Шыны әйнек бақалар: биологиясы мен эволюциясы

Family of amphibians

The glass frogs belong to the amphibian family Centrolenidae (order Anura), native to the Central American Rainforests. The general background coloration of most glass frogs is primarily lime green, the abdominal skin of some members of this family is transparent and translucent, giving the glass frog its common name. The internal viscera, including the heart, liver, and gastrointestinal tract, are visible through the skin. When active their blood makes them visible; when sleeping most of the blood is concealed in the liver, hiding them. Glass frogs are arboreal, living mainly in trees, feeding on small insects and only coming out for mating season. Their transparency conceals them very effectively when sleeping on a green leaf, as they habitually do.) Glass frogs originated in South America and dispersed multiple times into Central America. Character evolution seems to be complex, with multiple gains and/or losses of humeral spines, reduced hand webbing, and complete ventral transparency. The taxonomical classification of the glass frogs has been problematic. In 1991, after a major revision of the species and taxonomic characters, the herpetologists Pedro Ruiz Carranza and John D. Lynch published a proposal for a taxonomic classification of the Centrolenidae based on cladistic principles and defining monophyletic groups. That paper was the first of a series of contributions dealing with the glass frogs from Colombia that led them to describe almost 50 species of glass frogs. The genus Centrolene was proposed to include the species with a humeral spine in adult males, and the genus Hyalinobatrachium to include the species with a bulbous liver. for the species with basal webbing among outer fingers (part of the previous Cochranella ocellata species group). Four genera (Centrolene, Cochranella, Hyalinobatrachium, Nymphargus) have been shown to be poly or paraphyletic have placed them (and their sister taxon, the family Allophrynidae) closer to the family Leptodactylidae. The monophyly of Centrolenidae is supported by morphological and behavioral characters, including: 1) presence of a dilated process on the medial side of the third metacarpal (an apparently unique synapomorphy); 2) ventral origin of the musculus flexor teres digiti III relative to the musculus transversi metacarpi I; 3) terminal phalanges T shaped; 4) exotroph, lotic, burrower/fossorial tadpoles with a vermiform body and dorsal C shaped eyes, that live buried within leaf packs in still or flowing water systems; and 5) eggs clutches deposited outside of water on vegetation or rocks above still or flowing water systems. Several molecular synapomorphies also support the monophyly of the clade.

The evolutionary advantage of a partly clear skin and an opaque back was a mystery, as it did not seem to be effective as camouflage. It was found that the colour of the frog's body changed little against darker or lighter foliage, but the legs were more translucent and consequently changed in brightness. By resting with the translucent legs surrounding the body, the frog's edge appears softer, with less brightness gradient from the leaf to the legs and from the legs to the body, making the outline less noticeable. This camouflage phenomenon, in which the frog's edges are softened to match the relative brightness of its surroundings, is referred to as edge diffusion. Herpetology researchers study the pros and cons of transparency in glass frogs, it was established that the transparency offers more than regular color changes in the skin itself through limited pigments. Experiments with computer generated images and gelatine models of opaque and translucent frogs found that the translucent frogs were less visible, and were attacked by birds significantly less often. Photographs of the frogs were taken both at nighttime and during the day, results showed little to no visibility of the frogs on any leaves in the daytime or nighttime. It was found in 2022 that these frogs have the ability to conceal red blood cells concentrated inside their livers, increasing transparency when they are vulnerable. While this would cause massive clotting in most animals (including humans), glass frogs are able to regulate the location, density, and packing of red cells without clotting. The findings could advance medical understanding of dangerous blood clotting.

Glass frogs are generally small, ranging from in length. They appear light green in color over most of their bodies, except for the skin along the lower surface of the body and legs, which are transparent or translucent. An endangered species of glass frog found in Peru was compared to the N. mixomaculatus species and the following results were recorded: no humeral spine, no webbed fingers between II and III, finger I shorter than II, no vomerine teeth, no ulnar and tarsal tubercles or folds, no white pigment in the visceral or hepatic peritonea, and differing coloration and spots.

Mating begins by the call of a male tree frog, who is perched either on the underside or top of a leaf over a lake edge or a stream. Once a female has responded to the male's call, mating begins on the leaf in the amplexus physical position, in which the male wraps his arms around the female and attaches himself to her back. Once the physical mating process has concluded, the female produces her eggs onto the leaf before departing, leaving the male to defend the newly laid eggs against predators.

The Centrolenidae are a diverse family, distributed from southern Mexico to Panama, and through the Andes from Venezuela and the island of Tobago to Bolivia, with some species in the Amazon and Orinoco River basins, the Guiana Shield region, southeastern Brazil, and northern Argentina. The biggest threats they have are deforestation, invasive species, pollution, habitat loss and illegal pet trade. These many threats have led to a decline in the population of this species.

Glass frogs are mostly arboreal. They live along rivers and streams during the breeding season, and are particularly diverse in montane cloud forests of Central and South America, although some species occur also in Amazon and Chocóan rainforest and semideciduous forests. Hyalinobatrachium valerioi glass frogs are carnivores, their diet mainly including small insects like crickets, moths, flies, spiders, and other smaller frogs. The eggs are usually deposited on the leaves of trees or shrubs hanging over the running water of mountain streams, creeks, and small rivers. One species leaves its eggs over stones close to waterfalls. The method of egg laying on the leaf varies between species. The males usually call from leaves close to their egg clutches. These eggs are less vulnerable to predators than those laid within water, but are affected by the parasitic maggots of some fly species. Some glass frogs show parental care: in many species, glass frog females brood their eggs during the night the eggs are fertilized, which improves the survival of the eggs, while in almost a third of species, glass frog males stay on guard for much longer periods. After they hatch, the tadpoles fall into the waters below. The tadpoles are elongated, with powerful tails and low fins, suited for fast flowing water. Outside of the breeding season, some species live in the canopy. The majority of amphibians use cutaneous respiration, or the process of breathing through the skin. Due to the importance of the skin, amphibians are very sensitive to what goes through their permeable skin, the stratum corneum is the main skin barrier which is much thinner than other classes such as mammals or birds. Chemicals and high amounts of elements in water or rainfall may disturb frogs’ health and possibly lives.