346 research outputs found
Linking Self-Incompatibility, Dichogamy, and Flowering Synchrony in Two Euphorbia Species: Alternative Mechanisms for Avoiding Self-Fertilization?
Background: Plant species have several mechanisms to avoid selfing such as dichogamy or a self-incompatibility response.
Dichogamy in a single flower may reduce autogamy but, to avoid geitonogamy, plants must show flowering
synchronization among all their flowers (i.e. synchronous dichogamy). It is hypothesized that one species would not
simultaneously show synchronous dichogamy and self-incompatibility because they are redundant mechanisms to reduce
selfing; however, this has not been accurately assessed.
Methodology/Principal Findings: This expectation was tested over two years in two natural populations of the closely
related Mediterranean spurges Euphorbia boetica and E. nicaeensis, which completely avoid autogamy by protogyny at the
cyathia level. Both spurges showed a high population synchrony (Z,79), and their inflorescences flower synchronously. In E.
nicaeensis, there was no overlap among the cyathia in anthesis of successive inflorescence levels and the overlap between
sexual phases of cyathia of the same inflorescence level was uncommon (4â16%). In contrast, E. boetica showed a high
overlap among consecutive inflorescence levels (74â93%) and between sexual phases of cyathia of the same inflorescence
level (48â80%). The flowering pattern of both spurges was consistent in the two populations and over the two successive
years. A hand-pollination experiment demonstrated that E. nicaeensis was strictly self-compatible whereas E. boetica was
partially self-incompatible.
Conclusions/Significance: We propose that the complex pattern of synchronized protogyny in E. nicaeensis prevents
geitonogamous crosses and, consequently, avoids selfing and inbreeding depression. In E. boetica, a high probability of
geitonogamous crosses may occur but, alternatively, this plant escapes selfing through a self-incompatibility response. We
posit that synchronous dichogamy and physiological self-incompatibility do not co-occur in the same species because each
process is sufficiently effective in avoiding self-fertilization.España Ministerio de Ciencia y TecnologĂa PLO CGL2005-03731; CGL2008-02533-EEspaña Ministerio de Ciencia y TecnologĂa MA CGL2009-0825
Spatial and temporal plant phenological niche differentiation in the Wadi Degla desert ecosystem (Egypt)
Twenty dominant plant species representing different life forms were investigated phenologically over a period of 36 months (January 2004 to December 2006). Plant populations were sampled at down-, mid-, and upstream sites in a desert wadi ecosystem. The results were analyzed using TWINSPAN, DCA and CCA techniques. Five phenological niches were apparent: (1) species flowering all year round, with peaks in spring and autumn such as Ochradenus baccatus; (2) species flowering during winter including Lycium shawii and Tamarix nilotica; (3) species flowering during spring, e.g., Zilla spinosa, Zygophyllum coccineum and Capparis spinosa; (4) species flowering during summer including Iphiona mucronata and Deverra triradiata; and (5) species flowering during autumn that include Atriplex halimus and two Anabasis species. The climatic variables, including temperature, rainfall and relative humidity, affect the phenological niches and between-species differences. Within-species variations occurred between years and there were no between-site variations for most study species. The different plant species exhibited phenological diversity along the course of the wadi ecosystem. The phenological niches are species-specific and environmentally dependent rather than local selective pressures
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