The frogs of Baja California: Scientists assess amphibian disease

Date:
February 7, 2022
Source:
University of California - Santa Barbara
Summary:
Biologists from Southern and Baja California have published the
first major account of the amphibian disease chytridiomycosis in
the Mediterranean region of Baja California. Their results indicate
that the disease is more prevalent on the peninsula than in similar
areas of Southern California.



FULL STORY ========================================================================== There's a pandemic sweeping across the globe. No, not COVID, a different
one.

For decades, a brutal fungal infection has been decimating amphibians worldwide.


==========================================================================
"We call it a panzootic," said Andrea Adams, an assistant researcher
in the Earth Research Institute at UC Santa Barbara. "It's like a
pandemic, only with animals." Scientists are hard at work investigating
the disease's origin, trajectory, genetics and impact in an effort to
safeguard vulnerable and valuable biodiversity. Biologists from Southern
and Baja California have published the first major account -- and most comprehensive study -- of the amphibian disease chytridiomycosis in the Mediterranean region of Baja California. Their results, which appear
in Global Ecology and Conservation, indicate that the disease is more
prevalent on the peninsula than in similar areas of Southern California.

"Contrary to what we had expected," said Adams, the lead author, "what's
going on in Baja California is very different than what's going on with
chytrid fungus in Southern California, where the species are pretty much
the same, and the environment is very similar." Chytrids form a large
group of mostly soil-dwelling fungi. They're quite common, and generally
pose no harm. However, two species have evolved to infect the skin of amphibians. In highly infected animals, the skin responds by thickening.

This has a downside. "You probably heard frogs drink through their skin,"
Adams said. It's true. They also exchange salts and minerals through
their skin. So when their skin thickens, it can be a death sentence for
many individuals.



==========================================================================
The team wanted to know what environmental and biological factors
influence chytrid infection in Baja California, particularly at different elevations.

Unfortunately, there has been little research on the topic in the
Mediterranean region of Baja California. "We knew chytrid was here,
but we didn't know how it was affecting different species or which
variables mattered most," said co- author Anny Peralta-Garci'a, director
of Conservacio'n de Fauna del Noroeste, a nonprofit organization dedicated
to research and conservation in Baja California, especially for less charismatic species.

Along with UC Santa Barbara professor Cherie Briggs, Adams teamed up with Peralta-Garci'a's group and Carlos A. Flores-Lo'pez, a researcher at
the Autonomous University of Baja California, to carry out a survey of
the disease in local frogs. The scientists collected samples quarterly
from November 2015 to October 2016. They visited three sites in Baja California, each at a different elevation. The lowest is a perennial
stream about 12 miles south of Ensenada. The area's hot springs make it
a popular recreational spot. The middlemost location is about 2,000 feet
up in the foothills of the Sierra San Pedro Ma'rtir, a mountain range
in northern Baja California.

Lastly, the team surveyed a mountain meadow 6,700 feet high in Sierra
de San Pedro Ma'rtir National Park, where despite some impacts from
livestock, native amphibians still appear to thrive.

The Mexican team spent 2-3 days per location catching animals at
night. They swabbed the frogs' skin to collect samples of the fungus, then released them back into the wild. Altogether, they collected enough data
to analyze the disease prevalence and load in four species, including the endangered California red-legged frog and the invasive American bullfrog.

"We found that when it comes to chytrid infection, the most important
things are where you live and who you are," Adams said. In other words, elevation and species. Chytrid infections were more common and more
intense at higher elevations, where the cooler, moister environment
provides ideal conditions for the fungus.



==========================================================================
Some species are also more susceptible to the infection than others. For instance, the California red-legged frog was among the most infected,
with the highest observed infection intensity and prevalence compared
to other species.

The team found that chytrid was much more prevalent in Baja California,
where 68% of animals they surveyed had the fungus, compared to 15%
in Southern California, as observed in a previous study.

The difference was particularly striking for California red-legged
frogs. In another study in Southern California, only 30% of the species
was infected. "In Baja California, we found that 99% of the California red-legged frogs at the highest-elevation site were infected," Adams
remarked.

Not only was the disease more prevalent, infected animals also carried
a higher pathogen load in Baja California. The team was curious when
the fungus first arrived in Baja California. If it appeared recently,
that could help explain the high infection intensities compared with
Southern California. "When the fungus first arrives to a place it can
cause die-offs and declines in susceptible species," Adams explained.

Fortunately, the San Diego Natural History Museum has a wealth
of amphibian specimens from Baja California that the team used to
investigate the history of chytrid's arrival. The scientists found the
fungus in specimens collected as early as 1932. Previous research found
the earliest record of chytrid detection from Baja California is 1926.

For comparison, the first record of the fungus in Southern California
was found in specimens from Los Angeles County in 1915. This makes some
sense, as invasive species often arrive at ports of entry and then fan
out into the landscape. The combined ports of Los Angeles and Long Beach
are the largest on the West Coast.

So, if chytrid has been in both places -- Baja California and Southern California -- for about the same amount of time, what could explain
the differences the team found? Much like the SARS-CoV-2 virus, the
chytrid fungus has evolved over time. As the fungus mutates and adapts,
more virulent or infectious strains may emerge in different locations.

Understanding what's going on will require long-term monitoring, tracking individuals over time and establishing baselines. "These data help
us prioritize sites that need conservation actions," Peralta-Garci'a
said. "For example, La Grulla, our highest elevation site, needs to
continue to be monitored for disease." The group is continuing their
sampling and rehabilitation work, though getting samples tested will
require more funding.

"Right now, our main focus is trying to increase populations of
California red- legged frogs in Baja California and Southern California," Peralta-Garci'a said.

They've had success reintroducing eggs, which lack keratin, so are not susceptible to the fungus, to historical sites in California. This means
eggs can't transfer the fungus from one site to another.

Adams does similar work in the United States. "Anny and I
are actually doing very similar things," she said. "We are
both working to find the best ways to bring these frogs back
to places they've disappeared from, and we learn a lot from
each other." Chytrid is always part of the discussion, she
added. "We can still be moving forward on chytrid questions and
chytrid monitoring, while also trying to remedy species declines." ========================================================================== Story Source: Materials provided by
University_of_California_-_Santa_Barbara. Original written by Harrison
Tasoff. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Andrea J. Adams, Anny Peralta-Garci'a, Carlos A. Flores-Lo'pez,
Jorge H.

Valdez-Villavicencio, Cheryl J. Briggs. High fungal
pathogen loads and prevalence in Baja California amphibian
communities: The importance of species, elevation, and historical
context. Global Ecology and Conservation, 2022; 33: e01968 DOI:
10.1016/j.gecco.2021.e01968 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220207124842.htm

--- up 9 weeks, 2 days, 7 hours, 13 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)