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Journal Article

Outcrossing Rates of Two Endemic Shorea Species from Sri Lankan Tropical Rain Forests

Darlyne A. Murawski, Bama Dayanandan and Kamaljit S. Bawa
Biotropica
Vol. 26, No. 1 (Mar., 1994), pp. 23-29
DOI: 10.2307/2389107
Stable URL: http://www.jstor.org/stable/2389107
Page Count: 7
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Outcrossing Rates of Two Endemic Shorea Species from Sri Lankan Tropical Rain Forests
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Abstract

An allozyme analysis of the mating systems of Shorea congestiflora and S. trapezifolia provide for the first quantitative estimates of outcrossing in a rain forest plant of the Old World tropics. Prior to recent deforestation, both endemic species formed vast co-dominant stands with other dipterocarp trees in the southwest of Sri Lanka. Outcrossing rates were determined from seed cohorts collected from trees in the Sinharaja Biosphere Reserve. Eighty-seven percent of the seeds of S. congestiflora were the result of the maternal tree mating with other unrelated individuals. This high population outcrossing rate is typical of the limited number of rain forest trees studied in the neotropics. The range of outcrossing rates for individual trees of this species suggest that self-incompatibility systems may be variable among individuals. S. trapezifolia exhibited a mixed-mating strategy with only 54 and 62 percent of seeds resulting from outcrossing in two succeeding years. Differences between the outcrossing rates of the two species may reflect average differences in the degree of self-incompatibility. Apomixis could not be detected in either species from comparisons of progeny multilocus genotypes relative to maternal genotypes.

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