Abstract
The factors determining regional adaptation in salmonids are still unclear, but it is known that changes in their habitat imply changes in their population structure. In this preliminary study we integrate habitat data, molecular analyses (from both nuclear microsatellite and mitochondrial loci) and life-history traits (measured on archaeological vertebrae and modern scales) of two sympatric salmonid species: Atlantic salmon and brown trout. We propose that water temperature and geological characteristics changed the biogeographic patterns of these species through asymmetric migration and different (but complementary) population growth rates. As a consequence, differences in a life-history trait (mean number of years at sea) and population sizes were detected between regions, suggesting a process of substitution of Atlantic salmon by brown trout.
Highlights
Climate and geology affect natural populations of salmonids
The Sea Surface Temperature (SST) map of the study area (Fig. 1) showed differences in water temperatures of up to 2°C: colder in the western than in the eastern area of Cape Peñas. These differences were consistent across years (2002 and 2003) and marked during the summer season (Supplementary Material S2)
The differences in population genetics are not related to the genetic population structure of the species because Cape Peñas has no influence on this (Horreo et al 2011a)
Summary
Climate and geology affect natural populations of salmonids. Both factors modify populations’ structure through changes in water temperatures (Horreo et al 2011a) and differences in geological substrate (Perrier et al 2011). These changes disrupt the original local adaptations (Frankel & Soulé 1981) and their evolutionary potential (Koljonen et al 2002), and can be especially important in small populations because the smaller the population size, the greater the chance of genetic drift occurring (Ellstrand and Elam 1993). In the genus Salmo, phenological or LHTs such as runtiming and age at maturity vary with a clinal (latitudinal) relation to temperature at scales of hundreds to thousands of kilometres
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