Petals, pigments and pollinator preferences
As the world population rises, we will need to grow more food. Insect pollination is essential or beneficial for ~75% of crops, including most fruit, nuts, and commodity crops such as coffee and cocoa, yet there is evidence of significant global decline in insect numbers: this conflict is central to my research. Solutions involve developing self-fertile cultivars (time-consuming and not always possible), large-scale increase of pollinator numbers (possible but involving significant input or change over large areas), or the production of new cultivars which are more attractive to insects and which provide them with more or better nectar and pollen rewards for visiting (the basis of my research). With this latter approach, it will be possible to not only use the existing insect resource more efficiently, but also to increase the available food supply for pollinators, helping to boost their populations. Focussing on strawberries, an important commercial crop whose quality and yield are increased by insect pollination, I have measured nectar and pollen rewards in 20 commercial varieties of strawberry, identifying variation in nectar production based on temperature in some varieties, and variation in pollen quantity and viability. Using an image-recognition program I wrote, I have characterised variation in floral shape for the same varieties, identifying significant variation between varieties in flower size and shape. In our bee behaviour laboratory, I have used plastic artificial ‘flowers’ and lab colonies of bumblebees to test bee responses to the limits of observed variation in shape, in terms of recognition and finding speed, and found that more stellated flower outlines result in a small but non-significant decrease in the time it takes bees to find the 'flowers’. I have conducted experiments to measure bee feeding and vomiting rates when provided with nectar of differing sugar concentrations, which informs models which predict the sucrose concentration within nectar which maximises energy return to the nest. I have also tested bee decision-making when faced with rewards with varying ease of access, and found that bees can trade off the sugar reward within nectar against the energetic cost of accessing that nectar. These experiments help to inform efforts to produce crop varieties which maximise the rate of energy return to the nest. Finally, I have shown that previous observations of the nectar preferences of bumblebees conducted at laboratory scale are relevant at nectar concentrations and quantities found naturally in crop plants. Another floral trait which is highly relevant to pollinators is floral colour. Parallel to the strawberry research, I have been investigating the molecular mechanism of floral colour production in both the model plant Arabidopsis thaliana (which has white flowers) and a pink-flowered species in the closely related genus Aethionema. I have produced transformed Arabidopsis lines which overexpress pairs of transcription factors, which give information on which combinations produce the most pigment in that species. Additionally, using a comparative transcriptomic approach, I have identified transcriptional activators which are likely to be implicated in flower colour in Aethionema. However, experiments to ectopically express these activators in Nicotiana tabacum have not shown any increase in petal colour, indicating that the promoter sequences from Aethionema are not sufficient to drive heterologous expression.
Aethionema, Bumblebee drinking, Bumblebees, Crops, Flower colour, Flower shape, Flowers, Insect vision, Pollination
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