Natural hybridization between an outcrossing and a selfing Phlox (Polemoniaceae): the maternal species of F-1 hybrids

Natural F-1 hybrids between the outcrossing Phlox drummondii and the predom inantly selfing P. cuspidata were examined to ascertain the proportion of h ybrid individuals mothered by each species. Species-specific restriction fr agment patterns (both nrDNA and cpDNA.) were established as markers, and sy nthetic hybrids of known parentage were utilized to determine that the chlo roplast genome is maternally inherited. Of 89 mature natural hybrids examin ed, approximately two thirds were mothered by P. drummondii, the outcrosser . That the outcrosser should mother most hybrids is expected since it is de pendent upon incoming pollen for fertilization, and hybrids may result when heterospecific pollen is received. The fact that the highly selfing P. cus pidata mothered nearly one third of the hybrids is surprising, and may be r elated to both pre-zygotic and post-zygotic factors. Which species mothers hybrids has important implications for the potential for introgression as w ell as its direction.