Molecular evidence for natural hybridization between two Melastoma species endemic to Hainan and their widespread congeners

Abstract

Natural hybridization plays an important role in speciation, genetic exchange, and adaptive evolution. However, it can also lead to the extinction of rare species or can generate super invasive species. Studies of natural hybridization involving rare species can therefore provide valuable information for species protection. In Melastoma, M. penicillatum and M. dendrisetosum are endemic to Hainan, China. M. dendrisetosum is at the edge of extinction, with a wild population of less than 300 individuals. Based on morphological observations during our field survey, we found that there are putative hybrids formed between the two endemic species and their widespread congeners, i.e. M. candidum × M. penicillatum and M. sanguineum × M. dendrisetosum. In this study, we sequenced four low-copy nuclear genes and five chloroplast DNA intergenic spacers of the putative hybrids and their putative parents. We found that these putative hybrids showed chromatogram signal additivity between putative parental species on differentially fixed sites at these nuclear genes. Haplotype networks also showed that at all four nuclear loci analyzed, alleles of the putative hybrids were shared with those of their putative parental species. The results above confirmed that hybridization occurred between M. candidum and M. penicillatum, and between M. sanguineum and M. dendrisetosum. Also, we found an extremely low level of genetic diversity in M. dendrisetosum relative to the three other species of Melastoma. It appears that there are strong ecological isolation between M. candidum and M. penicillatum as well as between M. sanguineum and M. dendrisetosum, and habitat disturbance caused by highway construction may have promoted hybridization between these species. Therefore, the key to protecting these two species endemic to Hainan is to reduce habitat disturbance. Artificial propagation of the species is another possible way to expand their population sizes.