Identification of two genes causing reinforcement in the Texas wildflower Phlox drummondii

The blooming of a species Speciation, the accumulation of traits that prevent successful mating between populations, is a major source of biotic diversity. Most of the traits involved are by-products of adaptations that occur while species diverge in geographic isolation, but natural selection also acts directly to reduce mating between incipient species through a process called reinforcement. The genes involved in the evolution of one particular reinforcement trait have now been identified. A colour shift in the native Texas wildflower Phlox drummondii occurs in response to selection against hybridization with a closely related species. Dark-red flowers emerge (produced by the possible allelic combinations) as a result of mutations in two genes associated with synthesis of anthocyanin pigments. This result indicates that the evolution of reinforcement traits may involve only a small number of genetic changes with relatively large effect. This reinforcement trait can also reduce fitness in hybrid offspring, thus further facilitating the process of speciation.