Adaptive introgression in subdivided populations leaves distinct genomic footprints under global and local selection: a case study in Ciona intestinalis
Adaptive introgression, the transfer of beneficial alleles between species through hybridization, is increasingly recognized as an important source of adaptation to novel environments. However, the theory of adaptive introgression has primarily been developed for a single panmictic population, whereas many empirical examples involve spatially subdivided populations. In such systems, a…
Adaptive introgression, the transfer of advantageous genes between species via hybridization, is an emerging concept in evolutionary biology. Initially conceived for a single, mixing population, the theory now incorporates spatially divided populations. This scenario presents a unique challenge: a genetically beneficial mutation may either be at the forefront of a sweeping adaptation or be confined to a specific group where it is suppressed by local selection.
Our research team devised a straightforward prediction based on the correlation between the presence of a beneficial mutation and the length of the gene transfer tract. Simulations support this hypothesis, indicating a positive relationship when the advantageous mutation is undergoing a continuous sweep, but no correlation when local adaptation is the governing factor.
To validate our prediction, we examined a well-documented instance of adaptive introgression in the sea squirt Ciona intestinalis. Employing a technique called haplotagging, we were able to piece together the genome sequences of individuals, revealing their local ancestry. Our findings offer compelling evidence in favor of the model of local adaptation rather than a global selective sweep.
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