1 Tahrcountry Musings: The significance of visual ‘nectar guides’

Sunday, July 31, 2011

The significance of visual ‘nectar guides’

Floral signposts: testing the significance of visual ‘nectar guides’ for pollinator behaviour and plant fitness

Dennis M. Hansen,Timotheüs Van der Niet and Steven D. Johnson

 July 27, 2011Proc. R. Soc. B

Yesterday we were  discussing about the leaves that act like neon signs in restaurants. Here is another feature that is akin to what we were discussing. This time it is nectar guides, contrasting patterns on flowers that direct pollinators towards a concealed nectar reward.

The researchers experimentally investigated the role of nectar guides in a natural system, the South African iris Lapeirousia oreogena, whose flowers have a clearly visible pattern of six white arrow markings pointing towards the narrow entrance of the long corolla tube. The sole pollinator is a long-proboscid nemestrinid fly.
The investigators painted over none, some or all of the white arrow-markings with ink that matched the colour of the corolla background. Aarrow-marking removal had little effect on the approaches by flies to flowers from a distance, but it significantly, and according to the words of the researchers dramatically reduced the likelihood of proboscis insertion. The researchers say export of pollen dye analogue (an estimate of male fitness) was reduced to almost zero in flowers from which all nectar guides had been removed, and fruit set (a measure of female fitness) was also significantly reduced. 
According to the researchers their experiments confirm that the markings on L. oreogena flowers serve as nectar guides and suggest that they are under strong selective maintenance through both male and female fitness components in this pollination system.

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