Verónica Gutiérrez

Promiscuous speciation with gene flow in silverside fish genus Odontesthes (Atheriniformes, Atherinopsidae) from south western Atlantic Ocean basins.

The present paper integrates phylogenetic and population genetics analyses based on mitochondrial and nuclear molecular markers in silversides, genus Odontesthes, from a non-sampled area in the SW Atlantic Ocean to address species discrimination and to define Managements Units for sustainable conservation. All phylogenetic analyses based on the COI mitochondrial gene were consistent to support the monophyly of the genus Odontesthes and to include O. argentinensis, O. perugiae-humensis and some O. bonariensis haplotypes in a basal polytomy conforming a major derivative clade. Microsatellites data revealed somewhat higher genetic variability values in the O. argentinensis-perugia populations than in O. bonariensis and O. perugia-humensis taxa. Contrasting population genetics structuring emerged from mitochondrial and microsatellites analyses in these taxa. Whereas mitochondrial data supported two major groups (O. argentinensis-perugia-humensis vs. O. bonariensis-perugiae-humensis populations), microsatellite data detected three major genetic entities represented by O. bonariensis, O. perugiae-humensis and an admixture of populations belonging to O. argentinensis-perugiae respectively. Therefore, the star COI polytomy in the tree topology involving these taxa could be interpreted by several hypothetic scenarios such as the existence of shared ancestral polymorphisms, incomplete lineage sorting in a radiating speciation process and/or reticulation events. Present findings support that promiscuous and recent contact between incipient species sharing asymmetric gene flow exchanges, blurs taxa boundaries yielding complicated taxonomy and Management Units delimitation in silverside genus Odontesthes from SW Atlantic Ocean basins.

Species complex delimitation and patterns of population structure at different geographic scales in Neotropical silver catfish (Rhamdia: Heptapteridae)

The Neotropical catfish genus Rhamdia inhabits rivers and lakes from Mexico to Argentina. Previous studies have found that the taxonomy of this genus, as well as that of R. quelen, remains controversial. The present study aims to contribute to the understanding of Rhamdia systematics by delimiting putative species, and to elucidate the pattern of genetic differentiation of Rhamdia at different geographic levels within the cis-andean region. Species boundaries were defined by Generalized Mixed Yule Coalescent and Automatic Barcode Gap Discovery methods, and by phylogenetic analyses of cytochrome b (cyt b) sequences. Moreover, we performed phylogeographic analyses based on cyt b sequences and microsatellite markers. Patterns of differentiation were analyzed at three nested geographic levels: in the main cis-andean basins (macrogeographic scale); in the second major Neotropical basin system (mesogeographic scale), which encompasses La Plata basin, Patos-Merin basin, and the coastal lagoons draining to SW Atlantic Ocean; and finally, in the three most important coastal lagoons for artisanal fisheries in Uruguay (microgeographic scale). Sixteen species were found within Rhamdia, divided into two clades (cis- and trans-andean clades), each composed of eight putative species. Cis-andean Rhamdia species have probably diverged due to vicariance events occurring between and within basins since late Miocene-Pleistocene. Microgeographic scale analysis based on cyt b and microsatellite data revealed a high genetic structuring among the studied coastal lagoons. Mitochondrial and microsatellite markers enabled to identify three different populations, corresponding to the three coastal lagoons analyzed, which would have diverged recently and could be considered as different Management Units.

Characterization of partial Hox gene sequences in annual fish of the subfamily Cynolebiatinae (Cyprinodontiformes, Rivulidae)

Hox genes encode a family of transcription factors implicated in conferring regional identity along the anteroposterior axis in developing animal embryos. These genes are organized in genomic clusters, expressed collinearly and highly conserved in vertebrates. Among teleost, South American annual killifishes of the Cynolebiatinae subfamily represent an excellent model in development studies because their embryos are capable of undergoing reversible developmental arrest (diapause) at three well-defined morphological stages. They are also an excellent model for evolutionary studies due to the high rates of mutation of their mitochondrial genome, their karyotypic divergence and their morphological variability. In this study, three partial homeobox sequences were isolated from different species of the Cynolebiatinae subfamily. Phylogenetic analyses and sequence comparisons revealed that they belong to the anterior Hox complex group, specifically to paralogue groups 1 and 3. This is the first time that partial Hox genes have been described in species of the Cynolebiatinae subfamily.

Isolation and characterization of eight microsatellites from the South American annual fish Austrolebias charrua

Austrolebiascharrua is an endemic annual fish of Uruguay and Brazil. Eight microsatellite markers were developed in order to clarify its population genetic structure. All of them constitute polymorphic loci. The number of observed alleles ranged from 6 to 14, the mean expected heterozygosity from 0.65 to 0.92 and the Shannon-Wiener Diversity Indices from 1.31 to 2.39. This study is the first report of microsatellites in annual killifish and they will be a helpful tool to implement conservation strategies in this endangered species.