The Testudines, chelonians or tortoises are an order of reptiles belonging to the Testudinata clade.
There are 14 families that add up to around 356 species, occurring in tropical and temperate regions of the globe, some of which are threatened with extinction. The popular terms tortoise (freshwater), tortoise (land) and turtles (marine) do not reflect taxonomic classification. The order of Testudines is phylogenetically divided into two major groups: Cryptodira (anteroposterior neck retraction) and Pleurodira (lateral neck retraction). The phylogenetic position among the Amniota remains an enigma, being considered by some authors to be close to lepidosaurs (evidenced by morphological data) or archosaurs (evidenced by molecular data).
Anatomia e fisiologia
Skull and neck retraction
Lateral view of the skull and jaw of Chelonia mydas. Source: Hofling et al. (2019)
Turtle skulls do not have temporal fenestrae, that is, they have an anapsid condition. Goodrich (1930), Boulenger (1918) and Broom (1924) emphasized that the arrangement of bones in the temporal region of turtles does not resemble that of true Anapsida. Furthermore, studies of the ontogeny of the adductor musculature of the mandible reveal similarities between turtles and Diapsid. Thus, today it is known that Testudines are Diapsida with secondary loss of temporal fenestrae.
Throughout evolution, there has been a tendency towards the loss of some dermal bones in the skull of turtles: lacrimal, epipterygoid and ectopterygoid are lost in many groups; the nasal occurs only in the family Chelidae. In the circum-orbital series, one element disappears: according to some authors, the post-frontal, according to others, the post-orbital.
All current Testudines have an expanded optical capsule that reduces the space within the adductor chamber, decreasing the volume of the adductor musculature of the mandible. This, added to the anapsid condition, would generate a problem of low bite force. Thus, during evolution there was an independent origin of different solutions to increase adduction force: in Pleurodira, the adductor muscle of the mandible passes over a pulley-shaped projection of the pterygoid (pterygoid trochlear process), while in Cryptodira the trochlear process is formed by the optical capsule itself.
Carapace (left) and plastron (right) of Testudines, above schematic with keratinized epidermal plates and below schematic with dermal bone plates. Source: Pough (2008)
Today's tortoises have a horny, toothless beak. The fossil record reveals that rmphotheca arose early in the evolution of turtles, although some basal groups still had teeth (such as Odontochelys semitestacea). The secondary palate is present (consisting of horizontal plates on the medial part of bones such as the premaxillary, maxillary, palatine and pterygoid), but poorly developed. Unlike the secondary palate of Crocodylia, in which the choanae are located at the height of the pterygoid bones, in Testudines the choanae are located rostrally at the level of the vomer.
Neck retraction occurs laterally in Pleurodira and anteroposteriorly in Cryptodira. In some species of Chelidae (Pleurodira), the neck may be longer than the hull. In some species of Trionychia and Kinosternidea (Cryptodira), there is the ability to stretch the head over the carapace for defense or hunting. In the case of current sea turtles, there was a loss of the ability to retract the neck.
Hull
The shell of turtles is formed by the carapace (dorsal) and plastron (ventral). Both have keratinized epidermal plates above dermal bone plates (no overlap in position and number). The carapace is composed of neural plates fused to the vertebrae, costal plates fused to flattened ribs, and peripheral plates. The plastron is composed of pairs of epidermal plates (such as gular, humeral, pectoral, abdominal, femoral, and anal); located underlyingly there may be the following dermal bone plates: paired epiplastrons derived from clavicles; endoplastron derived from the interclavicle; pairs of hyoplastron, hypoplastron and xifiplastron. The girdles are internal to the rib cage.
Flexible areas (hinges) may be present on the hooves of many Testudines, such as Kinosternon. Leatherback turtles (Dermochelys coriacea) have a carapace formed by cartilage with thousands of small polygonal bones.
If turtles evolved from a common marine ancestor, the presence of heavy abdominal ribs (gastralia) may have contributed to buoyancy control, resulting in the emergence of the plastron before the carapace (evidenced by the Odontochelys fossil). The carapace may have evolved as a defensive structure, but there are also recent hypotheses that turtle ancestors were fossorial, in which shell ossification may have been a way of dealing with soil pressure when digging. However, it should be remembered that other fossorial vertebrates show a reduction in ossification, forming a relatively soft body, which does not support the hypothesis.
Digestive system
Chelonians have a toothless keratinized horny beak. Salivary glands are well-developed lobuloalveolar structures. In the case of fruit-eating turtles, there is an increase in amylase-secreting salivary glands. In the stomach, the presence of food stimulates acid secretion (but the visual and chemical stimulus itself can induce the secretion of gastric juice). In warmer months, proteolytic activity is faster. In Galápagos tortoises (Geochelone nigra), 1 cm diameter gravels are found in the feces, but the exact role of these gastroliths in mechanical digestion is still uncertain. The intestinal tract of herbivorous turtles is larger than that of carnivores to expand the surface area of mutualism with bacteria.
The turtle pancreas also has exocrine and endocrine function, but, as in other reptiles, the exocrine pancreas consists of more branched tubules than the acini and lobules of mammals. The liver, on the other hand, is less organized in lobules than in mammals.
Sistema respiratório
Primitive amniotes used the movement of the rib cage to generate negative pressure, causing ventilation, this mode of breathing being retained as the primary ventilation mechanism of lepidosaurs and living birds. In Testudines this is not possible due to the fusion of the ribs to the rigid shell, instead it is used by the cranial (pectoral and serratus) and caudal (transversus abdominis and oblique abdominis) muscles which, through contractions, move the visceral mass, exerting length or expanding the lungs that are connected to the hoof in the dorsal and lateral region, already in the ventral region they are connected to a sheet of connective tissue attached to the viscera.
For air inspiration to occur, the abdominal oblique muscles, which connects the plastron to the caudal limiting membrane (a dome-shaped connective tissue located in the posterior region), and the serratus, which starts from the carapace and inserts into the pectoral girdle, are contracted. When contracting the abdominal oblique, the limiting membrane is pulled ventrally and contracting the serratus makes it move the pectoral girdle to the anterior region, increasing the volume of the visceral cavity, allowing lung expansion. For air expiration, the transversus abdominis muscle, which is inserted into the carapace and connected to the caudal limiting membrane, and the pectoral muscle, which connects the pectoral girdle with the plastron, are used. When contracting the transversus abdominis, the caudal limiting membrane moves to the dorsal direction, and by contracting the pectoral muscles, the shoulder girdle moves into the hoof, decreasing the volume of the visceral cavity, exerting pressure on the lungs, causing expiration.
In aquatic turtles, both marine and freshwater, there are different mechanisms for carrying out respiration, such as the use of the water's own hydrostatic pressure to transport air from the inside to the outside of the lungs. In addition, in some groups gas diffusion, O2 absorption and CO2 release occur in the pharyngeal or cloaca epithelium. These epithelia are highly irrigated, and may even have projections that increase the contact surface, where there is a continuous flow of water, and gas exchange occurs.
Cardiovascular system
The circulatory system in vertebrates is composed of a muscular pump (heart) that provides pressure to the system, causing the fluid to travel through a system of vessels continuously, nourishing and oxygenating the different types of tissues and organs. The system can be divided into two circuits, the systemic, where the blood pumped by the heart transports oxygenated blood to the body (head, trunk and appendages), and the pulmonary circuit, where the pumping of deoxygenated blood to the lungs occurs, oxygenating -O.
The heart of Testudines has the right and left atria completely separate, and a single large ventricle divided into three interconnected subcompartments, a muscular crest, which is partially fused to the wall of the ventricle, divides it into the cavum pulmonale, which communicates with the pulmonary artery. , and cavum venosum, which communicates with the left and right aortic arches, the third subcompartment, cavum arteriosum, is situated dorsal to the others and is connected to the cavum venosum through an intraventricular canal.
The flow of deoxygenated blood occurs through the venous sinus to the right atrium, which empties into the cavum venosum, whereas the oxygenated blood empties into the cavum arteriosum. Both atria are separated from the ventricle by valves in the form of flaps that confine the blood in the subcompartments, contractions of the atrium allow the opening of the valves and the contraction of the ventricle allows them to close, this arrangement allows that mixing between the oxygenated bloods does not occur. and deoxygenated, even without a permanent morphological division.
Excretory system
Turtles have two kidneys connected to an extensible vesicle located near the cloaca to carry out the excretion of nitrogen compounds, this compound being urea for several species. However, the type of excretion depends on the way of life, turtles that inhabit desert regions, with low water availability, excrete uric acid and urates, spending more energy to conserve more water in the body. Sea turtles, on the other hand, excrete ammonia (a way in which there is less energy expenditure, but a greater loss of water), in addition to performing osmoregulation through the secretion of salt glands.
Nervous and sensory system
The turtle brain is arranged in the midline of the skull, formed like a tube during development and undergoes further specialization of regions, twists and expansions that characterize the adult form. It can be divided into telencephalon, diencephalon, midbrain, metencephalon and myelencephalon. Two layers of meninges cover the brain.
Sensory organs are the environment's sensing systems from behavioral foraging factors such as predation and detection of safe food. Turtles have well-developed vision, being able to respond to the wide range of the light spectrum, in addition to the presence of small oil droplets in the cone cells, which have the property of reducing the overlap in the sensitivity of the wavelengths of light between adjacent cones, which can be an indication of color discrimination. Color perception is of great importance for food selection, where a color can be very attractive to a species. This can be observed through behavioral studies, as chelonians of the species Chelonoidis denticulata and Chelonoidis carbonaria, common in South America, have a preference for foods that are red and yellow to green and blue.
Smell is another important sense for obtaining different information from the environment, helping in the search and selection of food, observing the presence of a partner or enemy, in addition to the recognition of its territory. Turtles have two different types of chemoreceptive system, the olfactory system and the vomeronasal system. The odor particles are captured by the nostrils, which pass through the pharyngeal duct, until they reach the olfactory epithelium. The vomeronasal organ is located at the base of the nasal cavity,[20] this organ is closely linked to the chemical perception used for communication. Smell is of great importance in aquatic species, especially in regions of high turbidity, where chemical signals are spatial guides for these species.
TURTLE EGGS
number of eggs placed in the artificial hole, from 30 eggs placed in the hole the hatching percentage decreases.
Bonach (2003) found the same problems of reducing the success rate in transferred turtle nests, suggesting that the transfer was only done in eggs with more than 28 days of incubation.
Thus, the process of transferring eggs to new nests, being these, divided and two holes, proved to be adequate, as the survival rates were similar compared to unmanaged nests and superior to those transferred with one hole.
There was no significant difference between the three types of pit management in incubation time, with an average of 59 days of incubation and in hatchling size (carapace length, height and weight).
Geographic distribution
Sea turtles live in all five oceans except polar regions such as Canada, the Nordic countries, southern Chile and Argentina, as well as all of Antarctica. Land tortoises are located on all continents, with the exception of Antarctica, and are very common in tropical forests. They are found throughout Africa, regions of Asia, Europe and Oceania, in addition to most of the Americas, with less distribution in icy territories, such as Canada, Greenland and the Andes region.
Ecological Paper
Over time, turtle populations have greatly decreased, which has resulted in a reduction in their ecological roles as members of their communities. However, the disappearance of this species can result in several ecological losses.
Turtles are sentinels of the seas if an environment is unbalanced, so are turtles. As they have a series of marine relationships and influences, turtles indicate the quality of the environment. This is because they participate in reducing the decomposition time of organisms, transforming them into smaller particles. In addition, in their transit, turtles carry nutrients and energy through the food they ingest and desert and can help in the biodiversity of the flora, as in the case of the hawksbill turtle, which in its coastal phase feeds on sponge and algae. This diet allows less common types of sponges to grow, which increases the variety of life on the reef. Without these animals, sponges can overgrow and suffocate slow-growing corals, causing them to die.
As an effect, they also affect the soil. An example of the degree of ecosystem disturbance that turtles are capable of achieving is shown in the nesting of green turtles and loggerhead sea turtles on Heron Island, Australia. These species have a profound effect on the peripheral vegetation of the island. Thousands of turtles nest during the period from October to March, affecting a strip of coastal vegetation averaging 14.8 m wide (Rogers 1989), uprooting plants, burying others with sand, flattening small bushes and breaking branches of larger bushes. A single turtle can affect an area of more than 2 m in diameter.
Also, loggerhead sea turtles in Moreton Bay, Australia, use an unusual foraging strategy that causes considerable disturbance to the seafloor (Preen 1996). To gain access to buried food sources, sea turtles dig pits up to 1.5 m wide and 0.3–0.45 m deep. This habit has a substantial impact on the biomass, species composition and dynamics of some seagrass beds and associated fauna.
Therefore, in an environment with little human interference and balanced, turtles live well and carry out their life cycle peacefully.
With other marine animals, turtles provide substrate and food. The fish swim along its shell to escape predators and feed on microalgae, bacteria and dead tissue, as there is a great diversity of organisms that are not seen with the naked eye in the turtle's shell. In addition, there are barnacles that live in its head and hull.
Through spawning, turtles connect marine and terrestrial habitats. This process is important for the fertilization of coastal beaches and for local fauna and, consequently, the structure of flora communities. By introducing nutrients into beach ecosystems, sea turtles can help maintain stable dune systems that are essential for their reproductive success. The spawning period occurs between December and March and the sea turtles return, after fertilization, to their beaches of origin and with the help of the currents of the planet's magnetic poles, which serve as a guide for these turtles. Female turtles spawn at night on these beaches, as they are less likely to be captured, as it is a dark environment and cooler sand, due to the high temperature during the day. On dry land, with its anterior fins, the formation of the bed, a hole, and the pit, with the posterior fins, is carried out, thus spawning. After the process, the female turtles return to the sea. The time it takes for turtles to hatch from their eggs depends on the temperature of the sand. The temperature needs to be between 25°C and 30°C for the development of embryos, also temperatures above 30°C produce more female turtles, while those below 29°C, more males, taking about two months for the hatchlings. hatch from their eggs and go to sea.
When the eggs are seen in the turtle's nest, it is marked with wooden stakes or the eggs are moved by technicians, for the preservation and safety of the embryos' development.
However, even the eggs and hatchlings of turtles are preyed upon by foxes and other animals (such as dogs, for example), in addition to being common for hatchlings to be captured by crabs, birds (frigate, seagull). In the sea, small turtles are consumed by large fish and, as they grow, the risk of predation decreases. But they are still targets for tiger sharks, killer whales, crocodiles and jaguars.
As predators:
They eat straws and other plastics.
tortoises
The ecological role of tortoises (freshwater turtles) is decreasing, which has affected the maintenance of habitat heterogeneity and resulted in the loss of certain features of the environment, such as small swamps and the extinction or decline of some plant species (Iverson 1987, Griffiths et al. 2011, Froyd et al. 2014). Some turtles of this species participate in cleaning up rivers polluted with dead bodies in India or in the search for carrion, as they have the ability to survive in polluted waterways, which is a characteristic that makes them a tangible benefit (Moll 1980).
tortoise
Land turtles, or “tortoises”, are of great importance in seed dispersal and germination. Most tropical and temperate woody plants rely on vertebrates for seed dispersal. Because of this, the reduced presence of turtles (MacFarland et al. 1974) in ecosystems resulted in changes in vegetation and even extinction of other species. Today, turtles are being used to restore ecosystems that have suffered from declining tortoise populations (Opuntia megasperma var. megasperma; Gibbs et al. 2008). As in the Galapagos, where the positive effect on a rare tree-like cactus species is seen (Hunter and Gibbs 2014). Turtle densities do not need to be particularly high to reverse woody plant invasion and restore plant communities to more natural conditions. For example: Galapagos tortoises regularly move large amounts of seeds over long distances. Mayapple seeds eaten by this species of turtle germinate faster and are more likely to succeed than seeds not eaten.
In addition, there are burrowing tortoise species, the excavated mounds in front of the burrows contribute to environmental heterogeneity and increased plant species diversity (Kaczor and Hartnett 1990) and their burrows provide shelter for more than 350 vertebrates and invertebrates. (Johnson et al. 2017), many of whom are unable to dig burrows on their own. Included are some species of owl, several species of lizard, some types of frogs, red foxes, bobcats, rodents, rabbits, among other declining species such as eastern indigo snakes and rattlesnakes.
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