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L'introgression de l'ADN mitochondrial chez l'omble de fontaine, Salvelinus fontinalis, dans l'est du Québec: caractérisation, distribution géographique et signification évolutive = Mitochondrial DNA introgression in brook char, Salvelinus fontinalis, from Eastern Quebec : characterization, geographical distribution and evolutionary significance.

Glémet, Hélène Cécile (1997). L'introgression de l'ADN mitochondrial chez l'omble de fontaine, Salvelinus fontinalis, dans l'est du Québec: caractérisation, distribution géographique et signification évolutive = Mitochondrial DNA introgression in brook char, Salvelinus fontinalis, from Eastern Quebec : characterization, geographical distribution and evolutionary significance. Thèse. Québec, Université du Québec, Institut national de la recherche scientifique, Doctorat en sciences de l'eau, 127 p.

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Résumé

A population of brook char (Salvelinus fontinalis) from lac Alain situated in the Portneuf river system of eastem Quebec was discovered to be introgressed with the mitochondrial DNA (mtDNA) of the more northerly occurring Arctic char (S. alpinus). Individuals from this population resembled typièal brook char based on allozyme analysis and several morphological and meristic characteristics. Based on RFLP analysis, all individuals were fixed for the Arctic char mtDNA haplotype, despite the present absence of Arctic char in the watershed. The geographical extent of mtDNA introgression was determined by the genetic assessment of populations from both within the Portneuf river system, as well as from neighboring watersheds. Introgressed populations were restricted to lakes occurring along one branch of the Portneuf river system, otherwise, elsewhere in the watershed. populations were that of geneticaIly pure brook char. AlI populations tested from neighboring drainages were aIso geneticaIly pure brook char. It is probable that a combination of biogeographical conditions coupled with positive selection for mtDNA introgression led to the present-day distribution of introgressed S.fontinalis. The evolutionary importance of mtDNA introgression was investigated by using an experimental approach which involved the assessment of physiological performance of both introgressed and non-introgressed brook char at different levels of biological organization. This approach aIlowed any physiologicaI advantage imparted by the intDNA of an arctic species (via the proteins it encodes), to be identified in introgressed brook char. As a tirst step of this approach, the catalytic efficiency, as weil as the thermal sensitivity of cytochrome C oxidase (CCO), an enzyme partly encoded by mtDNA was determined in red muscle mitochondria DifferentiaI responses in catalytic efficiency and QIO values between char groups were observed for CCO and suggest an influence by the mitochondriaI genome on enzyme structure and function. Based on these enzymatic differences, the prediction at the sub-cellular level of mitochondrial function, was that introgressed S. fontinalis would have mitochondria which function better al cold temperatures. Indeed, introgressed S. fontinalis were found to have heightened mitochondrial capacity at low temperatures (6 °C) based on the oxidation of malate and succinate in isolated red muscle mitochondria. These results provide supporting evidence for a mitochondrial genome influence on enzyme structure and function, as well as an influence at the sub-cellular level of mitochondrial function which is not neutral. The aerobic capacity and swimming performance of fish were evaluated using energetic parameters determined by swimming respirometry. At low temperatures, introgressed S. fontinalis were found to have a metabolic scope for aerobic activity similar to that of non-introgressed S. fontinalis. Further analysis of the metabolic scope revealed the potential for accommodating feeding metabolism was also similar between fish groups. These findings suggest that there is no apparent physiological basis related to swimming metabolism that could be of selective value to introgressed S. fontinalis. Still, further studies should be undertaken that evaluate the possibility of such a basis existing at earlier stages in the life history of introgressed S. fontinalis. Taken together the results from this study demonstrate, for the first time, that mtDNA variation resulting from introgressive events can be functionally important at the molecular and sub-cellular level and may be selectively maintained in natural populations. These findings are of particular interest to population and evolutionary biologists as mtDNA variation is traditionally believed to be of neutral consequence at all levels of biological organization.

Type de document: Thèse
Directeur de mémoire/thèse: Bernatchez, Louis
Co-directeurs de mémoire/thèse: Blier, Pierre
Mots-clés libres: ADN mitochondrial; omble de fontaine; Salvelinus fontinalis; espèce; évolution; fertilisation; hybridation; poisson; population; Québec
Centre: Centre Eau Terre Environnement
Date de dépôt: 09 oct. 2013 20:24
Dernière modification: 18 nov. 2015 21:15
URI: http://espace.inrs.ca/id/eprint/1563

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