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We present a systematic review of the extinct species included in the family Caenolestidae, one of the few South American metatherian groups that has survived to the present. We perform a cladistic analysis based on a data matrix consisting of all extant and extinct species that have been referred to this family, 100 morphological characters and two sets of molecular data (cytochrome b and cytochrome c oxidase I). Morphological and molecular data were analysed separately and in combination, under maximum parsimony and maximum likelihood methods. As a result, caenolestids are recovered as a monophyletic group within which we formally recognize three new taxa: Caenolestoides miocaenicus gen. & sp. nov., Gaimanlestes pascuali gen. & sp. nov. and Stilotherium parvum sp. nov. from the Early Miocene of Patagonia, Argentina. Stilotherium is the earliest diverging lineage of caenolestids followed by Gaimanlestes, while C. miocaenicus was recovered as the extinct species most closely related to extant caenolestids.

The Amazon is probably the most diverse realm on Earth, and is considered to be the primary source of diversity and a center of dispersal for Neotropical terrestrial organisms. Yet, the assumption that the Amazon basin is a primordial place of fish species origination and dispersal into other drainages still need to be tested. We addressed this issue by inferring a time-stratified biogeographic history and reconstructing the ancestral habitat preference ofHypostomus, a continentally widespread and species-rich Neotropical genus. We found thatHypostomusemerged in the Western Amazon (∼14.7 Ma), when the Western Amazon River was flowing northwards and disconnected from the Eastern Amazon. We show that dispersal events in the first half ofHypostomusevolution occurred from the Western Amazon into adjacent basins, initiating its Neotropical radiation. The ancestral preferred habitat consisted in small rivers with running waters, a predominant habitat in river headwaters. Because of strong niche conservatism in the early evolution ofHypostomus, we suggest that most of the out-of-Western-Amazon dispersal occurred via headwater captures. The radiation ofHypostomuswas further promoted by major reconfigurations of river basins, which opened dispersal opportunities into new drainages. Diversification in habitat preference coincided with colonization of basins already occupied by congenerics, indicative of niche shifts triggered by inter-specific competition and species coexistence. By analyzing the evolutionary history ofHypostomus, we show that Western Amazon was the main center of fish dispersal in the Neotropical Region from Middle Miocene to the present, supporting the cradle hypothesis of fish origination and dispersal.

We conducted a review of the Neotropical genus Acrobrycon. A previous study synonymized the two recognized species in the genus: A. ipanquianus, distributed from the western portion of the Amazon River to the northwest region of the La Plata River Basin, and A. tarijae, described from the Lipeo River in Bolivia. We revisited this result by collecting additional morphometric, meristic, and genetic data (COI mitochondrial gene) for 24 individuals distributed along La Plata River Basin in Argentina, and discussed our results in the context of multiple biogeographic process of isolation in this basin. Our results revealed a more complex history of diversification and geographic distribution across Acrobrycon species than previously suspected. We present new evidence that leads us to reconsider the validity of A. tarijae, which is distinguished from A. ipanquianus by the number of vertebrae (37-39 vs. 41-42), pleural ribs (12-13 vs 14), and unbranched anal-fin rays (v-vi vs. ii-iii). These results were supported by molecular analysis which showed a genetic divergence >4% between both nominal species, also, indicated two major genetic clusters of A. tarijae: the first group consisted of specimens from the Bermejo, Pilcomayo, Itiyuro and Juramento River Basins (northern Argentina), and the second group is composed by specimens from the southernmost basins, such as the Salí River in Tucumán and the Quinto River in the province of San Luis. These results suggest that the genetic structure may be a consequence of the geographical distance that separates the two groups and the type of drainage.

1. The distribution of genetic diversity across a species distribution range is rarely homogeneous, as the genetic structure among populations is related to the degree of isolation among them, such as isolation by distance, isolation by barrier, and isolation by environment. 2. Jenynsia lineata is a small viviparous fish that inhabits a wide range of habitats in South America. To decipher the isolation processes that drive population structuring in J. lineata, we analyzed 221 sequences of the mitochondrial cytochrome c oxidase I gene (COI), from 19 localities. Then, we examined the influence of the three most common types of isolation in order to explain the genetic variation found in this species. 3. Our results revealed a marked structuration, with three groups: (a) La Plata/ Desaguadero Rivers (sampling sites across Argentina, Uruguay, and Southern Brazil), (b) Central Argentina, and (c) Northern Argentina. A distance-based redundancy analysis, including the explanatory variables geographical distances, altitude, latitude, and basin, was able to explain up to 65% of the genetic structure. A variance partitioning analysis showed that the two most important variables underlying the structuration in J. lineata were altitude (isolation by environment) and type of basin (isolation by barrier). 4. Our results show that in this species, the processes of population diversification are complex and are not limited to a single mechanism. The processes that play a prominent role in this study could explain the high rate of diversity that characterizes freshwater fish species. And these processes in turn are the basis for possible speciation events., Instituto de Limnología "Dr. Raúl A. Ringuelet", Laboratorio de Sistemática y Biología Evolutiva

Distribution history of the widespread Neotropical genus Hypostomus was studied to shed light on the processes that shaped species diversity. We inferred a calibrated phylogeny, ancestral habitat preference, ancestral areas distribution, and the history of dispersal and vicariance events of this genus. The phylogenetic and distribution analyses indicate that Hypostomus species inhabiting La Plata Basin do not form a monophyletic clade, suggesting that several unrelated ancestral species colonized this basin in the Miocene. Dispersal to other rivers of La Plata Basin started about 8 Mya, followed by habitat shifts and an increased rate of cladogenesis. Amazonian Hypostomus species colonized La Plata Basin several times in the Middle Miocene, probably via the Upper Parana and the Paraguay rivers that acted as dispersal corridors. During the Miocene, La Plata Basin experienced marine incursions, and geomorphological and climatic changes that reconfigured its drainage pattern, driving dispersal and diversification of Hypostomus . The Miocene marine incursion was a strong barrier and its retraction triggered Hypostomus dispersal, increased speciation rate and ecological diversification. The timing of hydrogeological changes in La Plata Basin coincides well with Hypostomus cladogenetic events, indicating that the history of this basin has acted on the diversification of its biota., Facultad de Ciencias Naturales y Museo, Laboratorio de Sistemática y Biología Evolutiva

Lustosa-Costa, Silvia Yasmin, Bogan, Sergio, Queiroz, Luiz Jardim De, Montoya- Burgos, Juan I., Paracampo, Ariel, Maiztegui, Tomas, Cardoso, Yamila P. (2021): Distribution extension of Hypostomus uruguayensis (Siluriformes: Loricariidae) in Argentina and first record for Bolivia. Molecular, morphology and biogeography data. Zootaxa 4996 (1): 194-198, DOI: https://doi.org/10.11646/zootaxa.4996.1.12

El genero Rhamdella esta incluido en la familia Heptapteridae e integrado por seis especies distribuidas en Argentina, Brasil y Bolivia. Rhamdella aymarae fue descripta originalmente para la cuenca arreica del rio Itiyuro, en el norte de Salta, Argentina. Segun una propuesta filogenetica basada en caracteres morfologicos R. aymarae y R. rusbyi son el grupo hermano de las especies restantes de este genero. En este articulo citamos por primera vez la presencia de Rhamdella aymarae para la cuenca del rio Pilcomayo y extendemos su distribucion a la provincia de Santiago del Estero. Realizamos tambien una reconstruccion filogenetica basada en el marcador mitocondrial COI, la cual permitio corroborar la asignacion taxonomica de los ejemplares estudiados y demostro que el genero Rhamdella no es un grupo monofiletico. Esta contribucion muestra evidencia de que las relaciones entre los generos de la familia Heptapteridae requieren de estudios mas detallados para definir su clasificacion.

Fil: Cabrera, Maria Belen. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - La Plata. Instituto de Investigaciones Biotecnologicas. Universidad Nacional de San Martin. Instituto de Investigaciones Biotecnologicas; Argentina

Rivers and lake systems in the southern cone of South America have been widely influenced by historical glaciations, carrying important implications for the evolution of aquatic organisms, including prompting transitions between marine and freshwater habitats and by triggering hybridization among incipient species via waterway connectivity and stream capture events. Silverside fishes (Odontesthes) in the region comprise a radiation of 19 marine and freshwater species that have been hypothesized on the basis of morphological or mitochondrial DNA data to have either transitioned repeatedly into continental waters from the sea or colonized marine habitats following freshwater diversification. New double digest restriction-site associated DNA data presented here provide a robust framework to investigate the biogeographical history of and habitat transitions in Odontesthes. We show that Odontesthes silversides originally diversified in the Pacific but independently colonized the Atlantic three times, producing three independent marine-to-freshwater transitions. Our results also indicate recent introgression of marine mitochondrial haplotypes into two freshwater clades, with more recurring instances of hybridization among Atlantic- versus Pacific-slope species. In Pacific freshwater drainages, hybridization with a marine species appears to be geographically isolated and may be related to glaciation events. Substantial structural differences of estuarine gradients between these two geographical areas may have influenced the frequency, intensity and evolutionary effects of hybridization events.

Made available in DSpace on 2022-04-28T19:28:26Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-04-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung With 149 currently recognized species, Hypostomus is one of the most species-rich catfish genera in the world, widely distributed over most of the Neotropical region. To clarify the evolutionary history of this genus, we reconstructed a comprehensive phylogeny of Hypostomus based on four nuclear and two mitochondrial markers. A total of 206 specimens collected from the main Neotropical rivers were included in the present study. Combining morphology and a Bayesian multispecies coalescent (MSC) approach, we recovered 85 previously recognized species plus 23 putative new species, organized into 118 ‘clusters’. We presented the Cluster Credibility (CC) index that provides numerical support for every hypothesis of cluster delimitation, facilitating delimitation decisions. We then examined the correspondence between the morphologically identified species and their inter-specific COI barcode pairwise divergence. The mean COI barcode divergence between morphological sisters species was 1.3 ± 1.2%, and only in 11% of the comparisons the divergence was ≥2%. This indicates that the COI barcode threshold of 2% classically used to delimit fish species would seriously underestimate the number of species in Hypostomus, advocating for a taxon-specific COI-based inter-specific divergence threshold to be used only when approximations of species richness are needed. The phylogeny of the 108 Hypostomus species, together with 35 additional outgroup species, confirms the monophyly of the genus. Four well-supported main lineages were retrieved, hereinafter called super-groups: Hypostomus cochliodon, H. hemiurus, H. auroguttatus, and H. plecostomus super-groups. We present a compilation of diagnostic characters for each super-group. Our phylogeny lays the foundation for future studies on biogeography and on macroevolution to better understand the successful radiation of this Neotropical fish genus. Department of Genetics and Evolution University of Geneva, Quai Ernest-Ansermet 30 Laboratorio de Sistemática y Biología Evolutiva Facultad de Ciencias Naturales y Museo Universidad Nacional de La Plata, Paseo del Bosque S/N, B1900FWA, La Plata, Consejo Nacional de Investigaciones Científicas y Técnicas Museu de Ciências e Tecnologia Pontifícia Universidade Católica do Rio Grande do Sul, Av. Ipiranga 6681 Coordenação de Biodiversidade Programa de Coleções Científicas e Biológicas Instituto Nacional de Pesquisas da Amazônia, Av. André Araújo 2936 Museu de Biologia Professor Mello Leitão Instituto Nacional da Mata Atlântica, Av. José Ruschi 4 Department of Psychology University of Gothenburg, Haraldsgatan 1 Departamento de Morfologia Instituto de Biociências Universidade Estadual de São Paulo, Rua Professor Doutor Antonio Celso Wagner Zanin 250 Laboratório de Toxicologia Ambiental Laboratório de Genética Molecular de Microrganismos Fundação Oswaldo Cruz, Av. Brasil 4365 Departamento de Ciências do Mar Universidade Federal de São Paulo, Av. Doutor Carvalho de Mendonça 144 Department of Herpertology and Ichthyology Museum of Natural History of Geneva, Route de Malagnou 1 Departamento de Vertebrados Vista Museu Nacional do Rio de Janeiro/Universidade Federal do Rio de Janeiro, Quinta da Boa Departamento de Morfologia Instituto de Biociências Universidade Estadual de São Paulo, Rua Professor Doutor Antonio Celso Wagner Zanin 250 FAPESP: 2014/26508-3 FAPESP: 2016/09204-6 CNPq: 424668/2018-1 CNPq: CO; 307775/2018-6 FAPESP: FAPESP FAPESP: granted to CO CNPq: LJQ; 306054/2006-0 Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung: SNSF 3100A0-104005

Hypostomus commersoni Valenciennes 1836, Hypostomus cordovae (Günther 1880) and Hypostomus laplatae (Eigenmann 1907) have been little studied since their original descriptions. This study shows a comprehensive review of these species from the Lower La Plata Basin, including their taxonomic history, distribution, color patterns, morphology, and ecological and molecular phylogenetic data. Morphological and phylogenetic analyses based on D-loop sequences suggested that H. commersoni can be separated into two subclades, or subgroups. Based on these results and on the non-overlapping distribution range of the two subclades, we conclude that they represent two distinct species, thereby revalidating H. spiniger. The results also suggest that H. paranensis should be considered as species inquirenda and H. cordovae as valid species. This integrated approach provides key information for assessing the conservation status and biogeographic aspects of the genus Hypostomus in the Lower La Plata Basin. Fil: Cardoso, Yamila Paula. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Laboratorio de Sistemática y Biología Evolutiva; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina Fil: Brancolini, Florencia. Universidad Nacional de San Martín. Instituto de Investigación e Ingeniería Ambiental. - Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigación e Ingeniería Ambiental; Argentina Fil: Protogino, Lucila Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentina Fil: Paracampo, Ariel Hernán. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentina Fil: Bogan, Sergio. Universidad Maimónides; Argentina. Fundación de Historia Natural Félix de Azara; Argentina Fil: Posadas, Paula Elena. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Laboratorio de Sistemática y Biología Evolutiva; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina Fil: Montoya Burgos, Juan Ignacio. Universidad de Ginebra; Suiza

With an estimate of around 9,000 species, the Neotropical region hosts the greatest diversity of freshwater fishes of the world. Genetic surveys have the potential to unravel isolated and unique lineages and may result in the identification of undescribed species, accelerating the cataloguing of extant biodiversity. In this paper, molecular diversity within the valuable and widespread Neotropical genus Hoplias was assessed by means of DNA Barcoding. The geographic coverage spanned 40 degrees of latitude from French Guiana to Argentina. Our analyses revealed 22 mitochondrial lineages fully supported by means of Barcode Index Number, Automatic Barcode Gap Discovery and phylogenetic analyses. This mtDNA survey revealed the existence of 15 fully supported mitochondrial lineages within the once considered to be the continentally distributed H. malabaricus. Only four of them are currently described as valid species however, leaving 11 mitochondrial lineages currently “masked” within this species complex. Mean genetic divergence was 13.1%. Barcoding gap analysis discriminated 20 out of the 22 lineages tested. Phylogenetic analyses showed that all taxonomically recognized species form monophyletic groups. Hoplias malabaricus sensu stricto clustered within a large clade, excluding the representatives of the La Plata River Basin. In the H. lacerdae group, all species but H. curupira showed a cohesive match between taxonomic and molecular identification. Two different genetic lineages were recovered for H. aimara. Given the unexpected hidden mitochondrial diversity within H. malabaricus, the COI sequence composition of specimens from Suriname (the type locality), identified as H. malabaricus sensu stricto, is of major importance., Facultad de Ciencias Naturales y Museo

Austrolebias wichi, new species, is herein described from seasonal ponds of the Bermejo river basin in the Western Chacoan district in northwestern Argentina. This species was found in a single pond, a paleochannel of the Bermejo River, which is seriously disturbed by soybean plantations surrounding it. Despite intensive sampling in the area, this species was only registered in this pond where it was relatively scarce. Therefore, we consider this species as critically endangered. This species is the sister species of A. patriciae in our phylogenetic analyses and is similar, in a general external aspect, to A. varzeae and A. carvalhoi. It can be distinguished among the species of Austrolebias by its unique color pattern in males. Additionally, from A. varzeae by presenting a supraorbital band equal or longer than the infraorbital band (vs. shorter) and from A. patriciae by the convex dorsal profile of head (vs. concave). Further diagnostic characters and additional comments on its ecology and reproduction are provided., Laboratorio de Sistemática y Biología Evolutiva, Instituto de Limnología "Dr. Raúl A. Ringuelet"

San Luis province presents arheic and endorheic basins that are poorly understood in terms of their ichthyological composition. The samples taken recently from the main basins of this province have yielded data of undisputed biogeographic value for the knowledge of the ichthyofauna of San Luis, as well as for drawing up lists of species for watersheds with poor or absent previous records. Here, we cite Jenynsia multidentata from the Desaguadero and Bebedero rivers, Cnesterodon decemmaculatus for Chorrillos River, and Oligosarcus jenynsii for Luján, Quines and Quinto rivers. We add five taxa to the Nogolí River that have not been previously reported. We also present for the first time a list of the fish fauna from the Conlara, Luján and Quines basins. Our results provide 34 new records of freshwater fish distribution., Facultad de Ciencias Naturales y Museo

Squirrels have been traded in the pet market for several decades, and numerous species have established in the wild. The Asiatic species Callosciurus erythraeus and Callosciurus finlaysonii have been introduced into other parts of Asia, in Europe and South America. In this study, (1) we conducted a genetic characterization of C. erythraeus introduced into Argentina and compared them with native and introduced populations in Asia, and (2) we analyzed genetic variation among the four invasion foci in Argentina in order to corroborate that the pathway of invasion was a single introduction event in the country and subsequent translocations. We analyzed mitochondrial (cytochrome b, Cyt b; cytochrome oxidase c subunit I, COI and D-loop) and nuclear (recombination activating gene I, RAGI) DNA markers using the classical method (DNA barcoding gap analysis) and also the Automatic Barcode Gap Discovery method (ABGD). The markers D-loop, COI, and RAG1 indicated that the introduced squirrels from the different invasion foci formed a monophyletic group that, together with only one haplotype for the D-loop and COI markers, supported the hypothesis of one introduction event into Argentina followed by subsequent translocations. Unexpectedly, sequences from squirrels captured in Argentina were more related to C. finlaysonii than to C. erythraeus for D-loop and Cyt b markers. However, intraspecific variation among sequences of C. erythraeus belonging to different subspecies or collected in different regions was large and comparable with the distance to the sequences from Argentina. The ABGD method also indicated large genetic variability within C. erythraeus and close proximity between squirrels from Argentina and C. finlaysonii. The complex taxonomy of Callosciurus, as occurs with the sister species C. erythraeus and C. finlaysonii, requires a thorough systematic revision. A simultaneous analysis of diagnostic morphological characters and genetic markers is needed and will provide new insight regarding the worldwide invasion of Asiatic squirrels., Centro Regional de Estudios Genómicos

Trichomycterus barbouri (Eigenmann, 1911) es una especie poco conocida que presenta una distribucion discontinua desde el rio Beni en Bolivia, cuenca del rio Amazonas, hasta el noroeste y centro de la Argentina, en la cuenca del Rio de la Plata. Se describen nuevos registros de T. barbouri en tres rios de la llanura chacopampeana, dos en la provincia de Santiago del Estero y uno en el rio Cuarto, en la provincia de Cordoba. Estos reportes permiten ampliar el area de distribucion conocida para la especie, extendiendo mas al sur su limite austral. Trichomycterus barbouri es la unica especie del genero que esta ampliamente distribuida en la llanura chaco-pampeana

Ctenomys (tuco-tuco) is the most numerous genus of South American subterranean rodents and one of the most genetically diverse clades of mammals known. In particular, the genus constitutes a very interesting model for evolutionary studies of genetic divergence and conservation. Ctenomys magellanicus is the southernmost species of the group and the only one living in Isla Grande de Tierra del Fuego (Argentina). This species presents two chromosomal forms (Cm34 and Cm36) fragmented into demes distributed from the north region (steppe) to the south region (ecotone) of the island, respectively; no hybrids or overlapping areas were detected. To study the historical demography and the spatial genetic structure of the C. magellanicus population we used mitochondrial DNA (mtDNA) (D-loop and cytochrome b) and microsatellite loci. Nine mtDNA haplotypes were identified, three of them belonging to the north and the other six to the south. Shared haplotypes between regions were not detected. mtDNA and microsatellite genotypes showed a marked pattern of population structure with low values of genetic flow between regions. The south is made up of small populations or isolated demes making up an endogamic metapopulation with unique alleles and haplotypes. Also, the results suggest a northward expansion process starting from an ancestral haplotype from the south. That population might have lived at a refuge through the adverse Pleistocene environmental conditions that took place at Tierra del Fuego. Results of this study are relevant to the conservation of C. magellanicus, suggesting that each region (north and south) might be considered as an Evolutionarily Significant Unit.

Despite recent taxonomic evaluations of Mephitidae and North American hog-nosed skunks, southern South American species of Conepatus have not been thoroughly examined in a systematic context. Conepatus chinga and Conepatus humboldtii were described more than 150 years ago, based on external characters such as hair coloration and size. Although historically recognized as valid species, to date no detailed systematic analysis has been performed for either of these taxa. Herein, we evaluated the taxonomic status of C. chinga and C. humboldtii within the southern part of South America using geometric morphometrics of the skull and mandible, mitochondrial DNA analysis using the cytochrome b and cytochrome oxidase c subunit I genes, and also control region and pelage pattern variation. We failed to find morphological (skull shape and pelage coloration patterns) or molecular differences between these two species; thus, we considered that the specimens assigned to C. chinga and C. humboldtii belong to the same species. Our results indicate that environmental variation seems to be responsible for shape and size variation in Conepatus skulls from southern South America. © 2013 The Linnean Society of London

Neotropical freshwater fishes have reached an unrivalled diversity, organized into several areas of endemism, yet the underlying processes are still largely unknown. The topographical and ecological characteristics of the Guyanas Region make it an ideal area of endemism in which to investigate the forces that have shaped this great diversity. This region is thought to be inhabited by species descending from Amazonian ancestors, which would have used two documented routes that, however, hardly explain the entrance of species adapted to running waters. Here, we investigate the evolutionary history of Pseudancistrus brevispinis, a catfish endemic to this region and exclusively found in running waters, thus making it an ideal model for investigating colonization routes and dispersal in such habitats. Our analyses, based on mitochondrial and nuclear markers, revealed an unexpected diversity consisting of six monophyletic lineages within P. brevispinis, showing a disjoint distribution pattern. The lineages endemic to Guyanas coastal rivers form a monophyletic group that originated via an ancestral colonization event from the Amazon basin. Evidence given favours a colonization pathway through river capture between an Amazonian tributary and the Upper Maroni River. Population genetic analyses of the most widespread species indicate that subsequent dispersal among Guyanas coastal rivers occurred principally by temporary connections between adjacent rivers during periods of lower sea level, yet instances of dispersal via interbasin river captures are not excluded. During high sea level intervals, the isolated populations would have diverged leading to the observed allopatric species. This evolutionary process is named the sea level fluctuation (SLF) hypothesis of diversification.

Within the Loricariidae, the genus Hypostomus is one of the most diversified freshwater catfish groups. Using new se-quence data from the mitochondrial Control Region (D-loop) we examined the phylogeny of this genus. Our phylogeneticanalyses suggest that, in the Paraná river basin, species diversity in the genus Hypostomus has been shaped by two proc-esses: 1) by inter-basin diversification, generating groups of species that inhabit different basins, as a result of dispersalevents; and 2) via intra-basin speciation as a result of basin fragmentation due to past marine transgressions, which pro-duced groups of species within a basin. Using the D-loop as a molecular clock, each event of diversification was datedand linked with documented hydrological events or sea level changes. We also assessed the possible dispersal routes be-tween the Paraná and Uruguay rivers, in addition to the obvious dispersal route via the Río de la Plata estuary. Finally, wedescribe a new species of Hypostomus inhabiting Middle Paraná river, Hypostomus arecuta n. sp. This species can be sep-arated from all other Hypostomus by having light roundish dots on a darker background and by number of premaxillary/ dentary teeth.

The present work extends to Argentina the distribution of Hypostomus aspilogaster originally described from Uruguay River in southern Brazil. The examined specimens were sampled in the stream Mandisoví Grande, affluent of Uruguay River in Entre Ríos province, and in Punta Lara, from Río de la Plata basin, in Buenos Aires province, Argentina. This represents the first country record for this species., Facultad de Ciencias Naturales y Museo