Evolutionary History and Whole Genome Sequence of Pejerrey (Odontesthes bonariensis): New insights into Sex Determination in Fishes
Open AccessRecent reduction in the cost of DNA sequencing has enabled unprecedented opportunities to obtain genomic resources for non-model organisms. The main product of this dissertation is the whole-genome sequence of the pejerrey, Odontesthes bonariensis (Atherinopsidae, Atheriniformes, Teleostei), a freshwater species with high value for aquaculture and recreational fisheries and an emerging model system to study the evolution of sex determination in vertebrates. Genomic resources have the potential to quickly expand scientific knowledge by providing direct access to big genetic datasets. This dissertation introduces the first version of the pejerrey genome assembly and annotation based on a shotgun sequencing approach using the Illumina platform of three genomic libraries with different insert sizes. The pejerrey is one of the few fish species known to undergo temperature-dependent sex determination (TSD). Although a major sex-determining gene has been identified recently in several species of Odontesthes, the temperature at which pejerrey eggs or larvae are exposed to during the first weeks of life is a major factor determining phenotypic sex, overriding the effect of the genotype. A direct application of the newly assembled and annotated pejerrey genome provides insight into the regulatory network affecting TSD in fishes. This study reveals potential mechanisms to explain how genetic, environmental, and chemical factors interact in a sex-determining network during key developmental stages of pejerrey. A new perspective is presented on the role of steroid hormones affecting expression of a conserved genetic toolkit shared by species with different sex determination systems.To enhance the comparative value of the new genomic resources and place the pejerrey in a well-resolved phylogenetic context, this dissertation provides a new phylogenetic hypothesis based on analyses of new sequence data collected for eight molecular markers for a representative sample of 103 atheriniform species, covering 2/3 of the genera in this order. The new phylogenetic hypothesis is used to recommend some changes in the current classification and is calibrated with six carefully chosen fossil taxa to provide an explicit timeframe for the diversification of this group. Ancestral habitat reconstructions are inferred to test biogeographic hypotheses to explain current distribution of marine and freshwater taxa. Post-Gondwanan divergence times among families are consistent with extensive marine dispersal along the margins of continents with repeated invasion of freshwater habitats.
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Campanella_gwu_0075A_12476.pdf | 2018-01-16 | Open Access |
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