And I thought red leaves were just pretty.

Via PhysOrg we learn that trees might have evolved all their autumnal splendor not for the benefit of humankind's viewing, but to protect themselves from aphids.

Along with his colleagues, Professor Jim Hardie from the Division of Biology at Imperial and Dr Marco Archetti from Oxford University, Dr Döring has theorised that the production of red pigments in leaves could be concealing the yellow leaf colour that is highly attractive to tree-damaging insects such as aphids.

Yellow pigments are present in leaves in the spring and summer but only become visible in autumn when the tree breaks down and recovers green chlorophyll from leaves before they fall off. The red colour, on the other hand, is caused by pigments called anthocyanins that are produced in the autumn, just before leaf fall.

To test their theory, ... Dr Döring ... sampled the colour of hundreds of leaves from many different tree species and used the results from the trap experiment to predict how attractive the colour of each leaf would be for the insects. He found that red leaves were much less attractive than green or yellow ones for aphids.

The team speculate that some tree species may benefit from producing red leaves as a safety mechanism to fight off aphids. If these insects land on them to lay their eggs in large numbers, this could affect the growth of the trees in spring and potentially reduce their fitness.

...

The question of why some trees stay yellow and would not use red to conceal themselves is maybe down to the relative cost of the insect attack on the tree, explains Dr Döring: "In theory, if insect attack is generally high, causing higher costs than the costs for the production of red anthocyanins in autumn, trees would benefit from being red. If the costs entailed by the insects is lower, then you can afford to stay yellow.”

Cool. Of course, when I go every morning to walk in to work and classes, I likely won't be thinking about aphids and tree color, merely reveling in the wonderfulness that is the mutli-varied hues of autumn in Michigan. (Not as nice as Vermont apparently is, but then again Tree Town is usually quite stunning enough in its own right.)