Morphologically cryptic Amazonian bird species pairs exhibit strong postzygotic reproductive isolation

We possess limited understanding of how speciation unfolds in the most species-rich region of the planet—the Amazon basin. Hybrid zones provide valuable information on the evolution of reproductive isolation, but few studies of Amazonian vertebrate hybrid zones have rigorously examined the genome-wi...

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Bibliographic Details
Published in:Proceedings of the Royal Society. B, Biological sciences Biological sciences, 2018-03, Vol.285 (1874), p.20172081-20172081
Main Authors: Pulido-Santacruz, Paola, Aleixo, Alexandre, Weir, Jason T.
Format: Article
Language:English
Subjects:
Animals
Birds
Brazil
Clines
Evolution
Female
Forests
Genetic Speciation
Genome
Genomes
Genomic Clines
Heterozygosity
Hybrid Zones
Hybrids
Loci
Male
Passeriformes - anatomy & histology
Passeriformes - genetics
Passeriformes - physiology
Reproductive Isolation
River basins
Selection
Sibling species
Speciation
Species richness
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Summary:We possess limited understanding of how speciation unfolds in the most species-rich region of the planet—the Amazon basin. Hybrid zones provide valuable information on the evolution of reproductive isolation, but few studies of Amazonian vertebrate hybrid zones have rigorously examined the genome-wide underpinnings of reproductive isolation. We used genome-wide genetic datasets to show that two deeply diverged, but morphologically cryptic sister species of forest understorey birds show little evidence for prezygotic reproductive isolation, but substantial postzygotic isolation. Patterns of heterozygosity and hybrid index revealed that hybrid classes with heavily recombined genomes are rare and closely match simulations with high levels of selection against hybrids. Genomic and geographical clines exhibit a remarkable similarity across loci in cline centres, and have exceptionally narrow cline widths, suggesting that postzygotic isolation is driven by genetic incompatibilities at many loci, rather than a few loci of strong effect. We propose Amazonian understorey forest birds speciate slowly via gradual accumulation of postzygotic genetic incompatibilities, with prezygotic barriers playing a less important role. Our results suggest old, cryptic Amazonian taxa classified as subspecies could have substantial postzygotic isolation deserving species recognition and that species richness is likely to be substantially underestimated in Amazonia.
ISSN:0962-8452
1471-2954
DOI:10.1098/rspb.2017.2081