Reading Practice 31

[1] Frogs are known as one of the most diverse scientific order of vertebrate species in the world. Nevertheless, they are often overlooked by humans. In fact, these carnivorous amphibians date back in fossil record to the early Triassic period in Madagascar. However, molecular dating suggests they may even date back to the Permian period over 265 million years ago. As a result, their ancient pedigree contributes to the fact that frogs can be found all over the planet—even in subarctic climates. In spite of this range of inhabitation, the majority of frog species are found in tropical rainforests where they enjoy the greatest diversity. In short, frogs are composed of a unique anatomy and have prolific reproduction habits leading to a broad population.

 

[2] The scientific order of Anura consists entirely of a different species of frogs. Frogs share numerous characteristics across species. They have a stout body, large protruding eyes, cleft tongues, folded limbs and no tail. Moreover, one of the more intriguing characteristics of frogs is their skin. Frogs have glandular skin which can secrete liquids and mucus. Because of these secretions a frog can simply cause its skin to taste particularly foul to a predator, or they can be highly toxic even to touch and ingest. The skin itself has a broad palette of colours. Similar to snakes, the skin colours and patterns of frogs are intended either to disguise or to ward off would-be predators. Some species have evolved colours to camouflage into their habitat and avoid predators. Conversely, other species have developed bright, vivid colours to advertise their toxicity to any hungry predators. The skin is semi permeable, which means frogs are vulnerable to severe dehydration in dry environments. This leads to their preference for tropical, damp and humid habitats.

 

[3] As a result of being an amphibious species, certain frogs choose different environments to lay their eggs. For example, a minority group of frog species will actually lay their eggs on land; however, the vast majority choose to lay their eggs in water where they will hatch into tadpoles. Tadpoles are an aquatic larvae complete with tails – which disappear later – and internal gills. As tadpoles’ natural habitat is ponds and streams, they have a diet of planktivorous and herbivorous foods. As tadpoles mature into adults, their bodies develop characteristic features of frogs and consequently, they adopt a much more carnivorous diet. In addition, adult frogs are one of the more efficient converters of food into body mass. The importance of this characteristic is that frogs are an integral part of almost any ecosystem they belong to as a key nutritional source for predators. Although they are diminutive in size, they have a large impact on the dynamics of ecosystems.

 

[4] Frogs, like many other species, have specific breeding seasons that can trigger hormone-dependent sexual characteristics. In addition to an arsenal of vocal cords to attract mates, male frogs develop special pads on their thumbs to provide a firmer grip while mating with a female. This firm grip stimulates the female, and as a result they will release eggs to be fertilized. Sperm is ejected directly from the cloaca directly onto the eggs, typically wrapped in jelly, as the female lays them. The sexual organs -testes and ovaries – are attached to frogs’ kidneys, due to their small-sized anatomy. Fertilized eggs will later develop into tadpoles.

 

[5] Frogs are not only valued by humans for food, but also for their roles in literature, symbolism and religion among various cultures around the world. However, the global frog population has been in decline since the 1950s. Since the 1980s, more than 120 species have become extinct. Moreover, a third of the frog species is threatened by extinction. A major problem for the global frog population is a fungal disease known as chytridiomycosis. This emerging disease is a mystery to conservation biologists and threatens frogs around the world. The frog population may continue to decline if a solution is not found to combat this disease. Frogs are now a key focus for the conservation movement and biologists as they face many new challenges in a changing ecosystem.