Just as careful blending of eye shadow can make a difference to our looks, a recent study has shown how flowers go to considerable trouble to fine tune their shades. In the relentless competition to attract bees, a slight edge can make the difference between life and death of a gene.
John Innes Centre researchers in the group of Professor Enrico Coen working alongside colleagues in Austria, China and Australia, investigated shades of yellow in wild populations of snapdragons (Antirrhinum majus).
The study makes use of a remarkable natural research resource in the Pyrenees – a hybrid zone where two varieties meet. One variety has yellow flowers with a magenta spot to highlight the bees entry point; the other has a complementary signpost, magenta flowers with a yellow spot.
The colour difference between varieties depends on seven genes which interact to control how the flower paints itself magenta and yellow. Three control the magenta paintbrush, four the yellow.
In the hybrid zone, genes from the two varieties mix to give a display of different colour combinations, including orange and white. While perhaps appealing to a gardener, the hybrid colour combinations are less attractive to bees, so natural selection keeps the geographic region of gene mixing narrow, only 1 km wide. The narrowness of the mixing region allows researchers to estimate the strength of natural selection on each gene.
The team has shown how four paintbrush genes work together to create a gradient of yellow. For the variety with magenta flowers, the gradient is steep, producing a yellow spot. For the variety with yellow flowers, the gradient is shallow, giving a graded blush of yellow. The effect of an individual paintbrush can be very subtle, hardly visible to the human eye, yet detectable by bees, bringing it under the radar of natural selection. The study shows how the effects of the four genes multiply to produce the two different yellow gradients.
First co-author of the study Dr Desmond Bradley said: “We have looked at how fascinating colour patterns in nature are formed and shaped, the genes that make such patterns and how their working together has been selected over evolutionary time to favour the dance and visit of bees.”
“Together these four genes act together to precisely hone the yellow gradient. Some genes have very subtle effects, but each contributes to the gradient pattern that is monitored by the bee. Even those patterns which we could hardly discern can be distinguished by the bee in the hybrid zone.”
Molecular gradients control a wide range of processes in biology, from butterfly wing colour patterns to drosophila egg development.
But it was not known how natural selection acts to hone such gradients, nor if it acts on one gene or multiple genes with different degrees of effect.
This study addressing this question offers a mechanism that may explain other molecular gradients in biology.
The Shaping of developmental gradients through selection on multiple loci in Antirrhinum, is in Science Advances
Science Advances
Experimental study
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The Shaping of developmental gradients through selection on multiple loci in Antirrhinum