By Eric Yang ’28
Amphibian species are today considered by biologists at Harvard the vertebrate class most threatened by the onslaught of climate change and various other factors, with 2 out of every 5 amphibians facing extinction. Climate change, a largely man-made crisis, is the main culprit for these problems, particularly its role in creating devastating droughts. With so much land and potential frog habitats being destroyed in favor of agriculture, frogs and other amphibians are already contending with limited space and resources to survive.
Droughts are especially catastrophic, as frogs need to stay moist in order to absorb water and thus the oxygen they need to breathe. However, oxygen intake through a frog’s skin is equally useless if the body of water a frog occupies doesn’t have enough oxygen. Such a scenario is often seen when a large number of frogs gather in small puddles of water, likely the remnants of a stream dried out by drought.
However, drought does not only kill frogs directly; the ability of a drought to concentrate frogs into smaller areas facilitates the rapid spread of disease. Unfortunately, this situation is becoming increasingly common, according to Anat Belasen, a researcher at University of Texas at Austin and a research affiliate with the Smithsonian Conservation Biology Institute. “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,” Belasen explains. “They are suddenly getting hit with a really large number of spores and getting sick and dying.”
Similarly, when paired with the effects of climate change, patches of wet soil particularly appealing to frog species are continuously being taken up by large agricultural pots across the globe, making unadulterated habitats rare. As the barrier between human activity and frog habitats grows even thinner, more frog populations are being found on agricultural plantations and being introduced to harmful pesticides and pathogens, which in many cases ultimately kill them. “In areas where more of those lands have been converted to agriculture, we see a higher risk of frogs being infected with the fungus,” Belasen points out, describing the presence of Bd Infection in frogs in Southern California caused by chytrid fungus, a pathogen from Asia that has long affected numerous amphibian species across the world.
The deleterious impact of the chytrid fungus virus is particularly central to the tragic story of the Gastric Brooding Frog. The Northern and Southern Gastric Brooding Frogs, previously native to Queensland, Australia, are best known for the unusual manner in which the frog species reproduces; the fertilized eggs are swallowed by the female frog, where the eggs sit in the stomach of the mother frog for around six weeks. During this time, the mother frog’s body stops producing stomach acid, allowing her offspring to hatch and develop into tadpoles, and eventually into premature frogs. Finally, after these six weeks have past, the mother frog ejects each frog through her mouth. This strange behavior was observed by environmental scientist Michael Tyler in 1974, who wrote breakthrough papers on the matter later on in the decade.
Unfortunately, the introduction of chytrid fungus drove the population of Gastric Brooding Frogs to extinction. During the normal breeding cycle, when female frogs had their offspring stored in their stomachs, the pressure on their lungs grew to the point where their sole means for getting oxygen was through their skin. The chytrid fungus disrupted this vital process by damaging the skin cells of frogs, effectively ending the reproductive cycle of the Gastric Brooding Frog, alongside dozens of other amphibians performing similar processes. The last Gastric Brooding Frog that was ever seen was spotted in 1984, just a mere 10 years after its discovery.
The mass extinction of frog species within the last century has largely been the result of human activity and human contributions to climate change. However, conservation efforts have been somewhat successful in rekindling frog populations. The Anamalai Flying Frog, native to Kerala in Southern India, had previously reached critically low numbers in population. However, due to efforts by the Wildlife Trust of India, as well as other residents of the region – specifically cardamom farmers who owned the plantations where these endangered frogs were found to dwell around the most – the population of this species has slowly increased over the last few years. They succeeded using a plethora of strategies, from digging waterholes to promoting organic farming practices rather than pesticide use. The Anamalai Flying Frog is one of 120 frog species that have potentially been saved from extinction in the last 40 years due to the efforts of conservationists, and though is just one of the countless other frog species facing similar issues in the presence of humans, its survival reveals that there is much that can be done.
