Population genetics and comparative morphology of two serpentine Phlox species

<p>Hybridization between rare and widespread species can result in loss of genetic integrity for the rarer species, which can have management and conservation implications. One rare species, <em>Phlox hirsuta</em>, is a serpentine endemic in northern California, and it frequently co-occurs with a widespread congener, <em>P. speciosa</em>. Putative hybrids were recognized based on intermediate morphology, so the possibility of hybridization was explored using floral morphological and molecular data. Ninety-eight individuals of <em>P. hirsuta</em> and <em>P. speciosa</em> were collected from each of three populations, and floral features were measured and compared. Eleven microsatellite loci were amplified for species and putative hybrids, and inter- and intraspecific genetic diversity and relationships were investigated with multiple methods. Variation in morphological and molecular data was recognized. Floral variation was greater for <em>P. hirsuta</em> than <em>P. speciosa</em>. Putative hybrids were genetically allied with <em>P. speciosa</em>, but two individuals of <em>P. hirsuta</em> were resolved to have genetic similarity with <em>P. speciosa</em>. While hybridization is possible between the species, it is uncommon and appears to be primarily unidirectional, with <em>P. speciosa</em> as the hypothesized male parent and <em>P. hirsuta</em> as the hypothesized female parent. The small number of recognized hybrids may be due to ineffective interspecific pollination, early acting inbreeding depression, hybrids being less fit than parents, and/or small sample sizes. Reinforcement does not appear to play a role in secondary contact between species. Both microsatellite loci and floral morphology varied across the small geographic range of <em>P. hirsuta</em>, suggesting local differentiation and adaptation are possible over short distances.</p>