Triad hybridization via a conduit species
Peter R. Grant, B. Rosemary Grant
Abstract
Significance Introgressive hybridization of pairs of species can affect the evolution of their populations in several important ways. More rarely, three species form an interbreeding complex (triad), but little is known of the consequences. A long-term study of interbreeding Darwin’s finches on Daphne Major island, Galápagos, shows that Geospiza fortis acts as a conduit for the passage of genes from Geospiza fuliginosa , a rare immigrant, to Geospiza scandens , a resident. Surprisingly, the species and the derived dihybrids and trihybrids had approximately equal fitness. Gene flow increased in frequency and apparently caused a morphological convergence of the resident species. These findings illustrate how evolutionary change is potentially increased by hybridization among three species and the assembly of novel combinations of genes.