Annual Temperatures and Dynamics of Food Availability are Associated with the Pelagic-Benthic Diversification in a Sympatric Pair of Salmonid Fish

Fish diversification into sympatric ecomorph pairs demonstrates a striking parallelism across a number of taxa in numerous lakes. However, there is a dearth of information on environmental conditions, which may orchestrate divergence processes across generations. Here we explore whether the environmental factors affecting food and reproductive niche distinctions could trigger the divergence of the lacustrine-riverine fish species into two morphs based on kokanee Oncorhynchus nerka of the Lake Kronotskoe. We reveal drastic differences in temperature on the tributary reproduction sites affecting the early ontogeny timing and disrupting the time of lakeward migration of the morphs. The juveniles of the benthivorous morph run into the lake in spring during the food abundance peak on the slope, while the planktivorous kokanee migrates to the lake in the summer when the pelagic zone abounds with zooplankton. The dynamics of this food niches is determined by water temperature dynamics and may be stable for long periods of time, thus making each morph adapting to similar condition throughout generations. We suggest that the pelagic-benthic divergence could be explained by the factors, which are extrinsic for fish , making our results applicable for numerous cases of this microevolutionary pathway all over the Holarctic.