Disclaimer:

The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

---

Common name: Western clawed frog

Synonyms and Other Names: Silurana tropicalis, Western clawed frog

Taxonomy: available through www.itis.gov

Identification: Xenopus tropicalis is a small, primarily aquatic frog. They are easily distinguished from most native frogs by their flattened and streamlined bodies, eye placement on top of the head, and fully webbed feet with claws on the first three toes (Evans et al. 2015). One common native look-alike is Gastrophryne carolinensis which can be distinguished from X. tropicalis by examining eye placement. Tadpoles of the genus Xenopus including both X. tropicalis and X. laevis, can be distinguished from native tadpoles by the presence of whisker-like barbels (Cannatella and Trueb 1988).  Xenopus tadpoles transition from sucking air bubbles to air breathing by breaking the surface tension of the water a few days of hatching (Phillips 2019). This air breaching breathing technique distinguishes them from native tadpoles. Xenopus tadpoles also school with their heads tipped downward (Caldwell 1989) unlike native tadpoles.

Xenopus tropicalis is sexually dimorphic, with adult females typically growing larger in size than adult males (Goodman et al. 2021; Herrel et al. 2012). Males have relatively longer limbs with nuptial pads which aide them in amplexus (clasping) for breeding. In addition to size, males and females differ in call sound and larynx shape (Herrel et al. 2012; Olmstead et al. 2009).

Xenopus tropicalis may be confused with the prolific invader X. laevis. Adult X. tropicalis are far smaller than X. laevis, growing up to only 4-6 cm in length, rather than the larger 5-14 cm. Xenopus tropicalis has a trill-type call with modulation intensity higher compared to X. laevis (Tobias et al. 2011). The presence of unfused nasal bones, absence of vomer bones which are unpaired bones within the nasal cavity, and fusion of the first two presacral vertebrae that are located above the rectum are all characteristics of X. tropicalis that can be used to morphologically distinguish them from small specimens of X. laevis (Cannatella and Trueb 1988).

Size: 4-6 cm length

Native Range: Distributed throughout the West African rainforest belt (Herrel and Bonneaud 2012).

Alaska	Hawaii	Puerto Rico & Virgin Islands	Guam Saipan

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Ecology: Xenopus tropicalis are aquatic frogs found in small, isolated puddles throughout tropical forests (Herrel et al 2012). Both tadpoles and adults prefer slow moving or stagnant waters (Evans et al. 2015). Adults spend the dry season under rocks and roots in riverbanks where moisture is retained (Herrel and Bonneaud 2012). Mass migrations of X. tropicalis over land after heavy rain have been observed in their native range. These mass migrations typically coincide with breeding season (Herrel et al. 2012). Xenopus tropicalis have a short generation time of just 4-6 months compared to the 1–2-year generation time of X. laevis. Females lay 1,000-3,000 eggs per ovulation (Amaya et al. 1998). Males engage in amplexus or clasp onto the back of females to fertilize eggs as they are externally released from the female (Herrel et al. 2012). In their invasive range in Florida, X. tropicalis have only been found to successfully breed in ephemeral ponds that fish do not inhabit (Goodman 2020).

Xenopus tropicalis are generalist predators that feed primarily on invertebrates, both terrestrial and aquatic (Imasuen and Aisien 2016). Cannibalism has been observed in native populations of X. tropicalis. Unlike native frog and toad tadpoles, X. tropicalis tadpoles are filter feeders (Goodman 2020; Imasuen and Aisien 2016). They also possess a specialized vocal organ for underwater sound and lateral line organs that allow them to sense movement in the water (Evans et al. 2015). Due to differences in larynx morphology, male and female X. tropicalis have different sounding calls (Herrel et al. 2012). In its native range, X. tropicalis is known to host at least ten helminth (worm) parasites (Imasuen and Aisien 2015). Like many tropical species, X. tropicalis has a narrow temperature range for which they can still function appropriately compared to more temperate frogs like the X. laevis. Their critical thermal minimum is 12C and their critical thermal max is 34C. However, X. tropicalis has a lower optimal temperature for swim speed at 24C compared to X. laevis which is 27C (Herrel and Bonneaud 2012).

Means of Introduction: The introduction of the established breeding population of X. tropicalis in Riverview, FL is unknown. However, they are commonly used in genetics research as a model organism and are found in the pet trade (Goodman et al. 2021). The first Xenopus spp. found in Riverview, FL was found near an animal import facility in the 1970’s and was identified as Xenopus laevis. Species identification of the specimen remains contested, as the specimen was destroyed (Goodman 2020). Subsequent sampling in 2016 (Hill et al. 2017) revealed a breeding population of Xenopus spp. in Hillsborough County, Florida that was initially believed to be Xenopus laevis. However, DNA sequence data and osteological comparisons performed in 2021 confirmed the breeding populations to be Xenopus tropicalis (Goodman et al. 2021). In their native range, overland dispersal has been observed during periods of heavy rain (Herrel and Bonneaud 2012).

Status: Established in a small area in Riverview, Hillsborough Co., FL (Goodman et al. 2021).

Impact of Introduction: The impacts of this species are currently unknown. The absence of data does not equate to lack of effects. It does, however, mean that research is required to evaluate effects before conclusions can be made.

Remarks: Xenopus tropicalis is the only diploid (containing two sets of chromosomes) species in the genus Xenopus which makes them more popular for genetics research than Xenopus laevis (Amaya et al. 1998; Hellsten et al. 2010). Xenopus tropicalis is the first amphibian to have had its entire genome sequenced (Hellsten et al. 2010).

Environmental DNA has been used to detect X. laevis in bodies of water which was developed using the 12S gene from X. laevis and closely related species. Target sequences of DNA are able to amplify 12 species including both X. tropicalis and X. laevis (Secondi et al. 2016). 

Compared to X. laevis, X. tropicalis is more climatically restricted which may affect their ability for dispersing northward from their current invasive range (Goodman 2020; Herrel and Bonneaud 2012).

References: (click for full references)

Amaya, E., M.F. Offield, and R.M. Grainger. 1998. Frog genetics: Xenopus tropicalis jumps into the future. Trends in Genetics 14(7):253-255.

Caldwell, J.P. 1989. Structure and behavior of Hyla geographica tadpole schools, with comments on classification of group behavior in tadpoles. Copeia 1989(4):938-948. https://www.jstor.org/stable/1445980?seq=1.

Cannatella, D.C., and L. Trueb. 1988. Evolution of Pipoid Frogs: Morphology and Phylogenetic Relationships of Pseudhymenochirus. Journal of Herpetology 22(4):439-456. https://www.jstor.org/stable/1564339.

Evans, B.J., T.F. Carter, E. Greenbaum, V. Gvoždík, D.B. Kelley, P.J. McLaughlin, O.S.G. Pauwels, D.M. Portik, E.L. Stanley, R.C. Tinsley, M.L. Tobias, and D.C. Blackburn. 2015. Genetics, morphology, advertisement calls, and historical records distinguish six new polyploid species of African Clawed Frog (Xenopus, Pipidae) from West and Central Africa. PLoS ONE 10(12):1-51. http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0142823

Goodman, C.M. 2020. The potential for spread of a novel invader, the tropical clawed frog (Xenopus tropicalis), in Florida. Unpublished M.S. thesis. University of Florida, Gainesville, FL.

Goodman, C.M., G.F.M. Jongsma, J.E. Hill, E.L. Stanley, Q.M. Tuckett, D.C. Blackburn, and C.M. Romagosa. 2021. A case of mistaken identity: genetic and anatomical evidence reveals the cryptic invasion of Xenopus tropicalis in Central Florida. Journal of Herpetology 55(1):62-69. https://doi.org/10.1670/20-083.

Hellsten, U., R.M. Harland, M.J. Gilchrist, D. Hendrix, J. Jurka, V. Kapitonov, I. Ovcharenko, N.H. Putnam, S. Shu, L. Taher, I.L. Blitz, B. Blumberg, D.S. Dichmann, I. Dubchak, E. Amaya, J.C. Detter, R. Fletcher, D.S. Gerhard, D. Goodstein, T. Graves, J.V. Grigoriev, J. Grimwood, T. Kawashima, E. Lindquist, S.M. Lucas, P.E. Mead, T. Mitros, H. Ogino, Y. Ohta, A.V. Poliakov, N. Pollet, J. Robert, A. Salamov, A.K. Sater, J. Schmutz, A. Terry, P.D. Vize, W.C. Warren, D. Wells, A. Wills, R.K. Wilson, L.B. Zimmerman, A.M. Zorn, R. Grainger, T. Grammer, M.K. Khokha, P.M. Richardson, and D.S. Rokhsar. 2010. The genome of the western clawed frog Xenopus tropicalis. Science 328(5978):633-636. https://www.science.org/doi/full/10.1126/science.1183670?casa_token=Xe39J5ZNZM0AAAAA%3AE3a2jfWR0xtTnAvvEaPjHSHLILOLfxAjCm5A65JphnVCUo0nbBgjSaGEKVa8rjCkviHEIHPmZx9M7GtY.

Herrel, A., and C. Bonneaud. 2012. Temperature dependence of locomotor performance in the tropical clawed frog, Xenopus tropicalis. Journal of Experimental Biology 215(14):2465-2470. https://journals.biologists.com/jeb/article/215/14/2465/10855/Temperature-dependence-of-locomotor-performance-in.

Herrel, A., and C. Bonneaud. 2012. Trade-offs between burst performance and maximal exertion capacity in a wild amphibian, Xenopus tropicalis. Journal of Experimental Biology 215(17):3106-3111. https://journals.biologists.com/jeb/article/215/17/3106/11040/Trade-offs-between-burst-performance-and-maximal.

Herrel, A., L.N. Gonwouo, E.B. Fokam, W.I. Ngundu, and C. Bonneaud. 2012. Intersexual differences in body shape and locomotor performance in the aquatic frog, Xenopus tropicalis. Journal of Zoology 287(4):311-316. https://zslpublications.onlinelibrary.wiley.com/doi/full/10.1111/j.1469-7998.2012.00919.x casa_token=HZGCCig4jtEAAAAA%3AslOWULEj364JeQWqUvwFPJdPoJNrkeLH8mmVKg2GBRvQbnV1POoWakEanFB3KSBKyus5zQbOabze9m666w.

Hill, J.E., K.M. Lawson, and Q.M. Tuckett. 2017. First record of a reproducing population of the African clawed frog Xenopus laevis Daudin, 1802 in Florida (USA). BioInvasions Records 6(1):87-94. https://www.reabic.net/journals/bir/2017/1/BIR_2017_Hill_etal.pdf.

Imasuen, A.A., and M.S.O. Aisien. 2015. Helminth parasites of Silurana tropicalis from the Okomu National Park, Edo State, Nigeria. Nigerian Journal of Parasitology 36(1):61-66.

Imasuen, A.A., and M.S.O. Aisien. 2016. Diets of Silurana tropicalis from two rainforest habitats in Edo State,
Nigeria. Nigerian Society of Experimental Biology (NISEB) 16(4):130-134. https://www.ojs.klobexjournals.com/index.php/nisebj/article/view/270.

Olmstead, A.W., J.J. Korte, K.K. Woodis, B.A. Bennett, S. Ostazeski, and S.J. Degitz. 2009. Reproductive maturation of the tropical clawed frog: Xenopus tropicalis. General and Comparative Endocrinology 160(2):117-123. https://www.sciencedirect.com/science/article/pii/S0016648008003821.

Phillips, J. 2019. The biomechanics and evolution of air-breathing in anuran tadpoles. Unpublished M.S. thesis. University of Connecticut, Storrs, CT. https://digitalcommons.lib.uconn.edu/gs_theses/1378/.

Secondi, J., T. Dejean, A. Valentini, B. Audebaud, and C. Miaud. 2016. Detection of a global aquatic invasive amphibian, Xenopus laevis, using environmental DNA. Amphibia-Reptilia 37:131-136. https://brill.com/view/journals/amre/37/1/article-p131_14.xml?ebody=pdf-67975.

Tobias, M.L., B.J. Evans, and D.B. Kelley. 2011. Evolution of advertisement calls in African clawed frogs. Behaviour 148(4):519-549. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3978194/.

Author: Stratton, L.D.

Peer Review Date: 3/21/2024

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.