Parallel divergent adaptation along replicated altitudinal gradients in Alpine trout

Irene Keller,Etienne Bezault,Jolanda Schuler,Ole Seehausen

doi:10.1186/1471-2148-12-210

Irene Keller, Etienne Bezault + Show 2 more

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https://doi.org/10.1186/1471-2148-12-210

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Abstract

BackgroundThe European trout (Salmo trutta species complex) occurs across a very wide altitudinal range from lowland rivers to alpine streams. Historically, the major European river systems contained different, evolutionarily distinct trout lineages, and some of this genetic diversity has persisted in spite of extensive human-mediated translocations. We used AFLP-based genome scans to investigate the extent of potentially adaptive divergence among major drainages and along altitudinal gradients replicated in several rivers.ResultsThe proportion of loci showing evidence of divergent selection was larger between drainages than along altitudinal transects within drainages. This suggests divergent selection is stronger between drainages, or adaptive divergence is constrained by gene flow among populations within drainages, although the latter could not be confirmed at a more local scale. Still, altitudinal divergence occurred and, at approximately 2% of the markers, parallel changes of the AFLP band frequencies with altitude were observed suggesting that altitude may well be an important source of divergent selection within rivers.ConclusionsOur results indicate that adaptive genetic divergence is common both between major European river systems and along altitudinal gradients within drainages. Alpine trout appear to be a promising model system to investigate the relative roles of divergent selection and gene flow in promoting or preventing adaptation to climate gradients.

Highlights

The European trout (Salmo trutta species complex) occurs across a very wide altitudinal range from lowland rivers to alpine streams
Such divergent selection may lead to the evolution of traits beneficial under the environmental conditions specific to a particular population, a process known as local adaptation [1,2]
Remnants of phylogeographic structure in spite of human-mediated dispersal Historically, each of the three major European drainage systems examined in this study would have harbored different evolutionary lineages of trout (Figure 1) which were characterized by considerable genetic divergence [21] and are considered four distinct species: historically allopatric S. trutta, S. rhodanensis and S. marmorata/ S. cenerinus, where the latter two were historically sympatric within the Po drainage

Summary

Introduction

The European trout (Salmo trutta species complex) occurs across a very wide altitudinal range from lowland rivers to alpine streams. For example, we expect a pronounced decrease in ambient temperature with increasing altitude but concomitant patterns may include a reduction in the diversity and a change in the composition of local communities of prey, competitors, parasites and pathogens [14,15,16]. These changes are expected to result in divergent selection on a range of traits, and genetic changes correlated with altitude have been reported from various species [17,18], including salmonid fishes [19,20]

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