Guillermo D'Elía

Species groups and the evolutionary diversification of tuco-tucos, genus Ctenomys (Rodentia: Ctenomyidae)

Abstract We present the most comprehensive study to date of species groups in Ctenomys (tuco-tucos), a species-rich genus of Neotropical rodents. To explore phylogenetic relationships among 38 species and 12 undescribed forms we sequenced the complete mitochondrial cytochrome-b genes of 34 specimens and incorporated 50 previously published sequences. Parsimony, likelihood, and Bayesian phylogenetic analyses were performed using additional hystricognath rodents as outgroup taxa. The basal dichotomy of Ctenomys splits C. sociabilis from the remaining tuco-tucos, within which 8 main species groups were identified: boliviensis, frater, mendocinus, opimus, magellanicus, talarum, torquatus, and tucumanus. Whereas most of these groups refer to previous clades proposed on the basis of chromosomes or morphology, the torquatus and magellanicus species groups are novel taxonomic hypotheses. However, relationships among species groups are poorly resolved. Furthmore, the positions of C. leucodon, C. maulinus, and C. tuconax are conflicting or unresolved, and they might represent additional independent lineages. On the basis of molecular dating, we estimate that most species groups originated approximately 3 million years ago.

Molecular Phylogeny of Tuco-Tucos, Genus Ctenomys (Rodentia: Octodontidae): Evaluation of the mendocinus Species Group and the Evolution of Asymmetric Sperm

The phylogenetic relationships among 23 individuals representing 14 species of underground hystricognath rodents of the genus Ctenomys were studied by analyzing variation of complete cytochrome b gene sequences. Maximum parsimony, neighbor joining, and maximum likelihood analyses were performed, using the octodontine genera Octodon and Tympanoctomys as outgroups. Our analyses support previous studies based on chromosomes and skull morphology that suggested a clade comprised of Argentinean and Uruguayan populations of C. rionegrensis. This clade is closely related to one comprised of C. flamarioni and the C. mendocinus species complex. Our analyses provide evidence that the symmetric sperm morph, which is common to other South American hystricognath rodents, is the plesiomorphic character state in Ctenomys and in Hystricognathi. Our analyses do not support the hypothesis that the sperm morphs define two major lineages of tuco-tuco species, because species with asymmetric sperm are diphyletic on the basis of cytochrome b sequences, and this morphology appears to have evolved twice in Ctenomys.

A NEW SPECIES OF AKODON (RODENTIA, CRICETIDAE) FROM THE NORTHERN CAMPOS GRASSLANDS OF ARGENTINA

Abstract Integrated analyses of morphological, chromosomal, and molecular data resulted in the description of a new species of the genus Akodon, endemic to the Northern Campos in southern Misiones, Argentina. The new species presents a unique combination of characters, including a narrow zygomatic plate almost without a free upper border, short rostrum, short tail (40% of the head–body length), small and flat auditory bullae, diploid complement of 2n = 36, and several molecular synapomorphies. Phylogenetic analysis, based on cytochrome-b gene sequences, indicates that the Brazilian species Akodon lindberghi is sister to the new species, although this relationship is weakly supported. We comment on the conservation significance of our study, considering that these perisylvan grasslands are suffering substantial human disturbance by agriculture and burning practices.

Phylogeography of Loxodontomys micropus with comments on the alpha taxonomy of Loxodontomys (Cricetidae: Sigmodontinae)

Abstract Loxodontomys micropus is a rodent that is widely distributed in Andean and Patagonian Argentina and Chile. This range covers a heterogeneous area that has been influenced by geologic and palaeoclimatic events, such as the glaciations during the Neogene. To investigate the genetic structure, phylogeographic pattern, and biogeographic history of this sigmodontine rodent we analyzed a 801-base-pair fragment of the mitochondrial genome (cytochrome-b gene) of 87 specimens from 24 localities from Argentina and Chile. Results indicate that L. micropus has a shallow genealogy that is geographically structured and is a taxon characterized by an historical population expansion. We discuss the distribution of the genetic variation of L. micropus in relation to population history and the concordance with other codistributed sigmodontine rodents. On the basis of molecular evidence, we suggest that the L. pikumche, corresponding to the second extant species of the genus, could be a junior synonym of L. micropus.

Differentiation in the Atlantic Forest: phylogeography of Akodon montensis (Rodentia, Sigmodontinae) and the Carnaval-Moritz model of Pleistocene refugia

Abstract According to the Carnaval–Moritz (CM) model of Pleistocene refugia, during the Last Glacial Maximum, forested areas of the Atlantic Forest (AF) were restricted to isolated refugia and later expanded to their current distribution. Phylogeographic patterns of several vertebrate species corroborated the existence of the so-called Pernambuco, Bahia, and São Paulo refugia in the central and northern AF. Here we shift focus to the neglected southern and interior AF by addressing the phylogeography of the mouse Akodon montensis as inferred through analysis of cytochrome-b gene sequences of 86 specimens collected at 36 localities in Argentina, Brazil, and Paraguay. Three main clades were recovered with average genetic divergence of 2.5%: a northern clade, differentiated in the Bahia refuge, a southern clade—for which we propose the Rio Grande do Sul refugium—and a central clade (widely extending from coastal Brazil to Argentina and Paraguay). Within the latter, genetic diversity and historical demographic estimations support differentiation in the São Paulo refugium and their later population expansion toward interior AF. Additionally, no riverine barrier effect was found associated with the main river in the interior AF, the Paraná River. Taken as a whole, the phylogeographic pattern of A. montensis and its recent population history are mainly concordant with the CM model. Resumen Según el modelo Carnaval–Moritz de refugios Pleistocénicos, durante el Último Máximo Glacial, el Bosque Atlántico (BA) se fragmentó a refugios aislados desde los cuales posteriormente se expandieron hasta ocupar su distribución actual. Los patrones filogeográficos de varios vertebrados corroboran la existencia de los refugios de Pernambuco, Bahía y São Paulo en las zonas central y norte del BA. En este estudio nos enfocamos en el BA sur e interior mediante el estudio filogeográfico del ratón Akodon montensis en base a secuencias del gen citocromo–b de 86 especímenes colectados en 36 localidades en Argentina, Brasil y Paraguay. Se observaron 3 clados principales que divergen en promedio en 2.5%; un clado norte, diferenciado en el refugio de Bahía; un clado sur que se diferencia en el aquí propuesto refugio de Río Grande do Sul; y un clado central ampliamente distribuido desde la costa de los estados de Río de Janeiro y São Pablo en Brasil hasta el Paraguay oriental. Dentro de éste último, las estimaciones de diversidad genética y demografía histórica sustentan un escenario de diferenciación en el refugio de São Pablo y posterior expansión poblacional hacia el BA interior. Adicionalmente, se muestra que el Río Paraná no afecta la estructura filogeográfica de A. montensis en el BA interior. En su conjunto, el patrón filogeográfico de A. montensis y su historia poblacional reciente son concordantes con el modelo Carnaval–Moritz.

Lizards on ice: evidence for multiple refugia in Liolaemus pictus (Liolaemidae) during the last glacial maximum in the Southern Andean beech forests.

Historical climate changes and orogenesis are two important factors that have shaped intraspecific biodiversity patterns worldwide. Although southern South America has experienced such complex events, there is a paucity of studies examining the effects on intraspecific diversification in this part of the world. Liolaemus pictus is the southernmost distributed lizard in the Chilean temperate forest, whose genetic structure has likely been influenced by Pleistocene glaciations. We conducted a phylogeographic study of L. pictus in Chile and Argentina based on one mitochondrial and two nuclear genes recovering two strongly divergent groups, Northern and Southern clades. The first group is distributed from the northernmost limit of the species to the Araucanía region while the second group is distributed throughout the Andes and the Chiloé archipelago in Southern Chile. Our results suggest that L. pictus originated 751 Kya, with divergence between the two clades occurring in the late Pleistocene. Demographic reconstructions for the Northern and Southern clades indicate a decrease in effective population sizes likely associated with Pleistocene glaciations. Surprisingly, patterns of genetic variation, clades age and historical gene flow in populations distributed within the limits of the Last Glacial Maximum (LGM) are not explained by recent colonization. We propose an “intra-Andean multiple refuge” hypothesis, along with the classical refuge hypothesis previously proposed for the biota of the Chilean Coastal range and Eastern Andean Cordillera. Our hypothesis is supported by niche modelling analysis suggesting the persistence of fragments of suitable habitat for the species within the limits of the LGM ice shield. This type of refuge hypothesis is proposed for the first time for an ectothermic species.

Discovery of Juliomys (Rodentia, Sigmodontinae) in Paraguay, a new genus of Sigmodontinae for the country's Atlantic Forest

No abstract available

Rodent diversity in South America: transitioning into the genomics era

The goal of this perspective is to propose a concerted effort for the study of the diversity of South American rodents to transition into the genomic era. We first review progress made in the last few decades in our understanding of the age, geographical origins, phylogenetic relationships and diversity of caviomorph and sigmodontine rodents, two major components of the South American fauna. Then, we examine their current representation in genomic/transcriptomic databases, and outline a research program to obtain a set of genomes and transcriptomes that represent major groups within each of these two lineages. We propose standards for voucher specimens and associated data and explore the role of museums and research collections in this endeavor. We envision a concerted international effort to guide and accelerate progress in the field.

The phylogenetic position of the enigmatic Atlantic forest-endemic spiny mouse Abrawayaomys (Rodentia: Sigmodontinae)

BackgroundThe phylogenetic position of the sigmodontine genus Abrawayaomys, historically assigned to the tribe Thomasomyini or considered a sigmodontine incertae sedis, was assessed on the basis of nuclear and mitochondrial DNA sequences obtained from four individuals from different localities in the Atlantic forest of Brazil. Sequences of Abrawayaomys were analyzed in the context of broad taxonomic matrices by means of maximum-likelihood (ML) and Bayesian analyses (BA).ResultsThe phylogenetic position of Abrawayaomys differed depending on the gene analyzed and the analysis performed (interphotoreceptor retinoid-binding protein (IRBP) ML: sister to Thomasomyini; IRBP BA: sister to Akodontini; cytochrome (Cyt) b ML: sister to Neotomys; and Cyt b BA: sister to Reithrodontini). With the sole exception of the BA based on Cyt b sequences, where the Abrawayaomys-Reithrodon clade had strong support, all sister-group relationships involving Abrawayaomys lacked any significant support.ConclusionsAs such, Abrawayaomys constitutes the only representative so far known of one of the main lineages of the sigmodontine radiation, differing from all other Atlantic forest sigmodontine rodents by having a unique combination of morphological character states. Therefore, in formal classifications, it should be regarded as a Sigmodontinae incertae sedis.

New data on the endemic Patagonian long-clawed mouse Notiomys edwardsii (Rodentia: Cricetidae)

Abstract The monotypic Notiomys is the most poorly-known genus of Abrotrichini, a recently erected tribe of South American sigmodontine rodents. Based on a large sample, mostly recovered from owl pellets but including trapped individuals, we refine the known geographic distribution of this mouse (providing 20 new contemporary recording localities and four fossil occurrences), relate this to the principal Patagonian environmental units, add new data on the type locality of the species, and comment on its conservation status. In addition, we present a detailed external and craniodental description and provide data showing geographic variation of some skull features. Finally, we provide preliminary data on genetic variation (cytochrome b gene sequences) that demonstrate the existence of a low degree of observed differentiation (ca. 0.7%) between the populations analyzed.