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.
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.
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.
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.
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.
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.
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.
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