Global warming may reroute evolution

February 16, 2011
The common milkweed (Asclepias syriaca) being eaten by a monarch caterpillar (Danaus plexippus). Credit: Rachel Vannette

( -- Rising carbon dioxide levels associated with global warming may affect interactions between plants and the insects that eat them, altering the course of plant evolution, research at the University of Michigan suggests.

The research focused on the effects of elevated on common milkweed, Asclepias syriaca. Milkweed is one of many plants that produce toxic or bitter to protect themselves from being eaten by insects. These chemical defenses are the result of a long history of interactions between the plants and insects such as monarch caterpillars that feed on them.

Plant defenses—and insect eating patterns—also respond to environmental factors such as rising carbon dioxide. This suggests that elevated carbon dioxide could affect plant by altering the "selection pressure" that plant-eating insects exert on plants.

Selection pressure, the driving force of evolution, induces changes in the genetic composition of a population. It works like this: if insects inflict too much damage on plants, the plants can't reproduce as successfully. This sets up a situation in which any plants that, by chance, have inherited insect-deterring traits are at an advantage. Because of that advantage, such traits are likely to spread through the population, urged on by "pressure" from the insects.

Researchers Rachel Vannette and Mark Hunter investigated whether different genetic "families" of the common milkweed from a single population in Northern Michigan would respond differently to increasing carbon dioxide levels in the atmosphere and if so, how those responses might affect the plants' chances of being eaten by insects.

"Specifically, we examined the response of milkweed plants to elevated carbon dioxide in terms of plant growth, asexual reproduction, and the production of chemical and physical defenses," Vannette said. Although all plants grew larger in response to elevated carbon dioxide, and all plant families showed similar growth and reproductive responses, plant families responded differently to elevated carbon dioxide in their production of chemical and physical defenses against plant-eating insects.

In particular, their production of heart poisons called cardenolides differed. While some plant families responded to elevated carbon dioxide by increasing cardenolide production, most decreased production—by as much as 50 percent.

"That's a big difference if you're a caterpillar," said Vannette, who is a graduate student in Hunter's research group. Hunter is the Henry A. Gleason Collegiate Professor of Ecology and Evolutionary Biology. Because the insects that consume milkweed, including monarch caterpillars, choose their host plants carefully and select specific plants based on the plants' concentration of toxic compounds, these specialist insects can act as agents of selection on milkweed plants.

Countering the shift away from chemical defenses was a shift toward physical defenses and resistance. "The plants had tougher leaves, and they were better at tolerating herbivory by caterpillars—they grew back faster," Vannette said.

Taken together, the results provide evidence that in response to elevated carbon dioxide, genetically-based differences in plant defense mechanisms and the changing plant-insect interactions that result may influence how adapt to changing climate.

Will the plants' changing defense strategies help or hinder monarchs?

"We don't know yet," Vannette said, "but that's a question we're investigating."

The findings appear in the March issue of Global Change Biology.

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5 / 5 (5) Feb 16, 2011
I don't want to sound rude, but isn't this obvious? An ecosystem is more than a few discrete constituent parts observed in isolation. If you tweak settings, so to speak, on one end of the spectrum, the effects will ripple beyond what was tweaked.
2 / 5 (1) Feb 16, 2011
Yeah it is obvious... a project from a student?
2.6 / 5 (5) Feb 16, 2011
Almost sounds like an April Fool's joke: "Let's write an article on evolution AND global warming JUST to get people excited!"
1 / 5 (4) Feb 16, 2011
1 / 5 (3) Feb 16, 2011
tricks are for kids
2.7 / 5 (7) Feb 16, 2011
Breaking news: ecosystems adapt to changing conditions. Chaos feared to be immanent.
2.3 / 5 (3) Feb 16, 2011
Guys. Please don't spoil my fun.
I want to see frothing at the mouth, conspiracy stories, blood on the carpet, things written in CAPS.
Where are the Drongos and clowns?
1 / 5 (2) Feb 16, 2011
... things written in CAPS.

And with LOTS of exclamation points!!!!

Although I'm hooked on it, arguing with crackpots is a dubious sort of hobby. A guy named Wheels over on PANDA'S THUMB descibed it as "like trainspotting -- but more like spotting train wrecks".
3 / 5 (4) Feb 17, 2011
Global Warming is such a powerful scam...that people are still writing about it. It is worse than religion.
5 / 5 (3) Feb 17, 2011
Global Warming is such a powerful scam...that people are still writing about it. It is worse than religion.

Global warming is ascually really happening. The only issue, which by some people drives their blood pressure high, is the level of responsibility of man for the warming of the global climate. Science should not be mismatched with ideology (see Nobel Peace prize 2007).
5 / 5 (2) Feb 17, 2011
orsr: I second that. The implications of AGW vs just plain GW are staggering. For example in this case for AGW the result is: We are destroying the planet, we've to stop the pollution. While in the case of plain GW we can just say: Yep, that's the nature for you. Adapt or perish. Next slide please.
not rated yet Feb 17, 2011
orsr: I second that. The implications of AGW vs just plain GW are staggering. For example in this case for AGW the result is: We are destroying the planet, we've to stop the pollution. While in the case of plain GW we can just say: Yep, that's the nature for you. Adapt or perish. Next slide please.

But, as in all things, it's not all or nothing. I'm not saying it's either (to be honest I haven't researched the issue enough to make a judgment for myself), but it is possible that it's both. Again, small changes in the system can provoke large changes in the system.
2 / 5 (3) Feb 17, 2011
JRDarby: Well, there is actually no dispute whether we have a finger in the pie. That one is a positive yes, but the AGW supporters are suggesting that we are the main culprit, and as such we should cease the pollution completely. Also they're painting the apocalyptic visions; if we choose to ignore it. In an ideal world, where it costs us nothing, we would certainly go for it, no questions asked. But the whole economy would be involved, and the costs would be stupendous. So in the end the question is cui bono. Is the threat real, the end results so destructive, and the chance of reverting the current prospect plausible ? Will it be worth the risks ? On the other side are those, who see it as a 'tunneling' of the economy by the politically motivated parties, trying to seize the power. The AGW skeptics (as well as me) believe, that the visions are not realistic, that we can't affect the outcome, and we should rather invest the money to prepare ourselves for the consequences; if any.
3 / 5 (2) Feb 17, 2011
Breaking news: ecosystems adapt to changing conditions. Chaos feared to be immanent.

Women, children, minorities hardest hit.

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