CT scan of Xenopus fraseri © Edward L. Stanley

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Scientists unravel mystery of Victorian frog

An international team of scientists including Dr Jeff Streicher, Senior Curator of Amphibians and Reptiles at London’s Natural History Museum, have unraveled the secrets of two nearly 170-year-old frog specimens.

The two frogs were collected by Louis Fraser, a British zoologist who worked with Sir Richard Owen, founder of the Natural History Museum, and were added to the museum collection in 1852.

Unique to these frogs was the combination of two morphological features, vomerine teeth, specially adapted to grip prey, and a prehallux or extra claw. Whilst these traits were seen in similar species they were not seen together in any other Xenopus and so Louis Fraser’s frogs were declared a new species, Xenopus fraseri. However, their place on the evolutionary tree, geographic distribution, and ecology has since been debated due to a lack of genetic samples and poor records of their origin.

To establish Mr Fraser’s frogs’ place in the Xenopus family tree the team generated and analysed complete mitochondrial genome sequences from all Xenopus species, using sensitive techniques similar to approaches used to sequence the genomes of Neanderthals.

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 Natural History Museum’s collections are an essential resource to scientists trying to understand the natural world.’

The results showed that X. fraseri is distinct from other species and identified its minimal geographic distribution in northern Ghana and northern Cameroon. The data revealed a more diverse habitat preference by the species than previously presumed. Thought to be rainforest endemic the team found that the species occurs in arid regions of northern Cameroon and northern Ghana.

Ben Evans, lead author of the study and a professor of biology at McMaster University added, ‘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.’

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.

The paper Xenopus fraseri: Mr. Fraser, where did your frog come from? is published in PLOS One journal.



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