for 432 rodent species to construct a species presence-absence matrix. We used piecewise regressions to identify latitudinal breakpoints in turnover and nestedness, and conducted multiple regressions and variation-partitioning approaches to assess the contribution of each set of postulated drivers in shaping beta diversity patterns. Beta diversity decreases from north to south. The highest turnover was located at the Northern Andes (5 degrees N and 10 degrees S) and western-central Andes (20 degrees S and 35 degrees S). Nestedness was higher below 40 degrees S and in some areas of the western-central Andes between 15 degrees and 20 degrees S. Turnover and nestedness registered breakpoints coincident with the Central and Southern Andes limit. Turnover explained most of the beta diversity for all segments, although within the Southern Andes there was also some contribution of nestedness. In all segments, beta diversity was mainly explained by spatial factors with minor contributions from spatially structured climate (Northern Andes), interaction of all factors (Central Andes), and the interaction between current climate and history (Southern Andes). Beta diversity of Andean rodents decreases latitudinally, with turnover as the dominant process and nestedness with higher contribution in the Southern Andes. Beta diversity break points partially support Andean orogenic history reflected among latitudinal segments. Figure 3 of this manuscript is recommended for promoting this research. Los Andes son reconocidos como una de las regiones mas ricas en especies de la tierra, ya que su levantamiento favorecio la formacion de nuevos habitats y actuo como barrera climatica. Este evento orogenico se estructuro latitudinalmente en 3 segmentos, cada uno con tiempos de formacion caracteristicas ambientales y condiciones historicas diferentes. La region Andina ha sido un importante escenario en la historia evolutiva de los pequenos mamiferos y es considerada la region con mayor riqueza y recambio de especies. Por lo tanto, es un excelente escenario para evaluar los mecanismos que estructuran los patrones de diversidad beta del ensamble de roedores. Aqui evaluamos el patron espacial de la diversidad beta de roedores a lo largo de la Cordillera de los Andes, descomponiendolo en recambio y anidamiento, con el fin de comprender los procesos subyacentes que determinan la composicion de especies. Exploramos el papel de los factores espaciales, climaticos e historicos sobre los patrones de diversidad beta utilizando mapas de distribucion geografica para 432 especies de roedores obtenidos de la Base de Datos de Diversidad de Mamiferos y construimos una matriz de presencia-ausencia de especies (PAM). Utilizamos regresiones por tramos (picewise) para identificar los puntos de quiebre latitudinales en recambio y anidamiento, y realizamos regresiones multiples y particion de la varianza para evaluar la contribucion de cada conjunto de factores en la conformacion de los patrones de diversidad beta. La diversidad beta disminuye de Norte a Sur, con un mayor recambio en los Andes del Norte (5 degrees N y 10 degrees S) y en la zona central oeste (20 degrees S y 35 degrees S). El anidamiento fue mas alto por debajo de los 40o S y en algunas areas del centro oeste entre los 15 degrees y 20 degrees S. Tanto el recambio como el anidamiento registraron puntos de quiebre coincidentes con el limite entre el segmento Central y el Sur. El recambio explica la mayor parte de la diversidad beta para todos los segmentos, aunque el anidamiento contribuye tambien a la diversidad beta de los Andes del Sur. En todos los segmentos andinos la diversidad beta se explico principalmente por factores espaciales con una menor contribucion del clima actual (NA), por la interaccion de todos los factores (CA) y la interaccion entre el clima historico con el actual (SA).

Few cases of hantavirus pulmonary syndrome have been reported in northeastern Argentina. However, neighboring areas show a higher incidence, suggesting underreporting. We evaluated the presence of antibodies against orthohantavirus in small rodents throughout Misiones province. Infected Akodon affinis montensis and Oligoryzomys nigripes native rodents were found in protected areas of Misiones.

Subterranean rodents of the genus Ctenomys (tuco-tucos) are endemic to South America and have experienced relatively recent radiation. There are about 67 recognized species that originated in approximately 1-2 MY. They stand out for their species richness, extraordinary chromosomal diversity, and wide range of habitat they occupy in the continent. Phylogenetic relationships among species of tuco-tucos have been challenging to resolve. Groups of closely-related species have been suggested, but their relationships must be resolved. This study estimates the phylogeny of the genus using massive sequencing, generating thousands of independent molecular markers obtained by RADseq, with a taxonomic sampling that includes 66% of the recognized species. The sequences obtained were mapped against the C. sociabilis genome, recovering up to 1,215 widely shared RAD loci with more than 19,000 polymorphic sites. Our new phylogenetic hypothesis corroborated the species groups previously proposed with cytochrome b gene sequences and provided a much greater resolution of the relationships among species groups. The frater group is sister to all other tuco-tucos, whereas some of the earlierliest proposals placed the sociabilis group as sister to all other tuco-tucos. Ctenomys leucodon, previously proposed as an independent lineage, is associated with the frater group with moderate statistical support. The magellanicus and mendocinus are sister groups in a major clade formed by the boliviensis, talarum, tucumanus, torquatus, and opimus groups. Ctenomys viperinus, included in the phylogeny for the first time, belongs to the tucumanus group. This multi-locus phylogenetic hypothesis provides insights into the historical biogeography of understanding this highly diverse genus.

Akodon montensis is abundant and widely distributed in the Atlantic Forest, which southern limits extends to northern Argentina, principally in the Misiones province. Chromosomal data from more centrally distributed populations in Brazil showed significant chromosome diversity; however, data from its southern boundaries are scarce. To explore the chromosomal diversity of this species, we conducted conventional chromosome staining, C-banding, CMA 3 /DAPI fluorochromes, and in situ hybridization with a telomere probe in samples from Argentina. Most specimens had the standard karyotype 2n = 24, although numerical variations due to aneuploidies and supernumerary (B) chromosomes were detected. We registered novel structural polymorphisms for pair 11 and sex chromosomes, and a rearrangement involving pairs 2 and 4, possibly due to a spontaneous chromosomal mutation. Most A. montensis females are homogametic with XX sex chromosomes, although XY and X0 females were observed. Most individuals carrying B chromosomes had 1 B and, to a lesser extent, 2 and 3 B. The chromosomal variability detected at the southern limit of A. montensis distribution is high and similar to other geographically distant populations, despite the fact that it could be a region recently colonized. Some of these variations are unique and could have originated independently in southern populations, while others are shared throughout the species distribution and may have originated earlier.

‘Rewilding’ is a nature conservation strategy gaining prominence worldwide. Established in the Northern Hemisphere, rewilding initiatives have increasingly been proposed in Argentina, but their relative merits, feasibility of implementation and accountability have lacked adequate analysis and discussion. Recently, 125 scientists and practitioners wrote an article to assess the justification and methods of current rewilding initiatives in Argentina. Rather than engaging in a constructive debate with the scientific community, one of the major organizations behind these initiatives threatened to sue the authors for libel. We strongly reject this baseless threat. Scientific discussions around this and other conservation topics of societal concern should be addressed in an academic context and conducted in a respectful and rational manner, embracing the right of scientists and practitioners to express themselves freely and without fear of coercion.

Rodentia has a high species number and chromosomal variability. The South American genus Akodon is one of the most speciose muroids, with more than 40 species included in several species groups. Here, we characterize cytogenetically specimens of Akodon from central-western Argentina. Subsequently, we reviewed and analyzed the cytogenetic data for this genus, build a phylogeny and mapped chromosome changes to interpret its evolution. Specimens of A. dolores from central-western Argentina have 2n=42-44/FNa=44 (46, 48) due to a Robertsonian rearrangement. Our data expand the distribution range known for this polymorphism and confirm its geographic structure. Other specimens had 2n=40/FNa=40, representing populations of A. oenos, A. polopi, and A. spegazzinii. All karyotypes have a low amount of heterochromatin, concentrated in centromeres and sex chromosomes, as in other rodents. The complement with 2n=40/FNa=40 is the most frequent in Akodon and is shared by most species in some groups. Chromosome numbers are very diverse. The FNa shows less variability; FNa=42 was recovered as ancestral, excluding A. mimus, which was connected at the base of the Akodon tree and has FNa=44. This indicates a complex chromosome evolution in Akodon, and suggests that reductions and increases in the 2n and FNa evolved independently in some lineages.

South American subterranean rodents of the genus Ctenomys are among the most diverse mammals at the species level, integrating a monotypic family of recent origin. Contrasting with their general morphological conservatism, chromosome variability is very high. Also, molecular data showed a shallow genetic divergence within several species groups with mitochondrial markers, leaving doubts about the taxonomic status of some lineages and the evolutionary significance of their chromosomal diversity. Here, we reviewed and reanalysed published chromosome data of Ctenomys and contrasted it with molecular data, including ancestral chromosomal state reconstructions in a phylogenetic hypothesis based on mitochondrial cytochrome b gene sequences. One hundred seventy-eight different chromosome complements were recorded for 48 Ctenomys species. Some species are polymorphic and/or polytypic, with differentiated populations. Both 2n and FNa showed a wide variation, but FNa had a greater dispersion. With the exceptions of C. lessai and C. maulinus, in all other species, the X chromosome is biarmed. The Y chromosome is quite variable in morphology and size. In general, biarmed and uniarmed autosomes within karyotypes are nearly equally represented, departing from the pattern of other mammals. This may be due to fast-evolving heterochromatin. The chromosomal reconstructions suggest that the ancestral karyotype of the genus could have had an intermediate 2n and high FNa. Most of the species groups recovered in the phylogeny show wide chromosomal variability, the most extreme being the torquatus group. This diversity was apparently generated in a short time, indicating an accelerated rate of chromosome evolution in this clade and the whole family.

En 2021, Jayat et al. propusimos una nueva especie de roedor sigmodontino, nombrada Phyllotis pehuenche, para las poblaciones del complejo de especies de Phyllotis xanthopygus del sudoeste de la provincia de Mendoza y el oeste de la provincia de Neuquén, Argentina. La descripción formal de la especie, publicada en un material suplementario electrónico modificable, no cumple con los requerimientos establecidos en la enmienda sobre publicaciones electrónicas (ICZN 2012) de la Cuarta Edición del Código Internacional de Nomenclatura Zoológica (ICZN 1999), haciendo que el nombre no esté disponible. El objetivo de esta nota es cumplir con los requerimientos del código y hacer el nombre disponible. Aquí ofrecemos una versión resumida de la descripción original de esta especie. En esta nota, ofrecemos un tratamiento taxonómico para P. pehuenche, incluyendo su sinonimia, localidad tipo, holotipo y paratipos, proveyendo la etimología del epíteto específico, y ofreciendo una diagnosis para la especie y comentarios acerca de su distribución geográfica. Con toda la información provista, cumplimos con los lineamientos del Código Internacional de Nomenclatura Zoológica (ICZN 1999, 2012) haciendo el nombre disponible.

RESUMEN.La provincia de Misiones tiene una gran diversidad de roedores, algunos de ellos, como Calomys tener, cuentan con pocos registros y su presencia en el territorio provincial ha sido ampliamente discutida.Los objetivos de este trabajo fueron: a) aportar información de una nueva localidad de presencia, b) describir morfológicamente, y c) analizar la variabilidad molecular del citocromo b de Calomys tener.A partir de campañas de muestreo realizadas en 2017 y 2018, se capturaron cuatro individuos que fueron identi cados morfológica y molecularmente como C. tener.Estos nuevos registros amplían la distribución

Incomplete lineage sorting (ILS) and introgression have been increasingly recognized as important processes involved in biological differentiation. Both ILS and introgression result in incongruences between gene trees and species trees, consequently causing difficulties in phylogenetic reconstruction. This is particularly the case for rapid radiations, as short internodal distances and incomplete reproductive isolation increase the likelihood of both ILS and introgression. Estimation of the relative frequency of these processes requires assessments across many genomic regions. We use transcriptomics to test for introgression and estimate the frequency of ILS in a set of three closely related and geographically adjacent South American tuco-tucos species (Ctenomys), a genus comprising 64 species resulting from recent, rapid radiation. After cleaning and filtering, 5764 orthologous genes strongly support paraphyly of C. pearsoni relative to C. brasiliensis (putatively represented by the population of Villa Serrana). In line with earlier phylogenetic work, the C. pearsoni - C. brasiliensis pair is closely related to C. torquatus, whereas C. rionegrensis is more distantly related to these three nominal species. Classical Patterson's D-statistic shows significant signals of introgression from C. torquatus into C. brasiliensis. However, a 5-taxon test shows no significant results. ILS was estimated to have involved about 9% of the loci, suggesting it represents an important process in the incipient diversification of tuco-tucos.

Abstract Based on previously published molecular (mitochondrial) and herein provided morphological (qualitative and quantitative data) evidence, we describe a new species of leaf-eared mouse of the genus Phyllotis. The new species is morphometrically distinct when compared with other phylogenetically or geographically close species of Phyllotis, showing several quantitative differences in their external and craniodental characters (e.g., proportionally broader nasals and interorbital region, and proportionally smaller tympanic bullae). The new species is endemic to central Argentina, occurring on rocky grasslands at elevations of 650–2,800 m a.s.l. This is the only species of Phyllotis inhabiting the Central Sierras, a mountain system of medium elevation, isolated from the Andes by low elevation arid and semiarid environments.

Rodents are an important component of South America fauna. Their high diversity has motivated researchers to continually review their taxonomy, genetic diversity, species limits, and phylogenetic relationships. Here, we applied DNA-barcodes for assessing the taxonomic and genetic diversity in the two major lineages of South American rodents: caviomorphs and sigmodontines. We analysed 335 COI barcodes in 34 morphologically determined species from 39 localities along central Andes and arid lands of Argentina. Neighbour-joining and maximum likelihood reconstruction provided clear separation between species. The Barcode Index number and Bayesian Poisson tree processes were used to confirm concordance between sequence clusters and species designations by taxonomy. We found deep divergence within the Phyllotis xanthopygus species complex, with distances up to 13.0% between geographically separated lineages. Minor divergences (3.30% and 2.52%) were found within Abrothrix hirta, and Tympanoctomys barrerae, respectively, with differentiation in their genetic lineages. Also, we documented geographically separated clusters for Akodon spegazzinii and A. oenos with up to 2.3% divergence, but clustering methods failed to distinguish them as different species. Sequence results show a clear barcode gap with a mean intraspecific divergence (0.56%) versus a minimum nearest-neighbour distance averaging (10.1%). Distances between congeneric species varied from 4.1 to 14%, with the exception of two related forms within Euneomys and the sister species Akodon spegazzinii and A. oenos. This study constitutes a substantial contribution to the global barcode reference library. It provides insights into the complex phylogeographic patterns and speciation scenarios in rodents, while highlighting areas that require in-depth taxonomic and integrative research.

Phyllotis Waterhouse 1837 is one of the most studied genera of South American cricetid rodents. As currently understood, it includes 20 small to medium‐sized species of predominantly rocky habitats. Among them, populations of the yellow‐rumped leaf‐eared mouse, traditionally referred to P. xanthopygus (Waterhouse 1837), are the most widely distributed, extending from central Peru to southern Chile and Argentina. Based mostly on molecular evidence, previous studies suggested that P. xanthopygus constitutes a species complex, being characterized by geographically structured and genetically divergent clades. In this work, we compare the molecular phylogenetic hypothesis for populations distributed on the eastern slopes of the central Andes with morphometric evidence using univariate and multivariate analyses. Quantitative morphological and molecular evidence suggests that at least four nearly cryptic species of the P. xanthopygus complex occur from southern Bolivia to west‐central Argentina. Three of these taxa have available names; one of them, P. caprinus, is currently recognized to the species level; the other two, the clades of P. x. posticalis‐P. x. rupestris and P. vaccarum, are both recognized as subspecies of P. xanthopygus. The remaining taxon represents a new species distributed in the west‐central Andes of Argentina. We discuss our morphological results in the light of other sources of evidence (e.g. qualitative and quantitative state characters, genetic and phylogenetic studies, and cytogenetic data) and name the new species as P. pehuenche, honouring the original native people that historically inhabited west‐central Andes of Argentina.

The genus Euneomys is mostly distributed in the open environments of the central and southern Andes, adjacent Patagonian steppes of Argentina and Chile, and in several islands of the Tierra del Fuego Archipelago. This genus includes three living species: E. chinchilloides, E. fossor, and E. mordax. Euneomys fossor is a poorly known species, with an uncertain geographic provenance and known from a single specimen, whose distinction from the other species of the genus has not been accurately assessed. Here, using qualitative and quantitative morphological evidence, plus published information about karyotypes and genetic variation, we evaluate the taxonomic status of E. fossor and E. noei, a nominal form usually considered a synonym of E. mordax. Based on multivariate analysis of cranial measurements and morphological discrete traits, we recognize two main morphotypes within Euneomys, one referable to E. chinchilloides (with dabbenei, petersoni, and ultimus as synonyms), and another including E. fossor, E. mordax, and E. noei. The recognition of two major groups within Euneomys is also supported by molecular and chromosomal data. By the principle of the priority, the names of E. chinchilloides and E. fossor applies for each one of these morphotypes. In addition, after discussing the pros and cons of replacing the name mordax by fossor, we emended the type localities of both forms.

The leaf‐eared mouse, Phyllotis xanthopygus (Waterhouse 1837) is a widely distributed sigmodontine rodent in South America, with populations ranging from central Peru to southern Argentina and Chile. Previous morphological and molecular contributions have suggested that P. xanthopygus represents a species complex. In order to characterize and disclose this cryptic species complex, we perform a molecular genetic/phylogenetic analysis of representative samples across its geographical distribution. Phylogenetic analyses were based on sequences of cytochrome‐b gene (801 base pairs; n = 114 specimens) and analysed by maximum likelihood and Bayesian approaches. We also employed a Bayesian implementation of the Poisson tree processes (bPTP) as a unilocus species delimitation method. Results from our phylogenetic analyses retrieve eight well‐supported clades. Five of these clades belong to populations known as P. xanthopygus s.l., which were paraphyletic to the closely related species P. bonariensis , P. caprinus , and P. limatus , displaying strong genetic divergences (>8%). The (bPTP) analyses recovered ten species within P. xanthopygus s.l. plus related forms (i.e. P. bonariensis , P. caprinus , and P. limatus ). Our results, coupled with chromosomal and morphological evidences, support the recognition of these clades at the species level and provide a new framework to characterize the leaf‐eared mice complex. Our study highlights the importance of integrative approaches in disentangling the biodiversity of Neotropical rodents.