Molecular Signatures of Reticulate Evolution within the Complex of European Pine Taxa

Bartosz Łabiszak,Witold Wachowiak

doi:10.3390/f12040489

Bartosz Łabiszak, Witold Wachowiak

Open Access

https://doi.org/10.3390/f12040489

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Abstract

Speciation mechanisms, including the role of interspecific gene flow and introgression in the emergence of new species, are the major focus of evolutionary studies. Inference of taxonomic relationship between closely related species may be challenged by past hybridization events, but at the same time, it may provide new knowledge about mechanisms responsible for the maintenance of species integrity despite interspecific gene flow. Here, using nucleotide sequence variation and utilizing a coalescent modeling framework, we tested the role of hybridization and introgression in the evolutionary history of closely related pine taxa from the Pinus mugo complex and P. sylvestris. We compared the patterns of polymorphism and divergence between taxa and found a great overlap of neutral variation within the P. mugo complex. Our phylogeny reconstruction indicated multiple instances of reticulation events in the past, suggesting an important role of interspecific gene flow in the species divergence. The best-fitting model revealed P. mugo and P. uncinata as sister species with basal P. uliginosa and asymmetric migration between all investigated species after their divergence. The magnitude of interspecies gene flow differed greatly, and it was consistently stronger from representatives of P. mugo complex to P. sylvestris than in the opposite direction. The results indicate the prominent role of reticulation evolution in those forest trees and provide a genetic framework to study species integrity maintained by selection and local adaptation.

Highlights

Since Darwin’s original work, the origin of species and mechanisms of speciation has been a major focus of evolutionary biology
A growing body of evidence indicates that speciation can occur despite the homogenizing effect imposed by interspecific gene flow [4,5,6,7], and hybridization is regarded as an important force shaping the genetic diversity of species that can lead to the emergence of new species [8,9,10,11,12,13]
The nuclear dataset was comprised of 48 nuclear loci with no signatures of selection and a mean length of 404 bp, and 794 SNPs identified in four pines

Summary

Introduction

Since Darwin’s original work, the origin of species and mechanisms of speciation has been a major focus of evolutionary biology. In recent years the understanding of these processes has shifted from a simple divergence model driven by the long-lasting isolation with a gradual accumulation of reproductive isolation between two lineages and encompasses a wide range of complex scenarios within the speciation continuum framework [1,2]. Within this framework, speciation is understood as a process with no fixed endpoints and a lack of clear boundaries between each stage. Studies of closely related species can inform us about the different stages of the complex speciation continuum and the production of novel genetic diversity of potential adaptive importance [14]

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