Abstract
Introgression may lead to discordant patterns of variation among loci and traits. For example, previous phylogeographic studies on the genus Quasipaa detected signs of genetic introgression from genetically and morphologically divergent Quasipaa shini or Quasipaa spinosa. In this study, we used mitochondrial and nuclear DNA sequence data to verify the widespread introgressive hybridization in the closely related species of the genus Quasipaa, evaluate the level of genetic diversity, and reveal the formation mechanism of introgressive hybridization. In Longsheng, Guangxi Province, signs of asymmetrical nuclear introgression were detected between Quasipaa boulengeri and Q. shini. Unidirectional mitochondrial introgression was revealed from Q. spinosa to Q. shini. By contrast, bidirectional mitochondrial gene introgression was detected between Q. spinosa and Q. shini in Lushan, Jiangxi Province. Our study also detected ancient hybridizations between a female Q. spinosa and a male Q. jiulongensis in Zhejiang Province. Analyses on mitochondrial and nuclear genes verified three candidate cryptic species in Q. spinosa, and a cryptic species may also exist in Q. boulengeri. However, no evidence of introgressive hybridization was found between Q. spinosa and Q. boulengeri. Quasipaa exilispinosa from all the sampling localities appeared to be deeply divergent from other communities. Our results suggest widespread introgressive hybridization in closely related species of Quasipaa and provide a fundamental basis for illumination of the forming mechanism of introgressive hybridization, classification of species, and biodiversity assessment in Quasipaa.
Highlights
Introgressive hybridization was first described by Anderson and Hubricht (1938) in a study on plant hybridization
Introgressive hybridization has been detected in a variety of isolated populations that have come into secondary contact
We analyzed the phylogenetic relationships of mitochondrial DNA (mtDNA)
Summary
Introgressive hybridization was first described by Anderson and Hubricht (1938) in a study on plant hybridization. Many authors regard introgressive hybridization as a creative factor by introducing an unprecedented genetic material during speciation and exploring mechanisms of gene flow between populations (Arnold, 1997; Jiggins & Mallet, 2000; Templeton, 1989) This perspective is common in botanical studies, and botanists verify that groups of interbreeding species of ecological, morphological, genetic, and evolutionary differences are not influenced by extensive hybridization (Hedrick, 2013; Templeton, 1989). We captured a large sample of specimens that were distributed from west to east of South China and studied them using mtDNA and nuclear genes to test whether introgressive hybridization extensively occurs in Quasipaa in the sympatric distribution region. This study provides a fundamental basis for elucidating the forming mechanism of introgressive hybridization, classification of species, and genetic diversity assessment in Quasipaa
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