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Mystery surrounding two Victorian frogs is solved
An international team of scientists solved a lingering mystery behind some 170-year-old frog specimens.
The two frogs have been in the Museum collection since 1852, after being collected by British zoologist Louis Fraser. They are both representatives of the same species, which is known as Fraser's clawed frog (Xenopus fraseri).
The animals have a unique combination of features: small bony protrusions on the roof of their mouths known as vomerine teeth, and an extra claw.
When they were discovered these traits had not been seen together in any other clawed frogs (Xenopus). So in 1905 Louis Fraser's frogs were declared a new species.
However, this species' place on the evolutionary tree, geographic distribution, and ecology has since been debated because of a lack of genetic samples and poor records of origin.
A CT scan of one of the frogs in the Museum collection © Edward L. Stanley
Ben Evans, lead author of a new study on the frogs and a professor of biology at McMaster University, says, 'The ancient condition of the only two specimens available to us posed many challenges for understanding its distinctiveness using DNA and knowing exactly where they came from.
'The accurate identification of species is so important because it allows us to study change in populations, better understand how evolution occurs, and explore the processes that drive diversification, extinction and adaption.'
The team, which included Dr Jeff Streicher, Senior Curator of Amphibians and Reptiles at the Museum, used DNA sequencing to try to understand more about the delicate specimens.
They generated and analysed complete mitochondrial genome sequences from the frogs, using sensitive techniques similar to approaches used to sequence the genomes of Neanderthals.
They also sequenced complete or nearly complete mitochondrial genomes from 29 other Xenopus species, used high-resolution scanning to compare the internal and external anatomy of these and other specimens and, through intensive field work, managed to collect additional specimens of Fraser's frog in several regions of West Africa.
New ways of analysing DNA are allowing scientists to revisit old specimens and look at them in a new light
Dr Streicher explains, 'Obtaining DNA from specimens that have been preserved in spirit for well over a hundred years is something that has only become achievable in the last few decades.
'The recent advances in DNA extraction and sequencing are allowing us to revisit specimens and challenge assumptions made in the past. The Museum's collections are an essential resource for scientists trying to understand the natural world.'
The results showed that Fraser's clawed frog is indeed distinct from other species. And while it was previously thought to have lived in lowland tropical forests in West Africa, researchers found it actually lives in the relatively hot and arid regions of northern Cameroon and northern Ghana.
In the summer of 2020, the team plans to travel to Nigeria to continue their efforts to understand biodiversity and genome evolution of African clawed frogs.
With global amphibian populations in decline, it is hoped such research can add to conservation efforts aiming to afford wild populations better protection.
