The outcomes of natural hybridization are incredibly varied, ranging from hybrid speciation to extinction of parental taxa. Orphan hybrid populations or lineages are those that occur in the absence of the parental taxa, presenting a challenge for understanding their origins. They can arise in a number of ways. They may arise through dispersal beyond the range of the parental taxa. The hybrid populations may become orphaned by driving the disappearance of their progenitors from the landscape, through genetic swamping or competitive exclusion. In North American Aquilegia (commonly known as columbines), interspecific hybridization is a striking evolutionary phenomenon. Throughout their natural distribution, intergrading floral forms often occur in zones where species range overlap
A recent study by Groh et al. and published in AoBP describes the investigation of an “orphan” hybrid population between Aquilegia formosa and Aquilegia flavescens, two western North American taxa, in which the latter species is absent both locally and regionally. The authors present analyses of floral morphology, nuclear admixture, and maternally-inherited plastid sequence to confirm hybridity and discuss possible origin scenarios. Plants from the orphan hybrid population were on average intermediate between typical A. formosa and A. flavescens for most phenotypes examined and showed evidence of genetic admixture. Whilst long-distance pollen dispersal cannot be ruled out, it is suggested that A. flavescens may have formerly occupied the region and was lost locally through continued genetic assimilation with hybrid individuals.
Jeff Groh completed an honours degree in Plant Biology in 2018 from the University of British Columbia under the supervision of Dr. Quentin Cronk. His undergraduate thesis research focused on local and regional patterns of hybridization in the genus Aquilegia. While at UBC, Jeff also worked in the group of Dr. Dolph Schluter, studying evolutionary ecology of three-spine stickleback. In 2018 Jeff joined the Ortiz-Barrientos lab at University of Queensland as an American Australian Association Scholar, where he currently studies parallel adaptation using genomics approaches in Senecio. Jeff will pursue a PhD in population genetics at UC Davis beginning in 2019. Jeff is interested in evolutionary genetics and evolutionary ecology, and aspires to research the connections between microevolutionary processes and broad patterns of biodiversity.
Groh, J. S., Percy, D. M., Björk, C. R., & Cronk, Q. C. B. (2018). On the origin of orphan hybrids between Aquilegia formosa and Aquilegia flavescens. AoB PLANTS, 11(1). https://doi.org/10.1093/aobpla/ply071