Novel Tools for Conservation Genomics: Comparing Two High-Throughput Approaches for SNP Discovery in the Transcriptome of the European Hake

The growing accessibility to genomic resources using next-generation sequencing (NGS) technologies has revolutionized the application of molecular genetic tools to ecology and evolutionary studies in non-model organisms. Here we present the case study of the European hake (Merluccius merluccius), one of the most important demersal resources of European fisheries. Two sequencing platforms, the Roche 454 FLX (454) and the Illumina Genome Analyzer (GAII), were used for Single Nucleotide Polymorphisms (SNPs) discovery in the hake muscle transcriptome. De novo transcriptome assembly into unique contigs, annotation, and in silico SNP detection were carried out in parallel for 454 and GAII sequence data. High-throughput genotyping using the Illumina GoldenGate assay was performed for validating 1,536 putative SNPs. Validation results were analysed to compare the performances of 454 and GAII methods and to evaluate the role of several variables (e.g. sequencing depth, intron-exon structure, sequence quality and annotation). Despite well-known differences in sequence length and throughput, the two approaches showed similar assay conversion rates (approximately 43%) and percentages of polymorphic loci (67.5% and 63.3% for GAII and 454, respectively). Both NGS platforms therefore demonstrated to be suitable for large scale identification of SNPs in transcribed regions of non-model species, although the lack of a reference genome profoundly affects the genotyping success rate. The overall efficiency, however, can be improved using strict quality and filtering criteria for SNP selection (sequence quality, intron-exon structure, target region score)

Assessing patterns of hybridization between North Atlantic eels using diagnostic single-nucleotide polymorphisms

The two North Atlantic eel species, the European eel (Anguilla anguilla) and the American eel (Anguilla rostrata), spawn in partial sympatry in the Sargasso Sea, providing ample opportunity to interbreed. In this study, we used a RAD (Restriction site Associated DNA) sequencing approach to identify species-specific diagnostic single-nucleotide polymorphisms (SNPs) and design a low-density array that combined with screening of a diagnostic mitochondrial DNA marker. Eels from Iceland (N=159) and from the neighboring Faroe Islands (N=29) were genotyped, along with 94 larvae (49 European and 45 American eel) collected in the Sargasso Sea. Our SNP survey showed that the majority of Icelandic eels are pure European eels but there is also an important contribution of individuals of admixed ancestry (10.7%). Although most of the hybrids were identified as F1 hybrids from European eel female × American eel male crosses, backcrosses were also detected, including a first-generation backcross (F1 hybrid × pure European eel) and three individuals identified as second-generation backcrosses originating from American eel × F1 hybrid backcrosses interbreeding with pure European eels. In comparison, no hybrids were observed in the Faroe Islands, the closest bodies of land to Iceland. It is possible that hybrids show an intermediate migratory behaviour between the two parental species that ultimately brings hybrid larvae to the shores of Iceland, situated roughly halfway between the Sargasso Sea and Europe. Only two hybrids were observed among Sargasso Sea larvae, both backcrosses, but no F1 hybrids, that points to temporal variation in the occurrence of hybridization

Population Structure of Lutjanus purpureus (Lutjanidae - Perciformes) on the Brazilian coast: further existence evidence of a single species of red snapper in the western Atlantic

The present study focus on the mitochondrial control region to investigate phylogeographic patterns and population structure in Lutjanus purpureus, and to evaluate the genetic similarity between L. purpureus and L. campechanus. For the initial analysis, 810 base pairs sequence from control region were obtained from 239 specimens of L. purpureus collected from four localities off the Brazilian coast. The results revealed the presence of a single panmictic population characterized by high values of genetic diversity. The 299 base pairs hypervariable portion were used for the combined analysis of L. purpureus and L. campechanus, being 275 haplotypes identified in the 414 specimens. Phylogenetic tree and haplotype network did not indicate phylogeographic substructuring between the two species, but rather an intense intermingling of individuals. Considering their marked morphological similarity, the molecular data presented here indicate that only one species of red snapper exists in the western Atlantic.<br>Para o presente estudo utilizou-se a região controle mitocondrial para investigar os padrões filogeográficos e a estrutura populacional de Lutjanus purpureus e para avaliar a similaridade genética entre L. purpureus e L. campechanus. Para a análise inicial foram obtidas sequências de 810 pares de bases (pb) da região controle para 239 espécimes de L. purpureus de quatro localidades da costa brasileira. Os resultados mostraram a presença de uma população panmítica caracterizada por altos valores de diversidade genética. Utilizou-se um segmento de 299 pb da porção hipervariável para comparar L. purpureus e L. campechanus. Dos 414 indivíduos analisados foram identificados 275 haplótipos. A árvore filogenética e a rede de haplótipos não mostraram subestruturação filogeográfica entre as duas espécies, com intensa mistura de indivíduos. Considerando a grande similaridade morfológica, os dados moleculares apresentados, aqui indicam que apenas uma única espécie de pargo vermelho existe ao longo do atlântico ocidental