Decreased genetic diversity in immune system could impact endangered
toad survival

Date:
April 28, 2022
Source:
North Carolina State University
Summary:
A new study examines immune system diversity in the critically
endangered Wyoming toad and finds that genetic bottlenecks could
impact a species' ability to respond to new pathogens. The findings
could inform captive breeding strategies for endangered animal
populations.



FULL STORY ==========================================================================
A new study from North Carolina State University examines immune system diversity in the critically endangered Wyoming toad and finds that
genetic bottlenecks could impact a species' ability to respond to new pathogens. The findings could inform captive breeding strategies for
endangered animal populations.


==========================================================================
The Wyoming toad, Anaxyrus baxteri, suffered a severe population
decline throughout the latter part of the 20th century due to factors
including habitat destruction and fungal infection. The toad was brought
into a captive breeding program in the 1990s in order to save the
species. Scientists estimate a current wild population of only 400 to
1,500 animals, meaning that the toad is considered critically endangered.

"Population reduction in this species created a genetic bottleneck
to begin with, meaning the level of genetic diversity is already very
small," says Jeff Yoder, professor of comparative immunology at NC State
and co-corresponding author of a paper describing the work. "This is
the first study to look specifically at genetic diversity in the immune
systems of these toads and how it could impact them as a population."
Yoder, with co-corresponding author Alex Dornburg of the University of
North Carolina at Charlotte, performed RNA sequencing on immune tissues
from three healthy, retired Wyoming toad breeders. Study co-author
Michael Stoskopf, who was on the Wyoming Toad Recovery Implementation
Team established in 2008, obtained the samples.

"We were focused specifically on sequences encoding toll-like receptors
-- TLRs -- and the proteins of the major histocompatibility complex,
or MHC, expressed in these tissues," says Kara Carlson, first author
of the study and current Ph.D. candidate at NC State. "These sets of
genes are major components of the immune system." TLRs are the first responders of the immune system, and are similar, or well- conserved,
between species. The MHC, on the other hand, is a large and diverse group
of genes that varies between species and individuals. It can determine
why one group is more resistant to a particular pathogen than another.



==========================================================================
"MHC genes are some of the most rapidly evolving sequences in the genome," Carlson says. "So in a healthy population there's a lot of variety that
gets passed along to descendants, enabling the species at large to adapt
to different pathogens. However, if disease survivors do so because of
their MHC, then that group would have a similar MHC.

"The Wyoming toads that were brought into captivity to save the species
were all able to resist the fungus that had decimated the population, but
that could mean that their immune diversity is reduced." The researchers compared the TLR and MHC of the three Wyoming toads to each other, as
well as to samples from a common toad and a cane toad. Both the common
toad and the cane toad showed more MHC diversity than the Wyoming toad,
even though the cane toad underwent a similar genetic bottleneck.

"The small sample size in this study -- which was unavoidable due to
the endangered status of the toad -- nevertheless lays an important
framework for conservation," Carlson says.

"Amphibians in general don't have as many genomic resources as other organisms," Yoder says. "And captive breeding from a small population
further decreases genetic diversity. But while these toads may be better protected against the fungal infection that nearly wiped them out, they
may not be equipped to deal with new pathogens down the road." "While we weren't necessarily surprised by the lack of immunogenic diversity in the Wyoming toad, it does spark an important question," Dornburg says. "How equipped are other species of conservation concern for a battle with an emergent pathogen?" "By understanding the genetic diversity of the immune system we can inform captive breeding to increase the chance of a species
to resist disease in the wild," Yoder adds. "Studies like this one are invaluable for captive breeding practices going forward." The research
appears in Conservation Genetics and was supported by the North Carolina
State University Research and Innovation Seed Funding (RISF) Program,
the North Carolina State University Center for Comparative Medicine and Translational Research (CCMTR) and the National Science Foundation (NSF).


========================================================================== Story Source: Materials provided by
North_Carolina_State_University. Original written by Tracey Peake. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Kara B. Carlson, Dustin J. Wcisel, Hayley D. Ackerman, Jessica
Romanet,
Emily F. Christiansen, Jennifer N. Niemuth, Christina Williams,
Matthew Breen, Michael K. Stoskopf, Alex Dornburg, Jeffrey A. Yoder.

Transcriptome annotation reveals minimal immunogenetic diversity
among Wyoming toads, Anaxyrus baxteri. Conservation Genetics,
2022; DOI: 10.1007/s10592-022-01444-8 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/04/220428103948.htm

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