The genetic mechanisms underlying hybridization are poorly understood despite their potentially important roles in speciation processes, adaptative evolution, and agronomical innovation. In this study, transcription profiles were compared among three populations of brook charr and their hybrids using microarrays to assess the influence of hybrid origin on modes of transcription regulation inheritance and on the mechanisms underlying growth. We found that twice as many transcripts were differently expressed between the domestic population and the two wild populations (Rupert and Laval) than between wild ones, despite their deeper genetic distance. This could reflect the consequence of artificial selection during domestication. We detected that hybrids exhibited strikingly different patterns of mode of transcription regulation, being mostly additive (94%) for domestic 3 Rupert, and nonadditive for Laval 3 domestic (45.7%) and Rupert 3 Laval hybrids (37.5%). Both heterosis and outbreeding depression for growth were observed among the crosses. Our results indicated that prevalence of dominance in transcription regulation seems related to growth heterosis, while prevalence of transgressive transcription regulation may be more related to outbreeding depression. Our study clearly shows, for the first time in vertebrates, that the consequences of hybridization on both the transcriptome level and the phenotype are highly dependent on the specific genetic architectures of crossed populations and therefore hardly predictable.
Brook trout ( Salvelinus fontinalis (Mitchill, 1814)) supports a lucrative fish aquaculture industry in Quebec and production of this species is mainly oriented to stock enhancement supporting sport fisheries. The aim of this study was to verify the expression of interstrain heterosis, i.e., increased performance of first generation hybrid progeny, during the first stages of development in brook trout. Two wild populations that were recently introduced to fish production in Quebec, the Laval (L) and the Rupert (R) strains, and a domestic strain (D) that is present in most Quebec fish farms were used in this study. The growth of 72 full-sibling families, representing three pure (♀D × ♂D, ♀L × ♂L, ♀R × ♂R) and five hybrid (♀D × ♂L, ♀D × ♂R, ♀L × ♂D, ♀L × ♂R, ♀R × ♂L) cross types, were surveyed from hatching to 2136 degree-days. Both heterosis and outbreeding depression were observed, depending on the hybrid cross type. The occurrence of heterosis was dependent on the developmental stage, and growth advantage at a very early developmental stage did not necessarily translate into bigger size later on. Outbreeding depression in growth (mass or length) was much less common than heterosis, and when occurring, it varied from 9.2% to 33.3% compared with 9.0% to 88.2% improvement in growth traits for heterosis. The results indicate that in early development, there was higher occurrence of heterosis relative to fish mass than to fish length and that, overall, the occurrence of heterosis was unpredictable.
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