Amphibians like frogs and toads are a great way to observe metamorphosis. They lay eggs that develop into tadpoles, and then these tadpoles develop into froglets and toadlets until at last we have our big, strong adults that come crawling out of the water.
Except, it doesn’t always go like that. There are some amphibians that buck the egg-to-tadpole supply chain and instead do something rather incredible: they give birth to live young.
Live-bearing toads
In 1905, this idea was presented to the Royal Prussian Academy of Sciences in Berlin by German researcher Gustav Tornier. Tornier was wielding a toad from Tanzania, the only one in the world at that time known to reproduce by giving birth to live young. We now know that it wasn’t so unique, and, in fact, all members of the “tree toad” Nectophrynoides genus share this unusual reproductive strategy (which is not to be confused with the unique gastric-brooding frogs).
The mothers seem to give birth to an astonishingly large number of juveniles.
Dr Mark Scherz
“These are truly live-bearing, so they give birth just like us,” herpetologist, evolutionary biologist, and study author Dr Mark Scherz of the Natural History Museum Denmark told IFLScience. “The fertilisation is internal, and the embryos develop all the way to the froglet stage before being born.”
“The mothers seem to give birth to an astonishingly large number of juveniles. Christian Thrane, first author on the study (who did his Bachelor’s thesis on these frogs), counted embryos in several females, and there were more than 100 in one female!” he added. Welp.
Meet Nectophrynoides uhehe.
Image credit: Michele Menegon
The marvels of “museomics”
At one time, all of these tree toads were known as Nectophrynoides viviparus, but we’ve since realized that rather than representing one species with a huge range, the group actually contains previously unrecognized diversity. We’ve already named a few, and now another three have been formally described: Nectophrynoides luhomeroensis, Nectophrynoides uhehe, and Nectophrynoides saliensis.
The team identified the new species by taking a close look at specimens housed in several natural history museums using “museomics”. This allowed them to secure DNA sequence data and compare specimens dating from a few years to over a century old and figure out exactly which populations the museum specimens belonged to.
The three new species are “pustular” toads with bulbous and brightly-colored bumps all over their bodies. Their home is Tanzania’s Eastern Arc Mountains, a place which is celebrated for its biodiversity with unique species found nowhere else on Earth.
Unfortunately, the region is also under threat due to habitat fragmentation. A previously identified species, Nectophrynoides asperginis, is already extinct in the wild, while Nectophrynoides poyntoni hasn’t been seen since it was first described back in 2003.
Live-bearing amphibians – what’s the cost?
During what appears to be an already difficult time for amphibians in Tanzania’s Eastern Arc Mountains, it’s important to better understand the unique wildlife living there if we’re going to protect it. Part of that involves understanding at what cost carrying around ~100 embryos comes to for a toad.
Viviparity is also likely much more energetically costly for females and may have important implications on the mobility and agility of individuals during gestation.
Christoph Liedtke
“While viviparity may allow for better protection of developing embryos from the environment to ensure higher survival rates, viviparous amphibians (as is the case for other vertebrates) tend to have less offspring per reproductive cycle compared to oviparous species,” study author Christoph Liedtke from the Spanish National Research Council told IFLScience.
“A potential downside may therefore be lower reproductive rates, although very little is known about embryo and offspring survival in these toads, and how this ultimately compares to the survival rates of toad species in the same family that can lay tens of thousands of eggs.”
“Viviparity is also likely much more energetically costly for females and may have important implications on the mobility and agility of individuals during gestation. It is noteworthy that viviparity is extremely rare in frogs and toads and so while it may bring very specific benefits, like being able to inhabit environments where suitable sites for aquatic larvae are scarce, generally speaking, egg laying is the more successful reproductive strategy.”
The future for Tanzania’s tree toads
Hats off to these female toads, then, and a reminder that conservation strategies have to take into account the unique lifeways of vulnerable species if we’re to protect against further extinctions within this remarkable group of amphibians.
Extinction risks are not the same for amphibians with different reproductive modes and understanding this relationship is critical.
Christoph Liedtke
“Effective conservation strategies require understanding the ecology and life history of organisms,” said Liedtke. “Extinction risks are not the same for amphibians with different reproductive modes and understanding this relationship is critical.”
“Viviparous amphibians clearly have very specific environmental needs that are directly or indirectly linked to their reproductive modes. As for how the description of these three new species is linked to conservation strategies: We show that distinct lineages inside the broader N. viviparus group are actually highly localized and we need to protect all of these distinct areas if we want to effectively conserve this diversity.”
The study is published in Vertebrate Zoology.
Source Link: “They Give Birth Just Like Us”: New Species Of Rare Live-Bearing Toads Can Carry Over 100 Babies
