African clawed frog

African clawed frog

Overview
The African clawed frog (Xenopus laevis, also known as the platanna) is a species of South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...

n aquatic frog
Frog
Frogs are amphibians in the order Anura , formerly referred to as Salientia . Most frogs are characterized by a short body, webbed digits , protruding eyes and the absence of a tail...

 of the genus Xenopus
Xenopus
Xenopus is a genus of highly aquatic frogs native to Sub-Saharan Africa. There are 19 species in the Xenopus genus...

. 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".

African clawed frogs can grow up to a length of 5 in (12 cm).
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Encyclopedia
The African clawed frog (Xenopus laevis, also known as the platanna) is a species of South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...

n aquatic frog
Frog
Frogs are amphibians in the order Anura , formerly referred to as Salientia . Most frogs are characterized by a short body, webbed digits , protruding eyes and the absence of a tail...

 of the genus Xenopus
Xenopus
Xenopus is a genus of highly aquatic frogs native to Sub-Saharan Africa. There are 19 species in the Xenopus genus...

. 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".

African clawed frogs can grow up to a length of 5 in (12 cm). They have a flattened head and body, but no tongue or external ears.

The species is found throughout most of Africa, and in isolated, introduced populations in North America, South America, and Europe. All species of the Pipidae family 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 food 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 lack true ears but have lateral lines running down the length of the body and underside, which is how they can sense movements and vibrations in the water. They use their sensitive fingers, sense of smell, and lateral line system to find food. Pipidae are scavengers and will eat almost anything living, dying or dead and any type of organic waste.

Description


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. Albino varieties are commonly sold as pets. “Wild-type” African Clawed Frogs are also frequently sold as pets, and often incorrectly labeled as a Congo Frog or African Dwarf Frog
African dwarf frog
African dwarf frogs are small aquatic frogs native to parts of Africa, spreading from tropical to subtropical areas primarily in the Congo region.-Description:...

 because of similar colorings. They are easily distinguished from African Dwarf Frogs because African Clawed Frogs have webbing only on their hind feet while African Dwarf Frogs have webbing on all four feet. They reproduce by laying eggs (see frog reproduction). Also, the clawed frogs are the only amphibians to have actual (though small) claws.

The average life-span of these frogs ranges from 5 to 15 years with some individuals recorded to have lived for 20–25 years. They shed their skin every season, and eat their own shedded skin.

Although lacking a vocal sac
Vocal sac
The vocal sac is the flexible membrane of skin possessed by most male frogs. The purpose of the vocal sac is usually as an amplification of their mating or advertisement call...

, 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. 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 usually about 20% smaller than females, with slim bodies and legs. Males make mating calls to attract females, sounding very much like a cricket calling underwater. Females are larger than the males, appearing far more plump with hip-like bulges above their rear legs (where their eggs are internally located). While they do not sing or call out like males do, they do answer back (an extremely rare phenomenon in the animal world).

Both males and females have a cloaca
Cloaca
In zoological anatomy, a cloaca is the posterior opening that serves as the only such opening for the intestinal, reproductive, and urinary tracts of certain animal species...

, which is a chamber through which digestive and urinary wastes pass and through which the reproductive system
Reproductive system
The reproductive system or genital system is a system of organs within an organism which work together for the purpose of reproduction. Many non-living substances such as fluids, hormones, and pheromones are also important accessories to the reproductive system. Unlike most organ systems, the sexes...

s also empty. The cloaca empties by way of the vent which in reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...

s and amphibians is a single opening for all three systems.

In the wild


In the wild, Xenopus laevis are native to wetland
Wetland
A wetland is an area of land whose soil is saturated with water either permanently or seasonally. Wetlands are categorised by their characteristic vegetation, which is adapted to these unique soil conditions....

s, ponds and lakes across arid/semiarid regions of southern Africa. Xenopus laevis and Xenopus muelleri occur along the western boundary of the Great African Rift
Great Rift Valley
The Great Rift Valley is a name given in the late 19th century by British explorer John Walter Gregory to the continuous geographic trench, approximately in length, that runs from northern Syria in Southwest Asia to central Mozambique in South East Africa...

. 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
Aphrodisiac
An aphrodisiac is a substance that increases sexual desire. The name comes from Aphrodite, the Greek goddess of sexuality and love. Throughout history, many foods, drinks, and behaviors have had a reputation for making sex more attainable and/or pleasurable...

, or as fertility medicine
Fertility medication
Fertility medication are drugs which enhance reproductive fertility. For women, fertility medication is used to stimulate follicle development of the ovary...

. Wild Xenopus are much larger than their captive bred counterparts.

Use in research


Although X. laevis does not have the short generation time and genetic simplicity generally desired in genetic model organism
Model organism
A model organism is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the organism model will provide insight into the workings of other organisms. Model organisms are in vivo models and are widely used to...

s, it is an important model organism in developmental biology
Developmental biology
Developmental biology is the study of the process by which organisms grow and develop. Modern developmental biology studies the genetic control of cell growth, differentiation and "morphogenesis", which is the process that gives rise to tissues, organs and anatomy.- Related fields of study...

. X. laevis takes 1 to 2 years to reach sexual maturity
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...

 and, like most of its genus, it is tetraploid. However, it does have a large and easily manipulable embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...

. 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
Roger Wolcott Sperry
Roger Wolcott Sperry was a neuropsychologist, neurobiologist and Nobel laureate who, together with David Hunter Hubel and Torsten Nils Wiesel, won the 1981 Nobel Prize in Medicine for his work with split-brain research....

 used X. laevis for his famous experiments describing the development of the visual system. These experiments led to the formulation of the Chemoaffinity hypothesis
Chemoaffinity hypothesis
The Chemoaffinity hypothesis states that neurons make connections with their targets based on interactions with specific molecular markers and, therefore, that the initial wiring diagram of an organism is determined by its genotype...

.


Xenopus oocyte
Oocyte
An oocyte, ovocyte, or rarely ocyte, is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in the ovary during female gametogenesis. The female germ cells produce a primordial germ cell which undergoes a mitotic...

s provide an important expression system for molecular biology
Molecular biology
Molecular biology is the branch of biology that deals with the molecular basis of biological activity. This field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry...

. By injecting DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

 or mRNA
Messenger RNA
Messenger RNA is a molecule of RNA encoding a chemical "blueprint" for a protein product. mRNA is transcribed from a DNA template, and carries coding information to the sites of protein synthesis: the ribosomes. Here, the nucleic acid polymer is translated into a polymer of amino acids: a protein...

 into the oocyte or developing embryo, scientists can study the protein products in a controlled system. This allows rapid functional expression of manipulated DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

s (or mRNA
Messenger RNA
Messenger RNA is a molecule of RNA encoding a chemical "blueprint" for a protein product. mRNA is transcribed from a DNA template, and carries coding information to the sites of protein synthesis: the ribosomes. Here, the nucleic acid polymer is translated into a polymer of amino acids: a protein...

). This is particularly useful in electrophysiology
Electrophysiology
Electrophysiology is the study of the electrical properties of biological cells and tissues. It involves measurements of voltage change or electric current on a wide variety of scales from single ion channel proteins to whole organs like the heart...

, 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
Oocyte
An oocyte, ovocyte, or rarely ocyte, is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in the ovary during female gametogenesis. The female germ cells produce a primordial germ cell which undergoes a mitotic...

. Translation of proteins can be blocked or splicing of pre-mRNA can be modified by injection of Morpholino
Morpholino
In molecular biology, a Morpholino is a molecule in a particular structural family that is used to modify gene expression. Morpholino oligomers are an antisense technology used to block access of other molecules to specific sequences within nucleic acid...

 antisense oligos into the oocyte (for distribution throughout the embryo) or early embryo (for distribution only into daughter cells of the injected cell).

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.

The first vertebrate ever to be cloned was an African clawed frog.

Additionally, several African clawed frogs were present on the space shuttle Endeavour
Space Shuttle Endeavour
Space Shuttle Endeavour is one of the retired orbiters of the Space Shuttle program of NASA, the space agency of the United States. Endeavour was the fifth and final spaceworthy NASA space shuttle to be built, constructed as a replacement for Challenger...

 (which was launched into space on September 12, 1992) so that scientists could test whether reproduction and development could occur normally in zero gravity.

X. laevis is also notable for its use in the first well-documented method of pregnancy
Pregnancy
Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...

 testing when it was discovered that the urine
Urine
Urine is a typically sterile liquid by-product of the body that is secreted by the kidneys through a process called urination and excreted through the urethra. Cellular metabolism generates numerous by-products, many rich in nitrogen, that require elimination from the bloodstream...

 from pregnant women induced X. laevis oocyte production. Human chorionic gonadotropin
Human chorionic gonadotropin
Human chorionic gonadotropin or human chorionic gonadotrophin is a glycoprotein hormone produced during pregnancy that is made by the developing embryo after conception and later by the syncytiotrophoblast .. Some tumors make this hormone; measured elevated levels when the patient is not...

 (HCG) is a hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...

 found in substantial quantities in the urine of pregnant women. 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.

As pets


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.

African Clawed Frogs are frequently mislabeled as African Dwarf Frogs in pet stores. The astute pet owner will recognize the difference, however, because of the following characteristics:
  • Dwarf frogs have four webbed feet. African Clawed Frogs have webbed hind feet while their front feet have autonomous digits.
  • African Clawed frogs are often found in albino varieties. No such morphology exists for the African Dwarf Frog.
  • African Dwarf Frogs have eyes positioned on the side of their head, while African Clawed Frogs have eyes on the top of their heads
  • African Clawed Frogs have curved, flat snouts. The snout of an African Dwarf Frog is pointed.

As a pest


African Clawed Frogs are voracious predators and easily adapt to many habitats. For this reason, they can easily become 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 frogs were discovered in a pond at San Francisco's Golden Gate Park
Golden Gate Park
Golden Gate Park, located in San Francisco, California, is a large urban park consisting of of public grounds. Configured as a rectangle, it is similar in shape but 20% larger than Central Park in New York, to which it is often compared. It is over three miles long east to west, and about half a...

. Much debate now exists in the area on how to exterminate these creatures and keep them from spreading. It is unknown if these frogs entered the San Francisco ecosystem through intentional release or escape into the wild.

Due to incidences 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, Virginia, Hawaii, Nevada, and Washington state. However, it is legal to own Xenopus laevis in Canada.

Known feral colonies of Xenopus do also exist in South Wales, UK.

External links