Abstract
The North-east American Rainbow smelt (Osmerus mordax) is composed of two glacial races first identified through the spatial distribution of two distinct mtDNA lineages. Contemporary breeding populations of smelt in the St. Lawrence estuary comprise contrasting mixtures of both lineages, suggesting that the two races came into secondary contact in this estuary. The overall objective of this study was to assess the role of intraspecific genetic admixture in the morphological diversification of the estuarine rainbow smelt population complex. The morphology of mixed-ancestry populations varied as a function of the relative contribution of the two races to estuarine populations, supporting the hypothesis of genetic admixture. Populations comprising both ancestral mtDNA races did not exhibit intermediate morphologies relative to pure populations but rather exhibited many traits that exceeded the parental trait values, consistent with the hypothesis of transgressive segregation. Evidence for genetic admixture at the level of the nuclear gene pool, however, provided only partial support for this hypothesis. Variation at nuclear AFLP markers revealed clear evidence of the two corresponding mtDNA glacial races. The admixture of the two races at the nuclear level is only pronounced in mixed-ancestry populations dominated by one of the mtDNA lineages, the same populations showing the greatest degree of morphological diversification and population structure. In contrast, mixed-ancestry populations dominated by the alternate mtDNA lineage showed little evidence of introgression of the nuclear genome, little morphological diversification and little contemporary population genetic structure. These results only partially support the hypothesis of transgressive segregation and may be the result of the differential effects of natural selection acting on admixed genomes from different sources.
Highlights
Numerous intraspecific phylogeographic studies show how many vertebrate species are composed of morphologically and genetically distinct lineages resulting from the vicariant isolation of intraspecific groups in isolated refugia, those created during Pleistocene continental glaciation events [1]
Several processes have been hypothesized to occur. If such intraspecific admixture produces hybrids of low fitness, reinforcement can lead to character displacement and the evolution of reproductive isolation between distinct morphotypes, a process that is the intraspecific analog of interspecific character displacement [2, 3, 4, 5]
The overall objective of this study was to assess the role of intraspecific genetic admixture in the morphological diversification of estuarine rainbow smelt
Summary
Numerous intraspecific phylogeographic studies show how many vertebrate species are composed of morphologically and genetically distinct lineages resulting from the vicariant isolation of intraspecific groups in isolated refugia, those created during Pleistocene continental glaciation events [1]. Historical divergence and subsequent secondary contact of distinct races may result in the genetic admixture of previously isolated gene pools. In such cases, several processes have been hypothesized to occur. If such intraspecific admixture produces hybrids of low fitness, reinforcement can lead to character displacement and the evolution of reproductive isolation between distinct morphotypes, a process that is the intraspecific analog of interspecific character displacement [2, 3, 4, 5]. According to the model of additive genetic variance, gene flow between divergent allopatric populations will tend to reduce differences between them [8]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
