Xenopus laevis is a scavenger and eats living, dead, or dying arthropods and other pieces of organic waste. It has a voracious appetite and attacks anything that passes in front of it. It uses extremely sensitive fingers, an acute sense of smell, and its lateral line systems to locate food. Lateral line systems, usually found in fish, detect vibrations in the water. It uses a hyobranchial pump to suck food into its mouth. The claws on its hind feet tear apart larger pieces of food. Tadpoles are exclusively filter feeders
(Avila and Frye, 1977; Beck, 1994)
Animal Foods: insects; aquatic or marine worms; aquatic crustaceans
Primary Diet: carnivore (Insectivore , Scavenger )
Xenopus laevis occurs naturally in southern Africa. There are substantial introduced populations in California, Chile, Great Britain, and probably many other locations around the world. (Nieukoop and Faber, 1994)
Biogeographic Regions: nearctic (Introduced ); palearctic (Introduced ); ethiopian (Native )
Xenopus laevis lives in warm, stagnant grassland ponds as well as in streams in arid and semi-arid regions. The ponds are usually devoid of any higher plant vegetation, and covered in green algae. Xenopus laevis can tolerate wide variation in water pH, but the presence of metal ions proves toxic. It thrives in temperatures from 60 to 80 degrees Fahrenheit. It is almost totally aquatic, only leaving the water when forced to migrate.
(Nieuwkoop and Faber, 1994; Beck, 1994; Kaplan, 1995, Jack Crayon, personal communication)
Habitat Regions: temperate ; tropical ; freshwater
Aquatic Biomes: lakes and ponds; rivers and streams
African clawed frogs can reach 15 to 16 years old in wild and feral populations. Captive animals have been known to live as long as 20 years.
Range lifespan
Status: wild: 16 (high) years.
Range lifespan
Status: captivity: 20 (high) years.
Average lifespan
Status: captivity: 8.8 years.
Average lifespan
Status: captivity: 15.0 years.
Xenopus laevis has a unique morphology because it lacks a tongue and a visible ear. The body is flattened and head is wedge-shaped and smaller than the body. It has two small eyes found on the top of the head and no eyelids. Its front limbs are small and are not webbed, and its hind legs are large and webbed and the three inside toes on either foot have claws. It has smooth slippery skin which is multicolored on its back with blotches of olive gray or brown and gray, while the underside is creamy white with a yellow tinge. It has lateral lines along its back. Males weigh about 60 grams, are about 5 to 6 centimeters long, and lack a vocal sac, which most male frogs have. Females weigh about 200 grams, are about 10 to 12 centimeters long, and have cloacal extensions at the end of the abdomen.
(Kaplan, 1995; Chang 1998)
Range mass: 60 to 200 g.
Range length: 5 to 12 cm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry
Sexual Dimorphism: female larger
Average basal metabolic rate: 0.012 W.
Xenopus laevis has been used extensively as a laboratory research animal, mostly in the field of vertebrate embryology because females are prolific egg layers and embryos are transparent, making it easy to observe the development of the embryo. During the 1940's, female X. laevis were injected with the urine of a woman. If the human was pregnant, then the injected frog would start to produce eggs. Xenopus laevis was the first vertebrate cloned in the laboratory. Magainins are a family of antibiotics found in the skin of X. laevis, which heals wounded skin rapidly. Magainin is an antibiotic, antifungal, antiparasitic, and antiviral, probably useful to the frog because of the stagnant, microbe filled waters in which it lives in. These magainins have been tested as an antibiotic cream, which works just as well as an oral antibiotic, but without the side effects. Xenopus laevis is also used in lab because it is very easy to care for, breed, and observe.
Positive Impacts: source of medicine or drug ; research and education
Human activities have transplanted this African frog all over the globe, where some claim it is pushing native species out of their niche (Beck 1994). Others argue that there is no documented case of this occurring (Jack Crayon, pers. comm.)
Development - Life Cycle: metamorphosis
It is an invasive species all over world because it was used in human pregnancy tests in the 1940's. When more effective means of pregnancy tests were made available, many X. laevis were released all over the world.
IUCN Red List of Threatened Species: least concern
Xenopus laevis is sexually mature in 10 to 12 months. Mating can take place during any time of the year, but is most common in the spring, and can take place up to four times per year. Males vocalize during the evening to attract females. Although the male lacks a vocal sac, it produces a mating call by rapid contractions of the intrinsic laryngeal muscles. This mating call sounds like alternating long and short trills. After the female hears this, she responds with either an acceptance call (a rapping sound) or a rejection call (slow ticking sound). This is a nearly unique behavior in the animal world; rarely does a female answer the males call. Mating often takes place at night, when there are few disturbances. The male develops mating pads on the underside of his forearms and hands. The mating embrace, amplexus, is pelvic, whereas most frogs have axillary (front limb) amplexus. The female can release hundreds of sticky eggs during the 3 to 4 hour event, which are typically attached to plants or other anchors, one or more at a time. The eggs grow into tadpoles, which filter feed. The tadpole metamorphoses into a small froglet, with the tail being absorbed into the body and sustaining its nutritional requirements during this period, which lasts about 4 to 5 days. The total change from egg to small frog takes about 6 to 8 weeks.
(Kaplan, 1995; Beck, 1994; Chang, 1998; Kelley, 1998, Jack Crayon, personal communication)
Breeding interval: African clawed frogs can breed up to 4 times each year.
Breeding season: Mating can take place during any time of the year, but is most common in the spring.
Range age at sexual or reproductive maturity (female): 10 to 12 months.
Range age at sexual or reproductive maturity (male): 10 to 12 months.
Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (External ); oviparous
African clawed frogs were first brought to California decades ago to help doctors figure out whether their patients were pregnant. After new technology made those pregnancy tests obsolete, the creatures were let loose, and thrived for decades in the state's drainage ditches and ponds.
Now there are signs that the proliferation of African clawed frogs may be putting native species in peril. A study published last week in the journal PLOS ONE reveals that they carry a deadly fungus responsible for wiping out vast numbers of amphibians around the world.
The spread of the deadly Batrachochytrium dendrobatidis fungus is contributing to one of the greatest disease-caused losses of biodiversity in recorded history. The fungus causes amphibians' skin to harden, interfering with the regulation of electrolytes and eventually causing cardiac arrest.
By Geoffrey Mohan, Los Angeles Times May 19, 2013, 9:56 p.m.
The African clawed frog (Xenopus laevis), also known as the xenopus, African clawed toad, African claw-toed frog or the platanna) is a species of African aquatic frog of the family Pipidae. Its name is derived from the three short claws on each hind foot, which it uses to tear apart its food. The word Xenopus means 'strange foot' and laevis means 'smooth'.
The species is found throughout much of Sub-Saharan Africa (Nigeria and Sudan to South Africa),[2] and in isolated, introduced populations in North America, South America, Europe, and Asia.[1] All species of the family Pipidae are tongueless, toothless and completely aquatic. They use their hands to shove food in their mouths and down their throats and a hyobranchial pump to draw or suck things in their mouth. Pipidae have powerful legs for swimming and lunging after food. They also use the claws on their feet to tear pieces of large food. They have no external eardrums, but instead subcutaneous cartilaginous disks that serve the same function.[3] They use their sensitive fingers and sense of smell to find food. Pipidae are scavengers and will eat almost anything living, dying, or dead and any type of organic waste.
It is a pest in many countries, including across Europe.[4]
These frogs are plentiful in ponds and rivers within the south-eastern portion of Sub-Saharan Africa. They are aquatic and are often greenish-grey in color. African clawed frogs have been frequently sold as pets, and sometimes incorrectly misidentified as African dwarf frogs. Albino clawed frogs are common and sold as animals for laboratories.
They reproduce by fertilizing eggs outside of the female's body (see frog reproduction). Of the seven amplexus modes (positions in which frogs mate), these frogs are found breeding in inguinal amplexus, where the male clasps the female in front of the female's back legs and squeezes until eggs come out. The male then sprays sperm over the eggs to fertilize them.
African clawed frogs are highly adaptable and will lay their eggs whenever conditions allow it. During wet rainy seasons they will travel to other ponds or puddles of water to search for food.[5] During times of drought, the clawed frogs can burrow themselves into the mud, becoming dormant for up to a year.[6]
Xenopus laevis have been known to survive 15 or more years in the wild and 25–30 years in captivity.[7] They shed their skin every season, and eat their own shed skin.
Although lacking a vocal sac, the males make a mating call of alternating long and short trills, by contracting the intrinsic laryngeal muscles. Females also answer vocally, signaling either acceptance (a rapping sound) or rejection (slow ticking) of the male.[8][9] This frog has smooth slippery skin which is multicolored on its back with blotches of olive gray or brown. The underside is creamy white with a yellow tinge.
Male and female frogs can be easily distinguished through the following differences. Male frogs are small and slim, while females are larger and more rotund. Males have black patches on their hands and arms which aid in grabbing onto females during amplexus. Females have a more pronounced cloaca and have hip-like bulges above their rear legs where their eggs are internally located.
Both males and females have a cloaca, which is a chamber through which digestive and urinary wastes pass and through which the reproductive systems also empty. The cloaca empties by way of the vent which in reptiles and amphibians is a single opening for all three systems.[10]
African clawed frogs are fully aquatic and will rarely leave the water except to migrate to new water bodies during droughts or other disturbances. Clawed frogs have powerful legs that help them move quickly both underwater and on land. Feral clawed frogs in South Wales have been found to travel up to 2 kilometres (1.2 mi) between locations.[11] The feet of Xenopus species have three black claws on the last three digits. These claws are used to rip apart food and scratch predators.
Clawed frogs are carnivores and will eat both living and dead prey including fish, tadpoles, crustaceans, annelids, arthropods, and more. Clawed frogs will try to consume anything that is able to fit into their mouths. Being aquatic, clawed frogs use their sense of smell and their lateral line to detect prey rather than eyesight like other frogs. However, clawed frogs can still see using their eyes and will stalk prey or watch predators by sticking their heads out of the water.[12] Clawed frogs will dig through substrate to unearth worms and other food. Their tongue is unable to extend like other frogs, so clawed frogs use their hands to grab food and shovel it into their mouths.
These frogs are particularly cannibalistic; the stomach contents of feral clawed frogs in California have revealed large amounts of the frog's larvae.[13] Clawed frog larvae are filter feeders and collect nutrients from plankton, allowing adult frogs that consume the tadpoles to have access to these nutrients. This allows clawed frogs to survive in areas that have little to no other food sources.
Clawed frogs are nocturnal and most reproductive activity and feeding occurs after dark. Male clawed frogs are very promiscuous and will grab onto other males and even other species of frogs.[14][15] Male frogs that are grasped will make release calls and attempt to break free.
If not feeding, clawed frogs will just sit motionless on top of the substrate or floating at the top with their heads sticking out.
The X. laevis liver responds to low temperatures by increasing production of type II iodothyronine deiodinase through increased food intake. This in turn spurs the thyroid to increase T3 to increase body temperature. (This T3 increase also induces germ cell apoptosis, mediated through genes left over from tadpole metamorphosis.)[16]
The effects of provocation of T hormone release are broadly differentiated by where it starts: If centrally, within the mediobasal hypothalamus, then it stimulates seasonal testicular growth; if peripherally, then testicular regression and cold-season thermogenesis.[16]
These observations are regarded as widely applicable across vertebrate thyroid systems.[16]
The lipidomics of Xenopus oocytes has been studied by Tian et al 2014 and Phan et al 2015.[17]
In the wild, X. laevis are native to wetlands, ponds, and lakes across arid/semiarid regions of Sub-Saharan Africa.[2][19] X. laevis and X. muelleri occur along the western boundary of the Great African Rift. The people of the sub-Saharan are generally very familiar with this frog, and some cultures use it as a source of protein, an aphrodisiac, or as fertility medicine. Two historic outbreaks of priapism have been linked to consumption of frog legs from frogs that ate insects containing cantharidin.[20]
X. laevis in the wild are commonly infected by various parasites,[18] including monogeneans in the urinary bladder.
Xenopus embryos and eggs are a popular model system for a wide variety of biological studies, in part because they have the potential to lay eggs throughout the year.[21][22][23] This animal is widely used because of its powerful combination of experimental tractability and close evolutionary relationship with humans, at least compared to many model organisms.[21][22] For a more comprehensive discussion of the use of these frogs in biomedical research, see Xenopus.
Xenopus laevis is also notable for its use in the first widely used method of pregnancy testing. In the 1930s, two South African researchers, Hillel Shapiro and Harry Zwarenstein,[24] students of Lancelot Hogben at the University of Cape Town, discovered that the urine from pregnant women would induce oocyte production in X. laevis within 8–12 hours of injection.[25] This was used as a simple and reliable test up through to the 1960s.[26] In the late 1940s, Carlos Galli Mainini[27] found in separate studies that male specimens of Xenopus and Bufo could be used to indicate pregnancy[28] Today, commercially available hCG is injected into Xenopus males and females to induce mating behavior and to breed these frogs in captivity at any time of the year.[29]
Xenopus has long been an important tool for in vivo studies in molecular, cell, and developmental biology of vertebrate animals. However, the wide breadth of Xenopus research stems from the additional fact that cell-free extracts made from Xenopus are a premier in vitro system for studies of fundamental aspects of cell and molecular biology. Thus, Xenopus is the only vertebrate model system that allows for high-throughput in vivo analyses of gene function and high-throughput biochemistry.[21]
Xenopus oocytes are a leading system in their own right for studies of various systems, including ion transport and channel physiology.[21] Xanthos et al 2001 uses oocytes to uncover T-box expression earlier than previously found in vertebrates.[30]
Although X. laevis does not have the short generation time and genetic simplicity generally desired in genetic model organisms, it is an important model organism in developmental biology, cell biology, toxicology and neurobiology. X. laevis takes 1 to 2 years to reach sexual maturity and, like most of its genus, it is tetraploid. It does have a large and easily manipulated embryo, however. The ease of manipulation in amphibian embryos has given them an important place in historical and modern developmental biology. A related species, Xenopus tropicalis, is now being promoted as a more viable model for genetics.
Roger Wolcott Sperry used X. laevis for his famous experiments describing the development of the visual system. These experiments led to the formulation of the chemoaffinity hypothesis.
Xenopus oocytes provide an important expression system for molecular biology. By injecting DNA or mRNA into the oocyte or developing embryo, scientists can study the protein products in a controlled system. This allows rapid functional expression of manipulated DNAs (or mRNA). This is particularly useful in electrophysiology, where the ease of recording from the oocyte makes expression of membrane channels attractive. One challenge of oocyte work is eliminating native proteins that might confound results, such as membrane channels native to the oocyte. Translation of proteins can be blocked or splicing of pre-mRNA can be modified by injection of Morpholino antisense oligos into the oocyte (for distribution throughout the embryo) or early embryo (for distribution only into daughter cells of the injected cell).[31]
Extracts from the eggs of X. laevis frogs are also commonly used for biochemical studies of DNA replication and repair, as these extracts fully support DNA replication and other related processes in a cell-free environment which allows easier manipulation.[32]
The first vertebrate ever to be cloned was an African clawed frog in 1962,[33] an experiment for which Sir John Gurdon was awarded the Nobel Prize in Physiology or Medicine in 2012 "for the discovery that mature cells can be reprogrammed to become pluripotent".[34]
Additionally, several African clawed frogs were present on the Space Shuttle Endeavour (which was launched into space on September 12, 1992) so that scientists could test whether reproduction and development could occur normally in zero gravity.[35][36]
Xenopus laevis also serves as an ideal model system for the study of the mechanisms of apoptosis. In fact, iodine and thyroxine stimulate the spectacular apoptosis of the cells of the larval gills, tail and fins in amphibians metamorphosis, and stimulate the evolution of their nervous system transforming the aquatic, vegetarian tadpole into the terrestrial, carnivorous frog.[37][38][39][40]
Stem cells of this frog were used to create xenobots.
Early work on sequencing of the X. laevis genome was started when the Wallingford and Marcotte labs obtained funding from the Texas Institute for Drug and Diagnostic Development (TI3D), in conjunction with projects funded by the National Institutes of Health. The work rapidly expanded to include de novo reconstruction of X. laevis transcripts, in collaboration with groups around the world donating Illumina Hi-Seq RNA sequencing datasets. Genome sequencing by the Rokhsar and Harland groups (UC Berkeley) and by Taira and collaborators (University of Tokyo, Japan) gave a major boost to the project, which, with additional contributions from investigators in the Netherlands, Korea, Canada and Australia, led to publication of the genome sequence and its characterization in 2016.[41]
X. laevis oocytes are often used as an easy model for the artificially induced expression of transgenes. For example, they are commonly used when studying chloroquine resistance produced by specialized transporter mutants.[42] Even so the foreign expression tissue may itself confer some alterations to the expression, and so findings may or may not be entirely identical to native expression: For example, iron has been found by Bakouh et al 2017 to be an important substrate for one such transporter in X. l. oocytes, but as of 2020 iron is merely presumptively involved in native expression of the same gene.[42]
Xenbase[43] is the Model Organism Database (MOD) for both Xenopus laevis and Xenopus tropicalis.[44] Xenbase hosts the full details and release information regarding the current Xenopus laevis genome (9.1).
Xenopus laevis have been kept as pets and research subjects since as early as the 1950s. They are extremely hardy and long lived, having been known to live up to 20 or even 30 years in captivity.[45]
African clawed frogs are frequently mislabeled as African dwarf frogs in pet stores. Identifiable differences are:
African clawed frogs are voracious predators and easily adapt to many habitats.[46] For this reason, they can easily become a harmful invasive species. They can travel short distances to other bodies of water, and some have even been documented to survive mild freezes. They have been shown to devastate native populations of frogs and other creatures by eating their young.
In 2003, Xenopus laevis frogs were discovered in a pond at San Francisco's Golden Gate Park. Much debate now exists in the area on how to exterminate these creatures and keep them from spreading.[47][48] It is unknown if these frogs entered the San Francisco ecosystem through intentional release or escape into the wild. San Francisco officials drained Lily Pond and fenced off the area to prevent the frogs from escaping to other ponds in the hopes they starve to death.
Due to incidents in which these frogs were released and allowed to escape into the wild, African clawed frogs are illegal to own, transport or sell without a permit in the following US states: Arizona, California, Kentucky, Louisiana, New Jersey, North Carolina, Oregon, Vermont, Virginia, Hawaii,[49] Nevada, and Washington state. However, it is legal to own Xenopus laevis in New Brunswick (Canada) and Ohio.[50][51]
Feral colonies of Xenopus laevis exist in South Wales, United Kingdom.[52] In Yunnan, China there is a population of albino clawed frogs in Lake Kunming, along with another invasive: the American bullfrog. Because this population is albino, it suggests that the clawed frogs originated from the pet trade or a laboratory.[53]
The African clawed frog may be an important vector and the initial source of Batrachochytrium dendrobatidis, a chytrid fungus that has been implicated in the drastic decline in amphibian populations in many parts of the world.[2] Unlike in many other amphibian species (including the closely related western clawed frog) where this chytrid fungus causes the disease Chytridiomycosis, it does not appear to affect the African clawed frog, making it an effective carrier.[2]
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: CS1 maint: multiple names: authors list (link) The African clawed frog (Xenopus laevis), also known as the xenopus, African clawed toad, African claw-toed frog or the platanna) is a species of African aquatic frog of the family Pipidae. Its name is derived from the three short claws on each hind foot, which it uses to tear apart its food. The word Xenopus means 'strange foot' and laevis means 'smooth'.
The species is found throughout much of Sub-Saharan Africa (Nigeria and Sudan to South Africa), and in isolated, introduced populations in North America, South America, Europe, and Asia. All species of the family Pipidae are tongueless, toothless and completely aquatic. They use their hands to shove food in their mouths and down their throats and a hyobranchial pump to draw or suck things in their mouth. Pipidae have powerful legs for swimming and lunging after food. They also use the claws on their feet to tear pieces of large food. They have no external eardrums, but instead subcutaneous cartilaginous disks that serve the same function. They use their sensitive fingers and sense of smell to find food. Pipidae are scavengers and will eat almost anything living, dying, or dead and any type of organic waste.
It is , including across Europe.