Dr Beverley Glover in the Department of Plant Sciences has been studying the interaction between pollinating animals and the surface structures of flowers in the Botanic Garden for over a decade.
One of the earliest experiments involved growing snapdragons (Antirrhinum majus), in which the flowers have conical petal epidermal cells, and a mutant snapdragon that instead has flat cells. A summer of watching bees visiting the flowers revealed that the bees preferred the conical-celled flowers to the flat-celled ones.
Building on this research with Professor Lars Chittka, an expert in bee vision and cognition at QMUL, we then investigated whether the bees could see the difference between conical-celled flowers and flat-celled ones. The conical cells focus light into the pigment and make the flower appear deeper in colour. Using painted artificial flowers we showed that the bees could distinguish between the two colours, but that they had no innate preference for either colour. Then we investigated whether the bees could see the difference between the two petal surfaces in a completely white flower, where humans can see no difference. Surprisingly, bees can, and we are currently trying to establish what the visual cue is that they are using.
We wondered also whether the bees could feel differences underfoot between the conical-celled and flat-celled petal surfaces. To test this we made dental wax casts of different petal surfaces, and then epoxy resin imprints of the casts, to give us perfect replicas of the surface texture. We offered these to our bees, with a ‘reward’ of sweet-tasting sucrose in one flower type, and a ‘punishment’ of bitter-tasting quinine in the other. The bees learned very quickly to feel the surface texture and then decide whether to drink or not. We are currently investigating whether changing the orientation of the flower makes any difference to this behavioural response, working on the idea that conical cells might provide ‘grip’ to insects that pollinate flowers from unusual angles.
More recently we have started to look at the finer details of petal surfaces. The fine striations of cuticle on many petal cells can also influence light, with regular patterns even producing iridescence. By making epoxy resin flowers in a variety of colours, some with and some without these iridescent structures on their surfaces, we are beginning to analyse how insects might respond to these detailed pollination cues.
The Botanic Garden has been an invaluable resource for all this work, providing outdoor research areas and horticultural expertise, and, most importantly, the inspiration that we find just from watching the flowers and insects getting on with their daily lives.