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Most caterpillars
avoid ants out of self-preservation. But some strike a deal with their
predators. In exchange for receiving nectar droplets, ants groom the
caterpillars and fend off other predators. Now researchers have shown
that such symbiotic relationships also come with a twist: Lycaenid
caterpillars, when threatened, increase their production of nectar to
entice the ants to stick around in a crisis.
Nature has many
examples of mutually beneficial relationships. But often the terms seem
set in stone. In the case of pollination, for example, many flowers
always offer bees the same amount of pollen. But some relationships have
a more dynamic balance. A yucca, for example, will step up its
self-defenses if its pollinator begins to take advantage of the
relationship. A team of researchers led by biologist Anurag Agrawal at
the University of Toronto in Canada wondered if adjustments like this
"inducible defense" might be found in the caterpillar-ant
relationship.
To find out,
Agrawal's team gently squeezed lycaenid caterpillars with tweezers to
mimic an ant attack. Caterpillars surrounded by ants oozed twice as much
sugar as they normally do when being groomed, the researchers report in
the 22 September issue of the Proceedings of the Royal Society of
London. The ants, in turn, spent 30% more time tending to the
caterpillars than their peers grooming the unsqueezed caterpillars.
"Organisms are not standing on a corner passing out dollars
bills," says Agrawal in explaining why he thinks those two findings
are related. "The [caterpillars] are giving them to those that help
them."
The study provides
researchers with another small piece of the puzzle that describes animal
behavior. "It shows how ideas about inducible defenses in plants can
provide novel insights into the evolution of symbioses between ants and
other insects," says biologist Naomi Pierce of Harvard University.
--JEANNE ERDMANN
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