Some frogs are adapting to deadly pathogen

http://www.eurekalert.org/pub_releases/2016-04/cu-sfa041316.php

Public Release: 13-Apr-2016
Some frogs are adapting to deadly pathogen
Cornell University

Some populations of frogs are rapidly adapting to a fungal pathogen called Batrachochrytrium dendrobatridis (Bd) that has decimated many populations for close to half a century and causes the disease chytridiomycosis, according to a new study.

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A previous lab study by the same researchers isolated an immune system allele (a variant of a gene) called allele Q that gave frogs immunity to chytridiomycosis, an infectious disease that typically causes skin to deteriorate.

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They verified that frogs in the field with allele Q did indeed survive Bd infections. Additionally, all of the members of one population survived Bd, but upon genetic analysis, these frogs each had alleles that were part of a group of functionally similar alleles (called a supertype) that also gave them immunity. The alleles of this supertype were not found within the populations previously studied in the lab or in any other populations in the field. Allele Q was not part of this super type.

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"These findings confirm that, at least under some environmental conditions, frogs can evolve tolerance to pathogens - even deadly ones - in their surroundings," Zamudio said.

The variations in immune system genes that give frogs tolerance to Bd infections are associated with a frog's ability to identify pathogens and launch an immune response.

Genetic analyses revealed that these immune system alleles and supertypes associated with survival in the field showed signs of positive selection, providing evidence that these alleles were increasingly inherited and rapidly evolving, Savage said. At the same time, alleles that were associated with susceptibility to Bd did not show signs of positive selection.

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