Using Genetic Analysis to Evaluate Hybridization as a Conservation Concern for the Threatened Species Quercus hinckleyi C.H. Muller (Fagaceae)

Premise of research. Hybridization among oaks is well documented and is of special concern in conservation efforts directed toward threatened or endangered Quercus, species such as Quercus hinckleyi. Methodology. This study uses DNA microsatellite analysis to characterize hybridization between the threatened oak Q. hinckleyi C.H. Muller and two putative hybridizing species, Quercus pungens Liebmann and Quercus vaseyana Buckley. The two potential hybridizers were sampled at Guadalupe Mountains National Park (GUMO), approximately 320 km from the current range of Q. hinckleyi. Quercus pungens and two possible hybrids located in near proximity to the relict populations of Q. hinckleyi were also sampled. Pivotal results. Genetic variability was high in all three species, with mean number of alleles per locus ranging from 12.625 to 17.875, mean observed heterozygosity from 0.734 to 0.807, and mean expected heterozygosity from 0.851 to 0.869. Quercus hinckleyi is genetically differentiated from the putative hybridizers and has two distinct genetic clusters within its metapopulation. The two hybridizer species from GUMO, where they are sympatric, are not differentiated. The population identified as Q. pungens found near Q. hinckleyi is genetically distinct from the GUMO samples and has five of eight genets with greater than 90% Q. hinckleyi introgression. Two of the 14 identified Q. hinckleyi in close proximity to this population had Q. pungens introgression. Bayesian clustering analysis showed that 5% of the samples identified as Q. hinckleyi in the field were hybrids, and one putative hybrid was confirmed genetically. Conclusions. While there is some hybridization in the Q. hinckleyi population, we found no evidence of genetic swamping. This may be explained by the spatial isolation of the Q. hinckleyi remnants relative to other oak species and by its common asexual (cloning) method of reproduction.