Genomic contributors of speciation: insights from nascent species boundaries
What genomic mechanisms are shaping the boundaries of diverging lineages is becoming the central question in speciation genomics. Here we addressed this question in a nascent warbler species complex in the Pacific West. With cross-time periods sampling, genomic analyses, and behavioral experiments in natural hybrid zone and ancient hybrid populations, we revealed two intriguing genomic contributors of speciation.
First, we found pleiotropic effect of plumage color gene block which demonstrates opposing dominance in a suite of species-specific plumage traits. Tracing this genetic region over space and time, we disclosed selection-migration balance in shaping variation of this gene block. Integrating the roles of these plumage traits in territorial signaling, we revealed the mechanism of selection underlying this color gene block.
The second genomic contributor strengthening the species boundary is mitonuclear coadaptation related to energy-fatty-acid metabolism associated with local climatic conditions. Specifically, there is asymmetrical introgression of mtDNA-associated nuclear genetic variants from the parental population of warmer habitat in the ancient hybrid population. Different from these two selection-driven genetic regions, the rest of the genome is mostly undifferentiated, consistent with the pattern of introgression homogenizing the genome while targets of selection are divergent. Collectively, the genomic contributors of speciation in this warbler species complex shed light on genomic evolution in the process of speciation.
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*ISYEB: Institut de Systématique, Évolution, Biodiversité, UMR 7205, EPHE, MNHN, CNRS, Sorbonne Université, Université des Antilles, Paris