Polymorphism for outcrossing frequency at the ray floret locus in senecio vulgaris L. III. causes

Abstract

Measurement of outcrossing rates of ray (female) and disc (hermaphrodite) florets of radiate plants sampled from two polymorphic populations of Senecio vulgaris showed that ray florets outcross at much greater frequencies. In one population from Leeds, the greater recorded outcrossing of radiate relative to non-radiate plants (Marshall and Abbott, 1984) can be entirely accounted for by the higher outcrossing of ray florets in radiate capitula while, in a second population, from Cardiff, the difference is partly explained by the same effect. It is concluded that the possession of female ray florets and the resulting functional protogyny exhibited by radiate capitula (Burtt, 1977), are major causes of the reported difference in outcrossing frequency between radiate and non-radiate morphs in polymorphic populations of S. vulgaris. There are however, additional factors, the nature of which have not yet been determined, which may also contribute to the difference in some populations (e.g., at Cardiff), if not all polymorphic populations.