I know what you’re thinking…how different can one frog be from all other frogs? My resounding response to you would be: VERY different! The African clawed frog (Xenopus laevis) is a peculiar creature since it lacks some features common to many other organisms but also possesses some very unique features. For example, these frogs have “claws”—not true claws, but rather cornified tips—yet they lack a tongue. Males lack vocal cords, yet they still produce calls to attract females. They are nearly completely aquatic however they can also lay dormant without water for up to a year! So, if you thought we were dealing with some ordinary frog, you were definitely wrong.
Native to Africa, the clawed frog’s preferred habitat is in warm stagnant pools of water; since they are nearly completely aquatic, they rarely leave those waters unless the pools dry up and they are forced to find another pool (Casterlin & Reynolds, 1980). When they are forced to move to wetter pastures, the heavy dependence on an aquatic medium is immediately obvious, as these frogs cannot gracefully hop like other frogs, and instead awkwardly crawl when stranded on land. Nonetheless, under extreme conditions when water is scarce they will dig into the mud and can lay dormant there for up to a year (Wu, Biggar & Storey, 2013)! Although this seems costly, I suppose they can “afford it” since their average lifespan is nearly fifteen years!
When not in dormancy, the African clawed frog is a voracious feeder and will consume a variety of items including organic material, insects, small fish, worms, and snails. When they are immersed in their preferred aquatic medium, they are able to easily sense their prey (and predators) using an internal lateral-line sensory system that is highly sensitive to vibrations in the water (Gorner, Moller & Weber, 2984). Once they’ve caught their meal, since these frogs lack tongues, they use their non-webbed front legs to push the food into their mouth and satiate their appetites.
If you’re still unimpressed, just wait till you hear about the African’s clawed frog’s most interesting trait: its medicinal potential. An African clawed frog’s skin exudes a substance that has antimicrobial properties which helps heal wounds more rapidly (Zasloff, 1978). This property has been thought to have evolved in response to living in the African clawed frog’s preferred habitat of stagnant waters. The idea is that more stagnant water has a higher proportion of microbes and thus antibacterial properties could confer a fitness advantage by mitigating the negative effects of internal microbial invasions (Woodhams et al., 2007).
Despite these many strange quirks, the African clawed frog has been considered an ideal laboratory model organism since the 1950s (Cannatella, 1993). There are several features that make this animal well-suited for the lab: 1. their eggs can be easily produced and reared via artificial means, 2. they have transparent egg casings which allow for direct observations of developmental stages, and 3. their eggs and embryos are easily manipulated and maintained (Kay & Peng, 1992). As a result of these valuable features, this species has been crucial to elucidating developmental mechanisms in cellular biology and other related fields.
Despite its largely positive impact in laboratory research, the African clawed frog has also had a prolific negative effect in the wild. Though this species is native to Sub-Saharan Africa, it has managed to invade four other major continents: Asia, Europe, North America, and South America. A recent review indicates that these invasions are ongoing, and that most were due to deliberate releases from the pet trade (Measey et al., 2012). Furthermore, no known populations were in decline and thus show a high potential risk for invasion into optimal uninvaded habitats in other parts of the world. Indeed, this species is so invasive it has been deemed a “domestic exotic” within its own habitat range in South Africa. Since the clawed frog can withstand a wide range of temperatures and pH levels, they have begun pushing out native species such as the X. gilli, who are highly specialized to low pH waters (Measey & Davies, 2011). There has been additional discussion concerning X. laevis’s role in distributing detrimental fungal pathogens to other anurans (another fancy word for frog or toad), however much of remains in the realm of speculation and warrants further study (Measey et al., 2012).
Ironically, despite that fact that I only recently learned about the African clawed frog, their domination in habitats throughout the world is extensive and progressing. Now you too can be aware of the clawed frog’s invasive qualities and the unique yet advantageous traits that allow them to be so successful in the wild.
Written by: Josie Hubbard
Cannatella, D. C., & De Sa, R. O. (1993). Xenopus laevis as a model organism. Systematic Biology, 42(4), 476-507.
Casterlin, M. E., & Reynolds, W. W. (1980). Diel activity and thermoregulatory behavior of a fully aquatic frog: Xenopus laevis. Hydrobiologia, 75(2), 189-191.
Gorner, P., Moller, P., & Weber, W. (1984). Lateral-line input and stimulus localization in the African clawed toad Xenopus sp. Journal of experimental biology, 108(1), 315-328.
Kay, B. K., & Peng, H. B. (1992). Xenopus laevis: practical uses in cell and molecular biology (Vol. 36). Academic press.
Measey, G. J., Rödder, D., Green, S. L., Kobayashi, R., Lillo, F., Lobos, G., & Thirion, J. M. (2012). Ongoing invasions of the African clawed frog, Xenopus laevis: a global review. Biological Invasions, 14(11), 2255-2270.
Woodhams, D. C., Rollins‐Smith, L. A., Alford, R. A., Simon, M. A., & Harris, R. N. (2007). Innate immune defenses of amphibian skin: antimicrobial peptides and more. Animal Conservation, 10(4), 425-428.
Wu, C. W., Biggar, K. K., & Storey, K. B. (2013). Dehydration mediated microRNA response in the African clawed frog Xenopus laevis. Gene, 529(2), 269-275. Zasloff, M. (1987). Magainins, a class of antimicrobial peptides from Xenopus skin: isolation, characterization of two active forms, and partial cDNA sequence of a precursor. Proceedings of the National Academy of Sciences, 84(15), 5449-5453.