Introgression analysis of the nine-spined stickleback

We analyzed taxonomically and geographically comprehensive genomic data from nine-spine sticklebacks to decipher the extent of introgression and its consequences for the diversification of this genus. Our results demonstrate that introgression is more prevalent than suggested by earlier studies. Although gene flow was generally bidirectional, it was often asymmetric and left unequal genomic signatures in hybridizing species, which might, at least partly, be due to biased hybridization and/or population size differences. In several cases, introgression of variants from one species to another was accompanied by transitions of pelvic and/or lateral plates, important diagnostic traits in nine-spine systematics, and frequently left adaptive signatures in the core gene regulatory networks of armor trait development.