RESUMO
Salmonid fishes are cold water piscivores with a native distribution spanning nearly the entire temperate and subarctic northern hemisphere. Trout in the genus Oncorhynchus are the most widespread salmonid fishes and are among the most important fish species in the world, due to their extensive use in aquaculture and valuable fisheries. Trout that inhabit northwestern Mexico are the southernmost native salmonid populations in the world, and the least studied in North America. They are unfortunately also facing threats to their continued existence. Previous work has described one endemic species, the Mexican golden trout (O. chrysogaster), and one endemic subspecies, Nelson's trout (O. mykiss nelsoni), in Mexico, but previous work indicated that there is vastly more biodiversity in this group than formally described. Here we conducted a comprehensive genetic analysis of this important group of fishes using novel genetic markers and techniques to elucidate the biodiversity of trout inhabiting northwestern Mexico, examine genetic population structure of Mexican trout and their relationships to other species of Pacific trout, and measure introgression from non-native hatchery rainbow trout. We confirmed substantial genetic diversity and extremely strong genetic differentiation present in the Mexican trout complex, not only between basins but also between some locations within basins, with at least four species-level taxa present. We also revealed significant divergence between Mexican trout and other trout species and found that introgression from non-native rainbow trout is present but limited, and that the genetic integrity of native trout is still maintained in most locations. This information will help to guide effective conservation strategies for this important group of fishes.
Assuntos
Genética Populacional , Truta/genética , Animais , Análise por Conglomerados , Frequência do Gene , Variação Genética , Geografia , Heterozigoto , México , Repetições de Microssatélites , Polimorfismo de Nucleotídeo Único , Truta/classificaçãoRESUMO
Levels and patterns of mitochondrial DNA (mtDNA) variation were examined to investigate the population structure and possible routes of postglacial recolonization of the world's northernmost native populations of brook trout (Salvelinus fontinalis), which are found in Labrador, Canada. We analyzed the sequence diversity of a 1960-bp portion of the mitochondrial genome (NADH dehydrogenase 1 gene and part of cytochrome oxidase 1) of 126 fish from 32 lakes distributed throughout seven regions of northeastern Canada. These populations were found to have low levels of mtDNA diversity, a characteristic trait of populations at northern extremes, with significant structuring at the level of the watershed. Upon comparison of northeastern brook trout sequences to the publicly available brook trout whole mitochondrial genome (GenBank AF154850), we infer that the GenBank sequence is from a fish whose mtDNA has recombined with that of Arctic charr (S. alpinus). The haplotype distribution provides evidence of two different postglacial founding groups contributing to present-day brook trout populations in the northernmost part of their range; the evolution of the majority of the haplotypes coincides with the timing of glacier retreat from Labrador. Our results exemplify the strong influence that historical processes such as glaciations have had on shaping the current genetic structure of northern species such as the brook trout.
Assuntos
Ecossistema , Variação Genética , Genoma Mitocondrial/genética , Camada de Gelo , Nucleotídeos/genética , Recombinação Genética , Truta/genética , Substituição de Aminoácidos/genética , Animais , Sequência de Bases , Canadá , Complexo IV da Cadeia de Transporte de Elétrons/genética , Água Doce , Genética Populacional , Geografia , Haplótipos/genética , Dados de Sequência Molecular , NADH Desidrogenase/genética , Fases de Leitura Aberta/genética , Filogenia , Dinâmica Populacional , Tamanho da Amostra , Alinhamento de SequênciaRESUMO
This study explored the use of the gene encoding the ß subunit of the major histocompatibility (MH) receptor as a population marker in Arctic charr Salvelinus alpinus. The use of this polymorphic marker allowed differentiation of the S. alpinus lineages previously defined using mitochondrial DNA (mtDNA) but also allowed differentiation between the populations studied within those lineages. The majority of the variation observed here occurred prior to the last glaciation event. Nevertheless, all S. alpinus populations were differentiated using both MH Class II ß (mh-IIß) sequences and allelic frequencies. The fact that all the populations studied presented high rates of non-synonymous: synonymous substitutions and high levels of interpopulation variation, suggested mh-IIß as an ideal marker to assess differentiation among S. alpinus populations in ways that may represent divergence both by genetic drift and natural adaptation to the local environment.
Assuntos
Genes MHC da Classe II/genética , Polimorfismo Genético , Truta/genética , Sequência de Aminoácidos , Animais , DNA Mitocondrial/genética , Frequência do Gene , Variação Genética , Genética Populacional , Dados de Sequência Molecular , Filogenia , Alinhamento de Sequência , Truta/classificaçãoRESUMO
The aim of this study was to analyze the morphological variation of brown trout (Salmo trutta) in the Duero basin, an Atlantic river basin in the Iberian Peninsula, where a spatial segregation of two divergent lineages was previously reported, based on isozyme, microsatellite and mtDNA data. In these studies, two divergent pure regions (Pisuerga and Lower-course) and several hybrid populations between them were identified. Morphological variation was evaluated in 11 populations representative of the genetic differentiation previously observed in the Duero basin, using multivariate analysis on 12 morphometric and 4 meristic traits. A large differentiation between populations was observed (interpopulation component of variance: 41.8 percent), similar to that previously detected with allozymes and microsatellites. Morphometric differentiation was also reflected by the high classification success of pure and hybrid individuals to their respective populations, using multivariate discriminant functions (94.1 percent and 79.0 percent, respectively). All multivariate and clustering analyses performed demonstrated a strong differentiation between the pure regions. The hybrid populations, though showing large differentiation among them, evidenced an intermediate position between the pure samples. Head and body shape traits were the most discriminant among the morphometric characters, while pectoral rays and gillrakers were the most discriminant among the meristic traits. These results confirmed the high divergence of the brown trout from the Duero basin and suggest some traits on which selection could be acting to explain the spatial segregation observed.