Rapid buildup of sympatric species diversity in Alpine whitefish.

David Bittner,Pascal Vonlanthen,Catherine E. Wagner,Carmela J. Doenz,Ole Seehausen

doi:10.1002/ece3.4375

Abstract

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.

Highlights

Over the past millennia, glacial dynamics led to dramatic changes in species diversity and ranges in the northern hemisphere (Hewitt, 2004)
Our study focuses on a postglacial adaptive radiation of Alpine whitefish (Coregonus spp.)
In Lakes Thun and Brienz, we find evidence for the most speciose known Alpine whitefish assemblage consisting of six fully sympatric whitefish species

Summary

| INTRODUCTION

Glacial dynamics led to dramatic changes in species diversity and ranges in the northern hemisphere (Hewitt, 2004). Despite occurring in geographic sympatry, speciation in the latter case is still often associated with spatial ecological gradients at a smaller scale (Seehausen et al, 2008) Such fine-scale structuring of ecological niches has been found to greatly facilitate speciation, both in empirical studies of adaptive radiations in fish (Hudson, Lundsgaard- Hansen, Lucek, Vonlanthen, & Seehausen, 2016; Seehausen et al, 2008) and in theoretical models (Doebeli & Dieckmann, 2003; Gavrilets, 2004). We assess whether the role of these axes for reproductive isolation and coexistence is different for species of presumable sympatric vs. allopatric origin

| MATERIALS AND METHODS

| DISCUSSION

Findings

CONFLICT OF INTEREST