Frogs With Disease-Resistance Genes May Escape Extinction

As frog populations die off around the world, researchers have identified
certain genes that can help the amphibians develop resistance to harmful
bacteria and disease. The discovery may provide new strategies to protect
frog populations in the wild.


New work, published in the online, open-access journal PLoS ONE, examines
how genes encoding the major histocompatibility (MHC) complex affect the
ability of frogs to resist infection by a bacterium that is commonly
associated with frog population declines.


"In the short term, captive management of frogs with complementary
disease-resistance genes may offer the best hope for saving species from
extinction," says Bruce Waldman, a biologist at Lincoln University in New
Zealand and one of the paper's authors. "Management practices that
maintain or enhance diversity in MHC genes may prove the key to
safeguarding frog populations in the wild."


"Massive die-offs of frogs may indicate environmental problems that
ultimately will affect other species, including humans," Waldman says. "But,
despite the concern, little is known about factors that make individuals
susceptible to disease."


Doctoral students Seth Barribeau and Jandouwe Villinger, working with
Waldman, exposed African clawed frog tadpoles to several doses of the
bacterium
Aeromonas hydrophila. They examined the number of tadpoles that survived
and measured how fast they grew.


Certain genes allowed tadpoles to survive bacterial infection but at a
cost, as these tadpoles sometimes grew more slowly. Among siblings,
patterns
of disease resistance corresponded to tadpoles' MHC genes rather than other
genes that they shared, demonstrating that the MHC genes conferred
immunity.


Programs currently are underway to rescue frogs from declining wild
populations and breed them in captivity to ensure that species are not lost
to
extinction. This study suggests that selective breeding of individuals
with known disease-resistance genes might produce frogs that can survive
infection by pathogens, even after the frogs are reintroduced into the
wild.


The research team studied the African clawed frog because its immune system
already had been well characterized, but as most frogs and toads have
similar immune systems, they believe that their results will be generally
applicable to all threatened and endangered amphibians.


Major Histocompatibility Complex Based Resistance to a Common Bacterial
Pathogen of Amphibians
Barribeau SM, Villinger J, Waldman B (2008)

PLoS ONE 3(7): e2692. doi:10.1371/journal.pone.0002692

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