Hybridization in the Fringed Orchids: An Analysis of Species Boundaries in the Face of Gene Flow
2023
Simone A. Evans | Dennis F. Whigham | Ida Hartvig | Melissa K. McCormick
Natural hybridization between closely related species in sympatry is an evolutionary process that is common in orchids. Once seen as a threat to parent species, interspecific genetic change is increasingly viewed as a source of novel variation in some ecological contexts. Terrestrial fringed orchids in the genus <i>Platanthera</i> contain several clades with high genetic compatibility among species and many putative hybrids. We used biallelic SNPs generated with 3RAD sequencing to study the hybrid complex formed from the parent species <i>P. blephariglottis, P. ciliaris,</i> and <i>P. cristata</i> with high resolution. The genetic structure and phylogenetic relationship of the hybrid complex revealed site-dependent gene flow between species. We documented extensive hybridization and cryptic hybrids in sympatric sites. Interspecific genetic exchange is particularly common between <i>P. blephariglottis</i> and <i>P. ciliaris</i>, with cryptic hybrids among putative <i>P. ciliaris</i> samples being more common than parental assignments in sympatric sites. Hybridization across the triad species complex can reticulate lineages and introduce adaptive alleles. Conversely, it can reduce diversification rates and introduce maladaptive alleles. Investigation into whether anthropogenic forces are eroding species boundaries, particularly the permeable <i>P. blephariglottis</i> and <i>P. ciliaris</i> boundary, is appropriate for conservation efforts.
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