These toads don’t start as tadpoles
The lifecycle of frogs is a classic example of metamorphosis that many of us encounter early in our education. Traditionally, frogs begin their journey as eggs, hatch into tadpoles, and eventually mature into adult amphibians. However, this narrative doesn’t encompass the full diversity of frog reproductive strategies. A fascinating subset of frogs, known as the Nectophrynoides genus or tree toads, has evolved a unique reproductive process that skips the tadpole stage entirely. Instead of laying eggs, these remarkable amphibians give birth to tiny, fully-formed “toadlets.” This intriguing adaptation is not only a testament to the evolutionary ingenuity of these creatures but also highlights the ongoing discoveries within the amphibian world.
Recent research published in the journal *Vertebrate Zoology* has unveiled three new species of Nectophrynoides living in the lush jungles of Tanzania, further expanding our understanding of these extraordinary tree toads. Co-author Mark Scherz from the Natural History Museum Denmark emphasizes that while the traditional metamorphosis of frogs is widely recognized, many species, including tree toads, exhibit a variety of reproductive modes that challenge conventional wisdom. The study involved examining historical specimens collected as far back as 1905, when German researcher Gustav Tornier first documented the live births of these toads. By employing a technique called museuomics, which extracts genomic data from preserved specimens in museums, the research team was able to confirm the existence of these new species and better understand their morphological diversity.
Despite their fascinating reproductive adaptations, tree toads face significant threats from habitat loss due to deforestation and climate change in the Eastern Arc Mountains of Tanzania, one of the most biodiverse regions on the planet. Alarmingly, many known tree toad species are teetering on the brink of extinction. For instance, Nectophrynoides asperginis is already extinct in the wild, and Nectophrynoides poyntoni has not been spotted since 2003. While the discovery of new species is a cause for celebration, it underscores the urgent need for conservation efforts to protect these unique amphibians and their habitats, ensuring that they can continue to thrive and reproduce in the wild. As researchers continue to explore and document the biodiversity of tree toads, it becomes increasingly clear that safeguarding their environments is crucial for the survival of these extraordinary creatures.
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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