Morphological and molecular evidence of natural hybridization in Shorea (Dipterocarpaceae) |
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Authors: | Koichi Kamiya Yik Yuen Gan Shawn K Y Lum Min Sheng Khoo Siew Chin Chua Nik N H Faizu |
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Institution: | (1) Natural Sciences and Science Education Academic Group, National Institute of Education, Nanyang Technological University, 1 Nanyang Walk, Singapore, 637616, Singapore;(2) Center for Tropical Forest Science—Arnold Arboretum Asia Program, 1 Nanyang Walk, Singapore, 637616, Singapore;(3) Faculty of Agriculture, Ehime University, 3-5-7 Tarumi Matsuyama, Ehime 790-0865, Japan |
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Abstract: | Shorea (Dipterocarpaceae) is a large genus in which many closely related species often grow together in Southeast Asian lowland
tropical rain forests. Many Shorea species share common pollinators, and earlier studies suggested occurrence of interspecific hybridization and introgression.
Here, we show morphological and molecular evidence of hybridization between Shorea species. In the census of all the trees of Shorea curtisii, Shorea leprosula, and Shorea parvifolia (>30 cm dbh) within the 164-ha area of Bukit Timah Nature Reserve in Singapore, we found 21 morphologically recognizable
hybrid individuals. All of the putative hybrids could be distinguished obviously from the parental species on the basis of
vegetative characters. Population genetic analysis of DNA sequences of two nuclear (GapC and PgiC) and chloroplast (trnL-trnF) regions demonstrated that each of the three species had several species-specific mutations. The nuclear sequences of the
putative hybrids were heterozygote at all the species-specific sites between two parental species. Hybrid between S. curtisii and S. leprosula was found most, while S. curtisii × S. parvifolia and S. leprosula × S. parvifolia hybrids were also found. Almost no shared polymorphism between populations of the parental species suggests rarity of introgression.
The study indicated that natural hybridization between sympatric Shorea species should not be uncommon, but all of the hybrid individuals were F1, and the post-F1 hybrids were considerably rare. |
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