These toads don’t start as tadpoles
The fascinating lifecycle of frogs, often characterized by their transformation from eggs to tadpoles and finally to adult amphibians, is a foundational concept in biology. However, a small yet remarkable group of frogs known as the Nectophrynoides genus, commonly referred to as tree toads, challenges this traditional narrative. These unique amphibians have evolved to skip the egg and tadpole stages entirely, giving birth to tiny, fully formed “toadlets.” Representing only about one percent of the world’s nearly 8,000 frog species, Nectophrynoides has recently expanded its ranks with the discovery of three new species in Tanzania’s lush jungles, as detailed in a study published in the journal *Vertebrate Zoology*.
The study’s co-author, Mark Scherz, highlights the significance of this discovery, stating that while the metamorphosis of frogs is widely recognized, many species exhibit diverse reproductive strategies that deviate from the classic model. To confirm the existence of these new species, researchers utilized a method called museuomics, extracting DNA from specimens collected over a century ago by German researcher Gustav Tornier. This innovative approach allowed scientists to uncover previously unrecognized diversity among these toads, shedding light on their evolutionary adaptations. The unique reproductive strategy of live birth is believed to have developed as a survival mechanism in their specific habitats, where access to water bodies for laying eggs is limited. However, this adaptation also places these tree toads at greater risk, as habitat loss due to deforestation and climate change threatens their survival.
The conservation status of Nectophrynoides species is alarming, with many already facing extinction. One species, Nectophrynoides asperginis, is extinct in the wild, while another, Nectophrynoides poyntoni, has not been observed since 2003. As researchers continue to uncover the remarkable diversity among these toads, it becomes increasingly clear that conservation efforts are crucial to ensure their survival. The Eastern Arc Mountains of Tanzania, a biodiversity hotspot, are rapidly disappearing, emphasizing the urgent need to protect these unique amphibians and their habitats. The discovery of new species is a hopeful reminder of the wonders of evolution, but without dedicated conservation strategies, the future of these extraordinary tree toads remains uncertain.
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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