Lessons from a Tanzanian Toad’s Extinction for the Amphibians and Reptiles of the US
In the words of Maya Angelou, “You may encounter many defeats, but you must not be defeated.” It’s in this spirit of perseverance that we resolve to apply the critical lessons learned from the extinction of the Kihansi spray toad from the wild in Tanzania to imperiled amphibians and reptiles in the US.
Several native species are on the brink like the Kihansi spray toad was before its demise, including the Houston toad, frosted flatwoods salamander, Dixie Valley toad, and flattened musk turtle. A recent study helps us understand what happened to the Kihansi spray toad and provides a path forward for buffering at-risk US amphibians and reptiles against the same fate.
In the heart of Tanzania’s Udzungwa Mountains, the Kihansi spray toad once thrived in the unique, mist-filled habitat of Kihansi Falls. But in 2000, the construction of the Lower Kihansi Hydropower Project drastically altered this delicate ecosystem, leading to a steep decline in the toad’s population. By March 2001, fewer than 2,000 individuals remained. Although conservation efforts, such as the installation of artificial sprinklers, initially seemed promising, the toad’s population suddenly and somewhat inexplicably crashed. It was declared extinct from the wild by 2009.
New research demonstrates how the Kihansi spray toad’s extinction from the wild was caused by a combination of habitat destruction, first, and then the subsequent arrival of BdCAPE, a lineage of a chytrid fungus called Batrachochytrium dendrobatidis, or Bd for short (Sewell et al. 2024).
Luckily, though, this isn’t the end of the story for the Kihansi spray toad. Before their extinction from the wild, 499 toads were collected for a captive breeding program. Reintroduction efforts began in 2012 (Mohamed & Msuya 2023). However, despite the installation of artificial sprinklers and other restoration measures, drastic changes to their specialized habitats, such as the plant community composition, make it unclear whether Kihansi spray toads can thrive again.
This “perfect storm” of habitat destruction coupled with disease provides powerful lessons for the conservation of amphibians and reptiles in the US. The BdCAPE lineage’s lethal impact on the Kihansi spray toad underscores the broader dangers of chytrid fungus, namely that rapid habitat changes and environmental stresses compound its impacts.
Bd is widespread throughout the US and other countries around the world. Over the past 30 years, it has resulted in worldwide declines in one of every 16 known amphibian species. In all, Bd has infected more than 500 amphibian species.
Because of the prevalence of the fungus and other pathogens, our strategy at ARC is to help native species cope with the new normal of disease in their habitats. Plus, disease is just one of the many catastrophes that threaten to bring small populations of imperiled species crashing down.
Our place-based approach of establishing Priority Amphibian and Reptile Conservation Areas (PARCAs) across the US, together with our conservation and habitat restoration efforts, buffer amphibian and reptile populations against these challenges.
This is critical because recovering from cataclysmic events, like disease, a hurricane, or a volcanic eruption, is much more difficult when species’ populations are also coping with other stressors, such as climate change, habitat destruction, and invasive species.
Our PARCA strategy is an effective solution because when habitats are healthy, populations of native species tend to be healthy, too. Our targeted, on-the-ground conservation actions in PARCAs increase the size, connectivity, and frequency of amphibian and reptile populations across the landscape, giving them the boost they need.
For example, for federally listed Endangered Houston toads in Texas, our approach is to work with partners to pair reintroduction efforts with widespread habitat protection and improvement. Many of these efforts take place on private lands, where the last pockets of potential habitat for the toads can be found, and, thus, collaborations with landowners are critical for restoring connectivity between their populations.
In Georgia and Florida, we’re using an impactful technique called headstarting with federally listed Threatened frosted flatwoods salamanders, one of the most imperiled salamanders in the US. Headstarting involves collecting eggs from the wild, rearing them in captivity until they hatch and grow past their most vulnerable stages, and then releasing them.
Because of their small range and patchy distribution in the Black Warrior River Basin in Alabama, the federally listed Endangered flattened musk turtle is more susceptible to a disease outbreak or other catastrophic occurrence. A legacy of dams built in the area blocks the water’s natural flow and fragments the habitat. We’re collaborating with partners to remove these barriers to restore connectivity and create larger, healthier populations.
At ARC, our multi-faceted, large-scale approach aims to incorporate the lessons learned from the story of the Kihansi spray toad before it’s too late. We’re working to ensure that amphibian and reptile populations in the US are resilient, capable of withstanding the pressures of disease and environmental change.
Not only do the findings of Sewell et al.’s new research (2024) into the causes of the Kihansi spray toad’s extinction serve as a stark reminder of the urgency of this work, but for us, it’s personal. These lessons strengthen our resolve to keep fighting to make sure that the same doesn’t happen to the vulnerable amphibians and reptiles of the US.
References
Mohamed, N, & Msuya, C. (2023). Reintroduction of the Kihansi spray toad Nectophrynoides asperginis back to its natural habitat by using acclimatizing cages. Tanzania Journal of Science, 45:570-583.
https://www.ajol.info/index.php/tjs/article/view/192925
Sewell, T R., van Dorp, L., Ghosh, P.N., Wierzbicki, C., Caroe, C., Lyakurwa, J.V., Tonelli, E., Bowkett, A.E., Marsden, S., Cunningham, A.A., Garner, T.W. J., Gilbert, T.P., Moyer, D., Weldon C., & Fisher M.C. (2024). Archival mitogenomes identify invasion by the Batrachochytrium dendrobatidis CAPE lineage caused an African amphibian extinction in the wild. Proceedings of the Royal Society B: Biological Sciences, 291: 20241157.
https://doi.org/10.1098/rspb.2024.1157
