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Mari N. Jensen
Subjecting aphids to heat stress shows that complex ecosystem interactions coupled with rapid evolution may buffer some species against environmental change.
Although ecologists expect climate change will harm many species, changes in the ecosystem combined with the potential for rapid evolution could buffer the harm to some species, according to a research team that includes University of Arizona biologist Nancy Moran.
The team studied how well populations of pea aphids, an agricultural insect pest, managed during increasing bouts of hot weather.
The number of aphids was influenced by the insects' interactions with predators plus their potential for rapid evolutionary adaptation, the researchers reported in the March 6 issue of the journal Science. The National Science Foundation funded the research.
"If you're interested in environmental change and how species are going to respond to it, you can't just look at a single species in isolation," said lead author Jason Harmon of the University of Wisconsin-Madison. "You have to think about those other species around it, and you have to think about the species' potential to change along with the environment."
Pea aphids, known to scientists as Acyrthosiphon pisum, have symbiotic bacteria within their cells. The bacteria, which are passed from mother to child, supply the insect with crucial nutrition. The aphids die if their bacteria die.
Moran, a UA Regents' professor of ecology and evolutionary biology, said, "Because we can experimentally manipulate aphid bacteria, we have an excellent model system to explore evolutionary adaptation."
Earlier work from Moran's lab showed that some symbiotic bacteria confer heat tolerance to their host aphids.
Although high temperatures do decrease pea aphid reproduction, the symbiotic bacteria bestow the aphids with a possible evolutionary defense. How well an aphid reproduces at higher temperatures is influenced by which bacteria it contains.
In field experiments, the researchers applied heat stress to populations of aphids that hosted different internal bacteria. Populations of the heat-sensitive aphids grew much more slowly, indicating that at hotter temperatures the heat-tolerant aphids would have the advantage.
The results show the potential for rapid evolution could have a large impact on how populations respond to environmental change.
"The new study shows the complexity of these effects in real populations," Moran wrote in an e-mail.
Which predatory lady bird beetle species was present also affected aphid survival, showing that the structures of local food webs may mitigate environmental changes.
Co-author Anthony Ives of the University of Wisconsin-Madison said, "Right now, a lot of work is focused on just individual species. To understand what happens to any one particular species, you need to broaden your scope and consider other species."
One of the take-home messages is predictions of the consequences of environmental change on populations must take into account both ecological and evolutionary complexities, Harmon said.
While predicting the response of species to climate change is complicated, Ives said, the new study may de-mystify complex processes by identifying specific factors that are relevant.
Ives hopes this new work will help other scientists take a broad ecological and evolutionary view when studying the effects of environmental change.
This story is modified from one written by Jill Sakai of the University of Wisconsin-Madison.
Mari N. Jensen