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Catching evolution's henchmen in the act

Smithsonian researchers share a $5 million NSF grant to track down Wolbachia

Smithsonian Tropical Research Institute

Everyone has mitochondria--the famous "powerhouse" of eukaryotic cells can hardly be considered a disease. But mitochondria may be relicts of an ancient invasion, an epidemic that took place 500 million years ago. Wolbachia, a bacterial group related to the ancestor of mitochondria, infects a wide range of insects and manipulates host reproduction to promote its own survival. A posse, with $5 million from the US National Science Foundation, is on its trail.

"Wolbachia kills males, causes immaculate conception, and perhaps even accelerates speciation," says Don Windsor, Staff Scientist at the Smithsonian Tropical Research Institute.

Windsor´s lab will collect insects in Panama, a biodiversity hot spot, and will take advantage of molecular tools to find out which Wolbachia strains tropical insects harbour.

Wolbachia strains are indistinguishable without DNA sequencing. "A strain that causes male-killing in a beetle can cause male feminization in a butterfly", says Gwen Keller, who's busy writing up her dissertation on the subject. "The first generation of molecular Wolbachia research allowed us to tell which invertebrates were infected and to identify strains based on one or two genes"

"Studies of basic ecology showed us the range of Wolbachia's manipulative effects. In the next few years, with a greater number of Wolbachia genes at our disposal, we'll be able to more accurately describe bacterial strains, especially now that we know strains can recombine when they share the same host. Wolbachia strains may soon be described by the mosaic of genes they carry rather than by a single gene sequence. These acquired gene mosaics may enable strains to survive better in new hosts."

This work is sponsored by a $5 million Frontiers in Biological Research (FIBR) grant from NSF to principal investigator Jack Werren at the University of Rochester. Werren has assembled a team of experts from seven laboratories to work out how Wolbachia functions from the molecular and cellular level all the way up through species and community levels.

FIBR monies sponsor multidisciplinary collaborations. That´s exactly what it takes to collect insects in Panama, Africa and Thailand, to isolate bacteria from their sex cells and to distinguish Wolbachia strains and find out what they´re up to.

Species are defined as groups of organisms that can´t mate with one another. Werren´s group found that insects infected by Wolbachia can´t produce offspring when they mate with closely related species infected with different Wolbachia strains. So bacterial infection has the same effect as a mountain range or river system in acting as a barrier to reproduction that among individuals of the same species.

Mothers pass Wolbachia on to their offspring, but nobody understands how the bacteria jump between species. Sequencing more Wolbachia genes and studying the bacteria's reproductive effects in a wider range of insect hosts will make it possible to determine if different insect species collected in the same geographical area have closely related Wolbachia strains.

Windsor´s group at STRI will be looking for additional help as they expand their molecular operations--specifically an undergraduate student and a post doctoral fellow. They will train both University of Panama and Princeton University students in Wolbachia screening techniques.

Within five years, they hope to have a much clearer understanding of how a tiny bacterial parasite meddles with its hosts and with our evolutionary history.

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The Smithsonian Tropical Research Institute is an international research center established in Panama by the Smithsonian Institution to increase knowledge of the past, present and future of tropical biodiversity and its importance to humanity. For more than 90 years, researchers, students and associates have conducted research in forest and marine habitats in Panama and at other sites throughout tropical regions of the world. http://www.stri.org

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