Lost frogs rediscovered in Brazil


Megaeloisa bocainensis. Photo Délio Baêta/Provided

From Cornell University in the USA:

Lost frogs rediscovered with environmental DNA

September 8, 2020

Scientists have detected signs of a frog listed extinct and not seen since 1968, using an innovative technique to locate declining and missing species in two regions of Brazil.

The frog, Megaelosia bocainensis, was among seven total species — including four other declining species, and two that had disappeared locally for many years — that were detected. The findings appeared in a paper, “Lost and Found: Frogs in a Biodiversity Hotspot Rediscovered with Environmental DNA,” published in August in Molecular Ecology.

Megaelosia bocainensis. A disappeared species from Parque Nacional da Serra da Bocaina, Brazil, known only from this museum specimen collected in 1968, and detected by eDNA surveys. In the study, the researchers collected and screened environmental DNA (eDNA) in the biodiverse Atlantic Coastal Forest and Cerrado grasslands of Brazil.

The eDNA technique offers a way to survey that can confirm the presence of species undetected by traditional methods, providing a tool for conservation scientists to evaluate the presence of threatened species, especially those with low population densities and those not seen in years.

After careful research to identify species at various levels of threat in these regions of Brazil, the researchers used the eDNA method to search for 30 target amphibian species in six localities where the frogs were known to previously live.

“Little bits of DNA in the environment don’t tell us about how many individuals there are or whether those individuals are healthy, but it does tell us that the species is still present,” said senior author Kelly Zamudio, the Goldwin Smith Professor of Ecology and Evolutionary Biology in the College of Arts and Sciences.

“This is one more kind of survey data, and for species that are declining or locally disappeared, it not only means they are there, but there’s now the potential to study them in more detail,” she said, noting that for many species, very little is known.

Around the world, conservationists have been challenged to keep pace with declining and disappearing amphibians. At the same time, living organisms leave DNA traces in the soil, water and air. Now, scientists are increasingly using highly sensitive sampling techniques to detect eDNA for conservation purposes.

In the study, the researchers targeted 13 frog species that have totally disappeared and are presumed extinct; 12 frogs that have disappeared locally but are still found in other parts of their range; and five species that were once very abundant and are still there but hard to find.

The researchers hiked into the sampling sites carrying battery packs, a shoebox-sized peristaltic pump and backpacks of sterile tubing. They used the pump and tubing to draw up to 60 liters of stream or pond water through a capsule fitted with a filter for capturing DNA. A buffer was then applied to stabilize and preserve the DNA on the filter.

Back in the lab, the researchers extracted the DNA, genetically sequenced it, weeded out genetic material from humans, pigs, chickens and other organisms until they could isolate all the frog DNA.

“Now you’ve got a subset of genetic sequences that we know only belong to frogs, and then it’s step by step, going finer and finer, until you get to the genus and species you are looking for,” Zamudio said.

Identifying M. bocainensis required clever detective work: The species disappeared long ago, and there were no tissues from which to extract DNA for comparison with the eDNA. But the researchers did have the sequences for all the sister species in the genus Megaelosia and they knew the ranges of the sister species and M. bocainensis.

“We know there’s a Megaelosia there,” Zamudio said, “we just don’t know which one it is, but the only one that has ever been reported there historically is the one that went missing. Do we believe it? That’s how far the analysis can take us.”

Zamudio added that samples from nearby areas may be worth collecting for more signs of M. bocainensis.

Carla Martins Lopes, a researcher at São Paulo State University in Brazil, is the paper’s first author.

The Brazilian National Council for Scientific and Technological Development and the São Paulo Research Foundation funded the study.

Burrowing frogs, new research


This 2019 video from India says about itself

Why a Burrowing Frog is called a burrowing frog? See this video. Indian Burrowing Frog (Sphaerotheca breviceps).

Burrowing frogs have digging implements on the side of their back feet. In the dry season, they dig down backwards into the sand in search of a moist spot where they can sleep until heavy rain awakens them from their slumber. A short burst of activity then follows. They climb up to the surface, feed and reproduce in monsoon before the dry season starts.

Taken at At BNHS Nature Reserve, BNHS Conservation Education (Cec Bnhs), Goregaon, Mumbai.

From the Florida Museum of Natural History in the USA:

How to get the upper body of a burrowing frog

September 1, 2020

You might think the buffest frogs would be high jumpers, but if you want shredded pecs, you should train like a burrowing frog. Though famously round, these diggers are the unsung bodybuilders of the frog world. We bring you tips from frog expert Rachel Keeffe, a doctoral student at the University of Florida, and physical therapist Penny Goldberg to help you get the burrowing body of your dreams.

But first, a caveat: According to Keeffe, no workout regimen can help you train your way into a highly specialized frog physique honed by 200 million years of evolution. To better understand burrowing frog anatomy, Keeffe and her adviser David Blackburn, Florida Museum of Natural History curator of herpetology, analyzed CT scans from all 54 frog families to show these frogs boast a robust and quirky skeleton that is more variable than previously thought.

“People think about frogs as being clean and smooth and slimy, or the classic ‘green frog on a lily pad,’ but a lot of them are dirty — they like to scoot around and be in the dirt,” Keeffe said. “Burrowing frogs are really diverse and can do a lot of cool things. And when you look at the skeletons of known burrowers, they’re very different from what you would call a ‘normal frog.'”

Burrowing frogs are found all over the world from deserts to swamps, but their underground lifestyle makes them difficult to study, Keeffe said. Most tunnel hind end-first with their back legs. But a few species are forward burrowers, using pointed snouts and powerful forelimbs bolstered by strong pectoral muscles to scrabble into the earth.

Keeffe’s sample of 89 frog species revealed radical differences in burrowing bone structure, from clavicles the size of eyelashes to other bones that are unusually thick.

“They’re so diverse that it’s challenging to think about even comparing them. It’s almost a black hole of work that we can do with forward burrowers because we tend to focus on the legs,” she said.

Some burrow to seek refuge, whether from arid temperatures or predators, and underground habitats can be hunting grounds or secluded hiding places. Other burrowing frogs can spend months at a time as deep as 3 feet belowground, surviving on a high-protein diet of termites and ants. The takeaway: If you want to compete for resources with the pros, don’t be afraid to put in the work.

Get the burly burrowing body

To train like a burrowing frog, Goldberg, assistant director of ReQuest Physical Therapy in Gainesville, recommended dedicating time to strengthening your upper back.

“In humans, the most important muscle group to focus on if you were to train like one of these frogs would be the scapular stabilizers,” she said. “These include 17 muscles, such as the lats and rotator cuff, with attachments all the way down to the pelvis that allow the upper back to generate power. To burrow like a forward burrower, you need to strengthen this entire region.”

One strengthening move Goldberg recommended is the “Prone W.” Lie facedown with elbows bent and palms on the floor. Squeeze your shoulder blades down and toward your spine as you lift your arms to the ceiling for a couple seconds at a time.

Like any elite athlete, burrowing frogs also maintain an optimal form. They’re often orb-shaped to improve their ability to hold water.

“Personally, if I were a sphere, I think it would be hard for me to dig, but it doesn’t seem to affect these frogs at all,” Keeffe said. “However, frogs with stumpy legs are definitely worse at jumping, and they tend to stagger when they walk.”

For these frogs, time away from the tunnels might be spent swimming instead, Keeffe said. To compete here, Goldberg recommends the breaststroke, adding that her top training tips for getting the upper back and pecs of a forward burrower would include pullups and pushups to develop the shoulder blade area.

“In my world, we would use resistance bands and pushing or pulling motions to train this area,” Goldberg said. “Anything focusing predominantly on building strength in the upper back region.”

If resistance bands are part of your workout routine, try grasping one with both hands and extending your arms while keeping your elbows straight. For best results, Goldberg recommended starting with three sets of 10.

Burrowing frogs might also hold key answers to gaps in scientists’ understanding of amphibian evolution at large. Keeffe’s analysis also found that forward-burrowing behavior evolved independently at least eight times in about one-fifth of frog families, and the trait’s persistence in the frog family tree suggests it’s a beneficial adaptation. Keeffe also found that forward burrowers tended to have a highly contoured humerus, the bone that connects the shoulder to the elbow in humans.

Understanding how bone shape relates to musculature can help scientists identify which frogs, both modern and extinct, are forward burrowers, a helpful tool given their covert behavior.

“Even though it can be frustrating, I like them because they’re secretive,” Keeffe said. “But the whole thing underlying this study is that frogs can do a lot of cool things — they don’t just jump and they’re not just green.”

CT scans were generated from the National Science Foundation-funded oVert project.

How treefrogs fool predators


This video says about itself:

Cross-Banded Treefrog Call

Impolite Science Nature: 2009 Trek to Panama. Duration: 0:50. The Cross-Banded Treefrog (Smilisca sila) was found in Santa Catalina on the banks of a small stream. This frog has more complex calls with a full moon and may be able to detect predatory bats.

Many frogs, including this one here, do not seem to be disturbed by red light, although it seems that frogs do see color at night very well.

From Purdue University in the USA:

Outsmarting the enemy: [Panama cross-banded] Treefrogs rely on illusions to find a mate without being eaten

May 6, 2020

Summary: Researchers have discovered that male treefrogs reduce their attractiveness to predators and parasites by overlapping their mating calls with their neighbors.

Treefrogs become easy targets for predators and parasites when they send mating calls, but they’re finding a way to fool their enemies with a little help from a wingman.

Researchers at Purdue University have discovered that male treefrogs reduce their attractiveness to predators and parasites by overlapping their mating calls with their neighbors. By overlapping their calls at nearly perfect synchrony with neighboring treefrogs, an auditory illusion takes effect and those enemies are more attracted to the leading call, leaving the other frogs to find mates without risking their life. The work was recently published in American Naturalist.

“The male frogs are essentially manipulating the eavesdroppers through creating this auditory illusion,” said doctoral student Henry Legett, who led the research with Ximena Bernal, associate professor of biological sciences at Purdue University. “Humans experience this illusion too, it’s called the ‘Precedence Effect.’ When we hear two short sounds in quick succession, we think the sound is only coming from the location of the first sound.”

Research at the Bernal lab focuses on the relationship between predation and communication — or what they simply refer to as eavesdropping.

“The illusion created by the male treefrogs calling in synchrony has no effect on female frogs, which was a surprising observation,” Bernal says.

“These male frogs have figured out a way to trick these enemies. We thought the females might be more attracted to the leading caller, but it didn’t really affect attraction at all. It’s a win-win for the frogs because it helps reduce attacks from those enemies who were hoping to prey on the male frogs and females are not tricked by the illusion.”

The study included experiments using playbacks of recorded calls from speakers and sound traps both in laboratory and field settings at the Smithsonian Tropical Research Institute in Panama, where Bernal is a research associate and frequently visits to work with students. Researchers discovered that after the initial male treefrog sends a mating call, other frogs follow suit within milliseconds.

“It’s so fast, it’s almost like a reflex,” Legett said. “There’s no way their brains have time to process that information. They hear their neighbor and they react immediately.”

Bernal and Legett said the research has cultivated even more questions about how frogs communicate.

“You have to wonder why a male frog would call first, given that if increases his chances of being eaten,” Legett said. “It’s a very strategic game they’re playing. The frog that calls first might not get lucky that time, but maybe he knows he’ll get his chance the next time he hears one of his friends make the first call. These are the questions we’ll keep asking as we move forward.”

How to help frogs and toads, video


This 24 April 2020 video from England says about itself:

Five ways to help frogs and toads | Natural History Museum [in London]

Common frogs are thought to be declining across Europe and the situation is so bad for common toads that they could disappear from the UK by 2030 if things don’t change. Here are five simple actions you could take to help.

Explore why frogs and toads are struggling in the UK and get more tips on how to help here.

Frog skulls, new research


This 2015 video says about itself:

Monster Frog – Documentary

Over the millennia, amphibians both large and small have dominated the Earth. Today, there are over 5000 different species of frogs inhabiting all corners of the globe—from tropical jungles and dark swamps to desert wastelands and frozen tundra. A select few evolved some extreme and bizarre adaptations to survive. An extraordinary family that comes in many weird forms, shapes and sizes.

From bone claws and glass skin to antifreeze and deadly poisons, we’ll show you the jumpers, the climbers, the killers and high flyers. And hidden deep in the jungles of Central Africa, the Goliath Frog still lives today. It is one of the largest and rarest frogs to ever walk the Earth. This is Monster Frog.

From the Florida Museum of Natural History in the USA:

Skulls gone wild: How and why some frogs evolved extreme heads

March 24, 2020

Many frogs look like a water balloon with legs, but don’t be fooled. Beneath slick skin, some species sport spines, spikes and other skeletal secrets.

While most frogs share a simple skull shape with a smooth surface, others have evolved fancier features, such as faux fangs, elaborate crests, helmet-like fortification and venom-delivering spikes. A new study is the first to take a close look at the evolution and function of these armored frog skulls.

Florida Museum of Natural History researchers used 3D data to study skull shape in 158 species representing all living frog families. Radically shaped skulls were often covered in intricate patterns of grooves, ridges and pits formed by extra layers of bone. The research team found that this trait, known as hyperossification, has evolved more than 25 times in frogs. Species with the same feeding habits or defenses tended to develop similarly shaped and patterned skulls, even if they were separated by millions of years of evolution.

“Superficially, frogs may look similar, but when you look at their skulls, you see drastic differences,” said Daniel Paluh, the study’s lead author and a University of Florida doctoral student. “Some of the weirdest skulls are found in frogs that eat birds and mammals, use their heads as a shield, or in a few rare cases, are venomous. Their skulls show how strange and diverse frogs can be.”

The last comprehensive study of frog skulls was published in 1973. Since then, scientists have doubled the number of described frog species, updated our understanding of their evolutionary relationships and developed new analytical techniques with the help of CT scanning.

This enabled Paluh to use 36 landmarks on frog skulls, scanned and digitized as part of the National Science Foundation-funded oVert project, to analyze and compare shapes across the frog tree of life.

“Before we had methods to digitize specimens, really the only way to quantify shape was to take linear measurements of each skull,” he said.

Not only do hyperossification and bizarre skull shapes tend to appear together, Paluh found, but they are often associated with frogs that eat either very large prey or use their heads for defense.

Frogs that eat other vertebrates — birds, reptiles, other frogs and mice — often have giant, roomy skulls, with a jaw joint near the back. This gives them a bigger gape with which to scoop up their prey, Paluh said, referencing Pacman frogs as one example. His analysis showed these species’ skulls are stippled with tiny pits, which could provide extra strength and bite force.

Nearly all frogs lack teeth on their lower jaw, but some, such as Budgett’s frogs, have evolved lower fanglike structures that allow them to inflict puncture wounds on their prey. One species, Guenther’s marsupial frog, has true teeth on both jaws and can eat prey more than half its body length.

Other frogs use their heads to plug the entrance of their burrows as protection from predators. These species tend to have cavernous skulls overlaid with small spikes. A few, such as Bruno’s casque-headed frog, were recently discovered to be venomous. When a predator rams the head of one these frogs, specialized spikes pierce venom glands just under the skin as a defense.

While the study showed a persistent overlap between hyperossification and fanciful skull shape, researchers aren’t sure which came first. Did frogs start eating large prey and then evolve beefier skulls or vice versa?

“That’s kind of a ‘chicken or the egg’ question,” Paluh said.

The common ancestor of today’s 7,000 frog species did not have an ornamented skull. But heavily fortified skulls do appear in even more ancient frog ancestors, said David Blackburn, Florida Museum curator of herpetology and study co-author.

“While the ancestor of all frogs did not have a hyperossified skull, that’s how the skulls of quite ancient amphibian ancestors were built,” he said. “These frogs might be using ancient developmental pathways to generate features that characterized their ancestors deep in the past.”

Previous studies proposed that frogs evolved hyperossification to prevent water loss in dry environments, but Paluh’s research found that habitat and hyperossification were not necessarily linked. The trait shows up in frogs that live underground, in trees, in water and on land.

But habitat does influence skull shape: Aquatic frogs tend to have long, flat skulls, while digging species often have short skulls with pointed snouts, a shape that also enables them to use their mouths like chopsticks to catch small, scurrying prey such as ants and termites, Paluh said. These species include the Mexican burrowing toad and the Australian tortoise frog — distant relatives that live in different parts of the world.

While the study sheds new light on frog skull shape, Blackburn said we still don’t know much about the basic biology of frogs.

“Weirdly, it’s easier for us to generate beautiful images of skulls than it is to know what these frogs eat,” Blackburn said. “Natural history remains quite hard. Just because we know things exist doesn’t mean we know anything about them.”

The study will publish this week in the Proceedings of the National Academy of Sciences.

Luminescent amphibians, new research


The ability to glow in a range of colors from green to yellow when exposed to blue light is common among amphibians like this green Pacman frog (Ceratophrys cranwelli), a new study reports. Photo J. Lamb, M. Davis

The ability to glow in a range of colors from green to yellow when exposed to blue light is common among amphibians like this green Pacman frog (Ceratophrys cranwelli), a new study reports.

By Erin Garcia de Jesus, February 27, 2020 at 11:00 am:

Glowing frogs and salamanders may be surprisingly common

Blue and UV light can make patterns invisible to humans in natural light appear on amphibians

Many animals — from marine species like fish to corals and land creatures like penguins and parrots — have a hidden skill: gleaming blue, green or red under certain kinds of light (SN: 11/17/17). But when it comes to amphibians, experts knew of only one salamander and three frogs that fluoresced — until now.

Jennifer Lamb and Matthew Davis, biologists at St. Cloud State University in Minnesota, shone blue or ultraviolet light on 32 species of amphibians, including salamanders, frogs and the wormlike caecilian, at varying life stages. To their surprise, all lit up, turning brilliant shades ranging from green to yellow, the researchers report February 27 in Scientific Reports.

The effect was strongest under blue light. Among all four-legged creatures, the ability to absorb higher-energy blue light and emit lower-energy green light had previously been documented only in marine turtles. The new finding suggests that biofluorescence is widespread among amphibians.

Different species glow in different patterns, the team found. Some, such as the eastern tiger salamander (Ambystoma tigrinum), reveal strips or blotches of color. In others, like the marbled salamander (A. opacum), bones and parts of their undersides light up.

Although the researchers didn’t test the mechanisms that amphibians use to glow, the animals may rely on fluorescent proteins or pigment-containing cells. Multiple mechanisms would hint that the ability evolved independently in different species, rather than being passed down by an ancient ancestor of modern amphibians.

Biofluorescence may help salamanders and frogs find one another in low light: Their eyes contain cells that are especially sensitive to green or blue light (SN: 4/3/17). Scientists could also harness the amphibians’ ability, using special lights to search for the animals during biodiversity surveys — particularly for those creatures that blend into their surroundings or hide in piles of leaves. Lamb already has hints that might work. As she’s prowled her family’s woods at night with blue light in hand, she’s spotted the telltale glow.

How tadpoles breathe, new research


This 2019 video is called This Is How a Tadpole Transforms Into A Frog.

From the University of Connecticut in the USA:

Tadpoles break the tension with bubble-sucking

February 26, 2020

When it comes to the smallest of creatures, the hydrogen bonds that hold water molecules together to form “surface tension” lend enough strength to support their mass: think of insects that skip across the surface of water. But what happens to small creatures that dwell below the surface of the water?

UConn researchers have taken a close look, and in research published recently in The Proceedings of the Royal Society B, have documented how tiny tadpoles are able to access air above the water’s surface, breathing without having to break through the surface tension.

Tadpoles often live in water with low oxygen levels where fewer predators lurk, but this also means the tadpoles need a way to get to air to breathe. Tadpoles have gills, but they don’t usually provide enough oxygen for them to survive, so most tadpoles also have lungs and breathe air as a back-up. But during the earliest period of their lives, tadpoles are too small to break through the water’s surface to breathe. Luckily for the tadpoles, they have a way to work around this problem, says ecology and evolutionary biology professor Kurt Schwenk.

Tadpoles will often charge upward toward the surface of the water, yet due to their small size and the surface tension of the water, they bounce back down. While watching this during an unrelated study on aquatic salamanders feeding on tadpoles, Schwenk noticed a bubble left behind after one tadpole’s visit to the underside of the water’s surface.

“Many researchers have observed tadpoles breathing at the surface before, but unless you look very closely and slow the action down, you can’t see what is actually happening,” says Schwenk.

Using high-speed macro-videography, Schwenk and graduate researcher Jackson Phillips captured hundreds of breathing events on film shooting at the super slow motion rate of 500-1000 frames per second. The tadpoles were seen to use a never-before-described breathing mechanism they call “bubble-sucking”, a novel breathing mechanism for vertebrates captured with novel technology.

“This research would have been much more difficult to do before high-speed video cameras were developed, and that is probably why the behavior has not been described before,” says Schwenk.

The researchers studied tadpoles from five species of frogs — four of which can be found in Connecticut. What they found was that tadpoles of all species were able to inflate their lungs within a few days of hatching, despite being too small to access air.

Instead of breaching the water’s surface, the tadpoles were seen to bubble-suck. To bubble-suck, the tadpoles first attach their mouths to the undersurface of the water. They then open their jaws wide and draw a bubble of air into the mouth. What happens next was visible through the skin of some of the tadpoles. The tadpoles empty their lungs into their mouths, where the air mixes with the fresh air of the newly sucked bubble. After the mouth closes, the air bubble is forced down into the lungs, but since the bubble is larger than their lung capacity, a portion of the air remains in the mouth, which is then expelled as a small bubble that floats to the surface. The entire process takes about three-tenths of a second.

Bubble-sucking appears to be an adaptation the tadpoles use while they are still small. When they grow large enough and charge the water’s surface, they are able to break the surface tension and “breach-breathe.” The researchers observed bubble-sucking in other species, as well — larval salamanders and even snails. They note that it is likely limited to organisms that can create the suction necessary, therefore arthropods, like insects, cannot bubble-suck.

“As a result of an accidental observation, my research has taken a turn — I never expected to work on these organisms,” Schwenk says. “Before, I thought that tadpoles were uninteresting. But now I find them deeply fascinating.”

Schwenk says this accidental discovery conveys an important point about research in general.

“These frog species are incredibly well-studied and very common,” he says. “Yet, one can learn new things even about the most common animals, which is a good lesson for students, because when getting into research, one can be left with the sense that it has all been done. The fact is, it hasn’t been — we just have to be observant and keep asking questions.”

Poison dart frog evolution, new research


This 2008 video is called A strawberry poison dart frog mother checks up on her tadpole brood.

From the Smithsonian Tropical Research Institute in Panama:

Imprinting on mothers may drive new species formation in poison dart frogs

What do marrying one’s parents, Oedipus complex have to do with evolution?

October 3, 2019

Summary: By rearing frogs with parents — or foster parents — of different colors, biologists discovered that behavior in response to color may be more important than genetics in the evolution of new species.

The old saying that people marry their parents may be true for poison dart frogs, and it may even lead to the formation of new species, according to a new study in Nature based on work at the Smithsonian Tropical Research Institute (STRI).

Strawberry poison dart frogs live on the mainland in Panama’s Bocas del Toro province and have been isolated on islands in the archipelago that formed during the past 10 million years as sea level rose. Only a single color morph exists on some islands — orange or green, for example, but on other islands several color morphs exist together, like blue and red frogs.

“In the past, people assumed that this group of brightly colored poison dart frogs were warning predators that their skin is toxic,” said Corinne Richards-Zawacki, research associate at STRI and professor of biological sciences at the University of Pittsburgh. “But predators don’t seem to care what color the frogs are, at least based on our earlier experiments. That’s why we started asking whether the way they choose mates might lead to populations of different colors on different islands.”

The team set up three different situations: baby frogs raised with two parents of the same color (red baby, red parents), baby frogs raised with each parent a different color (red baby, one red and one blue parent) and baby frogs raised by foster parents of a different color (red baby, blue parents). In each case they asked which color the female offspring would choose as mates and which color the male offspring would perceive as a rival.

“We discovered that female frogs with parents of the same color tended to choose mates of that same color, whereas frogs with foster parents of a different color would choose mates the color of the foster parents,” said Yusan Yang, who is completing her doctoral thesis at the University of Pitts-burgh. “The same was true for male-male aggression. This tells us that imprinting was more important than genetics when it comes to shaping these behaviors that are based on color.”

When baby frogs were raised with one parent of the same color and one parent of a different color, females chose mates the color of their mother, and males chose rivals the color of their mother, indicating that maternal imprinting was probably more important than paternal imprinting.

They also created a mathematical model showing that male aggression based on imprinting, in concert with female mate choice based on imprinting was enough to cause a scenario to evolve, where like mates with like, which could lead to two color morphs becoming separate species.

“We’re fascinated by the idea that behavior can play such an important role in evolution,” Richards-Zawacki said.

Poison frog colours, new research


This 2013 video from French Guiana is called Dendrobates tinctorius in its natural habitat.

From the University of Jyväskylä – Jyväskylän yliopisto in Finland:

Toxic frogs with weak defenses persist in the gene pool alongside stronger competitors

A multi-national team of evolutionary biologists shows that diversity exists even when expecting otherwise

September 2, 2019

Diversity is a hallmark of life and it shows up in unexpected places. A multi-national team of evolutionary biologists investigated how two types of poison frog co-exist when we expect only one. Their innovative study uncovers conditions where diversity flourishes against the odds, and offers new perspectives on chemical defense. The project was a collaboration between the University of Jyvaskylä, the University of Mississippi, Centre national de la recherche scientifique (CNRS) and John Carroll University. The findings were published in the Proceedings of the National Academy of Sciences (PNAS) on September 2nd 2019.

Many creatures carry warning colors that signal toxicity, such as wasps with yellow bands. The Dyeing Poison Frog (Dendrobates tinctorius) of French Guiana also has yellow stripes to keep predators away, but some have white stripes instead. This is an anomaly of evolution because predators learn to avoid warning colors through bad experience, and rare warning colors are harder to learn.

The team headed by Doctors Bibiana Rojas from University of Jyvaskyla and J.P Lawrence from the University of California Irvine propose evolutionary explanations for how nature allows rare warnings to persist.

Firstly, rare or weak signals can persist under the protection of stronger signals. The researchers show that predators learn to avoid more distasteful yellow frogs and generalize this avoidance to white frogs. Although the stronger defenses of yellow frogs should allow them to out-compete the whites over time, genomic analysis revealed that the population of white frogs is genetically separate from the yellows. Thus, diversity can exist within a single population (due to generalized learning) and between different populations (due to genetic isolation).

New methods to measure chemical defence were developed

The initial experiments were modest in scope, but strange results inspired the researchers to develop new methods.

“We faced the difficulty of not having an established method to quantify predator reaction to the chemical defenses. However, that difficulty turned into one of the biggest assets of our study, as we eventually succeeded at developing a method,” says Doctor Bibiana Rojas from University of Jyvaskyla.

The new method improves the ecological relevance and precision of measuring predator-prey interactions. Past studies have assumed that toxicity is everything, and measure it by injecting mice with defensive chemicals. But prey survival and evolution depends on whether they are eaten or spat out, not the blood chemistry of their predators. Thus, the researchers used skin extracts mixed with oats to get a separate measure of distastefulness. They show that toxicity and distastefulness are better considered independently.

“The biggest surprise came from the fact that the frogs [with] higher amount of toxins in their skin are not necessarily the ones that birds find most distasteful. This finding challenges previous assumptions that most toxic equals most unpalatable,” says Rojas.