Ancient hybridization leads to the repeated evolution of red flowers across a monkeyflower radiation
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Date
2023-06-05
Authors
Short, Aidan W.
Streisfeld, Matthew A.
Journal Title
Journal ISSN
Volume Title
Publisher
Oxford Academic
Abstract
The reuse of old genetic variation can promote rapid diversification in evolutionary radiations, but in most cases, the historical events
underlying this divergence are not known. For example, ancient hybridization can generate new combinations of alleles that sort into
descendant lineages, potentially providing the raw material to initiate divergence. In the Mimulus aurantiacus species complex, there is
evidence for widespread gene flow among members of this radiation. In addition, allelic variation in the MaMyb2 gene is responsible
for differences in flower color between the closely related ecotypes of subspecies puniceus, contributing to reproductive isolation by
pollinators. Previous work suggested that MaMyb2 was introgressed into the red-flowered ecotype of puniceus. However, additional
taxa within the radiation have independently evolved red flowers from their yellow-flowered ancestors, raising the possibility that
this introgression had a more ancient origin. In this study, we used repeated tests of admixture from whole-genome sequence data
across this diverse radiation to demonstrate that there has been both ancient and recurrent hybridization in this group. However,
most of the signal of this ancient introgression has been removed due to selection, suggesting that widespread barriers to gene flow
are in place between taxa. Yet, a roughly 30 kb region that contains the MaMyb2 gene is currently shared only among the red-flowered
taxa. Patterns of admixture, sequence divergence, and extended haplotype homozygosity across this region confirm a history
of ancient hybridization, where functional variants have been preserved due to positive selection in red-flowered taxa but lost in
their yellow-flowered counterparts. The results of this study reveal that selection against gene flow can reduce genomic signatures of
ancient hybridization, but that historical introgression can provide essential genetic variation that facilitates the repeated evolution
of phenotypic traits between lineages.
Description
12 pages
Keywords
Introgression, Mimulus, Genomics, Hybridization, Speciation, Radiations
Citation
Aidan W Short, Matthew A Streisfeld, Ancient hybridization leads to the repeated evolution of red flowers across a monkeyflower radiation, Evolution Letters, Volume 7, Issue 5, October 2023, Pages 293–304, https://doi.org/10.1093/evlett/qrad024