Pollinator movements and the polymorphism for outcrossing rate at the ray floret locus in Groundsel, Senecio vulgaris L.

Abstract

The relative attractiveness to pollinators (syrphid flies) of the radiate and non-radiate morphs of Senecio vulgaris was recorded in an artificial stand in which morphs occurred at equal frequency. Pollinators showed marked discrimination in favour of the radiate morph ; 72 per cent of 336 visits were to plants bearing radiate capitula. Analysis of pollinator flights between plants showed a bias for radiate to radiate transitions (R-R), followed by non-radiate to radiate (N-R), then radiate to non-radiate (R-N) transitions. Flights between non-radiate plants (N-N) were very infrequent. The greater frequency of N-R relative to R-N transitions resulted from an increase in preference for the radiate morph as pollinators moved from the first to the second plant during a flight sequence. A cause of this behaviour is suggested. Given certain assumptions, the observed pattern of intermorph transition flights would explain, in part, the greater female outcrossing by the radiate morph based on intermorph crossing, and, in turn, the higher female outcrossing rate of radiate relative to non-radiate disc florets recorded previously in some polymorphic populations.