The propagation of admixture-derived adaptive radiation potential.

Kotaro Kagawa,Ole Seehausen

doi:10.1098/rspb.2020.0941

Abstract

Adaptive radiations (ARs) frequently show remarkable repeatability where single lineages undergo multiple independent episodes of AR in distant places and long-separate time points. Genetic variation generated through hybridization between distantly related lineages can promote AR. This mechanism, however, requires rare coincidence in space and time between a hybridization event and opening of ecological opportunity, because hybridization generates large genetic variation only locally and it will persist only for a short period. Hence, hybridization seems unlikely to explain recurrent AR in the same lineage. Contrary to these expectations, our evolutionary computer simulations demonstrate that admixture variation can geographically spread and persist for long periods if the hybrid population becomes separated into isolated sub-lineages. Subsequent secondary hybridization of some of these can reestablish genetic polymorphisms from the ancestral hybridization in places far from the birthplace of the hybrid clade and long after the ancestral hybridization event. Consequently, simulations revealed conditions where exceptional genetic variation, once generated through a rare hybridization event, can facilitate multiple ARs exploiting ecological opportunities available at distant points in time and space.

Highlights

Adaptive radiation (AR) is a major focus in evolutionary biology
If spontaneous mutations are allowed after the initial hybridization event, admixture between sub-lineages will restore old and generate a new genetic variation by reshuffling de novo mutations after they had arisen in isolation in either sub-lineage
This means that our results do not generally deny the possibility of recurrent AR with spontaneous mutations alone, AR was extremely unlikely without hybridization-induced genetic variation under our simulation conditions

Summary

Introduction

Adaptive radiation (AR) is a major focus in evolutionary biology. One remarkable observation in empirical AR research is that the same lineage often made multiple ARs at geographically distant places or recurrent radiations in the same site through time, while closely related and ecologically similar lineages fail to radiate [1,2,3,4,5,6,7,8,9]. Genomic studies of African cichlid fishes suggest that genetic variation generated through a single ancient hybridization episode has promoted several ARs in geographically distant lakes at different points in time in eastern central Africa [12] This may imply that the lineage retained its elevated evolvability through episodes of diversification and range expansion. 50 000 generations) after the original hybridization episode, implying that the hybridization-induced evolvability persisted over a very long period of time [12] These observations imply that the rare and unlikely event of hybridization between lineages of the right genetic distance may only need to occur once for promoting recurrent ARs in the hybrid lineage

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Discussion

Conclusion