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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California Budget Crisis and the Future of the Aerial Fish Stocking Program

For years, the California Department of Fish and Game (CDFG) has used a 1981 Beech King Air airplane to stock backcountry lakes. This aircraft has been specially modified to conduct these stocking operations and is apparently the only aircraft in the state capable of carrying out this task. The Sacramento Bee recently reported that in an effort to cut state spending, California Governor Jerry Brown has proposed reducing the vehicle fleet owned by the CDFG, and the King Air is on the list of vehicles to be auctioned off (link). The CDFG is petitioning to keep vehicles that represent special circumstances, and I'd be surprised if the King Air was not included in that petition. So, this story is still unfolding, but if the King Air is auctioned off it could end the CDFG aerial stocking program. 

This issue is of particular interest to me because I've been critical of the CDFGs aerial stocking program for some time, because of its history of poor oversight and shaky justification. For example, there are numerous examples of the wrong lakes being stocked. With today's sophisticated navigational instruments, it seems hard to imagine how this could happen. In reality, the aerial stocking program does not take advantage of these navigational advances, and still utilizes a rudimentary and error-prone method of identifying the target lakes. Mistakes can have disastrous consequences for species such as the imperiled mountain yellow-legged frog and are simply unacceptable. Second, in a paper published in 2004 we showed that of the hundreds of backcountry lakes being stocked in the central and southern Sierra Nevada, 70% actually contained self-sustaining trout populations and did not need to be stocked to provide recreational fisheries. By stocking these lakes, the CDFG was wasting scarce dollars that could have been used much more effectively elsewhere.

Fortunately, the CDFG has improved the scientific underpinnings of their aerial fish stocking program in recent years, but those changes have raised further questions. Most importantly, the CDFG has dramatically reduced the number of lakes being stocked, in part to eliminate the unnecessary stocking of lakes that contained self-sustaining trout populations and also to reduce impacts to native species. With this reduced number of stocking localities, the cost per lake of stocking has undoubtedly sky-rocketed because the underlying costs (including that of the King Air) remain unchanged. Does it really require a multi-million dollar airplane to stock a handful of backcountry lakes? Maybe the action of putting the stocking plane on the State's auction block will force the CDFG to evaluate the cost-effectiveness of their aerial stocking program. 

This could get interesting.

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The Origin of the Amphibian Chytrid Fungus

The amphibian chytrid fungus (Batrachochytrium dendrobatidis: Bd) is the cause of the most spectacular loss of vertebrate biodiversity in recorded history. To date, at least 200 species have been driven extinct and hundreds more have suffered major declines. Even amphibians within the world's best protected ecosystems have been hard-hit, including California's mountain yellow-legged frog (Rana muscosa, Rana sierrae). This amphibian pathogen appears to have emerged in just the last 50 years, subsequently spreading around the world at lightning speed. 

So, where did Bd come from and what allowed its recent emergence? These are questions that researchers have asked since its description in 1999. Using the best available methods, molecular biologists from around the world have slowly but surely been zeroing in on the answers. In 2003 and 2007, studies by Morehouse et al. and Morgan et al., respectively, used evidence that Bd had little genetic variation to suggest that Bd was a recently emerged clone, not a pathogen with a long evolutionary history with amphibians. Results published in 2009 by James et al. supported these interpretations and suggested that the emergence of Bd may have been caused by a single hybridization event.

A just-published paper by Farrer et al. now advances this story even further. Using sequences of entire Bd genomes, Farrer et al. found evidence of multiple distinct Bd strains with apparently non-overlapping distributions. However, they also found a single lineage that was globally distributed, more virulent than the geographically isolated strains, and associated with worldwide frog die-offs. Based on this evidence, they suggest that contact between two previously isolated strains produced a hypervirulent strain that subsequently spread globally, causing amphibian declines and extinctions in its wake. They further postulate that the global amphibian trade was likely responsible for bringing these genetically isolated strains into contact with each other.

Another research group is using similar methods to provide an even more detailed view of the emergence of Bd as an amphibian pathogen, and will hopefully publish their results in the near future. I suspect that we haven't yet heard the final word of this evolving story. Given the likely role of human commerce in driving the emergence of Bd, there are important lessons here for biodiversity conservation in the Anthropocene. Namely, as our increasingly global economy moves goods around the world we will inevitably also move less desirable things, including invasive animals and plants but also invisible things like pathogens. The spread of introduced pathogens from their new introduction points will often be impossible to control, and decimation of naive animal and plant populations into which they come into contact is all but guaranteed. Bd provides a sobering example of what is to come.  

The citation for the latest paper is as follows: Farrer, R. A., et al. 2011. Multiple emergences of genetically diverse amphibian-infecting chytrids include a globalized hypervirulent recombinant lineage. Proceedings of the National Academy of Sciences, USA 108:18732-18736. [link]

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