These toads don’t start as tadpoles
Frogs are often remembered for their classic lifecycle, transitioning from eggs to tadpoles and finally to adult amphibians. This familiar metamorphosis is a hallmark of nearly all of the planet’s approximately 8,000 frog species. However, a small yet fascinating group of frogs known as Nectophrynoides, or tree toads, has evolved a unique reproductive strategy that skips the egg and tadpole stages entirely. Instead, these remarkable amphibians give birth to tiny, live “toadlets.” This adaptation is not just a quirky evolutionary twist; it reflects the specific environmental challenges these tree toads face in their habitats, particularly in the biodiverse yet vulnerable Eastern Arc Mountains of Tanzania.
In a recent study published in *Vertebrate Zoology*, researchers confirmed the existence of three new species of tree toads within the Nectophrynoides genus. This discovery adds to the understanding of their reproductive diversity, which has been largely overlooked in traditional biological narratives. Notably, the study involved revisiting the historic specimens collected by German researcher Gustav Tornier in 1905, which had been preserved in Berlin’s Museum für Naturkunde for over a century. Utilizing a technique called museuomics, the research team was able to extract DNA from these old specimens, providing critical insights into the genetic diversity and evolutionary history of these toads. As study co-author Mark Scherz notes, the findings challenge the conventional wisdom about amphibian reproduction and highlight the diverse strategies that different species have developed in response to their environments.
Despite the excitement surrounding the discovery of these new species, there is a pressing concern regarding their survival. The Eastern Arc Mountains, known for their rich biodiversity, are under threat from deforestation and climate change, which are contributing to the decline of many tree toad populations. Two of the newly identified species are already considered critically endangered, with one species believed to be extinct in the wild. The researchers emphasize that without concerted conservation efforts, the future of these unique toads—and the intricate ecosystems they inhabit—remains uncertain. The discovery of new species is a hopeful sign, but it underscores the urgent need for protective measures to ensure these toads can continue to thrive in their natural habitats.
A
frog’s lifecycle
is likely one of the earliest bits of science that many of us remember learning. They start as eggs, hatch into
tadpoles
, and soon grow into the recognizable adult amphibians. Pretty simple and straightforward, right?
While that remains true for the vast majority of the planet’s nearly
8,000 known frog species
, a handful of the amphibians have evolved a more streamlined reproductive process. Members of the
Nectophrynoides
genus (more commonly known as tree toads) don’t bother with the egg and tadpole stages. Instead, they give birth to tiny, live “toadlets.”
Nectophrynoides
comprise only about one percent of all frogs and toads, but that number is officially increasing. In a study published in the journal
Vertebrate Zoology
, biologists describe an additional three tree toad species discovered living in the jungles of Tanzania that have this tadpole-less life cycle.
Nectophrynoides, like this N. viviparus, live in the low vegetation. Credit: Michele Menegon
“It’s common knowledge that frogs grow from tadpoles—it’s one of the classic metamorphosis paradigms in biology,” Mark Scherz, study co-author and herpetology curator at the Natural History Museum Denmark,
said in a statement
. “But [frogs] actually have a wide variety of reproductive modes, many of which don’t closely resemble that famous story.”
To confirm these three newest tree toad species, Scherz and colleagues needed to consult some of the very first
Nectophrynoides
specimens ever collected. In 1905, German researcher Gustav Tornier announced the discovery of a Tanzanian toad whose live births contradicted common knowledge of the amphibians. Those initial specimens have since spent 120 years in the archives of Berlin’s Museum für Naturkunde. The team visited the museum and collected DNA samples from the original toads using a technique known as museuomics. As its name implies, museuomics is the process of obtaining genomic data from biological material housed in museums.
One of the newly described toad species, Nectophrynoides uhehe. Credit: Michele Menegon
Like its relatives, Nectophrynoides luhomeroensis has large skin glands all over its body. Credit: Michele Menegon
“Phylogenetic work from a few years ago had already let us know there was previously unrecognized diversity among these toads,” explained University of Copenhagen biologist and study co-author Christian Thrane. “But by travelling to different natural history museums and examining hundreds of preserved toads, I was able to get a better idea of their morphological diversity, so we could describe these new species.”
“Our museomics work was able to reveal exactly which populations those old specimens belonged to, giving us a lot more confidence for future work on these toads,” added University of Potsdam museuomics expert and study co-author Alice Petzold.
Nectophrynoides viviparus and its relatives vary greatly in color. Credit: Michele Menegon
The prevailing theory is that tree toads evolved their unique birthing strategy due to their habitats. Simply put, it’s easier to forgo laying eggs for live birth if your home is far from a habitable body of water. Unfortunately, the remarkable evolutionary adaptation is exacerbating the threat of extinction. The Eastern Arc Mountains of Tanzania are one of the most biodiverse regions on Earth, but they’re also disappearing due to
deforestation
and
climate change
.
The study’s authors noted that most known tree toads are already on the verge of eradication. One species,
Nectophrynoides asperginis
, is already extinct in the wild, while
Nectophrynoides poyntoni
hasn’t been seen since 2003. As wonderful as it is to find new examples of the impressive toads, conservation efforts will be the only way to ensure they can continue breeding new generations of toadlets.
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These toads don’t start as tadpoles
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