Differential outcrossing rates in dispersing and non-dispersing achenes inthe heterocarpic plant Crepis sancta (Asteraceae)

Citation
Po. Cheptou et al., Differential outcrossing rates in dispersing and non-dispersing achenes inthe heterocarpic plant Crepis sancta (Asteraceae), EVOL ECOL, 15(1), 2001, pp. 1-13
Citations number
39
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Environment/Ecology
Journal title
EVOLUTIONARY ECOLOGY
ISSN journal
0269-7653 → ACNP
Volume
15
Issue
1
Year of publication
2001
Pages
1 - 13
Database
ISI
SICI code
0269-7653(2001)15:1<1:DORIDA>2.0.ZU;2-G
Abstract
The association between mating systems and dispersal in plants has been stu died mostly in cleistogamous species where, generally, seeds produced by cl eistogamous (selfed) flowers are less dispersed than seeds produced by chas mogamous (potentially outcrossed) flowers. In heterocarpic Asteraceae, non- dispersing fruits (achenes) are produced at the periphery of the capitulum (outer florets) whereas dispersing achenes are produced by inner florets in the same capitulum. Since all the florets are protandrous, the outer flore t developing first are in female phasis when anthesis of inner florets take s place. Thus, outer florets can be potentially selfed by the inner florets of the same capitulum whereas the latter must be pollinated by flowers of other capitula. Therefore outer florets should be more inbred than inner fl orets. To test this hypothesis, we measured the natural outcrossing rate in outer and inner florets using allozymes in three populations of the hetero carpic Crepis sancta. The results showed that the outcrossing rate was high est for non-dispersed achenes. Moreover, among the outcrossed achenes withi n a capitulum it was observed that the number of paternal parents of non-di spersing achenes was higher than for dispersing achenes. The pattern observ ed was therefore the opposite to the pattern of cleistogamous plants and co ntradicts the putative pollination mechanism we proposed for Asteraceae. Th e results agree with the predictions of sib competition theory which consid ers that outcrossing may minimize competitive interactions among relatives (sibs) falling near the mother plant. Higher outcrossing rate in outer flor ets could also occur because pollinators are more attracted to these floret s.