Abstract
Natural hybridization can lead to various evolutionary outcomes in plants, including hybrid speciation and interspecific gene transfer. It can also cause taxonomic problems, especially in plant genera containing multiple species. In this study, the hybrid status of Melastoma affine, the most widespread taxon in this genus, and introgression between its putative parental species, M. candidum and M. sanguineum, were assessed on two sites, Hainan and Guangdong, using 13 SSR markers and sequences of a chloroplast intergenic spacer. Bayesian-based STRUCTURE analysis detected two most likely distinct clusters for the three taxa, and 76.0% and 73.9% of the morphologically identified individuals of M. candidum and M. sanguineum were correctly assigned, respectively. 74.5% of the M. affine individuals had a membership coefficient to either parental species between 0.1 and 0.9, suggesting admixture between M. candidum and M. sanguineum. Furthermore, NewHybrids analysis suggested that most individuals of M. affine were F2 hybrids or backcross hybrids to M. candidum, and that there was extensive introgression between M. candidum and M. sanguineum. These SSR data thus provides convincing evidence for hybrid origin of M. affine and extensive introgression between M. candidum and M. sanguineum. Chloroplast DNA results were consistent with this conclusion. Much higher hybrid frequency on the more disturbed Guangdong site suggests that human disturbance might offer suitable habitats for the survival of hybrids, a hypothesis that is in need of further testing.
Highlights
The roles of hybridization in plant evolution have been well recognized in the past few decades
We aimed to address the following two questions: 1) Is M. affine a hybrid between M. candidum and M. sanguineum? 2) If so, is there extensive introgression between these two species? To this end, we used 13 SSR markers to genotype multiple individuals of the three Melastoma taxa in two locations, where they are sympatric
We identified 55, 77 and 81 alleles for M. candidum, M. sanguineum and M. affine, respectively
Summary
The roles of hybridization in plant evolution have been well recognized in the past few decades (reviewed in [1]). Interspecific hybridization can lead to hybrid speciation by allowing adaptation to extreme or novel habitats [2], reinforcement of premating isolation as a response to maladaptive hybridization [3,4], and adaptive gene transfer through introgression [5]. Studies of hybridization are important for understanding interspecific relationships and evolutionary processes. It is interesting to study reproductive isolation in zones of hybridization and introgression, where species can maintain their identity in the face of extensive gene flow. Hybridizing species can exchange neutral or adaptive alleles, while genes underlying local adaptation or related to reproductive isolation will be impeded [6]. Differential introgression between hybridizing species, which refers to locusspecific patterns of introgression across the genomes, offers excellent opportunities to investigate the contribution of ecological processes to speciation [7,8,9]
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