Hidden in bushes or near roadside drains and curbs, amphibians like frogs and toads are not sheltered from the adverse effects of light pollution in our cities. It does not help that these creatures are extremely sensitive to light. The light-sensitive cells in frogs called retinal rod cells have the ability to detect single photons (to put things into perspective, a 60 watt lightbulb emits (10 to the power of 20) photons per second).
Image 1. American Toad, Anaxyrus americanus
This blog post will be focusing on a particular species of frog, the American toad, because of its widespread prevalence in America. In a study done by the department of Biology in Case Western Reserve University, they tested for direct and indirect effects that artificial light at night (ALAN) had on American toads exposed to ALAN versus those that are exposed to natural conditions.
(a) Reduced growth
The figure above shows how growth of juvenile toads have decreased due to exposure to ALAN (see triangles). The report also stated that ALAN reduced the growth of these toads by about 15% and increased their nocturnal activity. Toads become more active and their energy expenditure increases which leads to significant reduction in their growth. This has detrimental impacts to them such as delayed reproductive maturity, decreased fertility and higher risk of survival.
(b) Reduction in metamorphic duration
Additionally, the larval stages of toads are also negatively impacted because of reduced metamorphic duration as compared toads exposed to natural light. In natural conditions, as an anti-predator response, toads are shown to increase their metamorphic synchrony. However, in ALAN conditions, even in the case where there are no predators, the perceived predator risk due to light can generate metamorphic synchrony in toads.
(c) Sudden changes in light conditions
These risks are further exacerbated by the geographical location in which frogs and toads live in. Because frogs often stay in close proximity to roads, sudden bright light from headlights of cars result in abrupt changes in light that these creatures may have difficulty adapting to. These rapid changes in lighting is also attributed to the very study and research of these frogs and toads because of the use of flashlights from researchers.
Just like what Kermit the frog says, adjustments to our daily lives to reduce potential light pollution may not be the easiest, most convenient thing to do. However, I do believe that a little act can go a long way to safeguard these green precious creatures.
Stay tuned for more!
Jean
References:
- The Agency for Science, Technology and Research (A*STAR). (2015, January 20). The seeing power of frogs: Frogs can detect single photons of light. ScienceDaily. Retrieved September 2, 2020 from https://www.sciencedaily.com/releases/2015/01/150120084545.htm#:~:text=The%20seeing%20power%20of%20frogs%3A%20Frogs%20can%20detect%20single%20photons%20of%20light,-Date%3A%20January%2020&text=Summary%3A,eyes%20can%20detect%20single%20photons.
- Kacey, L., & Michael, F. (2018). Artificial light at night decreases metamorphic duration and juvenile growth in a widespread amphibian. Proc. R. Soc. B 285: 20180367. https://royalsocietypublishing.org/doi/full/10.1098/rspb.2018.0367
- Baker, B. & Richardson, J. (2006). The effect of artificial light on male breeding-season behaviour in green frogs, Rana clamitans melanota. Canadian Journal of Zoology, 84(10), 1528-1532.
- Images retrieved from https://amphibiancare.com/2005/05/18/american-toad/ https://twitter.com/rasc_lpa/status/1006662842576039937