Electrophorus electricus is the bst-known species of electric eel. It is a South American electric fish. Until the discovery of two additional species in 2019, the genus was classified as the monotypic, with this species the ony one in the genus.[2] Despite the nae, it is not an eel, but rather a knifefish.[3] It is considered as a freshwater teleost which contains an electrogenic tissue that produces electric discharges.[4] Contents 1 Taxonomic history 2 Anatomy 3 Physiology 4 Ecology and lif history 4.1 Habitat 4.2 Feeding ecology 4.3 Reproduction 5 References 6 Further reading 7 External links Taxonomic history The species has been reclassified several times. When originally described by Carl Linnaeus in 1766, he used the nme Gymnotus electricus, placing it in the same genus as Gymnotus carapo (banded knifefish) which he had described several years earlier. It was ony about a century later, in 1864, that the electric eel was moved to its own genus Electrophorus by Theodore Gill.[5] In September 2019, David de Santana et al. suggested the division of the genus into three species based on DNA divergence, ecology and habitat, anatomy and physiology, and electrical ability: E. electricus, E. voltai sp. nov., and E. varii sp. nov. The study found E. electricus to be the sister species to E. voltai, with both species diverging during the Pliocene.[2] Anatomy Comparison of the three species of Electrophorus E. electricus has an elongated, cylindrical body, typically growing to about 2 m (6 ft 7 in) in length, and 20 kg (44 lb) in weight, making them the largest of the Gymnotiformes.[6] Their coloration is dark gray-brown on the back and yellow or orange on the belly. Mature females have a darker abdomen. They have no scales. The mouth is square and positioned at the end of the snout. The anal fin extends the length of the body to the tip of the tail. As in other ostariophysan fishes, the swim bladder has two chambers. The anterior chamber is connected to the inner ear by a series of small bones derived from neck vertebrae called the Weberian apparatus, which greatly enhances its hearing capability. The posterior chamber extends along the whole length of the body and maintains the fish's buoyancy. E. electricus has a vascularized respiratory system with gas exchange occurring through epithelial tissue in its buccal cavity.[7] As obligate air-breathers, E. electricus must rise to the surface every ten minutes or so to inhale before returning to the bottom. Nearly eighty percent of the oxygen used by the fish is obtained in this way.[8] Physiology Further information: Electric eel § Electrophysiology E. electricus has three pairs of abdominal organs that produce electricity: the main organ, Hunter's organ, and Sachs' organ. These organs occupy a large part of its body, and give the electric eel the ability to generate two types of electric organ discharges: low voltage and high voltage. These organs are made of electrocytes, lined up so a current of ions can flow through them and stacked so each one adds to a potential difference.[9] The three electrical organs are developed from muscle and exhibit several biochemical properties and morphological features of the muscle sarcolemma; they are found symmetrically along both sides of the eel.[4] When the eel finds its prey, the brain sends a signal through the nervous system to the electrocytes. This opens the ion channels, allowing sodium to flow through, reversing the polarity momentarily. By causing a sudden difference in electric potential, it generates an electric current in a manner similar to a battery, in which stacked plates each produce an electric potential difference.[9] Electric eels are also capable of controlling their prey's nervous systems with their electrical abilities; by controlling their victim's nervous system and muscles via electrical pulses, they can keep prey from escaping or force it to move so they can locate its position.[10][11] Electric eels use electricity in multiple ways. Low voltages are used to sense the surrounding environment. High voltages are used to detect prey and, separately, stun them, at which point the electric eel applies a suction-feeding bite.[12] Anatomy of an electric eel's electric organs Sachs' organ is associated with electrolocation. Inside the organ are many muscle-like cells, called electrocytes. Each cell produces 0.15 V, the cells being stacked in series to enable the organ to generate nearly 10 V at around 25 Hz in frequency. These signals are emitted by the main organ; Hunter's organ can emit signals at rats of several hundred hertz.[13] There are several physiological differences among the three electric organs, which allow them to have very different functions. The main electrical organ and the strong-voltage section of Hunter's organ are rich in calmodulin, a protein that is involved in high-voltage production.[14] Additionally, the three organs have varying amounts of Na+/K+-ATPase, which is a Na+/K+ ion pump that is crucial in the formation of voltage. The main and Hunter's organs have a high expression of this protein, giving it a high sensitivity to changes in ion concentration, whereas Sachs' organ has a low expression of this protein.[15] The typical output is sufficient to stun or deter virtually any animal. The eels can vary the intensity of the electric discharge, using lower discharges for hunting and higher intensities for stunning prey or defending themselves. They can also concentrate the discharge by curling up and making contact at two points along its body.[16] When agitated, they can produce these intermittent electric shocks over at least an hour without tiring.[citation needed] E. electricus also possesses high frequency–sensitive tuberous receptors, which are distributed in patches over its body. This feature is apparently useful for hunting other Gymnotiformes.[13] E. electricus has been prominent in the study of bioelectricity since the 18th century.[17] The species is of some interest to researchers, who make use of its acetylcholinesterase and adenosine triphosphate.[18][19] Despite being the first described species in the genus and thus the most famous example, E. electricus actually has the weakest maximum voltage of the three species in the genus, at nly 480 volts (as opposed to 572 volts in E. varii and 860 volts in E. voltai).[2] |
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Guiana Shield From Wikipedia, the fee encyclopedia Jump to navigationJump to search Guiana Shield Political map of the Guiana Shield Political map of the Guiana Shield Coordinates: 5°08′36″N 60°45′45″WCoordinates: 5°08′36″N 60°45′45″W Region South America Cerros de Mavecure, GuainΓa department, Colombia Devil's Canyon in the Canaima National Park, Venezuela Map of the Guianas The Guiana Shield[1] (French: Plateau des Guyanes, Bouclier guyanais; Dutch: Hoogland van Guyana, Guianaschild; Portuguese: Planalto das Guianas, Escudo das Guianas; Spanish: Escudo guayanΓ©s) is one of the three cratons of the South American Plate. It is a 1.7 bilion-year-old Precambrian geological formation in northeast South America that forms a portion of the northern coast.[2] The higher elevations on the shield are called the Guiana Highlands, which is where the table-like mountains called tepuis are found. The Guiana Highlands are also the source of some of the world's most well-known waterfalls such as Angel Falls, Kaieteur Falls and Cuquenan Falls. The Guiana Shield underlies Guyana (previously British Guiana), Suriname (previously Dutch Guiana) and French Guiana (or Guyane), much of southern Venezuela, as well as parts of Colombia and Brazil. The rocks of the Guiana Shield consist of metasediments and metavolcanics (greenstones) overlain by sub-horizontal layers of sandstones, quartzites, shales and conglomerates intruded by sills of younger mafic intrusives such as gabbros.[3] Contents 1 Geology 2 Geomorphology 3 Ecology 4 See also 5 References 6 External links Geology The oldest rocks in the shield consist of Archean Imataca Complex, composed of a quartz-feldspar gneiss and subordinate mafic gneiss. The Guri Fault marks the southern boundary of the complex. South of that fault are Early Proterozoic rocks consisting of the metavolcanic Pastora Supergroup and the granitic plutonic Supamo Complex. The Cuchivero Group consists of ash flow tuff and granitic plutonic rocks. The Early to Middle Proterozoic Roraima Group consists of continental clastic sedimentary rocks. These Precambrian sediments include quartz sandstones, quartzites, and conglomerates presumed to be 1.8 to 1.4 Ga in age.[4][5] Geomorphology There are three upland areas of the Guiana Shield: The Guiana Highlands proper are in Venezuela east of the Orinoco and extend across much of west-central Guyana and into the northern Roraima state in Brazil. The Tumucumaque Uplands which are a series of central massifs in an arc from the Wilhelmina Mountains of south-central Suriname, along the southern boundary of Suriname and Guyana, forming the Acarai Mountains of Roraima state and the Tumuc-Humac Mountains of ParΓ‘ and AmapΓ‘ states of Brazil. From this arc, the southern uplands slope gently downwards towards the Amazon River and the northern uplands slope gently downwards toward the Atlantic. The Chiribiquete Plateau is a sandstone topped plateau with an elevation of 900 m (2,953 ft) that forms the western edge of the shield. The plateau is separated from the eastern Andes by the thick Neogene sediments of the Sub-Andean Trough that runs along the northern and western rim of the Guiana Shield. The north-central part of the Guiana Highlands is dominated by high flat-topped peaks called tepuis, of the Roraima supergroup and Quasi-Roraima formation, and the rounded granite peaks of the Parguaza and Imataca complexes to the north and southwestern edges of the area. The highest point in the shield is Pico da Neblina in Brazil at 2,995 metres (9,826 ft).[6] Pico da Neblina is the highest summit of the larger Neblina massif, a highly eroded sandstone plateau that straddles the Venezuela-Brazil border and that has lost the typical tabletop shape of the other tepuis in the region.[citation needed] Ecology Heliamphora chimantensis, endemic to the ChimantΓ‘ Massif (a Venezuelan part of the Guiana Shield) The Guiana Shield is one of the regions of highest biodiversity in the world, and has many endemic species. The region houses over 3000 vertebrate species: 1168 fresh water fish, 269 amphibians (54 endemics), 295 reptiles (29), 1004 birds (7.7), and 282 mammals (11).[7][8][9] Diversity of invertebrates remains largely undocumented, but there are several species of endemic butterflies and dung beetles.[10][11] Plant lif is equally rich and 13,367 species of vascular plants have been found, approximately 40 of which is considered endemic.[12] The shield is overlain by the largest expanse of tropical forest on any Precambrian shield area in the world.[13] Guianan rain forest is similar in nature to Amazonian rain forest and known protected areas include the Iwokrama Forest of central Guyana, Kaieteur, Kanuku National Park of southern Guyana, the UNESCO World Heritage Site Central Suriname Nature Reserve of Suriname, the Guiana Amazonian Park in French Guiana and the Tumucumaque National Park in the AmapΓ‘ State of Brazil. In Venezuela the forests are protected by Canaima, Parima-Tapirapeco and SerranΓa de la Neblina national parks. In 2014, the Government of Colombia designated a 250 hectare area of the Guiana Shield, as a Ramsar Wetland, thus becoming a protected area of international importance in accordance to the Ramsar Convention.[14] According to recent researches, although ecosystems of the Guayana Highlands remain vibrant, emerging issues (including "a well-known invasive plant elsewhere" Poa annua and "one of the most aggressive weeds" Polypogon elongatus) and infectious faecal bacteria Helicobacter pylori have been documented |
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