Identifying patterns of introgression in two species pairs of Texas Phlox
Authors: Samridhi Chaturvedi 1,2,3; Danielle Khost 3; Austin Garner 2,3; Ben Goulet-Scott 2,3; Antonio Serrato-Capuchina 2,3; Tim Sackton 3; Robin Hopkins 2,3
Affiliations: 1) University of California, Berkeley; 2) The Arnold Arboretum at Harvard University, Roslindale, MA; 3) Harvard University, Cambridge, MA
Keywords: Speciation & hybridization
Many diverging lineages have a history of hybridization and gene flow. Understanding these patterns of gene exchange across space and across their genomes can provide invaluable insights into how and when species form and diverge. Patterns of genomic diversity and divergence within and between species across space can be used to infer evolutionary histories of gene flow and admixture between species. Here, we study patterns of introgression between three Texas Phlox wildflowers – P. drummondii, P. cuspidata, and P. roemeriana. These three species live in adjacent and overlapping geographic ranges with sympatric zones shared between P. drummondii × P. cuspidata and P. drummondii × P. roemeriana. Notably, in the sympatric zone between P. drummondii and P. cuspidata, reinforcement has driven the evolution of flower color as a mechanism to decrease costly hybridization between the two species. No such pattern of reinforcement is evident in the other sympatric zone. In this study, we use genome-wide sequence data to estimate introgression between these two pairs of species – one with reinforcement (P. drummondii x P. cuspidata) and one pair without (P. drummondii x P. roemeriana). We combined extensive geographic sampling, greenhouse experiments, partial and whole-genome sequencing of multiple individuals, to study the history of admixture for each species pair and identify the direction and extent of introgression. Our results provide strong evidence of introgression and admixture between sympatric species with striking variation across populations depending on geographic location. This study characterizes patterns of introgression and local ancestry in these species at a genomic level.