Chloroplast capture between Clarkia xantiana xantiana and Clarkia xantiana parviflora

Abstract

Introgression occurs when genetic material from one gene pool gets incorporated into another gene pool. Introgression of chloroplast genomes is when one species inherits the chloroplast genome of another species, termed chloroplast capture. Understanding introgression can provide invaluable insight into reproductive barriers and speciation. Clarkia xantiana xantiana and Clarkia xantiana parviflora are subspecies that diverged about 65,000 years ago. Subspecies xantiana is an outcrossing species, while ssp. parviflora is a selfing species. We hypothesized that chloroplast capture is likely occurring between the two subspecies in sympatric areas, where they co-occur. In this study, we performed a phylogenetic analysis with about 200 complete chloroplast genomes of the subspecies from 6 different hybrid zones and 16 allopatric sites to determine whether chloroplast capture occurred. Additionally, we sampled more vigorously from 4 sympatric sites, where we then performed Polymerase Chain Reaction on those individuals to determine chloroplast genotype. In accordance with current theory, we found that chloroplast capture was asymmetric such that, chloroplasts flowed mainly from the selfing species, ssp. parviflora, into the outcrossing species, ssp. xantiana. There was, however, notable variation in asymmetry among sympatric populations.