COS 132-6 - Genomic detection of hybridization in Typha latifolia and T. angustifolia

Background/Question/Methods

Hybridization can yield profoundly different evolutionary outcomes, from the establishment of novel lineages to admixture and despeciation. The study of hybridizing species requires the accurate identification of parentals and admixed individuals, which becomes complex in hybrid swarms that include advanced-generation hybrids and backcrossed individuals. Broad-leafed and Narrow-leaved cattails (Typha latifolia and T. angustifolia) have sympatric distributions across the temperate northern hemisphere. They are reproductively compatible and, in some regions, produce the hybrid Typha × glauca. First-generation hybrids are formed after mating between T. angustifolia and T. latifolia as the maternal and paternal plants, respectively. Individuals of Typha × glauca are fertile and capable of producing advanced-generation hybrids and backcrossing with both parental species. In regions around the Laurentian Great Lakes, F1 hybrids are highly invasive, displacing parental species and altering wetland ecology; however, recent evidence suggests that advanced-generation hybrids suffer from hybrid breakdown. To better understand the dynamics of this hybrid system, our short-term goal is to differentiate F1s, advanced-generation hybrids and backcrossed individuals, something not possible using existing molecular markers. We combined total DNA extraction and the assay for transposase accessible chromatin with high-throughput sequencing protocols, producing a quick and cost-effective genome-wide library.

Results/Conclusions

We developed a library from 170 T. angustifolia, T. latifolia, and Typha × glauca plants across North America and Europe. We also present a reproducible workflow to identify species-specific single nucleotide polymorphisms (SNPs), i.e., loci with fixed alternative alleles in each of the two parental species. We have identified ~6000 species-specific SNPs between the parental taxa that will allow us to differentiate among F1s, advanced-generation hybrids and backcrossed individuals, and identify genetic regions of introgression across the genomes of T. latifolia and T. angustifolia. Our long-term goals are to 1) evaluate the distribution of genetic variation within the Typha hybrid swarm by quantifying the extent of introgression between the parental species and looking for recombination patterns across the Typha × glauca genome, 2) investigate potential adaptive introgressions, and 3) estimate the role of genetic introgressions on the Typha invasiveness around the Laurentian Great Lakes.