Thoughts on recent studies on asymmetrical introgression via hybridization

Gene flow from one population into another is facilitated by the migration of species resulting into genetic mix in the hybrids. The event of reproduction between different species is termed as hybridization which has been greatly reported in birds. The incorporation of species’ genetic material into the gene pool of another via hybridization is called “genetic introgression” or simply “introgression.” In the events where the genetic mix result in the exhibition of the characteristic of both parents is termed “symmetrical introgression” and when the characteristics of one parent is increasingly exhibited in the hybrids it is termed “asymmetrical introgression.” Collating the recent studies on asymmetric introgression and presenting thoughts on the methods and interpretation from these studies is the main aim of this paper. Major findings include evidences for differential introgression, hybrid zones are semipermeable tension zones, absence of correlation evidence of mating advantage between manipulated males and natural males in nature, hindrance to introgression of song with the permission of asymmetrical introgression of plumage by male behavioural responses, environmental variables providing adequate explanation for variation in morphometric traits despite differences in distance between sites, lack of adverse effects of hybridization on survival and reproductive character in first generation hybrids, evidence for species collapse via hybridization and evidence for rivers not being a complete barrier to hybridization across taxon pairs. I recommend the incorporation of ecological niche of the species into the models considered for avian hybridization in addition to development of tools to incorporate climatic fluctuations into reconstructions of genetic diversification by evolutionary ornithologists.