Affiliations: 1) Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 021382; 2) The Arnold Arboretum, Harvard University, Boston, MA 02131; 3) Informatics Group, Harvard University, Cambridge, MA 021382
Keywords: Speciation & hybridization
Natural selection directly favors the evolution of reproductive isolation between species through the process of reinforcement. During reinforcement, costly hybridization between co-occurring lineages can generate selection favoring traits that increase reproductive isolation. This important process has generated species across the tree of life, yet the mutations underlying this process and how they evolved by selection have remained unknown. Flower color variation in Phlox drummondii is the best documented case of reinforcement to date. P. drummondii and P. cuspidata display similar light-blue colored flowers in allopatry. However, in sympatry, P. drummondii has evolved dark-red flowers via selection to prevent maladaptive hybridization with P. cuspidata. Previous work inferred the divergence from light to dark colored flowers is controlled by cis-regulatory mutations at an R2R3-Myb transcription factor. We have applied population-level targeted long read genome sequencing in P. drummondii to identify and characterize mutations in the regulatory sequence of the R2R3-Myb associated with the transition from light to dark colored flowers. Through our sequencing efforts, we have begun to infer the evolutionary history of reinforcement mutations through space and time. This is the first characterization of the mutations underlying reinforcement, and a powerful demonstration of how targeted sequencing can elucidate the molecular basis of trait variation in non-model systems with large genomes.