Triad hybridization via a conduit species

Area of Science:

• Evolutionary biology
• Population genetics
• Speciation

Background:

• Introgressive hybridization influences population evolution by affecting species divergence, trait development, and genetic variation.
• Most studies focus on hybridization between two species, with three-species interbreeding complexes being rarer.
• The demographic and genetic consequences of three-species hybridization remain largely unknown.

Purpose of the Study:

• To investigate the demographic and genetic consequences of a three-species interbreeding complex in Darwin's finches.
• To understand the role of one species acting as a genetic conduit between two others.
• To examine the impact of introgressive hybridization on genetic and morphological convergence and fitness.

Main Methods:

• Long-term ecological and genetic study of Darwin's finches on Daphne Major island, Galápagos.
• Microsatellite analysis to track gene flow between *Geospiza fortis*, *Geospiza fuliginosa*, and *Geospiza scandens*.
• Monitoring of ecological conditions and fitness of parent species and their hybrids over 30 years.

Main Results:

• *Geospiza fortis* acted as a genetic conduit between *G. fuliginosa* and *G. scandens*.
• Gene flow from *G. fortis* into *G. scandens* increased under favorable ecological conditions over 30 years.
• Genetic and morphological convergence was observed in *G. scandens*, with dihybrids and trihybrids showing fitness equal to the parent species.

Conclusions:

• Introgressive hybridization among three species can create novel gene combinations, enhancing evolutionary potential.
• This study provides insights into the dynamics of three-species hybridization, particularly relevant to young adaptive radiations.
• The findings highlight the role of hybridization in facilitating adaptation and potentially influencing speciation processes.