Foothill yellow-legged frog, Rana boylii
Photo Credit: Brome McCreary
Foothill yellow-legged frog,
Rana boyliiPhoto: Rebecca Fabbri/USFWS
Scientists assemble a richer picture of the plight and resilience of the foothill yellow-legged frog | The Current
Almost unnoticed by the general public and noticed only by biologists and wildlife conservationists, is a pandemic far more deadly than the Covid-19 pandemic, or even the Medieval Black Death.
It kills a very high percentage of its victims, has already exterminated whole populations of frogs and other amphibians, and has contributed significantly to the global mass extinction currently underway.
It is, of course, the chytrid fungus
Batrachochytrium dendrobatidis, which, along with a closely-related fungus,
B. salamandrivorans, causes the fatal disease,
chytridiomycosis, in frogs and other amphibians.
As an example of the work of creationism's divine malevolence, it takes some beating for its sheer malevolent nastiness. It infects the skin of these amphibians, through which they breath, and causes it to thicken and fail as a respiratory organ, leading to suffocation, multiple organ failure and death.
Here is how I described it in my illustrated book,
The Malevolent Designer: Why Nature's God is not Good:
Exterminating Frogs with a Fungus.
Most of the examples I’ve talked about so far have been organisms and viruses that affect humans, but we are far from being the only species that Creationism’s putative intelligent designer seems to have taken an intense dislike to. For example, the world’s frogs and other amphibians are currently being decimated by chytridiomycosis, caused by a couple of related Chytrid fungi, Batrachochytrium dendrobatidis and B. salamandrivorans. It has been estimated that over 500 different species have been severely reduced in number by this fungal plague, with over 90 extinctions.
These fungi seem to have originated in an area of Southeast Asia by modification of a common, harmless, soil fungus. In that part of the world, the local population of amphibians seems to be resistant to the pathogenic forms of the fungi, suggesting that these fungi frequently become pathogenic and the local population have built up resistance to it.
According to research carried out by a team from the Fenner School of Environment and Society, Australian National University, ACT, Australia, it was resistance in the local population which probably kept the disease from spreading more widely, until human agency intervened to change the environment. They have related the increased trade in amphibian species to the spread of the fungi all over the world where they found species with no evolved resistance (42).
Figure 5 Frog Victims of Chytrid Fungus
Illustration: Catherine Webber-Hounslow
Recently, another team found that one of the factors that could have made these fungi so successful is that the frog’s immune response seems to have worked against it. Researchers from the University of Central Florida and the Smithsonian Conservation Biology Institute (SCBI) found that, in the frog Rana yavapaiensis, a species known to vary in its ability to survive attack by these fungi, those which showed an elevated immune response had a worse outcome that those with a lower response (43). Somehow, the frog’s ‘designed’ immune system was working against it and the fungi had been ‘designed’ to exploit this.
ID advocates would have us believe that, for reasons unknown, their putative intelligent designer has deliberately redesigned a soil fungus so it can overcome the immune system it designed to protect frogs from infections, and so exterminate over 90 species of amphibians that it designed earlier and severely endanger some 500 species in what has been described as the biggest single loss of biodiversity, albeit, aided and abetted by humans in this endeavour. Creationism’s intelligent designer must really hate the frogs it designed. Maybe a private definition of the word ‘intelligent’ is being employed here.
Now a team of researchers from multiple American wildlife and conservation agencies have looked in detail at the spread of this fungus in one particular frog which has declined so rapidly it is now an endangered species - the foothill yellow-legged frog,
Rana boylii. This small frog's range once extended from Oregon to Baja California.
They have shown that human agency is implicated in the spread of this fungus by not only spreading it around the world in trade, as the earlier Australian study found (
42), but with regard to the foothill yellow-legged frog specifically, by global warming, climate change and habitat destruction as more land is converted to agriculture. They have published their work, open access, in
Royal Society Open Science. It is also explained in a University of California Santa Barbara, news release:
Up to only a few inches in length, with a lemon-hued belly, the foothill yellow-legged frog may seem unassuming. But its range once stretched from central Oregon to Baja California. In 2023, it was listed under the federal Endangered Species Act. Its rapidly decreasing range is due in part to a fungal pathogen called Batrachochytrium dendrobatidis, or Bd, that has devastated amphibians around the world.
A team of researchers, including UC Santa Barbara’s Andrea Adams, has conducted the most comprehensive study to date of disease dynamics in foothill yellow-legged frogs. The team’s data — sourced from both wild frogs and specimens in museum collections — enabled them to track patterns of infection across a large geographic range. In a study published in Royal Society Open Science, the researchers reveal that drought, rising temperatures and the increasing conversion of land for agriculture appear to be the largest factors driving Bd infection in this species.
The researchers aimed to assemble as much data as they could, both in space and time. They surveyed in the creeks and rivers of California and Oregon, where they swabbed wild yellow-legged frogs for the presence of Bd. It also led them into fluorescent-lit museum collections to sample specimens from as far back as the 1890s.
The team leveraged a large network of people and institutions to amass this wealth of samples.
Many foothill yellow-legged frog field researchers had data that they weren’t actively analyzing, and so we were able to bring all of this data together and get it into a usable format that we could use to paint a much bigger picture of what is, and was, going on with Bd in this species.
Andrea J. Adams, co-author.
Earth Research Institute
University of California, Santa Barbara, CA, USA.
The team discovered that disease patterns of Bd aligned with historical frog declines. The pathogen began to spread in the 1940s from the southern coast of California, moving northward and eventually affecting nearly the entire region. The biggest factors driving infection seem to be drought, increasing temperatures and the use of ever more land for agriculture.
Bd is a fungus that is spread through spores in the water, but that spread may occur differently in foothill yellow-legged frogs in different regions and climates, the researchers found. In some places, drought increased infection, while in others, it did not, possibly because of the presence or absence of other species that can carry Bd and share the same water, such as American bullfrogs, a species introduced from eastern North America.
“If you combine the fact that there are bullfrogs building up the number of spores that these frogs are exposed to, and then they’re all kind of stuck in these small pools together, that explains why drought matters. They are suddenly getting hit with a really large number of spores and getting sick and dying.
These findings open more questions about what was stopping transmission and what allowed it to happen later.
Dr. Anat M. Belasen, co-first author
Department of Integrative Biology
University of Texas at Austin, Austin, TX, USA
And Department of Ecology and Evolutionary Biology,
Cornell University, Ithaca, NY, USA.
The progression of Bd in the foothill yellow-legged frog also differed from its course in other western amphibians. In many other species, the disease radiated from urban centers, rather than this clear south-to-north trend. What’s more, the disease showed up later in the foothill yellow-legged frog than in other species in its range.
Frogs switch from herbivores as tadpoles to carnivores as adults, which means they connect different nutrient cycles together in the food web. Their position at the center of the food chain also influences the ecosystem.
When you remove frogs from an ecosystem, what you get is less control of insects, things that the frogs would eat. There is also less food for things that eat the frogs, like snakes, birds and small mammals. It really throws things off and makes the ecosystem less stable and less functional.
“There are areas that have wet soils that would be alongside suitable habitat. In areas where more of those lands have been converted to agriculture, we see a higher risk of frogs being infected with the fungus.
Dr. Anat M. Belasen.
Co-author Jamie Bettaso swabs a wild foothill yellow-legged frog to test for fungal infection.
Photo Credit: Jamie Bettaso
The conversion of land for agriculture was another major factor influencing the spread of Bd. for these frogs.
In addition to disease hotspots, the team also identified a number of cold spots — areas where the pathogen is present but less influential. The existence of so many cold spots in different areas is a good sign, as it may mean that many areas have conditions suitable for keeping disease rates low, even as climate change increases temperatures and patterns of drought.
The authors are curious what might explain this clustering, especially when cold spots appear in unexpected locations: for example, places with similar habitat, land-use and climatic impacts as hotspots. It suggests there may be some genetic basis for the differences, whether on the pathogen side or the host side. Adams is currently researching the feasibility of reintroducing foothill yellow-legged frogs to Southern California.
The results of this paper shed a lot of light on the dynamics of where Bd occurs, what drives its spread and how the pathogen and frog may interact in the future.
We took a big snapshot of this species’ disease relationship through time. Earlier studies provided the researchers with glimpses into disease patterns in smaller geographic regions, “but now we have a much larger dataset that further confirms many of these patterns, and expands on them.
Andrea J. Adams.
More detail is given in the team's open access paper in
Royal Society Open Science:
Abstract
Species with extensive geographical ranges pose special challenges to assessing drivers of wildlife disease, necessitating collaborative and large-scale analyses. The imperilled foothill yellow-legged frog (Rana boylii) inhabits a wide geographical range and variable conditions in rivers of California and Oregon (USA), and is considered threatened by the pathogen Batrachochytrium dendrobatidis (Bd). To assess drivers of Bd infections over time and space, we compiled over 2000 datapoints from R. boylii museum specimens (collected 1897–2005) and field samples (2005–2021) spanning 9° of latitude. We observed a south-to-north spread of Bd detections beginning in the 1940s and increase in prevalence from the 1940s to 1970s, coinciding with extirpation from southern latitudes. We detected eight high-prevalence geographical clusters through time that span the species' geographical range. Field-sampled male R. boylii exhibited the highest prevalence, and juveniles sampled in autumn exhibited the highest loads. Bd infection risk was highest in lower elevation rain-dominated watersheds, and with cool temperatures and low stream-flow conditions at the end of the dry season. Through a holistic assessment of relationships between infection risk, geographical context and time, we identify the locations and time periods where Bd mitigation and monitoring will be critical for conservation of this imperilled species.
1. Introduction
Threatened species with large geographical ranges often require unique, regional conservation strategies to combat stressors such as infectious disease. Pathogen surveys and reporting have become standard for North American wildlife diseases [1,2]; however, relative risk across a landscape and among populations within species remains difficult to anticipate, especially when data are collected by separate research groups [3]. Central reporting databases [4], synthetic analyses and retrospective surveys can help assess disease threats and identify high-risk populations.
Among the most significant wildlife diseases, amphibian chytridiomycosis caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd) has contributed to declines of hundreds of species worldwide [5]; but see [6]. In North America, notable Bd-associated declines have occurred across the west including the southern Rocky Mountains [7,8], Arizona and New Mexico [9,10], Nevada [11] and California [12–14]. In several of these cases, infection outcomes varied widely among populations due to host-related and environmental factors including genetics, prior Bd exposure and abiotic conditions [15–17].
For the stream-dwelling foothill yellow-legged frog, Rana boylii, Bd's role in the species' changing abundance across its endemic range (California and Oregon, USA) is not well-understood. The species has declined for at least the last half-century, with extirpations reported from xeric lower latitudes [18], at the wetter northern range limit [19] and downstream of large dams range-wide [20]. A mix of abiotic and biotic factors influence Bd infection risk and disease dynamics in many systems, including elevation, latitude, climate, habitat quality and host characteristics [21]. The relative importance of these factors remains unclear in rivers with winter flood/summer drought flow regimes typical across R. boylii's geographical range. Bd is considered a significant potential threat to R. boylii [22] because it is implicated in the species' disappearance from rivers of California's South Coast [23] and in recent autumn die-offs of R. boylii in Central Coast streams [24,25]. A large-scale assessment of Bd infections is needed to clarify how infections relate to historical declines in some regions' rivers and persistence in others, identify clusters of increased infection risk across the species’ range, and evaluate how infection incidence and severity changes with the seasonality of the Mediterranean climate and across the diverse ecoregions that R. boylii occupies.
Here, we leverage data from over 2000 field and museum samples covering 124 years to synthesize knowledge and evaluate patterns of Bd infections in R. boylii. We use a combination of modelling approaches and spatial scan statistics to ask: (i) how are Bd detections in R. boylii are distributed over space and time, (ii) whether watersheds with high versus low Bd infection risk clustered historically and today, and (iii) how Bd infections are related to biotic and abiotic factors. Our results highlight priority populations for Bd mitigation, regions that are data-deficient and warrant further sampling and monitoring, and remaining gaps in our knowledge about Bd susceptibility in R. boylii. Our study serves as a resource for wildlife managers implementing disease mitigation and species recovery projects, such as re-introductions, and as an example of collaborative research to address conservation challenges in wide-ranging imperilled species.
Figure 1.
Distribution of
R. boylii samples assayed for Bd infection. Diamonds show museum samples (collected 1897–2005), circles show field samples (2005–2021). Filled symbols indicate Bd-positive samples. (a) Sampling locations across California and Oregon, USA. Symbols overlap in some localities; see inset barplots for sample sizes. Rana boylii clades are outlined and labelled, with California Endangered Species Act status abbreviated in parentheses: SSC = Species of Special Concern, TH = Threatened, EN = Endangered. (b) Spatio-temporal spread of Bd detections. Symbol size indicates sample size at the HUC-12 (sub-watershed) level. Generalized additive model (GAM) of latitude∼capture year + sample size in Bd-positive samples is shown with black curved line (R
2 = 0.133).
Photo of R. boylii in Napa County, CA by Marina De León.
Belasen A. M., Peek R. A., Adams A. J., Russell I. D., De León M. E., Adams M. J., Bettaso J., Breedveld K. G. H., Catenazzi A., Dillingham C. P., Grear D. A., Halstead B. J., Johnson P. G., Kleeman P. M., Koo M. S., Koppl C. W., Lauder J. D., Padgett-Flohr G., Piovia-Scott J., Pope K. L., Vredenburg V., Westphal M., Wiseman K. and Kupferberg S. J. (2024)
Chytrid infections exhibit historical spread and contemporary seasonality in a declining stream-breeding frog
R. Soc. Open Sci.11. 231270. 231270 DOI: 10.1098/rsos.231270
Copyright: © 2024 The authors.
Published by The Royal Society. Open access.
Reprinted under a
Creative Commons Attribution 4.0 International license (CC BY 4.0)
It must be thrilling for devotees of the putative divine malevolence to see the stunning success it is having exterminating so many species of frog, but one can't help but wonder what the ancestral frog did to incur this wrath. Did it maybe eat a forbidden mosquito or spawn out of wedlock?
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This book presents the reader with multiple examples of why, even if we accept Creationism's putative intelligent designer, any such entity can only be regarded as malevolent, designing ever-more ingenious ways to make life difficult for living things, including humans, for no other reason than the sheer pleasure of doing so. This putative creator has also given other creatures much better things like immune systems, eyesight and ability to regenerate limbs that it could have given to all its creation, including humans, but chose not to. This book will leave creationists with the dilemma of explaining why evolution by natural selection is the only plausible explanation for so many nasty little parasites that doesn't leave their creator looking like an ingenious, sadistic, misanthropic, malevolence finding ever more ways to increase pain and suffering in the world, and not the omnibenevolent, maximally good god that Creationists of all Abrahamic religions believe created everything. As with a previous book by this author, "The Unintelligent Designer: Refuting the Intelligent Design Hoax", this book comprehensively refutes any notion of intelligent design by anything resembling a loving, intelligent and maximally good god. Such evil could not exist in a universe created by such a god. Evil exists, therefore a maximally good, all-knowing, all-loving god does not.
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