Several new species of clawed frog discovered in sub-Saharan Africa

  • African clawed frogs are characterized by their flat bodies and vocal organs which can produce sound underwater, as well as the claws on their first three toes that give them their name.
  • Despite being commonly used as a study subject by developmental biologists, researchers say we're still learning quite a bit about the species.
  • Researchers from Canada's McMaster University say they’ve discovered a wealth of new information on the frog’s evolution using new techniques for analyzing DNA.

There are now 29 known species of African clawed frog.

Researchers in west and central sub-Saharan Africa say they’ve discovered six new species of the frog and added another, Xenopus calcaratus, back to the list of known species (it had previously been lumped in with a close relative, X. tropicalis).

The word Xenopus means “alien foot” or, basically, “strange foot,” in Latin.

African clawed frogs live in slow moving or stagnant water, according to a report in PLOS ONE describing the new species. The frogs are also characterized by their flat bodies and vocal organs which can produce sound underwater.

Named for the claws on its first three toes that are used to tear apart food, the African clawed frog is commonly used as a study subject by developmental biologists and for other research purposes. As such, you would think we already know pretty much all there is to know about the species — but you’d be wrong.

“Because the African clawed frog is used as a model organism for biological research, it would be understandable to think that scientists had already pinned down the number of species and other aspects of their diversity such as where they live and how they are related to one another,” Ben Evans, lead author of the study and an associate professor in the Department of Biology at McMaster University in Canada, said in a statement. “But this isn’t the case.”

Evans and team say they’ve discovered a wealth of new information on the frog’s evolution using new techniques for analyzing DNA.

For instance, the researchers found that all of the new species are “polyploids,” like most African clawed frogs, meaning their DNA doubled during their evolution, providing them with a redundant copy of all of their genes. But two of the new species were found to be “dodecaploids,” meaning their genomes were duplicated a “remarkable” six times, according to the report.

The researchers plan to travel to Ghana next year to gather further genetic data and search for what Evans calls “lost ancestors” of the African clawed frog, species that scientists believe to have existed in the past that passed their genomes on to the polyploid species that exist today.

“For biodiversity conservation, it is paramount that we understand how much diversity there is and where it occurs,” says Evans. “This is particularly crucial in the tropics, where global biodiversity is highest and in groups of organisms that have subtle physical differences between species and in which species diversity is therefore ‘cryptic.’”

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One of the new species of African clawed frog. Photo by Vacute; Gvocaron.
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Pictures of resurrected and new species in life.
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Comparison of external morphology of subgenera Xenopus (right, specimen of X. victorianus) and Silurana (left, X. calcaratus) including in Silurana rougher skin, relatively smaller eyes, relatively shorter subocular tentacle (in comparison to sympatric Xenopus species), and relatively less of eye covered by lower eyelid (top), relatively shorter feet (middle), and ventrally fused cloacal lobes, claw on prehallux, and lack of skin ridge on first pedal digit from the prehallus (bottom).
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African clawed frog. Photo by Wade Tregaskis.

CITATION

  • Evans BJ, Carter TF, Greenbaum E, Gvoždík V, Kelley DB, McLaughlin PJ, et al. (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): e0142823. doi:10.1371/journal.pone.0142823
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