The green tree leaves of summer are already starting to give way to the bright yellows and reds of autumn. We should have a brilliant display of colors throughout the fall.
For the most part, scientists thought that the changing of leaf color in autumn was simply an effect of the disappearance of chlorophyll and signaled that the leaves were about to fall. Over the past several years, however, researchers have found that the appearance of yellow, orange, and red leaves may have additional ecological impacts.
In 2005, researchers Martin Schaefer and Gregor Rolshausen proposed that the changing leaf color actually acts as a defensive signal against consumption by herbivores (plant-eating organisms). The "Defense Indication hypothesis," as they termed it, is based on their own work as well as on observations that support their ideas, but were made by other researchers. Their hypothesis (or, idea that will be tested through experiments and observations) is based on the fact that the signaling pathway that causes the production of anthocyanins also causes the production of defensive compounds to which herbivores have an aversion. After enough time, it is thought that herbivores learn to associate the defensive compounds with the colored leaves and avoid them altogether.
|The very hungry caterpillar ate lots of stuff, but not orange, red, or yellow leaves.|
While the primary cause of autumn leaf colors is the loss of chlorophyll, this paper discusses just one example of how the color change has a significant impact on other organisms. Like so many things in nature, one change often has the potential to ripple through the environment and bring about widespread ecological effects.
Contributed by: Kelly HallstromVisit Kelly’s blog, You Don’t Have To Be A Rocket Scientist
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Schaefer HM, & Rolshausen G (2006). Plants on red alert: do insects pay attention? BioEssays : news and reviews in molecular, cellular and developmental biology, 28 (1), 65-71 PMID: 16369938