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Journal Article

The Cycas pectinata (Cycadaceae) Complex: Genetic Structure and Gene Flow

Si-Lin Yang and Alan W. Meerow
International Journal of Plant Sciences
Vol. 157, No. 4 (Jul., 1996), pp. 468-483
Stable URL: http://www.jstor.org/stable/2475251
Page Count: 16
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The Cycas pectinata (Cycadaceae) Complex: Genetic Structure and Gene Flow
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Abstract

The Cycas pectinata complex is a group of poorly understood Asian cycads threatened by habitat destruction and overcollecting. We estimated the genetic variation in 17 isozyme loci across 39 populations representing 10 taxa in this complex from China, India, Thailand, and Vietnam. Three species from Thailand and an Indian endemic were also examined for comparison. Lower levels of intrapopulation variation than those reported for other gymnosperms were found in the C. pectinata complex. Our results support the hypothesis that low intrapopulation variation with relatively high spatial differentiation is a biological and evolutionary characteristic typical of cycads, unlike other gymnosperms. Large numbers of historically shared alleles and high genetic identities confirmed the close relationships of taxa in the complex. Strong gene flow occurred among local populations 2-7 km apart. Long-distance gene flow was restricted. The estimates of gene flow among taxa were generally low except between C. pectinata var. pectinata and the three southern Thailand endemics. Cycas sp. "clivicola," possessing the least gene diversity in the complex, is likely the youngest species. Cycas siamensis has the highest gene diversity in the complex and is probably the oldest species, centered in southern Thailand. This region, harboring more morphologically distinct taxa than any other, is a diversity center for the complex. These populations in southern Thailand should be given priority in conservation.

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