Researchers have recently identified three unique species of tree toads that bypass the typical egg and tadpole stages. Instead, the females give birth on land to tiny, fully-formed toadlets, each only a few millimeters in length.

This type of live birth is extremely rare among amphibians. Of the nearly 8,000 known species of frogs and toads, fewer than 1% give birth to live young. Scientists believe this unusual reproductive method may have evolved in response to environments where water is scarce, making traditional egg-laying less viable.

“Uncovering new species that give birth to live young gives us valuable insight into amphibian evolution,” said Dr. Diego José Santana, curator of amphibians at the Field Museum of Natural History in Chicago. Although not involved in the research, he emphasized how this discovery showcases the adaptability and diversity of amphibians.

The toads were discovered in Tanzania and had previously been grouped under the species Nectophrynoides viviparus. However, after analyzing dozens of physical characteristics, genetic data, and the vocalizations of wild individuals, scientists determined they were in fact three distinct species within the Nectophrynoides genus.

This reclassification gives researchers a better understanding of live-bearing tree toad diversity and supports conservation efforts. Some populations of Nectophrynoides are experiencing declines, particularly those with limited ranges, which are more susceptible to environmental changes such as deforestation and climate shifts, the study revealed.

The authors stressed the need for additional field studies to fully understand the habitats, range, and survival trends of these toads for effective conservation planning.

Characteristics That Set Them Apart

Typical water-breeding toads can release tens of thousands of eggs at a time — sometimes as often as every couple of weeks.

“Only a small portion of those tadpoles survive to adulthood,” explained Dr. Mark D. Scherz, lead author of the study released in the journal Vertebrate Zoology. Scherz is a curator of herpetology at the Natural History Museum of Denmark and associate professor at the University of Copenhagen.

In contrast, those that give birth to live young produce far fewer offspring at once, usually between 40 and 60 toadlets. However, some have been found carrying over 160 well-developed toadlets. These newborns may have a better chance at survival due to their advanced development at birth.

The first tree toad known to reproduce this way was described in 1905 by German herpetologist Gustav Tornier. Known as N. viviparus, this small species measures just 1.5 inches (37 millimeters) and has rounded toe pads and distinctive skin glands. Their coloration varies widely, from pale tones to deep black and red hues.

More than twelve species in the Nectophrynoides genus have now been found to give birth to live young. N. viviparus remains the most widespread species, present in both the Southern Highlands and Eastern Arc Mountains of Tanzania. Other members of the genus are only found in the Eastern Arc region.

Large distances or natural barriers between populations, as seen in these forested areas, often lead to the evolution of new species. Differences in genetics between N. viviparus in the two mountain ranges had previously raised questions about their classification. By 2016, scientists suspected that distinct species may be hiding within these separate populations.

In the new study, researchers assessed 257 toad specimens — some more than a century old — held in various European museums. They investigated physical anatomy and conducted DNA analysis, along with studying recorded calls of the toads in the wild. These vocalizations vary by species in sound frequency, rhythm, and pattern, helping the team distinguish between them. One analytical method used was the repeat interval-based bioacoustic identification tool, or RIBBIT.

Through differences in voice, genetic markers, and body features such as toe shape and limb glands, the researchers identified three new species: N. luhomeroensis, N. uhehe, and N. saliensis. Dissections showed some females carrying large yolk-rich eggs, while others contained developing toadlets—further evidence of their live-bearing nature.

The study also included a closer look at the original N. viviparus specimens to redefine the species and correct previous classifications.

“We’re now confident that species designations are accurate,” Scherz said. “This represents a major improvement in our understanding.”

Much of the new information came from existing museum samples, which highlights the value of natural history collections. “Taxonomy and collection-based science remain essential,” Santana emphasized. “Working with preserved specimens around the globe, we’re continually discovering overlooked species.”

A Family Tree Still Under Review

Scherz explained that more clarification is needed to sort out how to properly classify all species within the Nectophrynoides genus.

“Identifying these three new species is just one piece of a much larger puzzle,” he noted. For instance, the species N. tornieri, first cataloged in 1906, is now believed to include several genetically close but separate types.

However, beyond scientific classification, a more urgent issue is threatening these tree toads: habitat destruction. Their forest ecosystems are being lost due to human activity, climate change, and political instability. One species — the Kihansi spray toad, or N. asperginis — has already vanished from the wild. Another, N. poyntoni, hasn’t been observed in the wild since its discovery in 2003.

Additionally, large sections of their habitat have yet to be explored thoroughly. Scientists believe there may be even more unknown species awaiting discovery in the region.

“Time and again, we return to these sites and find completely new surprises,” Scherz said. “Our current understanding of species distribution is still incomplete.”