When one parasite sucks the life out of another parasite
The cast of characters
The sand live oak, a small, scrubby species of tree found along the Gulf coast from Florida to Texas, has a tough life, thanks to the parasites that live on it. It's attacked by gall wasps, which lay eggs on the tree. This induces the tree to grow a gall, or tumour, which is part of the tree, but becomes a home for the developing wasp larvae.
The oak also hosts the love vine. According to Dr. Scott Egan, an Assistant Professor of Ecology & Evolutionary Biology at Rice University in Houston, this vine resembles tangled, orange fishing line that covers the oak tree. The vine also grows modified root structures that connect to the tree and draw nutrition and moisture from it.
A student in Dr. Egan's lab was the first to notice that the relationship between the parasites. She noted root connections specifically to the galls in which juvenile wasps were growing. When these gall was dissected, the team found fully developed but mummified gall wasps inside. The vine had been sucking nutrients from the gall, which in turn killed the wasp.
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Another interesting observation was that the love vine was only attached to larger galls. Scientists think this may be the result of the vine inducing the gall to grow larger in order to provide more nutrients - so both parasites are inducing this tumour-like gall growth.
The researchers plan to investigate further to understand the mechanism by which the vine finds the tumour. Dr. Egan thinks there is some possibility this may be helpful in human cancer research. Researchers are also interested in finding similar interactions among the thousand of parasitic plants and galls known in nature.