Author: Sofie Andrade
Alright...alright. I already know what you’re thinking - “ Aren’t frogs the ones that turn into princes?”. Well, this article is about prince rejects so the title still applies! Anyways… Including the aforementioned Western Spadefoot Toad (Pelobates cultripes) (not to be confused with the spadefoot toads found in N. America), amphibians are one of the most vulnerable vertebrates with around 41% of the species endangered (2). These toads are found throughout the Iberian Peninsula - Southeast and Western France along the coast and in Spain. Their habitats are characterized as open landscapes like dunes, agricultural landscapes, fields, and meadows (2). These websites can provide additional background information on this species (2, 3). Apparently, living in Europe doesn’t solve all your problems. They, like many other species, are subject to human - caused pollutants invading their home.
Some of these pollutants include herbicides from agricultural runoff, changes in salinity, pH, temperature, and the presence of predators (native or invasive). The amount of amphibians that are classified as endangered makes them a species of interest (worthy of a prince, some might say) for researchers studying the effects of human pollution. It’s important to learn how amphibians respond to natural and anthropogenic stressors to inform ecological and conservation planning. Their results have pointed to interesting direct and indirect effects on the toads physiology.
Tadpoles are confined to their aquatic home until they complete their metamorphosis into their adult form. Their ability to recognize chemicals from natural predators is an important defense mechanism while they’re still developing. This recognition allows them to avoid an unfavorable run in with their predators by reducing their swimming activity by 44% (1). Now, consider this - what is a prince without a shield? (hint: a meal)
Chemical pollution from agricultural runoff has been found in the tadpoles aquatic home and studies have suggested that these chemicals affect the toads ability to recognize chemical cues from their predators (1). The most striking detail is that nonlethal levels of pesticides yielded these results (1). The good news? - the tadpoles have finally been chosen! Not so good news? - they’re about to become a popular menu item. The implications of these studies suggest non lethal amounts of stressors can have lasting effects on the toad population.
Whenever a tadpole is exposed to a stressor, like pollution, they deal by altering their physiology (4). Fantastic right!? Not exactly... These alterations can come with fitness trade-offs such as reduced immune competence, delayed growth, and a shorter lifespan (4). Researchers studied levels of a glucocorticoid present during stress and other physiological traits to determine how these toads body's respond to different types of stress. The results suggested that nonlethal levels of all the stressors influenced tadpole physiology. More details about the stressors observed in this study and their results can be found through this article (4). The significance of this direct response is that corticosterone (a glucocorticoid present at different levels in the presence of a stressor) can reduce an amphibian's lifespan and reproductive ability (4). These trade offs associated with the stress response can reduce their fitness (ability to survive and pass on genes).
Other studies suggest that tadpoles display different physiological responses to stressors when they experience more than one at the same time (5). This study attempted to see how frogs are affected by pollution in reality - where different compounds are mixed into the water. However, the study referenced for this posting did not have results supporting this outcome (5). All of the toads physiological responses could be accounted for based on previous results for individual stressors (5). This finding is not absolute and more research is needed to analyze the effects of multiple stressors acting on the toads, especially in the presence of predators experiencing the same stressors.
Even nonlethal quantities of pollutants can have an impact on a toads fitness. These results suggest potential causes for the amphibians' declining populations and resulting position on the IUCN list. These findings are important and necessary for the next steps in conservation planning for the toads and potentially other amphibians. There is still much research to be done to understand how pollutants affect toads in their many life stages, but the previously mentioned results of passed studies show promising progress on understanding these interactions.
How can you help?
The following are links to organizations that provide different ways to contribute to the protection and conservation of amphibians and their homes:
Photograph of whole toad credit: By Photo Jean-Laurent HentzOriginal uploader was Jean-Laurent Hentz at fr.wikipedia - Transferred from fr.wikipedia; transferred to Commons by User:DavidDelon using CommonsHelper, CC BY-SA 1.0, https://commons.wikimedia.org/w/index.php?curid=4996578
Photograph of toad leg credit: By Photo Jean-Laurent Hentz.The original uploader was Jean-Laurent Hentz at French Wikipedia. - Transferred from fr.wikipedia to Commons by DavidDelon using CommonsHelper, CC BY-SA 1.0, https://commons.wikimedia.org/w/index.php?curid=4996621
- Polo-Cavia, N., Burraco, P., & Gomez-Mestre, I. (2016). Low levels of chemical anthropogenic pollution may threaten amphibians by impairing predator recognition. Aquatic Toxicology, 172, 30–35.https://doi.org/10.1016/j.aquatox.2015.12.019
- AmphibiaWeb—Pelobates cultripes. (n.d.). Retrieved April 23, 2021, fromhttps://amphibiaweb.org/cgi/amphib_query?where-genus=Pelobates&where-species=cultripes
- Dufresnes, C., Strachinis, I., Tzoras, E., Litvinchuk, S. N., & Denoël, M. (2019). Call a spade a spade: Taxonomy and distribution of Pelobates, with description of a new Balkan endemic. ZooKeys, 859, 131–158. https://doi.org/10.3897/zookeys.859.33634
- Burraco, P., & Gomez-Mestre, I. (2016). Physiological Stress Responses in Amphibian Larvae to Multiple Stressors Reveal Marked Anthropogenic Effects even below Lethal Levels. Physiological and Biochemical Zoology, 89(6), 462–472.https://doi.org/10.1086/688737
- Burraco, P., Duarte, L. J., & Gomez-Mestre, I. (2013). Predator-induced physiological responses in tadpoles challenged with herbicide pollution. Current Zoology, 59(4), 475–484. https://doi.org/10.1093/czoolo/59.4.475
Author: Kathryn Anderson
Those that have lived in areas that experience snowfall, or at least freezing temperatures, are familiar with just how much more stressful stressful driving can be in those conditions. Personally, I can remember several times from my childhood in Pollock Pines, CA where my parents had lost control of our vehicle and sent us spinning. From those experiences, I learned to appreciate road salt. With 22 million tons of salt applied each year in the US as a de-icer, it seems as though many people share that sentiment (1). What not many people likely share, however, is an understanding of the consequences of road salt application. Like with many quick-fix anthropogenic behaviors, road salt application hurts the environment. The salt finds its way to nearby waterways, where freshwater wildlife get an unprecedented dose. The wood frog, rana sylvatica or lithobates sylvaticus, is one the animals that is affected.
Wood frogs are found throughout the Northeastern United States, Canada, and up into Alaska (2). They are the only frog found north of the arctic circle (3)! They spend most of the year dwelling within the boreal forests that dominate their geographic range. During the late winter and early spring, however, they come out of the forest and gather in shallow pools and wetlands to breed. Their black facial markings, which extend from the tip of their nose, around the eyes, and down the sides of their body, make them easy to identify. Otherwise, they are an unimpressive greenish brown. Males are about 38mm long (about the size of a walnut), and females are about 5mm longer at 43mm (4). Not only do they differ in size, but the lifespans and behaviors differ significantly.
The life of a male wood frog can be summed up by the phrase “live fast, die young”. While females take their time maturing, males mature much earlier and spend their energy trying-- and most of the time failing-- to find a mate. This activity involves singing a chorus to lure a female, and fighting with other males to clasp, or stay clasped to, a female. As a result of this energy demand, their lifespan is much shorter than that of a female. However, males outnumber females 6-to-1. While this is the natural way their population is set up, it leaves them vulnerable to outside intervention because females, the ones laying the eggs, are more ecologically valuable than males. Unfortunately, this already delicate balance of the sexes is the exact aspect disturbed by exposure to road salt..
Road salt pollution is known to be toxic to freshwater wildlife, and amphibians are particularly sensitive animals due to their absorbent skin (1). While studies have shown that road salt exposure can be deadly, other studies have explored the ways in which non-deadly exposure to road salt can affect wood frogs. As previously touched on, the most significant finding is the effect it has on the ratio of males to females within their populations. While a lot of people are familiar with the feminization of frogs from pesticide pollution thanks to sensationalist entertainment, the converse happens in this case. Exposure to road salt masculinizes a frog population. That is, the salt disturbs the development of tadpoles and leads to even more males than females within a population. One study in particular aimed at testing the combined effects of road salt and natural sources of stress such as competition, or the threat of being eaten (5). This study found that certain concentrations of road salt lead to a 15% increase in males.
Why does this matter? Wood frog populations are already male-dominated. While both sexes contribute to mating, and thus offspring, females are the ones laying the eggs. The amount of babies a population can have, then, is limited by the amount of egg-laying females in a population. Dwindling numbers of females means dwindling numbers of offspring, which causes dwindling population numbers. While this situation can seem heavy (and don’t get me wrong, it is serious), not all is lost.
While this threat to wood frogs can’t be excused since some road salts (those that contain magnesium and potassium) lead to masculinization, they aren’t doomed. The same study that confirmed a 15% increase in males failed to find the same results from exposure to particularly low and high concentrations of road salts, as well as in the traditional salt used as a de-icer. Table salt, the most common salt used as de-icer, did not have a significant effect on the male-to-female ratios. It is believed that wood frogs, due to how common exposure to this pollutant is, may have adapted to it. This idea is supported by the fact high salt concentrations resulted in very little effect on the wood frogs. Clearly, this issue is complex and requires more study. While it is clear that road salts do affect the wood frog, it is not as obvious just how severe the effect is, how salt exposure works to disturb sexual development, and what the implications are when considering just how the world is changing from human hands.
Despite all of this, wood frogs remain abundant and are not classified as being threatened, endangered, or even at risk of becoming endangered (6). Additionally, road salt use is becoming less and less ideal for use as a de-icer. More negative effects, such as roadway degradation and drinking water contamination, are realized and studies are being conducted to find alternative road de-icers. It seems as though we will eventually move on from road salt and find a way to rid us of our winter travel burdens in a way that won’t shift that burden onto the wildlife. In regards to this issue, the wood frog will be out of the metaphorical woods!
- M. R. Lambert, A. B. Stoler, M. S. Smylie, R. A. Relyea, D. K. Skelly, Interactive effects of road salt and leaf litter on wood frog sex ratios and sexual size dimorphism. Can. J. Fish. Aquat. Sci. 74, 141–146 (2017).
- E. J. Crespi, L. J. Rissler, N. M. Mattheus, K. Engbrecht, S. I. Duncan, T. Seaborn, E. M. Hall, J. D. Peterson, J. L. Brunner, Geophysiology of Wood Frogs: Landscape Patterns of Prevalence of Disease and Circulating Hormone Concentrations across the Eastern Range. Integr. Comp. Biol. 55, 602–617 (2015).
- Wood Frog. Natl. Wildl. Fed., (available at https://www.nwf.org/Home/Educational-Resources/Wildlife-Guide/Amphibians/Wood-Frog).
- R. D. Howard, Mating behaviour and mating success in woodfrogs Rana sylvatica. Anim. Behav. 28, 705–716 (1980).
- S. Leggett, J. Borrelli, D. K. Jones, R. Relyea, The Combined Effects of Road Salt and Biotic Stressors on Amphibian Sex Ratios. Environ. Toxicol. Chem. 40, 231–235 (2021).
- The IUCN Red List of Threatened Species. IUCN Red List Threat. Species, (available at https://www.iucnredlist.org/en).
"road-salt-snow-melting-on-street" by MN Pollution Control Agency is licensed under CC BY-NC 2.0 To view the terms, visit https://creativecommons.org/licenses/by-nc/2.0/
"File:Wood Frog - Lithobates sylvaticus, Lake Accotink Park, Springfield, Virginia (39440713811).jpg" by Judy Gallagher is licensed under CC BY 2.0
Author: Jeremy Schloss
Climate change talks often discuss environmental issues such as increasing natural disaster intensity and coral reef bleaching, but human-driven climate change can affect species in very subtle ways too. With rising temperatures, new dangerous diseases are appearing and wreaking havoc. Chytridiomycosis (commonly shortened to chytrid) is a fungal infection that has been destroying amphibian populations around the world for the past few decades. Humans have aided its spread through international trade and the pet trade (1). It requires water and moisture to spread and survive. This infection results in the spread of fungal spores across the skin of amphibians, a perfect moist home to grow. Since many amphibians breathe through their skin, the spread of the spores results in the suffocation and death of the animal (2).
One such skin-breathing amphibian is Salamandra salamandra, the Fire Salamander. Native to Europe, this salamander is identified by its bright yellow splotches on the back, stomach, and sides of its otherwise black body. Some variants may have yellow or red, but the pattern is unique to the individual. Their diet is mostly made up of insects, worms, slugs, and occasionally other amphibians. The unassuming salamanders also pack a hidden punch, a toxin called samandarin, which it stores in glands around its body. This compound can cause convulsions, hypertension, and hyperventilations in other vertebrates and has even been theorized to be a method of keeping infections away (3).
Rising temperatures can dramatically shift the ability of an animal to fight disease. All animals have a Thermal Neutral Zone, a range of temperature in which they function most optimally. Living outside of that range can affect how fast they digest, how much they need to eat, and even decrease the strength of the immune system. Salamanders are cold-blooded animals; they aren’t able to control their body temperature and instead rely on the environment for warmth and cooling. While salamanders might normally occupy warm areas, increasing temperatures force them to avoid heat and gather in the shade. Temperatures have also limited the space that is considered an escape from the heat, leading to larger gatherings in shade. This creates a dangerous space for disease spread.
Like the salamander, chytrid has its own thermal neutral zone between 17-25°C and over 30°C can be lethal to the fungus (2). While global temperatures have risen, locally this can lead to an increase in water evaporation and cloud formation. This can decrease the daytime temperature while increasing nighttime temperatures, potentially keeping the fungus within its favorable temperature range. Luckily, salamanders have some adaptations that may allow them to fight the disease. While their favorable temperature range is 17-21°C, they can survive up to five days in temperatures well over 25°C (4). Their ability to occupy this higher temperature may be their greatest advantage against the disease.
While there is not a solution to treating the fungal infection itself, we can still do a great deal to limit the spread and severity of the disease. Rigorous trade regulations can limit the spread of chytrid to uninfected areas. More carefully regulating the pet trade especially can reduce the risk of transporting infected animals. In general, making great efforts to reverse temperature increases and greenhouse gas emissions can reduce the spread of the disease in the wild and allow for salamanders to combat the disease through behavior.
Photograph of Salamandra salamandra- Credit: By Petar Milošević from Orle hill, Slovenia - Fire Salamander (Salamandra salamandra), CC BY-SA 4.0, https://commons.wikimedia.org/wiki/File:Fire_salamander_(Salamandra_Salamandra).jpg
Microscope photograph of chytrid infection- Credit: Public Domain, https://commons.wikimedia.org/wiki/File:Chytridiomycosis2.jpg
- Burrowes, P.A.; I.D.d. Riva (2017). "Unraveling the historical prevalence of the invasive chytrid fungus in the Bolivian Andes: implications in recent amphibian declines". Biological Invasions. 19 (6): 1781–1794.
- Whittaker, Kellie; Vredenburg, Vance. "An Overview of Chytridiomycosis". Amphibiaweb.
- Griffiths, R (1996). Newts and Salamanders of Europe. London: Academic Press.
- Beukema, W., Pasmans, F., Van Praet, S., Ferri‐Yáñez, F., Kelly, M., Laking, A., Erens, J., Speybroeck, J., Verheyen, K., Lens, L., Martel, A., & Auer, S. (2021). Microclimate limits thermal behaviour favourable to disease control in a nocturnal amphibian. Ecology Letters, 24(1), 27–37.
Author: Dorothy Aldridge
A turbulent battle between frogs and dams
All around the world, amphibian species of frogs and toads have been experiencing population declines. There are many causes for these declines including global warming, pollution, invasive predators, habitat destruction, and disease. But hope is not lost for our slimy friends. Understanding the threats to the survival of amphibians can give us the tools to make changes before it is too late. This frog blog will tell the story of the foothill yellow-legged frog’s fight for survival against damming in its homestreams.
What puts the Foothill Yellow-Legged Frog at risk?
The foothill yellow-legged frog is a species residing along the west coast of the United States from as far north as Oregon all the way down to Los Angeles, California . This frog has a splotchy brown color that allows it to blend into a habitat of rocky rivers and streams . The foothill yellow-legged frog has a bit of a goldie-locks complex when it comes to settling down. It requires the conditions to be juuust right in order to breed. It is the only species in Western North America that exclusively breeds in streams . Furthermore, these frogs require warm water and shallow river banks . Heavy currents frequently flush away their eggs deposited along the riverbed, so mates wait until the water conditions are calm to begin reproduction. These habitat necessities are threatened by the interference of dams which result in a slough of environmental changes to the river. Damming on the Trinity River and similar freshwater systems has multiple consequences to the foothill yellow-legged frog’s breeding, growth, and survival.
What’s so bad about dams?
Dams Destroy Breeding Habitat
Damming often alters downstream river structure, water depth, and vegetation . After the construction of the Trinity River dam, the vegetation following the dam forced the river to become deeper and narrower . This alteration destroyed 94 percent of berms and shallow bank breeding sites needed for foothill yellow-legged frogs to deposit their egg clutches .
Dams Release Unseasonal Water Flows
Dams alter the natural water flow of a river by restricting water flow and releasing high intensity flows throughout the seasons. The yellow-legged frogs have adapted to the danger of natural heavy spring flows by extending their breeding season into summer when the river is warmer and the water flow is calm . Unseasonal high flows released by the dam sweep away egg clutches along the river .
For the tadpoles that have already hatched, these flows tend to sweep the larger tadpoles out of refugia more frequently than the small tadpoles . This trend means that only smaller tadpoles which are weaker and generally less fit for reproduction will survive . These small tadpoles are more likely to be eaten by a number of predators in the river .
The high water flow also affects the activity of these young frogs. Tadpoles must spend more time hiding behind rocks to stay out of the turbulence . This means less time for foraging and gaining strength . These tadpoles must expend higher energy to swim in heavy flowing water and have much slower growth and development than yellow-legged frog tadpoles in calmer waters .
Dams Change the Water Temperature
The Trinity River Dam and many others across the foothill yellow-legged frog’s range are managed by fisheries which keep the water cooler to benefit fish species . Steelhead, Coho Salmon, and Chinook Salmon need lower temperatures for spawning and egg development . However summer river temperatures can be lowered by up to 12.1 degrees Fahrenheit . Unseasonal releases of this cold water results in the foothill yellow-legged frog laying eggs later, eggs hatching later, and smaller and leaner tadpoles .
What can be done?
Although the foothill yellow-legged frog has suffered the consequences of damming, hope is not lost for our slimy friends. Restoration projects may be done in order to save and reconstruct the habitat of the foothill yellow-legged frog. “Bank Feathering” restoration projects restore river bars to their original pre-dam form . These projects remove the vegetation that forces rivers to become deep and narrow . They also mechanically alter river banks to create gradual, sloping berms . The practice of bank feathering restores the shallow breeding habitat that these frisky frogs need to reproduce.
The foothill yellow-legged frog has not been forgotten in current management practices. The California Fish and Wildlife board provides an article focusing on conservation management considerations for the foothill yellow-legged frog including:
- restricting dam use during breeding season
- exclusion fences during periods of high flow
- relocation adults and eggs out of dam project area
- limiting water diversion rate from dams
Members of the Sacramento Zoo have partnered with the Rock Creek-Cresta Foothill Yellow-legged Frog Technical Group to help restore species population numbers
. Staff members and volunteers ventured along the Feather River, California to set up a project that will keep tadpoles out of the danger zone . They set up laundry baskets topped with mesh as incubators to keep tadpoles from being swept away during high energy outposts from upstream dams .
As you can see, the foothill yellow-legged frog is facing a turbulent battle for survival against dams. But, scientific research has allowed us to understand the specific threats that our stream-dwelling friends are facing. This has sparked restoration and management projects that ensure no tadpole is left behind.
Still interested and itching for more? Follow this link to watch a short video by the Center of Watershed Sciences on the life history and effect of dams of the foothill yellow-legged frog: Foothill Yellow-Legged Frog Video
- California Herps, Foothill Yellow-legged Frog - Rana boylii. California Herps: A Guide to the Amphibians and Reptiles of California (2021).
- S. W. Firley, Is the Foothill Yellow-Legged Frog in Hot Water - Because of Cold Water? US Department of Agriculture. (2017).
- A. J. Lind, H. H. Welsh, R. A. Wilson, The Effects of a Dam on Breeding Habitat and Egg Survival of the Foothill Yellow-legged Frog (Rana boylii) in Northwestern California. Herpetological Review, 27 (1996).
- S. J. Kupferberg, A. J. Lind, V. Thill, S. M. Yarnell, Water Velocity Tolerance in Tadpoles of the Foothill Yellow-legged Frog (Rana boylii): Swimming Performance, Growth, and Survival. Copeia, 1, 141–152 (2011).
- L. Vincent, Conservation in Action: Hopping to it to Save Frogs. Sacramento Zoo, (2019).
"Foothill Yellow-legged Frog (Rana boylii)" by Jonathan Hakim is licensed under CC BY-NC-SA 2.0
"Foothill Yellow Legged Frog" by born1945 is licensed under CC BY 2.0