Xenopus () (Gk., ξενος, xenos=strange, πους, pous=foot, commonly known as the clawed frog) is a genus of highly aquatic frogs native to sub-Saharan Africa. Twenty species are currently described within it. The two best-known species of this genus are Xenopus laevis and Xenopus tropicalis, which are commonly studied as model organisms for developmental biology, cell biology, toxicology, neuroscience and for modelling human disease and birth defects.
The genus is also known for its polyploidy, with some species having up to 12 sets of chromosomes.
Characteristics
Xenopus laevis is a rather inactive creature. It is incredibly hardy and can live up to 15 years. At times the ponds that Xenopus laevis is found in dry up, compelling it, in the dry season, to burrow into the mud, leaving a tunnel for air. It may lie dormant for up to a year. If the pond dries up in the rainy season, Xenopus laevis may migrate long distances to another pond, maintaining hydration by the rains. It is an adept swimmer, swimming in all directions with ease. It is barely able to hop, but it is able to crawl. It spends most of its time underwater and comes to surface to breathe. Respiration is predominantly through its well developed lungs; there is little cutaneous respiration.
Description
All species of Xenopus have flattened, somewhat egg-shaped and streamlined bodies, and very slippery skin (because of a protective mucus covering). The frog's skin is smooth, but with a lateral line sensory organ that has a stitch-like appearance. The frogs are all excellent swimmers and have powerful, fully webbed toes, though the fingers lack webbing. Three of the toes on each foot have conspicuous black claws.
The frog's eyes are on top of the head, looking upwards. The pupils are circular. They have no moveable eyelids, tongues (rather it is completely attached to the floor of the mouth) or eardrums (similarly to Pipa pipa, the common Suriname toad).
Unlike most amphibians, they have no haptoglobin in their blood.
Behaviour
Xenopus species are entirely aquatic, though they have been observed migrating on land to nearby bodies of water during times of drought or in heavy rain. They are usually found in lakes, rivers, swamps, potholes in streams, and man-made reservoirs.
Adult frogs are usually both predators and scavengers, and since their tongues are unusable, the frogs use their small fore limbs to aid in the feeding process. Since they also lack vocal sacs, they make clicks (brief pulses of sound) underwater (again similar to Pipa pipa). Males establish a hierarchy of social dominance in which primarily one male has the right to make the advertisement call. The females of many species produce a release call, and Xenopus laevis females produce an additional call when sexually receptive and soon to lay eggs. The Xenopus species are also active during the twilight (or crepuscular) hours.
During breeding season, the males develop ridge-like nuptial pads (black in color) on their fingers to aid in grasping the female. The frogs' mating embrace is inguinal, meaning the male grasps the female around her waist.
Species
Extant species
Xenopus allofraseri
Xenopus amieti (volcano clawed frog) Xenopus andrei (Andre's clawed frog) Xenopus borealis (Marsabit clawed frog) Xenopus boumbaensis (Mawa clawed frog) Xenopus calcaratus Xenopus clivii (Eritrea clawed frog) Xenopus epitropicalis (Cameroon clawed frog) Xenopus eysoole Xenopus fischbergi Xenopus fraseri (Fraser's platanna) Xenopus gilli (Cape platanna) Xenopus itombwensis Xenopus kobeli Xenopus laevis (African clawed frog or common platanna) Xenopus largeni (Largen's clawed frog) Xenopus lenduensis (Lendu Plateau clawed frog) Xenopus longipes (Lake Oku clawed frog) Xenopus mellotropicalis Xenopus muelleri (Müller's platanna) Xenopus parafraseri Xenopus petersii (Peters' platanna) Xenopus poweri Xenopus pygmaeus (Bouchia clawed frog) Xenopus ruwenzoriensis (Uganda clawed frog) Xenopus tropicalis (western clawed frog) Xenopus vestitus (Kivu clawed frog) Xenopus victorianus (Lake Victoria clawed frog) Xenopus wittei (De Witte's clawed frog)
Fossil species
The following fossil species have been described: †Xenopus arabiensis - Oligocene Yemen Volcanic Group, Yemen †Xenopus hasaunus †Xenopus romeri - Itaboraian Itaboraí Formation, Brazil †Xenopus stromeri cf. Xenopus sp. - Campanian - Los Alamitos Formation, Argentina Xenopus (Xenopus) sp. - Late Oligocene Nsungwe Formation, Tanzania Xenopus sp. - Miocene Morocco Xenopus sp. - Early Pleistocene Olduvai Formation, Tanzania