Discrete foraging niches promote ecological, phenotypic, and genetic divergence in sympatric whitefish (Coregonus lavaretus)

Abstract

Natural populations often vary in their degree of ecological, morphological and genetic divergence. This variation can be arranged along an ecological speciation continuum of increasingly discrete variation, with high inter-individual variation at one end and well defined species in the other. In postglacial fishes, evolutionary divergence has commonly resulted in the co-occurrence of a pelagic and a benthic specialist. We studied three replicate lakes supporting sympatric pelagic and benthic European whitefish (Coregonus lavaretus (L.)) morphs in search for early signs of possible further divergence into more specialized niches. Using stomach content data (recent diet) and stable isotope analyses (time-integrated measure of trophic niche use), we observed a split in the trophic niche within the benthic whitefish morph, with individuals specializing on either littoral or profundal resources. This divergence in resource use was accompanied by small but significant differences in an adaptive morphological trait (gill raker number) and significant genetic differences between fish exploiting littoral and profundal habitats and foraging resources. The same pattern of parallel divergence was found in all three lakes, suggesting similar natural selection pressures driving and/or maintaining the divergence. The two levels of divergence (a clear and robust benthic -pelagic and a more subtle littoralprofundal divergence) observed in this study apparently represent different stages in the process of ecological speciation.Electronic supplementary material The online version of this article

Latitudinal gradients in intraspecific ecological diversity

“…Moreover, our results suggest that within-species niche variation may actually be a driver of species diversity. First, within-population niche variation is predicted to facilitate speciation [26][27][28]. In line with this prediction, clades of amphibians and fishes in which resource polymorphisms have evolved are consistently more diverse than clades showing no such niche variation [29].…”

Divergent growth patterns between juveniles of two sympatric Arctic charr morphs with contrasting depth gradient niche preferences

“…In contrast, the eye size is only marginally different between upper-water Arctic charr with divergent trophic niches (Knudsen et al 2007(Knudsen et al , 2011. Similar adaptations in eye size of deep-water morphs compared with upper-water layer morphs are also found among European whitefish morph pairs (Harrod et al 2010;Siwertsson et al 2013b), indicating that vision is also an important trait for deep-water dwelling morphs. The present results suggest that the PB-morph has heritable adaptations to grow and feed during the long winter period with low light and stable low temperature conditions in subarctic lakes, traits that should be very beneficial for deep-water dwelling morphs.…”

“…There is an increasing awareness of specifically adapted deep-water morphs of postglacial fishes, both along the benthic zone (e.g. Kahilainen and Østbye 2006;Knudsen et al 2006;Vonlanthen et al 2009;Siwertsson et al 2013b) and along the pelagic zone (Helland et al 2008;Ohlberger et al 2008a, b) with clear thermal differences between the preferred habitats in the wild. Deepwater morphs of postglacial fishes may differ genetically from their sympatric upper-water morphs (Westgaard et al 2004;Praebel et al 2013) and may display inherited deep-water adaptations (i.e.…”

Foraging specialisms influence space use and movement patterns of the European eel Anguilla anguilla

“…Individual feeding specialisations can be 90 temporally stable and associated with the occurrence of discrete morphotypes (Skulason & 91 Smith 1995). Such foraging specialisms seem to be particularly common in fishes found in 92 post-glacial lakes (Garduno-Paz et al, 2010; Siwertsson et al, 2013). Interspecific 93 differences in head morphology of fish are known to reflect differences in feeding behaviour 94…”