Category Environtal Studies

          The red-eyed tree frog lives in the rain-forests of South America. Although it can swim, it spends much of its life out of water, among the leaves of trees where there are plentiful insects for food. The tree frog’s toes have sticky pads that enable it to grip branches as it climbs.

          Tree frogs are a diverse family of amphibians that includes over 800 species. Not all tree frogs live in trees. Rather, the feature that unites them has to do with their feet—the last bone in their toes (called the terminal phalanx) is shaped like a claw. Tree frogs also have toe pads to help them climb and many have extra skeletal structures in their toes. Tree frogs can be a variety of colors, but most of the species found in the United States are green, gray, or brown. Some of them, like the squirrel tree frog (Hyla squirella), are chameleon-like in their ability to change color.

          Although tree frogs can grow to be a range of sizes, most arboreal species are very small because they rely on leaves and slender branches to hold their weight. At 4 to 5.5 inches (10 to 14 centimeters) long, the white-lipped tree frog (Litoria infrafrenata) from Australia and Oceania is the largest tree frog in the world. The largest tree frog in the United States is the non-native Cuban tree frog, which reaches 1.5 to 5 inches (3.8 to 12.7 centimeters) in length. The world’s smallest tree frogs are less than an inch (2.5 centimeters) long!

          Tree frogs are found on every continent except Antarctica, but they’re most diverse in the tropics of the western hemisphere. About 30 species live in the United States, and over 600 can be found in South and Central America. Not surprisingly, lots of tree frogs are arboreal, meaning they live in trees. Special adaptations like toe pads and long legs aid them in climbing and jumping. Non-arboreal tree frogs find habitats in lakes and ponds or among moist ground cover.

          Tree frogs are consumed by many different carnivorous animals. Mammals, reptiles, birds, and fish all eat tree frogs. Many of the frogs rely on camouflage to protect themselves from predators, and the more arboreal species escape ground-dwelling predators by hiding in trees. Adult tree frogs are insectivores that eat flies, ants, crickets, beetles, moths, and other small invertebrates. However, as tadpoles, most of them are herbivores.

          Almost all male frogs attract mates with advertisement calls. Each frog species has its own call so female frogs can listen for potential suitors of their own species. The frog call that most people are familiar with—“Ribbet!”—belongs to the Baja California tree frog (Pseudacris hypochondriaca). The ribbeting call has been incorporated into outdoor scenes of many Hollywood movies, even outside of the frog’s range.

          Some frogs hatch as miniature adults. More commonly, however, tadpoles emerge from frog eggs. As tadpoles mature, they lose their tail and grow legs until they eventually reach their adult form. The lifespan of tree frogs varies among species. Some of them are long-lived, such as the Australian green tree frog (Litoria caerulea), which is often kept in captivity for upward of 15 years. Species with lifespans of less than three years are considered short-lived. North America’s gray tree frogs (Hyla versicolor and Hyla chrysoscelis) are somewhere in the middle with a lifespan of five to nine years.

Picture Credit : Google

          In ancient times, it was believed that salamanders could live in the middle of fires, as the cold of their bodies extinguished the flames around them. Of course, this is quite untrue, but the story may have come about because salamanders were often seen to run out of logs thrown onto the fire.

          In the first century AD, Roman naturalist Pliny the Elder threw a salamander into a fire. He wanted to see if it could indeed not only survive the flames, but extinguish them, as Aristotle had claimed such creatures could. But the salamander didn’t … uh … make it.

          Yet that didn’t stop the legend of the fire-proof salamander (a name derived from the Persian meaning “fire within”) from persisting for 1,500 more years, from the Ancient Romans to the Middle Ages on up to the alchemists of the Renaissance. Some even believed it was born in fire, like the legendary Phoenix, only slimier and a bit less dramatic. And that its fur (huh?) could be used to weave fire-resistant garments.

          Part of the problem, it seems, is that in addition to disproving the salamander’s powers, Pliny also wrote extensively that it had such powers—and then some. His Natural History, which has survived over the centuries as a towering catalog of everything from mining to zoology, describes the salamander as such: “It is so chilly that it puts out fire by its contact, in the same way as ice does. It vomits from its mouth a milky slaver [saliva], one touch of which on any part of the human body causes all the hair to drop off, and the portion touched changes its color and breaks out in a tetter,” a sort of itchy skin disease.

          Some 500 years later, Saint Isidore of Seville wrote that while other poisonous animals strike their victims individually, the salamander slays “very many at the same time; for if it crawls up a tree, it infects all the fruit with poison and slays those who eat it; nay, even if it falls in a well, the power of the poison slays those who drink it.” He also confirmed that it’s immune to the effects of fire.

          So right away the salamander was mythologized as both a miraculous survivor and a menace. Indeed, later on in the 1200s, an English writer told of one laying waste to Alexander the Great’s army simply by swimming in a river they drank from. All told, 4,000 soldiers and 2,000 horses supposedly perished after consuming the salamander’s dirty bath water. Which would be pretty embarrassing, if only it were true.

          Now, it was likely Europe’s fire salamander, with its vivid yellow-on-black coloration, that served as the inspiration for the legend, according to Nosson Slifkin in his book Sacred Monsters. As you might assume from its conspicuous colors, this species is in fact quite poisonous, secreting a neurotoxin to deter predators. And if it doesn’t feel like waiting to be attacked, it can actually fire this secretion at its approaching enemies. While the toxin can cause skin irritation in humans, it’s far from capable of poisoning 4,000 soldiers. But it’s likely this poisonous nature was simply scaled up for such myths.

          A few centuries later, none other than Leonardo Da Vinci added another curious characteristic to the salamander’s repertoire, claiming it “has no digestive organs, and gets no food but from the fire, in which it constantly renews its scaly skin.” The alchemist Paracelsus later confirmed this as its diet, elevating the salamander to the status of one of the four “elementals” that he substituted for the classical elements earth, fire, air, and water—the salamander of course being fire.

          Most amphibians lay their eggs in water. Frogs’ eggs are called spawn. They are protected from predators by a thick layer of jelly. Inside this a tadpole develops. When it hatches out, it is able to swim, using its long tail, and breathes through gills. As the tadpole grows, first hind legs and then fore legs begin to grow. Lungs develop, and the young frog is able to begin to breathe with its head above water. Gradually, the tail shortens until the young frog resembles its adult parents.

          In typical amphibian development, eggs are laid in water and larvae are adapted to an aquatic lifestyle. Frogs, toads, and newts all hatch from the eggs as larvae with external gills but it will take some time for the amphibians to interact outside with pulmonary respiration. Afterwards, newt larvae start a predatory lifestyle, while tadpoles mostly scrape food off surfaces with their horny tooth ridges.

          Metamorphosis in amphibians is regulated by thyroxin concentration in the blood, which stimulates metamorphosis, and prolactin, which counteracts its effect. Specific events are dependent on threshold values for different tissues. Because most embryonic development is outside the parental body, development is subject to many adaptations due to specific ecological circumstances. For this reason tadpoles can have horny ridges for teeth, whiskers, and fins. They also make use of the lateral line organ. After metamorphosis, these organs become redundant and will be resorbed by controlled cell death, called apoptosis. The amount of adaptation to specific ecological circumstances is remarkable, with many discoveries still being made.

          Egg Stage: Amphibian eggs are fertilized in a number of ways. External fertilization, employed by most frogs and toads, involves a male gripping a female across her back, almost as if he is squeezing the eggs out of her. The male releases sperm over the female’s eggs as they are laid. Another method is used by salamanders, whereby the male deposits a packet of sperm onto the ground. The female then pulls it into her cloaca, a single opening for her internal organ systems. Therefore, fertilization occurs internally. By contrast, caecilians and tailed frogs use internal fertilization, just like reptiles, birds, and mammals. The male deposits sperm directly into the female’s cloaca.

          Larval stage: When the egg hatches, the organism is legless, lives in water, and breathes with gills, resembling their evolutionary ancestors (Fish). During the larval stage, the amphibian slowly transforms into an adult by losing its gills and growing four legs. Once development is complete, it can live on land.

          Toads and frogs are similar in many ways, although toads usually have rougher, drier skins and may waddle rather than hopping as frogs do. Some toad spawn is produced in strings, like necklaces, rather than the mass of eggs laid by a frog. While these little amphibians might look very similar at first glance, there are actually a plethora of key differences between them. Frogs and toads may seem similar, but they are quite different. There are many physical differences, such as differences in skin, color, and body type. There are also differences in behavior. A frog will need to be in close proximity to a body of water, for instance, while a toad can be further away. Frogs also tend to hop higher than toads.

          If there was ever a tell-tale sign to indicate which amphibian you are looking at, it’s the texture of their skin. Toads are warty-looking, covered in little lumps and bumps, while Frogs are sleek and smooth. Toads also virtually always have dry skin, whereas frogs look wet even when they are out of the water.

          If you’ve spotted an amphibian making its way along a pavement or ambling through some grass, chances are it’s a toad. Toads cope much better with dry conditions than frogs, as their skin is more waterproof. Frogs lose moisture a lot more easily, and so are rarely seen too far away from water, which explains why they always look moist.

          Frogs have long legs, longer than their head and body, which are made for hopping. Toads, on the other hand, have much shorter legs and prefer to crawl around rather than hop. Frogs are lithe and athletic-looking, whereas toads are somewhat squat and dumpy. Their faces are different too; frogs have a pointed nose while toad noses are much broader. Spawn is another key indicator for which species you’re looking at. Frog spawn is laid in gooey clumps, whereas toads spawn floats in stringy lengths. Like their adult counterparts, frog tadpoles are slimmer whereas toad tadpoles are chunky. Frog tadpoles are also covered in gold flecks, while toad tadpoles are plain black in colour.

Picture Credit : Google

          Amphibians have different life cycles. Many live mainly on land, but most of them spend at least some of their lives in water. Frogs, toads, newts and salamanders are all amphibians. Frogs and salamanders are able to breathe through their damp skins to a certain extent, both in the water and on land, but toads must rely largely on their lungs and cannot remain in water for long.

          Amphibians! In order for water-dwelling animals to adapt to life on land, many new adaptations had to take place. First, they needed to be able to breathe air instead of obtaining oxygen from water. And fins don’t work well as legs! They needed to be able to move around well on land.

          What group of animals begins its life in the water, but then spends most of its life on land? Amphibians! Amphibians are a group of vertebrates that has adapted to live in both water and on land. Amphibian larvae are born and live in water, and they breathe using gills. The adults live on land for part of the time and breathe both through their skin and with their lungs as their lungs are not sufficient to provide the necessary amount of oxygen.

          There are approximately 6,000 species of amphibians. They have many different body types, physiologies, and habitats, ranging from tropical to subarctic regions. Frogs, toads, salamanders, newts, and caecilians are all types of amphibians.

          Most amphibians live in fresh water, not salt water. Their habitats can include areas close to springs, streams, rivers, lakes, swamps and ponds. They can be found in moist areas in forests, meadows and marshes. Amphibians can be found almost anywhere there is a source of fresh water. Although there are no true saltwater amphibians, a few can live in brackish (slightly salty) water. Some species do not need any water at all, and several species have also adapted to live in drier environments. Most amphibians still need water to lay their eggs.

          A very few fish give birth to live young, but most lay their eggs in the water, which is called spawning. A fish may lay millions of eggs, only a small proportion of which will grow into adults. A few fish, such as salmon and sticklebacks, build nests underwater to protect their eggs. They lay fewer eggs because more young survive. Dogfish and skates protect their eggs in black capsules. The empty capsules are often washed up on the beach, and it is these that are known as “mermaid’s purses”.

          Perhaps you’ve found a “mermaid’s purse” on the beach. Mermaid’s purses blend really well with seaweed, so you may also have walked right by one. Upon further investigation, you can learn more about what they are. The enchantingly named structures are the egg cases of skates and some sharks. This is why they are also known as skate cases.

          While some sharks bear live young, some sharks (and all skates) release their embryos in leathery egg cases that have horns and sometimes long tendrils at each corner. The tendrils allow them to anchor to seaweeds or other substrates. Each egg case contains one embryo. The case is made up of a material that is a combination of collagen and keratin, so a dried egg case feels similar to a fingernail. 

          In some areas, such as in the Bering Sea, skates seem to lay these eggs in nursery areas. Depending on the species and sea conditions, the embryo may take weeks, months or even years to fully develop. When they hatch out of one end, the baby animals look like miniature versions of their skate or shark parents. 

          If you find a mermaid’s purse on the beach or are lucky enough to see a “live” one in the wild or in an aquarium, look closely — if the developing skate or shark is still alive, you may be able to see it wiggling around. You also may be able to see it if you shine a light through one side. The egg cases on the beach are often light and already opened which means the animal inside has already hatched and left the egg case. 

          Mermaid’s purses usually get washed or blown to the high tide line of the beach, and they often get wrapped up in (and blend in well with) seaweeds and shells. As you’re walking along the beach, walk in the area where shells and ocean debris seems to have washed up, and you might be lucky enough to find a mermaid’s purse. You may be more likely to find one after a storm.