Tag Archives: amphibians

Frozen flower.

Climate change will make extreme cold more prevalent — and that’s bad news for some animals

It’s important to keep in mind that climate change doesn’t mean only warmer average temperatures — it also fosters weather variability and the prevalence of extreme cold temperature events, a new paper reports.

Frozen flower.

Image credits Manfred Richter.

A team of researchers from Binghamton University investigated the effect of climate change on amphibian health and susceptibility to parasites. The researchers focused on cold weather variability, a less-discussed consequence of climate change, and discovered that it makes amphibians more susceptible to some hazards while lessening the risk of others (such as parasites). They hope the study will help showcase the important role cold weather variability, not just warmer temperatures, play in the context of climate change.

Change goes both ways

“There is a lot of misconception that global climate change only refers to an increase in warming temperatures,” says Jessica Hua, assistant professor of biological sciences at Binghamton and paper co-author. “We feel that the research in this paper is important because it highlights that global climate change is more complex than just an increase in average temperature. In fact, global climate change is also predicted to increase the prevalence of extreme cold temperature events, as well as increase the amount of variation in temperature fluctuations.”

While climate change is recognized as “one of the most serious issues facing us today,” its impact on animal and plant populations isn’t known in depth. Weather variability, in particular, can have dramatic effects on natural systems. For example, rising mean temperatures prompt organisms to breed earlier in the spring, the team explains, which paradoxically increases their risk of experiencing wild fluctuations in temperature during early development — especially cold weather.

These temperatures don’t have to fall into the ‘deadly’ range to cause damage, the team adds, to alter how susceptible amphibians are to other stressors. To investigate the issue further, they placed wood frog embryos in various cold temperature regimes, researchers looked specifically at the consequences of exposure to these lower temperatures.

Amphibians exposed to constant cold conditions as embryos were more susceptible to road salt contamination, but were able to recover as they aged, the team reports. This is particularly relevant, as salt use on roads is predicted to increase exactly as these extreme cold temperature events are taking place. The frogs exposed to cold temperatures as embryos were also smaller overall as they aged, and developed at a slower pace. This ended up protecting them against parasites as their small stature made them less attractive targets.

These results were not anticipated, the team adds, and determining whether the impact from the cold was harmful or helpful for the amphibians overall is difficult to gauge.

“We initially predicted that exposure to cold temperatures would be stressful to developing embryos. As a consequence, we expected that exposure to stressful conditions early in life would make amphibians less able to deal with other stressors later in life (i.e. parasites),” Hua said. “We were also surprised because past studies have found that cooler temperatures can increase amphibian susceptibility to another parasite (the fungus, chytrid). In this case, the negative effects of the cooler temperatures on amphibians are driven by the fact that the fungus survived better in cooler temperatures.”

Amphibian populations are on the decline globally, so considering the effects of cold temperatures may be important in understanding how to better protect them in the future, the team concludes.

The paper “The effects of different cold-temperature regimes on development, growth, and susceptibility to an abiotic and biotic stressor” has been published in the journal Ecology and Evolution.

Cuban treefrogs. Photo: oseph Gamble

Hundreds of amphibian species all over the world killed by fungus infection, but there may yet be hope

Since the 1990s, biologists have witnessed a sudden demise of amphibian species. So far, hundreds of species have become extinct after becoming plagued by a wretched fungus. From mountain lakes to meadow puddles, no matter the continent, frogs are dying everywhere – a demise that might spell an ecological meltdown. There may still be hope yet, according to a recent study which found frogs can learn to fight and adapt to the killer fungus under certain conditions. If needed, the findings provide a solid basis for potential future efforts to interfere in the pandemic and save the world’s amphibians.

A killer fungus

Chytrid fungus, Batrachochytrium dendrobatidis.

Chytrid fungus, Batrachochytrium dendrobatidis.

Batrachochytrium dendrobatidis, Bd for short, is the fungus in question. Its spores land on the skin of amphibians, burrowing down deeper under the skin where it releases a poisonous toxin that slowly kills the host by paralyzing the immune cells. Since the fungus and its killing behaviour were first observed, scientists hypothesize the infections may have driven hundreds of species extinct. The death toll could increase by a couple of orders of magnitude if the phenomenon is left unchecked and a critical point is reached.

Amphibians are a vital part of the ecological food chain. They feed on mosquitoes and all sorts of insects, and their own turn make up an important food source for birds and other small animals. For instance, in the forests of the northeastern United States, the biomass of amphibians outweighs birds, mammals and all other vertebrates. If Bd is left unchecked, however, the world’s ecosystems, especially the fragile ones, could become seriously threatened.

The past two decades has seen a lot of studies on Bd published, which have significantly helped solve the problem by broadening our understanding of the fungus – how it infects its host, how it kills it, how it multiplies, genetics and so on. We’ve also learned that some amphibian populations have learned to fight Bd and even resurface after being nearly wiped out.

Will those who survive be the key?

Cuban treefrogs. Photo: oseph Gamble

Cuban treefrogs. Photo: oseph Gamble

Jason R. Rohr, an expert on the fungus at the University of South Florida, and colleagues believe these recovering amphibians produce a much stronger immune system in response to the Bd infection. To test this theory, several Cuban tree frogs were infected with Bd spores then inserted  in a heated chamber where they stayed at 86 degrees for 10 days. Heat kills the fungus, and the researchers repeated the procedure three times.

Exposing the frogs to Bd this many times significantly improved their immune response. They produced more immune cells, and the fungus produced fewer spores. Thus, exposed frogs had a much better chance of surviving an infection than a novice. Moreover, the immune response became stronger after each exposure.

Dr. Rohr and team also found that the frogs could avoid infections altogether by staying away from the fungus. In the experiment that proved this fact, oak toads were inserted in a double sided chamber; one side was contaminated with fungal spores, while the other was fungus-free. They found that toads that had never been exposed to the fungus would explore both sides of the chamber, becoming infected along the way. The toads that were previously exposed to the infection (then treated with heat as in the first experiment) tended to avoid the infected side of the chamber.

These experiments show that it is possible for amphibian populations to beat the fungus. It’s highly plausible that some infected specimens in the wild had managed to beat the infection by taking refuge in a warm spot. After that, these survivors stayed away from future infections and passed this information to offspring.

Resurfaced frog populations gives credence to this idea, but let’s not get ahead of ourselves too much. The odds are still in the favor of the Bd fungus, but is there anything we can do? Dr. Rohr says spraying populations with dead Bd spores might improve their chances of survival when hit by Bd infections. Karen R. Lips of the University of Maryland is skeptical of this particular solution, citing the fact that wild amphibians are already exposed to both live and dead spores. “We live in a Bd world,” she said. Even so, “any evidence that some amphibians are surviving with disease is good news,” she said.

The findings appeared in the journal Nature.

Gardiners-Seychelles-frog

This frog hears through its mouth

One of the smallest amphibians in the world, the  Gardiner’s Seychelles frog, is also one of the most eccentric. The frog doesn’t stand out through an over-glamorous coloring or some unique, wild mating call, but rather as a result of one of its weird biological features. This frog doesn’t have ears – yet it can hear. How? By receiving sound waves through its mouth.

Gardiners-Seychelles-frogAll frogs actually hear in a different way from all the other animals, in the sense they don’t have  an external cartilaginous sounding board – instead frogs have eardrums placed directly under the skin. But Seychelles frogs don’t even have this. Can it hear in the first place? Well, a team of researchers from a variety of French universities tested the Seychelles hearing range. They placed a frog in a room where they played recorded calls from other frogs through a speaker. The frog responded to these calls, signifying it could hear them.

Talk with your ears, listen with your mouth

The mystery deepened even further after the scientists had the frogs X-rayed and saw that their bones didn’t conduct sound, like human jawbones do for instance. So scientists made a wild guess: what if the frog could hear through its mouth by directing sound to its inner ear – a cavity within the frog’s skull that hosts reverberated noises?They performed a simulation  and, indeed, it showed that the frog was indeed capable of hearing through this method. This doesn’t mean it hears in this manner though – it just demonstrates that it could.

The Seychelles frog can only be found on a few islands in the Seychelles, off the coast of Madagascar. Scientists suspect that due to its isolation, the species’ hearing has evolved very little. Advanced hearing, characterized by the evolution of eardrums, dates back from the time of  the separation of Gondwana, an ancient supercontinent. Studying Sechelles frogs, researchers hope not only to unravel how this peculiar animal performs basic biological functions, but also how Gondwana animals might had looked and behaved like.

via PopSci

 

A beetle larva attached to the chest of an amphibian. (c) Gil Wizen / AFTAU

Beetle larvae devour amphibian predators – twist of odds in nature

A beetle larva attached to the chest of an amphibian. (c) Gil Wizen / AFTAU

A beetle larva attached to the chest of an amphibian. (c) Gil Wizen / AFTAU

In a classic David vs Goliath scenario, scientists have observed how the Epomis beetle larvae simply devour frogs, several times larger than the larvae. Thus the pray has become the predator, and vice versa, as the initial predatory frog finds itself sucked out of his lifeline by the larvae until nothing by a sac of bones remain.

It’s a truly freaky turn of events, but which by no means can be considered accidental or isolated – on the contrary. In what can only be considered a very tricky evolutionary maneuver, squirmy larvae cunningly attract frogs or toads by posing as dead meat, wiggling its antennae and jaws in an enticing pattern. These movements become more intensive as the would be predator approaches – like a dance. Whose the hypnotoad now?

Pray becomes predator

Enticed by this ‘siren call’, before the amphibian can get a clue of whatever’s happened, the beetle larvae suddenly eludes its predator and attaches on to the nearest surface of the frog’s body. From there on it starts sucking and draining. In some rare cases, frogs actually manage to swallow the larvae, only to regurgitate them out after a short while, time in which the larvae takes another swing and actually kills the frog.

In one “extraordinary” case, wrote Tel-Aviv University study researchers Gil Wizen and Avital Gasith, a larva survived in the stomach of an amphibian for two hours before the larger animal vomited it back up.

“The unharmed larva immediately demonstrated its unaffected feeding potency,” Wizen and Gasith noted.

The following video has been produced by Tel Aviv researchers, who recorded a live beetle larvae-frog encounter. It’s kinda graphic, so click at your own risk.

Frogs, hopeless in front of the larvae

Generally, ground beetles are a tasty, easy pray for frogs and toads, but for some time now researchers have noticed that the larvae of some species of ground beetles can be terribly ruthless on their own terms. To better observe this behavior in a controlled environment, researchers collected the larvae of two ground beetle species, E. circumscriptus and E. dejeani, and placed them in containers with a variety of frog and toad species.

There were 382 separate tests, and on each account the amphibian turned out dead. Only seven frogs and toads managed to swallow the larvae, but in each case, the amphibian quickly threw up its would-be meal. The regurgitated larvae quickly rallied and attached themselves to the amphibians’ mouths. At an 100% fatality rate, the beetle larvae are some mean, deadly critters.

“This study started as a side-study while checking the population status of toads in the coastal plain of Israel,” said Wizen who worked on the research in the lab of Avital Gasith at Tel-Aviv University. The phenomenon was first discovered in 2005 by Eldad Elron and Alex Shlagman.

“In Israel there are only six amphibian species and all of them are threatened by extinction,” he said.

The research was published Sept. 21 in the online edition of PLoS ONE.

Back when reptiles took on dry land

It was more than 300 million years ago that reptiles made tracks on earth. The exact moment when this happened is unknown, however; oh, and by exact moment, I’m talking about pinning it down to a couple million years (you gotta love geologists for their sense of time).

So, a discovery of fossilized footprints was recently made in the Bay of Fundy, New Brunswick, Canada. The track is 318 million years old, and it’s the oldest fossil found so far, so it’s probably very close to the “moment” I was mentioning above.

The footprints were discovered by Dr Howard Falcon-Lang of Royal Holloway, University of London. The results of his study, undertaken with Professor Mike Benton of the University of Bristol and Canadian colleagues, are published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.

It has long been suspected that it was reptiles and not their amphibian cousins that made this big leap, because amphibians need to return to the water in order to breed, while reptiles don’t. According to professor Benton:

“The footprints date from the Carboniferous Period when a single supercontinent (Pangaea) dominated the world. At first life was restricted to coastal swamps where lush rainforest existed, full of giant ferns and dragonflies. However, when reptiles came on the scene they pushed back the frontiers, conquering the dry continental interiors.”

Dr Falcon-Lang added: “The Bay of Fundy is such an amazing place to hunt for fossils. The sea-cliffs are rapidly eroding and each rock-fall reveals exciting new fossils. You just never know what will turn up next.”

So the Bay of Fundy, fossil hunting – on my to do list.