Identification of interspecific hybrids is often a subject of primary concern in the development of conservation strategies. Here we performed a genetic analysis combining mitochondrial DNA (mtDNA), microsatellites and single nucleotide polymorphic sites (SNPs) to assay the level of hybridization and introgression between an introduced babbler, Chinese hwamei Leucodioptron canorus, and its close relative, the endemic Taiwan hwamei L. taewanus in Taiwan. Fifty-five Chinese hwameis from the Asian mainland and 69 Taiwan hwameis, including nine morphological hybrids, were sampled and analyzed. Evidences of mitochondrial introgression were found in three hybrids and one Taiwan hwamei. Five unlinked interspecific SNPs were identified at nine anonymous nuclear loci with interspecific differentiation (total Fst=0.77) that was much higher than that at seven highly polymorphic microsatellite loci combined (total Fst=0.1). Bayesian cluster analysis based on five interspecific SNP loci and two highly differentiated microsatellite loci (Fst>0.08) suggested that twelve individuals sampled in Taiwan were likely F2 or backcross hybrids, among which eight were morphological intermediates. A total of 20.3% (14/69) individuals sampled in Taiwan were suggested to be hybrids, suggesting that fitness reduction in hybrids might be negligible. These results imply that without an effective management strategy, the entire Taiwan hwamei population could easily become an admixed with Chinese hwamei and loose its evolutionary integrity. To reduce introgressive hybridization, illegal trade of Chinese hwamei should be strictly regulated and only the expensive male Chinese hwameis should be legally imported to minimize the chance for Chinese hwameis being released into the field. In our study we also found interspecific SNP markers to outperform microsatellite loci in detecting hybridization and introgression between two closely related species, which may be ascribed to the lower level of homoplasy of SNP loci.
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