Neo-sex chromosome evolution and impact on speciation-with-gene flow in oceanic island birds

A major goal of evolutionary biology is to determine the genetic changes responsible for speciation— the formation of new species. Most species are formed when two populations that evolve in different geographic regions accumulate genetic differences that make them reproductively incompatible with one another. Sometimes, however, species come into geographic contact before speciation is complete and produce partially fertile hybrids.

These natural hybrids have mosaic genomes that allow the determination of which genes and/or chromosomes are responsible for reproductive incompatibility. Previous work in many animals and plants has shown, for instance, that sex-limited chromosomes play outsized roles in speciation. In the Solomon Islands, two honeyeater bird species hybridize and produce partially fertile hybrids.

These hybridizing honeyeaters are of particular interest because they possess both old and new, recently evolved, sex-limited chromosomes. The honeyeaters therefore present a rare opportunity to address important questions in the genetic evolution of new species, the evolution of new sex-limited chromosomes, and the role of sex-limited chromosomes in speciation.

The project will educate undergraduate students in integrative biology through direct involvement in field work then training in cutting-edge computational approaches. Through educational initiatives, the project will also help promote conservation in a remote island threatened by clear-cut logging.

This research project has three major aims. The first aim is to characterize the lineage-specific evolution of neo-sex chromosomes in two species of honeyeaters using comparative genomics analyses of ultrahigh quality genome assemblies. The second aim is to characterize the history of speciation, secondary contact, admixture, and natural selection using population genomics analyses of samples of each species and of their hybrids.

The third aim is to investigate behavioral and genetic factors that may impact the direction and genomic distribution of gene flow using field data on mate-choice and parentage. Together, these aims combine genomics and field approaches to provide novel insights into the interaction of genome evolution and the origin of species.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.