Rugged adaptive landscapes shape a complex, sympatric radiation.

Renny K Hadiaty,Fabian Herder,Jobst Pfaender,Ulrich K Schliewen

doi:10.1098/rspb.2015.2342

Abstract

Strong disruptive ecological selection can initiate speciation, even in the absence of physical isolation of diverging populations. Species evolving under disruptive ecological selection are expected to be ecologically distinct but, at least initially, genetically weakly differentiated. Strong selection and the associated fitness advantages of narrowly adapted individuals, coupled with assortative mating, are predicted to overcome the homogenizing effects of gene flow. Theoretical plausibility is, however, contrasted by limited evidence for the existence of rugged adaptive landscapes in nature. We found evidence for multiple, disruptive ecological selection regimes that have promoted divergence in the sympatric, incipient radiation of 'sharpfin' sailfin silverside fishes in ancient Lake Matano (Sulawesi, Indonesia). Various modes of ecological specialization have led to adaptive morphological differences between the species, and differently adapted morphs display significant but incomplete reproductive isolation. Individual fitness and variation in morphological key characters show that disruptive selection shapes a rugged adaptive landscape in this small but complex incipient lake fish radiation.

Highlights

Disruptive ecological selection favours adaptation to distinct environments [1,2], and may promote speciation, even in the absence of physical isolation [2,3,4,5,6]
In the landscape LD2 versus LD4 constructed from the complete dataset, the macroinvertebratefeeder T. opudi occupies a significant fitness peak, which is separated by a significant valley from fish-feeders (T. sp. ‘elongated’; electronic supplementary material, figure S5a)
Ecological speciation is considered a major driver of diversification [2,65], our knowledge on how ecological factors have contributed to lineage divergence and speciation in complex radiations remains limited [2,70]

Summary

Introduction

Disruptive ecological selection favours adaptation to distinct environments [1,2], and may promote speciation, even in the absence of physical isolation [2,3,4,5,6]. Using a random sample of sharpfins, we perform integrated analyses of an estimator for individual fitness, an array of morphological traits that influence ecological specialization, the habitat context and stomach contents. To estimate the actual number of clusters within the obtained range we applied the NbClust function [36,37] to the dataset This function uses 22 criteria to determining the number of clusters and indicated that five clusters (morphotypes) summarize the data most adequately (electronic supplementary material, table S1). We tested the reliability of our fitness proxy by investigating the correlation between relative liver mass and reproductive capacity (the ratio between log-transformed gonad weight and gutted body weight) with a subset of 127 female sharpfins. To identify whether morphotype means occupy an average peaks in the adaptive landscape, we compared (using methods described above) fitness values from the regions in the landscape that are occupied by two morphotypes with the values obtained in intermediate regions

Results

Discussion

Findings

Methods