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Experimental Assessment of Reproductive Interactions Between Sympatric Aster and Erigeron (Asteraceae) in Interior Alaska

W. Scott Armbruster and A. David McGuire
American Journal of Botany
Vol. 78, No. 10 (Oct., 1991), pp. 1449-1457
Stable URL: http://www.jstor.org/stable/2445283
Page Count: 9
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Experimental Assessment of Reproductive Interactions Between Sympatric Aster and Erigeron (Asteraceae) in Interior Alaska
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Abstract

Erigeron glabellus and Aster sibiricus have similar flowers, share pollinators, but bloom sequentially in interior Alaska. Both species depend on insect pollination for seed set: the Erigeron is self-incompatible, and the Aster is apparently self-compatible but allogamous. To test the hypothesis that sequential blooming is maintained by natural selection generated by reproductive interference, we manipulated the flowering time of Erigeron, forcing it to bloom simultaneously with Aster, and measured female fecundity in both species. We found no evidence of reduced female fecundity in either species caused by the presence of the sympatric "competitor" or by artificial pollination with the heterospecific pollen prior to conspecific pollination. Two-species mixtures of simultaneously blooming Aster and Erigeron experienced significant interspecific visitation, which may, under natural conditions, cause loss of pollen to alien stigmas and depressed male fecundity, at least in Erigeron. We found no evidence that sequential blooming in Erigeron and Aster is maintained by depressed female fecundity through pollinator sharing. If sequential blooming is maintained by natural selection, it seems more likely to be the result of selection generated by depressed male fitness through pollen loss to alien stigmas.

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