Reduced genetic diversity of immune system may affect survival of endangered toads

The Wyoming toad, Anaxyrus baxteri, suffered severe population declines throughout the late 20th century due to factors such as habitat destruction and fungal infections

"The decline in the population of this species created a genetic bottleneck in the first place, which means the level of genetic diversity is already very small," said Jeff Yoder, a professor of comparative immunology at North Carolina State University and a co-author of the study.

Yoder and co-corresponding author Alex Dornberg of the University of North Carolina at Charlotte performed RNA sequencing on the immune tissue of three healthy, retired Wyoming toad breeders

"We specifically focused on sequences encoding toll-like receptors (TLRs), and proteins of the major histocompatibility complex (MHC) that are expressed in these tissues," said the study's first author, currently at North Carolina State University (NC) State's Ph.

TLRs are the first responders of the immune system and are similar or conserved across species

"The MHC gene is one of the fastest-evolving sequences in the genome," Carlson said

"The Wyoming toads were bred in captivity to save the species, and they were all resistant to the fungus that caused the mass die-off of the species, but that likely means they have less immune diversity

The researchers compared the TLR and MHC of the three Wyoming toads, as well as samples from common toads and cane toads

"The small sample size of this study - which is unavoidable due to the endangered status of toads - nevertheless sets an important framework for conservation," Carlson said

"In general, amphibians don't have as many genomic resources as other organisms," Yoder said

"While we were not surprised by the lack of immunogenic diversity in Wyoming toads, it does raise an important question," Dornburg said

"By understanding the genetic diversity of the immune system, we can inform captive breeding to increase a species' chances of resisting disease in the wild," Yoder added

The study, published in the journal Conservation Genetics, was supported by the North Carolina State University Research and Innovation Seed Fund (RISF) program, the North Carolina State University Center for Comparative Medicine and Translational Research (CCMTR), and the National Science Foundation (NSF) ) support

Journal Reference :

1. Kara B.