Amphibian Chytrid Fungus in The News - Again

The American bullfrog (Lithobates catesbeianus) is currently raised on farms all over the world. Many of these farm-raised frogs are exported to other countries, frequently ending up in the U.S. It is now well-documented that bullfrogs on many of these farms are infected with the amphibian chytrid fungus (Batrachochytrium dendrobatidis; Bd). So, when the bullfrogs are exported so too is the Bd. Clearly, this could easily result in the spread of Bd and specific Bd strains to new areas. As a consequence, the pressure is increasing to restrict the export of these infected frogs. The New York Times recently published an informative article about this emerging and contentious issue. It remains to be seen whether the threat posed by the diseased frogs rises to a high enough level with the powers-that-be to override the cultural and economic concerns that surround this issue.


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Pacific Chorus Frogs As Disease Carriers?

Last week, the journal PLoS ONE published an interesting paper by Natalie Reeder and colleagues that suggested a potential role for the Pacific chorus frog (Pseudacris regilla) as a carrier of the amphibian chytrid fungus (Batrachochytrium dendrobatidis; "Bd"). Numerous media outlets covered the paper (e.g., San Francisco Chronicle), which in essence just adds a few details to a phenomenon that was already reasonably well-known. That is, chorus frogs can carry high-intensity Bd infections while showing few symptoms of disease (i.e., chytridiomycosis). As such, they appear to be more tolerant of chytridiomycosis than other amphibian species. For example, mountain yellow-legged frogs typically die when their Bd infection intensities approach 10,000 zoospore equivalents (2010 paper by Vredenburg and colleagues). In contrast, most chorus frogs in the Reeder study maintained infections at this level but showed few of the typical disease symptoms (excessive skin sloughing, lethargy, etc.) that result from Bd-caused changes to the frogs' skin. 

The apparent ability of chorus frogs to carry high-level Bd infections without suffering significant negative effects could make this species an effective carrier of Bd. That is potentially important in the Sierra Nevada, where chorus frogs and mountain yellow-legged frogs often exist in the same habitats. Could chorus frogs be responsible for spreading Bd to formerly uninfected mountain yellow-legged frog populations? This remains a distinct possibility, but it would still be only part of the story. For example, I've documented numerous successful invasions of Bd into mountain yellow-legged frog populations despite mountain yellow-legged frogs being the only amphibian species present. Without any chorus frogs in the vicinity, how did Bd disperse into these populations? We don't know, but clearly Bd is able to do so in the absence of chorus frogs. 

It also remains unknown how chorus frogs are able to tolerate these intense Bd infections. But the Reeder paper does provide an interesting observation. That is, some of the heavily infected frogs had highly localized Bd infections in which most of the skin surface was uninfected and a few areas were highly infected. That should allow normal skin functions to continue, with little impact on frog physiology. It remains to be seen how general this result is in chorus frogs because only a few of the study frogs showed this pattern of infection, but it does suggest interesting avenues for future research.

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A Grim Future For Amphibians

As I mentioned in my last post, on February 2 the mountain yellow-legged frog was listed under the California Endangered Species Act. I'm in the process of researching how this listing will affect the management of the frog and its habitat. In the mean time, I thought I'd share a recent story published in Scientific American that serves as a grim reminder of the dire circumstances that amphibians face today. You can view the story here. Let's hope that we can avoid a similar situation with the mountain yellow-legged frog. 
 
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Mountain Yellow-legged Frog is Listed Under California ESA

On Thursday, the California Fish and Game Commission voted unanimously to add both species of the mountain yellow-legged frog to the list of animals protected under California's Endangered Species Act (ESA). The southern mountain yellow-legged frog (Rana muscosa) was listed as "endangered" and the Sierra Nevada yellow-legged frog (Rana sierrae) was listed as "threatened". The reasons given for these different designations included a more severe decline and more highly fragmented distribution in R. muscosa than in R. sierrae. 

To start discussion of the frog agenda item, the chief of the Department of Fish and Game (DFG) Fisheries Branch, Stafford Lehr, gave a summary of the DFG mountain yellow-legged frog status review, and made the recommendation that both species be listed under the California ESA. After Mr. Lehr answered a few questions from the Commission, DFG Director Chuck Bonham made a brief statement in which he reaffirmed the DFG mission to protect California's biodiversity. Lisa Belenky from the Center for Biological Diversity (the group that originally petitioned the DFG to list both species) took the podium, commended the DFG status review for its thoroughness, and stated that although she thought both frog species should be listed as "endangered" she supported the DFG recommendations. With that, the Commission voted 5-0 to list both species. It was over in less than 30 minutes.

What made this listing decision different from most previous such decisions was the almost complete lack of controversy. Lehr, Bonham, and members of the Commission all mentioned that the unusually large amount of information associated with both species of the mountain yellow-legged frog provided a solid foundation for the DFGs threatened/endangered recommendation. I've long argued that science can (and should) play an important role in helping to resolve natural resource issues, and this listing decision strongly supported that role. Science clearly cannot provide all of the answers, but when conducted in a thorough manner it can at least provide sideboards to resource-related discussions. 

In my next post, I'll discuss what this listing likely means for frogs and potentially-affected user groups (e.g., anglers).

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State Listing Decision Nears for Mountain Yellow-legged Frog

On February 2, the California Fish and Game Commission will take up the issue of whether the mountain yellow-legged frog (Rana muscosa, Rana sierrae) should be listed as Threatened or Endangered under the California Endangered Species Act (ESA). This action was prompted by a listing petition [PDF] submitted by the Center for Biological Diversity in January 2010. Neither species currently has any special status under the California ESA, and the Center argued that those populations within California should be listed as Endangered. In response, during the last year the California Department of Fish and Game developed a Status Review [PDF] for both species, and concluded that listing of both species is warranted. 

At their February 2 meeting, the Commission will accept comments from the public regarding the listing petition or status review, and may vote on whether to list both species under the California ESA. Comments can also be sent to the Commission at the following address: Fish and Game Commission, 1416 Ninth Street, Box 944209, Sacramento, California 94244-2090 (or via e-mail to fgc@fgc.ca.gov). To be considered, comments must be received by the time of the February 2 meeting. The meeting starts at 8:30 AM in Sacramento, is open to the public, and will be broadcast live. The meeting agenda [PDF] states that the mountain yellow-legged frog item is the last item of the day, but there is no indication of at what time discussion of this item will begin.

The potential listing of both species under the U.S. Endangered Species Act also continues to move forward. As I've mentioned in previous posts, the U.S. Fish and Wildlife Service (USFWS) is leading a multi-agency effort to develop a Conservation Strategy for the mountain yellow-legged frog. At the recent California-Nevada Amphibian Populations Task Force meeting (Placerville, January 12-13), Steven Detweiler (USFWS) gave an update on the progress made to date. The group is tackling a range of challenging issues, including how best to restore mountain yellow-legged frog populations in the presence of chytridiomycosis (the disease caused by the amphibian chytrid fungus) and how to prioritize sites for restoration actions. A draft document is scheduled for release by the end of 2012. 

So, you can expect the mountain yellow-legged frog to be in the news a lot during the coming weeks and months. Stay tuned.

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