A genetic analysis of museum specimens has identified three previously unknown varieties of viviparous toads, which, unlike most, give birth to fully formed offspring and skip the aquatic tadpole stage.
An international team of scientists has confirmed the discovery of three new species of viviparous toads in Tanzania, a discovery that redefines the taxonomy of amphibians in the Eastern Arc mountains.
The research, led by Christian Thrane, used advanced museomics techniques to demonstrate that what was previously considered a single population of anurans is, in fact, a diverse complex of genetically distinct species that have evolved isolated by geographical barriers.
The study focused on the genus Nectophrynoides, a group of arboreal toads that has historically puzzled biologists. For decades, it was believed that there was a predominant species, the Nectophrynoides viviparus, widely distributed from the Southern Highlands to various mountain ranges like Udzungwa and Mahenge.
However, new evidence published in the journal Vertebrate Zoology refutes this homogeneity: the populations are separated and have developed unique characteristics.
A biological rarity: birth instead of eggs in viviparous toads
What makes this discovery exceptionally valuable is the reproductive strategy of these animals. While the vast majority of the nearly 8,000 species of frogs and toads in the world lay eggs that hatch into aquatic larvae (tadpoles), these Tanzanian amphibians perform internal fertilization.
The female viviparous toads gestate the offspring in their oviducts and give birth to tiny but fully developed toads, ready for terrestrial life.
Mark D. Scherz, curator of herpetology at the Natural History Museum of Denmark and co-author of the work, emphasizes that this phenomenon breaks with the classical paradigm of biological metamorphosis. According to H. Christoph Liedtke, a researcher at the CSIC in Spain, viviparity is an “evolutionary exception” present in less than 1% of known anurans, which elevates the scientific importance of these new species restricted to specific areas of the Tanzanian mountains.
The science behind the discovery: DNA from a century ago
To reach these conclusions, the researchers not only conducted fieldwork but also turned to “museomics.” This technique allowed them to extract and sequence DNA from specimens preserved over 100 years ago in European museums, including those collected by Gustav Tornier, who first documented this strange reproductive behavior in 1905.
Alice Petzold, from the University of Potsdam, highlighted that the analysis of this historical material was crucial to correctly map the ancient populations and distinguish them from the current ones, providing the necessary confidence to formally describe the new species.
Alert for forest conservation
Despite the scientific enthusiasm, the future of these viviparous toads in Tanzania is precarious. The Eastern Arc Mountains are a biodiversity hotspot but suffer constant pressure due to deforestation, mining activity, and the effects of climate change.
Experts like Michele Menegon and John V. Lyakurwa, from the University of Dar es Salaam, warn that the fragmentation of tropical forests directly threatens the survival of these endemic animals. With alarming precedents in the genus, such as the extinction in the wild of the Nectophrynoides asperginis, the protection of these ecosystems becomes urgent to prevent these evolutionary rarities from disappearing shortly after being correctly classified.
