It had been three decades since the frog species 'Craugastor escoces' was last sighted in its homeland Costa Rica. The species with the characteristic red belly had long been declared extinct by the International Union for Conservation of Nature (IUCN) when the doctoral candidate from Ulm University, Randall Jiménez and his colleague Gilbert Alvarado, scientist at the Universidad de Costa Rica (UCR) made their sensational discovery: They managed to catch a specimen of the species that was believed to be gone. The animal is now being examined at the UCR. The scientists hope to find indications on how to protect the rediscovered frog species in the future.
Around one third of amphibian species worldwide are listed as critically endangered. Professor Simone Sommer, Director of the Institute of Evolutionary Ecology and Conservation Genomics in Ulm likens the mass mortality of this taxonomic group to the extinction of the dinosaurs. Beyond the destruction of their habitats, climate change and pesticides, the infection with the so-called chytrid fungus seems to play a significant role. This fungus appears to block the oxygen uptake in amphibians through their skin and attacks the nervous system. The composition of the skin bacteria, the so-called skin microbiome, seems to play a big role in the defence against the chytrid fungus. The frequently fatal fungus infection potentially also affects another frog species called 'Lithobates vibicarius', however, some individuals appear to be resistant. Doctoral candidate Randall Jiménez, who works under the supervision of Simone Sommers, currently investigates the significance of the skin microbiome for the health of these frogs. In September 2016, he and his research colleague Gilbert Alvarado (UCR) discovered something unusual during their field research in the national park Juan Castro Blanco (Province of Alajuela, Costa Rica): 'We were working at night along a stream. Suddenly, in the light of our head torches we spotted a frog that is unusual for this region and that we could not identify,' the biologist from Ulm University with Costa-Rican heritage remembers. Their internet search provided the young researchers with first indications about their sensational catch — an expert from UCR later confirmed their suspicion: The female frog belongs to the species 'Craugastor escoces', also known as 'Heredia robber frog' or 'red-bellied frog', which had been pronounced extinct in 2004.
It is not only the frog that begs questions but also the spot where it was found: The former geographic range of this species is about 15 kilometres away. 'It remains unclear, if a small population has been at home in this national park for decades or if they settled there only recently,' Sommer and Jiménez explain.
Due to the rarity of their discovery and to protect the species the biologists refrained from killing the female for research purposes. The six centimetre long nocturnal animal has since been living in a well-tended terrarium at the Universidad de Costa Rica: 'We are keeping an eye on the area where we found her to see if we can find at least one other male animal that we can mate with the female. Our hope is to gain data for the reproduction and development of the species,' the researchers elaborate. The field work aims to measure the approximate size of the Craugastor escoces population as well as their state of health and possible environmental influences that might jeopardise their survival. All investigations strive to protect the frog species and facilitate their repopulation. In their quest to understand the relevance of the skin microbiome the researchers might just find the key to resistances against pathogenic organisms like the chytrid fungus and therefore the survival of individual specimen.
The rediscovery of the 'Heredia robber frog' was recently announced at a press conference as part of the UCR’s Environmental Week and was met with great interest by the media. Previously, another frog was rediscovered that had been declared extinct in this Central American country. 'Such findings give reason to hope that we can understand the resistances of single individuals or whole species and reduce the global decline of amphibians,' the scientists agree.