Displacement of native Patagonian freshwater silverside populations (Odontesthes hatcheri, Atherinopsidae) by introgressive hybridization with introduced O. bonariensis

Appraising the Genetic Makeup of an Allochthonous Southern Pike Population: An Opportunity to Predict the Evolution of Introgressive Hybridization in Isolated Populations?

Biological invasions are a major threat to the conservation of biodiversity, as invasive species affect native biota through competition, predation, pathogen introduction, habitat alteration, and hybridisation. The present study focuses on a southern pike population, Esox cisalpinus (Teleostei: Esocidae), that has been introduced outside the species' native range. Using microsatellite markers, this study's objective was to gather baseline genetic information and assess the presence of hybrids between this species and E. lucius in the introduced population. The resulting estimates of genetic diversity and effective population size are comparable to those observed in the species' native range. Although different methods yield contrasting and uncertain evidence regarding introgressive hybridization, the presence of late-generation hybrids cannot be completely ruled out. Large numbers of breeders as well as multiple introductions of genetically divergent cohorts and introgressive hybridisation may explain the high genetic diversity of this recently introduced southern pike population. The present study issues a warning that the conservation of southern pike' introgressive hybridisation between northern and southern pike might be underestimated. The genetic information gathered herein may unravel the origin, number of introduction events, and evolutionary trajectory of the introduced population. This information may help us understand the evolution of introgressive hybridisation in the southern pike's native areas.

Morphologic and genetic variation within a relict Andean catfish, Hatcheria macraei , and its relationship with Trichomycterus areolatus and Bullockia maldonadoi (Siluriformes: Trichomycteridae)

The South American siluriform fishes are found primarily in the Neotropical region, north and east of the Colorado River of Argentina, with a few relict species distributed southward and westward on both sides of the Andes Mountains. Three of these, the closely related trichomycterids Hatcheria macraei, Trichomycterus areolatus and Bullockia maldonadoi, have been subject to historical taxonomic and nomenclatural arrangements. Here, we amplify a 652-bp fragment of COI mtDNA from 55 H. macraei individuals and use publicly available Cytb mtDNA sequences of the three taxa to assess their relationship, genetic variation and haplotype distribution in relation to hydrographic basins. In addition, we extend a recent morphometric study on H. macraei by analyzing body shape in 447 individuals collected from 24 populations across their entire cis-Andean distribution. We identified some lineages previously assigned to T. areolatus that show a closer relationship to either B. maldonadoi or H. macraei, revealing new boundaries to their currently known trans-Andean distribution. We found a great morphologic variation among H. macraei populations and a high genetic variation in H. macraei, T. areolatus and B. maldonadoi associated with river basins. We highlight further integrative studies are needed to enhance our knowledge of the southern Andean trichomycterid diversity.

Hybridization is strongly constrained by salinity during secondary contact between silverside fishes (Odontesthes, Atheriniformes)

This study investigates a contact zone between two silverside fish species (marine Odontesthes argentinensis and freshwater O. bonariensis) in the estuarine Mar Chiquita lagoon along the Atlantic coast in Argentina (MChL), in which intermediate morphs had been reported. It has been suggested that admixture and introgression occur in MChL between these two species, but direct genetic evidence is lacking. Leveraging samples collected over several years (n = 676), we document the spatial distribution of both species and intermediate morphs within this habitat and collect landmark-based morphometric and multilocus genetic data (9876 loci for n = 110 individuals) to test the hypothesis of hybridization. Our analysis unambiguously characterizes intermediate morphs as F1 or F2 hybrids. We show that the low frequency of hybrid individuals in MChL may be explained by uneven abundance of parental species, which in turn are strongly affected by water salinity, limiting the size of the contact zone. Although hybrids seem to be fertile, their fitness may be reduced by external and intrinsic factors that may limit their success and suggest that this is an unstable hybrid zone. Genetic distinctiveness of both parental species is strongly supported by genome-wide data, explaining a known pattern of mitonuclear discordance as a consequence of hybridization followed by mitochondrial introgression. A clear signature of population genetic structure was detected in O. argentinensis, distinguishing MChL residents from marine populations of this species, that also was supported by distinctive morphometric features among these groups. Previous hypotheses of speciation in these fishes are discussed in the light of the new findings.

Mitochondrial genome architecture and phylogenetic relationships of Odontesthes argentinensis within Atherinomorpha

Silversides are a widely distributed group across South America, with several species occupying marine, freshwater and estuarine environments. Several authors suggest main transitions among these environments took place during Pleistocene, and were accompanied with rapid speciation events. This scenario produced very limited genetic and morphological differentiation among the species. However, most of these surveys have an incomplete coverage of the intraspecific genetic diversity of the taxa studied. In this work, we reconstructed six mitochondrial genomes of O. argentinensis using transcriptomic data, and used them-in combination with several nuclear markers retrieved from the same transcriptomes-to explore the effect of additional coverage of intraspecific diversity of this species in phylogenetic reconstructions. Unlike previous works, phylogenetic analyses failed to identify O. argentinensis as a monophyletic group in relation with closely related taxa. Our results suggest that several species of the genus, especially those related to O. argentinensis, need further taxonomic revision.

Tools for Evolutionary and Genetic Analysis (TEGA): A new platform for the management of molecular and environmental data

Population genetics studies the distributions and changes in population allele frequencies in response to processes, such as mutation, natural selection, gene flow, and genetic drift. Researchers daily manage genetic, biological, and environmental data of the samples, storing them in text files or spreadsheets, which makes it difficult to maintain consistency and traceability. Here we present TEGA, a WEB-based stand-alone software developed for the easy analysis and management of population genetics data. It was designed to: 1) facilitate data management, 2) provide a way to execute the analysis procedures, and 3) supply a means to publish data, procedures, and results. TEGA is distributed under the GNU AGPL v3 license. The documentation, source code, and screenshots are available at https://github.com/darioelias/TEGA. In addition, we present Rabid Fish, the first implementation of TEGA in the Genetics Labortory of the Faculty of Humanities and Sciences at the National University of the Litoral, where research focuses on population genetics studies applied to non-model organisms.

Inferring boundaries among fish species of the new world silversides (Atherinopsidae; genus Odontesthes): new evidences of incipient speciation between marine and brackish populations of Odontesthes argentinensis

Species of new world silversides (Actinopterygii; Atherinopsidae; genus Odontesthes) possess economic relevance, biological interest and ecological importance. In the present paper we: (A) investigate the molecular diversity in marine species of Odontesthes from the South West Atlantic Ocean (SWAO), and analyse their interspecific relationships and divergence by means of DNA Barcoding, including its freshwater congeners, as well. (B) Explore the suitability of DNA Barcoding to analyse the diversity and distribution of haplotypes in Odontesthes argentinensis, the only well documented marine species from the SWAO that exhibit putative estuarine and marine populations. Molecular analysis revealed 100% of agreement between morphological identification and molecular identity. Odontesthes argentinensis, Odontesthes platensis, Odontesthes smitti, Odontesthes nigricans and Odontesthes incisa were assigned to five different barcode index numbers (BINs). Maximum-likelihood analysis showed that all marine species of Odontesthes clustered separately in a unique monophyletic phylogroup, comprising five well defined haplogroups, with genetic divergence between groups ranging from 2.75 to 7.11%. The genetic analysis including freshwater congeners showed that O. incisa clustered alone occupying a basal position. The F_st pairwise comparisons within O. argentinensis support the existence of three population groups: one conformed by Mar Chiquita Lagoon (MCh) specimens, and the others by Mar del Plata/Mar Chiquita coast and San Blas Bay coastal specimens, respectively. The AMOVA showed significant overall differentiation (F_st = 0.238; p = 0.00001) for the entire data set. The previous/present evidence is discussed, and strongly suggests that incipient speciation is occurring in O. argentinensis argentinean populations, and specimens from MCh would be considered at present as the leading candidate of a marine to freshwater incipient speciation event.