Abstract
Phenotypic variation in populations of fishes that inhabit postglacial lakes is often associated with trophic specialisations. A common sympatric foraging divergence seen in Arctic charr is into either plankton or littoral-zoobenthos feeding specialisms. In this study, we report a sympatric polymorphic Arctic charr population which is not centred on this divergence but instead manifests as a plankton (pelagic)—profundal zoobenthos foraging specialisms. The head shape of profundal fish was round and robust, the body thick set and pectoral fins long and wide. In contrast, the head of pelagic fish was pointed and slender, the body fusiform in shape and with short, narrow pectoral fins. There was no difference between profundal and pelagic fish in gill raker number. Body lipid content was significantly higher in pelagic fish as were the number or Diphyllobothrium cysts. The carbon isotope ratio was more heavily depleted in profundal fish. There was no dietary overlap in the prey items recovered from stomach contents of profundal and pelagic fish. We suggest the proximate driver behind the sympatric divergence was the successful exploitation of the profundal zone. The consequences of this have led to the development of adaptations in morphology and behaviour to support and maintain this divergence.
Highlights
In some taxonomic groups, intraspecific genetic and phenotypic structuring within a population is common (Skulason & Smith, 1995; Smith & Skulason, 1996)
Intraspecific genetic and phenotypic structuring within a population is common (Skulason & Smith, 1995; Smith & Skulason, 1996). This is true for fishes in postglacial lakes (Taylor & McPhail, 1999; Jonsson & Jonsson, 2001; Østbye et al, 2006) and results in alternative phenotypes living in sympatry within a single lake (Knudsen et al, 2006)
This is seen in Arctic charr, Salvelinus alpinus (Linnaeus 1758) in which the structuring is based on the adaptation of foraging specialisms to alternative food resources (Malmquist et al, 1992; Adams et al, 1998; Amundsen et al, 2008; GardunoPaz et al, 2010)
Summary
Intraspecific genetic and phenotypic structuring within a population is common (Skulason & Smith, 1995; Smith & Skulason, 1996) This is true for fishes in postglacial lakes (Taylor & McPhail, 1999; Jonsson & Jonsson, 2001; Østbye et al, 2006) and results in alternative phenotypes living in sympatry within a single lake (Knudsen et al, 2006). The most commonly reported foraging divergence seen in sympatric populations of Arctic charr is that of a divergence into planktonic and littoral-zoobenthos feeding (Malmquist et al, 1992; Adams et al, 1998, 2003; Adams & Huntingford, 2002; Amundsen et al, 2008, Corrigan et al, 2011; Garduno-Paz et al, 2012)
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