The Hard Knock Life of Prince Rejects: A narrative of a Western Spadefoot Toads Home Life
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