Adaptive plasticity and genetic divergence in feeding efficiency during parallel adaptive radiation of whitefish (Coregonus spp.)

Parallel phenotypic divergence in replicated adaptive radiations could either
result from parallel genetic divergence in response to similar divergent selec-
tion regimes or from equivalent phenotypically plastic response to the
repeated occurrence of contrasting environments. In post-glacial fish, repli-
cated divergence in phenotypes along the benthic-limnetic habitat axis is
commonly observed. Here, we use two benthic-limnetic species pairs of
whitefish from two Swiss lakes, raised in a common garden design, with
reciprocal food treatments in one species pair, to experimentally measure
whether feeding efficiency on benthic prey has a genetic basis or whether it
underlies phenotypic plasticity (or both). To do so, we offered experimental
fish mosquito larvae, partially burried in sand, and measured multiple feed-
ing efficiency variables. Our results reveal both, genetic divergence as well
as phenotypically plastic divergence in feeding efficiency, with the pheno-
typically benthic species raised on benthic food being the most efficient
forager on benthic prey. This indicates that both, divergent natural selection
on genetically heritable traits and adaptive phenotypic plasticity, are likely
important mechanisms driving phenotypic divergence in adaptive radiation.