Rapid buildup of sympatric species diversity in Alpine whitefish
2018
Adaptive radiations in postglacial fish offer excellent settings to study the evolutionary
mechanisms involved in the rapid buildup of sympatric species diversity from a single lineage. Here, we address this by exploring the genetic and ecological structure of the largest Alpine whitefish radiation known, that of Lakes Brienz and Thun, using microsatellite data of more than 2000 whitefish caught during extensive species-targeted
and habitat-randomized fishing campaigns. We find six strongly genetically and
ecologically differentiated species, four of which occur in both lakes, and one of which
was previously unknown. These four exhibit clines of genetic differentiation that are
paralleled in clines of eco-morphological and reproductive niche differentiation, consistent
with models of sympatric ecological speciation along environmental gradients.
In Lake Thun, we find two additional species, a profundal specialist and a species introduced in the 1930s from another Alpine whitefish radiation. Strong genetic differentiation between this introduced species and all native species of Lake Thun suggests that reproductive isolation can evolve among allopatric whitefish species within
15,000 years and persist in secondary sympatry. Consistent with speciation theory,
we find stronger correlations between genetic and ecological differentiation for sympatrically than for allopatrically evolved species.
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