World Frog Day is upon us and with it a much-needed update on the status of one of the most iconic orders in the animal kingdom. With frogs living on every continent, (except Antarctica) and being found in a wide variety of ecosystems from mountain tops to deserts, its hard to imagine there is anyone in the world who isn’t aware of the existence of frogs. Further to the point, with such a wide variety of frogs, ranging in size from 7mm (Paedophryne amanuensis) to 32 centimeters (Conraua goliath) and with features ranging from transparent bellies (Hyalinobatrachium valerioi) to bony claws protruding from the fingertips in a way that would make Marvel’s Wolverine proud (Trichobatrachus robustus), I would wager that there is a frog in the world to meet every person’s aesthetic. While I have you here, and before you head off to find out what frog matches your personality type, lets take a moment to check in on how the frogs in the world are doing.
Long story short, not great! Frogs, and all amphibians for that matter, are some of the most endangered animals in the world. Pollution and climate change have higher impacts on frogs than many other animals due to the nature of their anatomy. Frogs have thin skin that allows for gas exchange while under water to prolong the timeframe they can stay submerged, but also makes them highly susceptible to chemical pollution in the water. For a quick example, salt runoff during winter road salting results in abnormal tadpole growth and altered metamorphic stages in wood frogs that live rivers adjacent to salted roads. Climate change also affects frogs heavily because a large portion of frogs are highly specialized to an ecological niche and geographic location. For instance, Oreophrynella nigra, commonly called the pebble toad, is a species found on two flat mountain tops (tepuis) in Venezuela. That’s it! Their adaptations include, but are not limited to, folding themselves up like a rock and tumbling down the sides of a slope to escape predators! That’s really cool but likely not going to keep them alive if they live even so far as the bottom of the same mountain.
Another major problem for frogs around the world is chytrid fungus (Batrachochytrium dendrobatidis). While present in nature and introduced across the world in the 1970’s this fungus results in a skin disease called chytridiomycosis that is frequently fatal to the infected host. Chytrid fungus generally spreads through an aquatic medium at warm temperatures above freezing and below 30°C. While the effects of a warming climate would then have varying effects on the story, one place that this is almost entirely negative is in captivity. Across the globe conservation efforts use captive breeding to rescue countless species from extinction. Often these efforts require the intake of wild individuals on a periodic basis to keep the genetic diversity strong, which means that every time new genetics are introduced there is a potential for chytrid to be introduced as well. In captivity, the frogs wouldn’t be exposed to the extremes of the temperature ranges to maximize survival, which would then support the growth of chytrid. Recent studies also suggest that survival of chytrid isn’t based on genetic diversity, but instead on the overall size and general robustness of the frogs themselves. There are treatments and steps being developed to protect and combat chytrid, but all it would take is one unfortunate instance to set back or possibly ruin an entire conservation effort.
At this point, you might be wondering what you can do with all this information. A great first step that you can take is to learn what species of frogs are native to your area! More often than not you will find out there are a lot more species than expected to keep an eye out for. Second, you can reach out to local conservation efforts and see if there are ways that you can help. Organizations like Wildlife Preservation Canada often have volunteer roles and suggestions for local and even at home initiatives that you can take part in to make a difference. While there are dozens of ways you can help the last, and simplest, way would be to continue the conversation with friends and family and continue raising awareness for our amphibious friends.
References
Kásler, A., Holly, D., Herczeg, D., Ujszegi, J., Hettyey, A. (2023). Chytridiomycosis and climate change: exposure to Batrachochytrium dendrobatidis and mild winter conditions do not increase mortality in juvenile agile frogs during hibernation. Animal Conservation. https://doi.org/10.1111/acv.12851
Grogan, L., Humphries, J., Robert, J., Lanctôt, C., Nock, C., Newell, D., McCallum, H. (2020). Immunological Aspects of Chytridiomycosis. Journal of Fungi. 6(4): 234. https://doi.org/10.3390/jof6040234
Berger, L., Robers, A., Voyles, J., Longcore, J., Murray, K., Skerratt, L. (2016). History and recent progress on chytridiomycosis in amphibians. Fungal Ecology. 19: 89-99. https://doi.org/10.1016/j.funeco.2015.09.007
Kilpatrick, A., Briggs, C., Daszak, P. (2010). The ecology and impact of chytridiomycosis: an emerging disease of amphibians. Trends in Ecology & Evolution. 25(2): 109-118. https://doi.org/10.1016/j.tree.2009.07.011
Smith, D., O’Brien, D., Hall, J., Sergeant, C., Brookes, L., Harrison, X., Garner, T., Jehle, R. (2022). Challenging a host–pathogen paradigm: Susceptibility to chytridiomycosis is decoupled from genetic erosion. Journal of Evolutionary Biology. 35(4): 589-598. https://doi.org/10.1111/jeb.13987
Kriger, K. & Hero, J. (2006). Large-scale seasonal variation in the prevalence and severity of chytridiomycosis. Journal of Zoology. 271(3): 352-359. https://doi.org/10.1111/j.1469-7998.2006.00220.x
Dananay, K., Krynak, K., Krynak, T., Benard, M. (2015). Legacy of road salt: Apparent positive larval effects counteracted by negative postmetamorphic effects in wood frogs. Environmental Toxicology and Chemistry. 34(10): 2417-2424. https://doi.org/10.1002/etc.3082
Lambert, M., Stoler, A., Smylie, M., Relyea, R., Skelly, D. (2016). Interactive effects of road salt and leaf litter on wood frog sex ratios and sexual size dimorphism. Canadian Journal of Fisheries and Aquatic Sciences. 74(2): 141-146. https://doi.org/10.1139/cjfas-2016-0324
Sanzo, D. & Hecnar, S. (2006). Effects of road de-icing salt (NaCl) on larval wood frogs (Rana sylvatica). Environmental Pollution. 140(2): 247-256. https://doi.org/10.1016/j.envpol.2005.07.013
Forgione, M. & Brady, S. (2022). Road salt is more toxic to wood frog embryos from polluted ponds. Environmental Pollution. 296. https://doi.org/10.1016/j.envpol.2021.118757
