hear call (148.4K RM file)
	hear call (7839.3K WAV file)

[call details here]

Description
Xenopus laevis is an aquatic frog that was first described by the French naturalist François-Marie Daudin in 1802 (Daudin 1802). It is a large frog; the male snout-vent length tends to be between the range of 45.6 to 97.5 mm, while females skew larger with a snout-vent length range between 57 and 147 mm. Their heads and bodies are depressed and flattened. They have small round eyes on the top of their heads that point dorsally. They lack eyelids and a tongue. Additionally, they have no vocal cords or sacs. The skin is smooth and the hind limbs are long and robust. The three inner toes of the large fully webbed feet have small black, keratinized claws on them (Cannatella and Sa 1993, Trueb 2003).

DIAGNOSIS:

Xenopus laevis has been extensively compared to another species in its genus, X. tropicalis. Though the two frogs look morphologically similar, they are not sister species (Evans et al. 2015). A cytogenetic analysis concluded that X. laevis is a tetraploid with 29 chromosomes. Meanwhile, X. tropicalis is a diploid species with only 20 chromosomes. Xenopus laevis also has a much larger genome than its tropical counterpart, and it reaches sexual maturity at a slower rate than X. tropicalis (Kashiwagi et. al 2010).

COLORATION:

In life, the body color is usually dark gray to greenish-brown dorsally and pale ventrally (Trueb 2003).

VARIATION:

Xenopus laevis exhibits sexual dimorphism in its size (Trueb 2003).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Angola, Botswana, Cameroon, Central African Republic, China, Congo, Congo, the Democratic Republic of the, Estonia, Gabon, Kenya, Lesotho, Malawi, Mozambique, Namibia, Nigeria, South Africa, Swaziland, Tanzania, United Republic of, Zambia, Zimbabwe. Introduced: Chile, France, Indonesia, Italy, Mexico, Portugal, United Kingdom, United States.

U.S. state distribution from AmphibiaWeb's database: Arizona, California, Florida, Texas

	View distribution map in BerkeleyMapper.
	View Bd and Bsal data (139 records).

This species occurs in savannas of the Republic of South Africa, Kenya, Uganda, the Democratic Republic of Congo, and Cameroon. The frog has a high tolerance to change in its environment and will survive in nearly any body of water. It can be found in water bodies ranging from ice-covered lakes to desert oases. Unlike most frogs, the African Clawed Frog can also survive in water with high salinity (Trueb 2003).

Xenopus laevis is one of the most widely distributed invasive species. It has been introduced in the United States, the United Kingdom, Portugal, Mexico, Italy, Chile, France, and Indonesia. It is also thought to be found in Sudan (IUCN 2020).

Life History, Abundance, Activity, and Special Behaviors
These frogs spend most of their life cycle in the water, only to leave when there is a drought. When a drought occurs, they will burrow into the drying mud. They can survive up to a year without food. Their diet consists of a wide range of animals including fish, crustaceans, insects, and other frogs. They will also scavenge on dead frogs, fish, birds, and small mammals (Trueb 2003).

Despite X. laevis’s lack of vocal apparatuses, vocalizations are made and consist of a series of clicks and buzzes (Cannatella and Sa 1993).

Female X. laevis become sexually mature from 10 to 24 months post-metamorphosis. Males become completely sexually mature later than their counterparts, but viable spermatozoa are present in their testes after 6 months post-metamorphosis (Kashiwagi et al. 2010). Gametes can be obtained from adults year-round (Carotenuto et al. 2023).

Interestingly, X. laevis froglets exhibit limb regeneration after being injured. Epithelial cells rapidly cover the froglets’ wounded surface to form a dermis-free epithelial structure. Mesoderm-derived tissues then allow the blastema to create a structure similar to the limb bud. The blastema grows as blastemal mesenchymal cells proliferate. These traits continue into adulthood and represent epimorphosis, or regeneration through somatic stem cells (Suzuki et. al 2006).

Larva
Xenopus laevis hatches from its egg as a tadpole, develops into a froglet, and later reaches maturity as an adult frog (Carotenuto et al. 2023, Zahn et al. 2022). Their embryos hatch from the vitelline membrane and become free-swimming (Carotenuto et al. 2023, Zahn et al. 2022). In feeding tadpoles, blood circulation from the heart to the gills is visible through the skin (Carotenuto et al. 2023, Zahn et al. 2022).

Trends and Threats
Xenopus laevis is listed as "Least Concern" on the IUCN Red List because of its wide distribution, ability to withstand many different habitats, and generally large population (IUCN 2020).

When exposed to the widely used pesticide Atrazine, X. laevis experiences gonadal abnormalities and hermaphroditism that do not occur naturally. Atrazine chemically castrates X. laevis and other amphibians residing near farming sites (Hayes et al. 2006).

Relation to Humans

RELATION TO HUMANS:

Xenopus laevis were initially brought to the U.S. in the 1950s to be used for human pregnancy tests. Doctors injected X. laevis specimens with patients’ urine. Induced spawning in the frogs indicated high chorionic gonadotropin levels and therefore pregnancy (Carotenuto et al. 2023).

Xenopus laevis has been among the few amphibians to travel to outer space. In one project, the NASA Ames Research Center used the model organism to study the virtual absence of gravity’s effect on amphibian development. Tadpoles that hatched in microgravity had thicker blastocoel roofs and lower blastopore lip latitudes. Their neurula stages were unimpaired, and they appeared unchanged externally. After experiencing microgravity, the tadpoles were able to develop as normal. It was concluded that microgravity did not affect early Xenopus embryogenesis (Souza et al. 1995).

Because it makes a hardy and popular pet, it can also be found in aquariums worldwide (Trueb 2003).

This species has been used as food in African countries (Trueb 2003).

Possible reasons for amphibian decline

Local pesticides, fertilizers, and pollutants

Comments
The genomics of X. laevis are complex. This frog is sister to X. gilli according to a summary phylogeny based on mitochondrial and autosomal gene trees (Evans et al. 2015).

Xenopus laevis is highly conserved. It has been a unique lineage for nearly 17.5 million years ago, which contributes to its utility as a model organism for human study. Comparatively, other commonly observed amphibians diverged at more recent earlier times. Bufo americanus has existed for only 1.3 million years, and Ambystoma tigrinum has existed for 10 million years (Hunt et al. 2020).

Both X. laevis and X. tropicalis are traditional model organisms. Xenopus tropicalis was the first amphibian to have its whole genome sequenced (Hellsten et al. 2010), and X. laevis followed six years later (Session et al. 2016). With these two whole genomes, Session et al. were able to identify genomic differences between the species and estimate their evolutionary rate. More specifically, X. tropicalis is diploid and X. laevis is tetraploid. And based on the rate of synonymous mutations in protein-coding genes, the two species diverged from each other about 48 mya, a date that is remarkably close to the estimate based on phylogenetic analysis of fossils, morphology, and other genomic sequences. Session et al. also calculated that the lineage of tetraploid Xenopus species originated 17 –18 mya from two now-extinct diploid ancestors.

Investigations into centromere sequences determined that the sequence of X. tropicalis differs from centromeric-associated repeats of X. laevis. This finding demonstrated that the centromere sequences of Xenopus quickly evolved after speciation, but were maintained across chromosomes within the individual species (Bredeson et al. 2023).

The distinct claws on X. laevis’s inner toes yielded this species’ common name: the African clawed frog (Cannatella and Sa 2003).

OTHER INTERESTING INFORMATION:

Despite the genomic revolution, the first complete genome of a frog, Xenopus tropicalis, was sequenced only in 2010. Session et al. (2016) have sequenced the genome of another species, Xenopus laevis. Because X. tropicalis is diploid and the X. laevis is tetraploid, important inferences can be made about genome evolution. Based on analysis of the rate of synonymous mutations in protein-coding genes, they estimated that the two species diverged from each other about 48 mya, a date is remarkably close to the estimate based on phylogenetic analysis of fossils, morphology, and other genomic sequences. They also calculated that the lineage of tetraploid Xenopus species originated 17–18 mya from two now extinct diploid ancestors (Written by David Cannatella).

Often conservationists lack information critical to developing recovery strategies for endangered species. The Cape Platanna, Xenopus gilli, is restricted in distribution to a few sites in southwestern Cape, South Africa, always in sympatry with Xenopus laevis, an invasive species. Vogt et al. (2017 PeerJ) assessed niche differentiation at two sites. The diet of X. gilli is much more diverse than that of X. laevis. Both consume large numbers of tadpoles of different amphibian species (reaching as high as 45% of prey), including congeners, but X. laevis, which is about three times as common as its congener, also consumes adult X. gilli and is thus a direct predator as well as a dominant competitor. Furthermore, dietary overlap is greater between smaller members of each species. An effective conservation strategy for X. gilli is likely to require removal of X. laevis (Written by David B. Wake).

As a disease vector, it is important to control mosquito populations. However, biological control with introduced mosquitofish (Gambusia affinis) has the unintended consequence of altering ecosystems. Watters et al. (2018) explored the effectiveness of using native amphibian larvae in Missouri instead. They found that Leopard frogs (Rana sphenocephala), while consuming a large number of mosquito larvae, ate fewer mosquitos than mosquitofish. The Spotted Salamander (Ambystoma maculatum), on the other hand, consumed as much mosquitos as mosquitofish. Moreover, there was a positive relationship between mosquito consumption and salamander larvae body size providing encouragement to assess more native amphibians for mosquito control. However Thorpe et al. (2018) indicate other considerations. They found a body size-dependent response to varying prey densities. With small African Clawed frog (Xenopus laevis) tadpoles, a type II functional feeding response is shown, increasing feeding rates with prey density until a threshold when the predator cannot keep up with the prey, while larger tadpoles exhibit type III response, characterized by lower than expected feeding rates at low and high densities but increasing feeding rates at increasing intermediate densities. This suggests a need for size diversity in biological control (Written by Ann T. Chang).

This species was featured as News of the Week on 17 June 2019:

Amphibians are unique among tetrapods in their ability to regenerate their appendages, like arms or tails, when removed. The particular mechanisms underlying appendage regeneration, however, are poorly known. A recent study (Aztekin et al. 2019) combined tail amputation experiments in tadpoles of the African clawed frog (Xenopus laevis) with single-cell RNA sequencing, allowing researchers to study how different genes work in individual cells of various cell types during tail regeneration. This study discovered a previously unknown cell type named the regeneration-organizing cell (ROC). Removing ROCs from severed tails demonstrated that ROCs are necessary for tadpoles to regrow their tails. Transplanting these cells to other areas of the embryo demonstrated these cells are sufficient to grow tail-like structures elsewhere in tadpoles. ROCs are normally found in the epidermis and migrate to the wound site after tadpole tails are amputated, secreting similar regenerative compounds that are produced when salamanders regrow limbs. The discovery of a new cell type that enables amphibian larvae to regrow appendages has exciting implications for tissue and organ transplant procedures and is an important reminder that we have much yet to learn about the amazing biology of amphibians (Written by Max Lambert).

This species was featured as News of the Week on 17 January 2022:

Oxygen is necessary for life in most non-photosynthetic organisms and without it, irreversible brain damage and death may be the consequence. However, these effects can be mitigated with hyperbaric oxygen medical therapy. Özugur et al. (2021) explored another potential therapy using microalgae. In their experiments, transcardially injected green algae or cyanobacteria into Xenopus laevis tadpoles traveled to the brain where they produced oxygen when exposed to light. This production was sufficient enough that when the tadpoles were placed in hypoxic conditions, the microalgae produced enough oxygen to rescue brain activity. While these results have a long way to go before they can be used in human medical procedures, there are many applications they can now be used in to enhance studies, such as improving oxygen levels in cell or tissue cultures, increasing control in graded oxygen experiments, and experimentation with bilateral imbalances of oxygen on neural and motor function. (Written by Ann Chang)

This species was featured as News of the Week on 8 January 2024:

Microplastics are becoming ubiquitous in waterways used by amphibians, and consequently tadpoles are ingesting those microplastics. There is growing concern of the effects of this environmental pollutant, however, few studies have quantified their effects. Ruthsatz et al. (2023) examined the effects of microplastics and climate change in lab experiments on the development of Xenopus laevis, African Clawed Frog. They found that microplastics increased larval metabolic and developmental rate as well as increased their corticosterone levels. The result of these changes led to juveniles that had wider bodies and longer limbs. Some of these changes were counteracted by the temperature treatments, but the authors noted that in other organisms the degree of temperature change can have opposing effects. Although the biological implications for these changes, particularly in amphibian species with more traditional life histories, is still murky, the illustration of this study that microplastics can cause sublethal and permanent changes to amphibian physiology and morphology is worth further investigation. (Written by Ann Chang)

References

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Cannatella, D. C., and Sa, R. O. (1993). Xenopus laevis as a model organism. Systematic Biology, 42(4), 476. [link]

Carotenuto, R., Pallotta, M. M., Tussellino, M., and Fogliano, C. (2023). Xenopus laevis (Daudin, 1802) as a model organism for bioscience: a historic review and perspective. Biology, 12(6), 890. [link]

Daudin, F.-M. (1802). An. XI. Histoire Naturelle des Rainettes, des Grenouilles et des Crapauds. Quarto version. Paris: Levrault.

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Hayes, T. B., Stuart, A. A., Mendoza, M., Collins, A., Noriega, N., Vonk, A., Johnston, G., Liu, R., and Kpodzo, D. (2006). Characterization of atrazine-induced gonadal malformations in African clawed frogs (Xenopus laevis) and comparisons with effects of an androgen antagonist (cyproterone acetate) and exogenous estrogen (17beta-estradiol): Support for the demasculinization/feminization hypothesis. Environmental health perspectives, 114 Suppl 1(Suppl 1), 134–141. [link]

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Original reference IDs: [4084][7276][9184]

Species Account Citation: AmphibiaWeb 2024 Xenopus laevis: African Clawed Frog <https://amphibiaweb.org/species/5255> University of California, Berkeley, CA, USA. Accessed Nov 21, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 21 Nov 2024.

AmphibiaWeb's policy on data use.