Format: ORAL

Alice L.M. Fairnie1, Babu Ram Paudel2, Kelly Shepherd3, Sam McCarren3, Eva Deinum4, Rob Ingle3, Lawrence D. Harder5, Bruce Anderson6, Nicola Illing3, Spencer C.H. Barrett1

1 University of Toronto, Ontario, Canada 2 Tribhuvan University, Kathmandu, Nepal 3 University of Cape Town, Cape Town, South Africa 4 Wageningen University & Research, Wageningen, The Netherlands 5 University of Calgary, Canada 6 Stellenbosch University, Stellenbosch, South Africa

Diverse floral mechanisms have evolved in angiosperms to promote cross-pollination and outcrossed mating. One such innovation is the sexual polymorphism enantiostyly (mirror-image flowers) where styles are deflected either left (L), or right (R) of the flowers midline. This asymmetry is usually associated with heteranthery, the structural specialization of anthers for feeding and pollinating functions. Pollinating anthers are reciprocally positioned to the style promoting bee-mediated cross-pollination between flowers of opposite handedness by buzz-pollinating bees. Cyanella has nine species mostly endemic to the Western Cape, South Africa; six are straight-styled and two possess enantiostyly. Here, we present current research on C. alba using multiple populations in the Biedouw valley and Bokkeveld plateau, all of which contained three sex phenotypes – left- and right-handed plants and those with a mixture of both flower types (L, R, M, respectively). Surveys of handedness revealed average frequencies of L=0.47, R=0.43, M=0.10 among 15 populations with an average daily display size of 1.6 flowers. Censuses of marked plants throughout two seasons in three populations revealed an increase in M frequency concomitant with decreases in L or R plants. Controlled crosses demonstrated moderate self-incompatibility, with plants incapable of autonomous self-pollination. Comparisons of open- versus controlled cross-pollinations revealed chronic pollen limitation of seed set. Despite 74 hours of observation, we observed only two short visits by buzz-pollinating bees and most flower visits were by beetles. Observations of stamen dimorphism at the northern range edge suggest that heteranthery may be breaking down in some populations enabling generalist pollination, perhaps in response to the absence of visits by bees capable of buzz pollination. Cyanella alba plants display few flowers daily and this could enable enantiostyly to function effectively without genetic determinism of floral polymorphism. Breakdown of heteranthery in some populations has probably resulted from a lack of buzz pollination.