The use of environmental DNA (eDNA) in biological monitoring of the Natterjack toad (Epidalea calamita)

Abstract

Environmental DNA (eDNA) is a promising new tool in the field of conservation management, which can contribute to non-destructive species determination as well as improved data on species occurrence. Still, it is important to gain knowledge on how eDNA works compared to conventional monitoring methods in order to evaluate the detection efficiency.

In this study, I have investigated the use of eDNA as a compliment to the traditional survey methods used in Sweden’s national biogeographical monitoring of the red listed Natterjack toad (Epidalea calamita). E. calamita occurs in 4 different counties, Västra Götaland having a large viable population distributed on small islands in Kattegat. In Skåne, Blekinge and Halland, where the species is not considered common, it occurs in a much wider range of habitats such as coastal rock-pools, heath meadows and gravel pits. The difference in population status and county, have resulted in two slightly different survey and sampling methodologies. The study demonstrates that eDNA proved to be a useful tool for species identification and species occurrence. The assurance of species identification and low amount of potential false positives and negatives, provide justification for the usefulness of eDNA in the national monitoring of E. calamita. However, difference in results between counties indicates that there is a need for site-specific protocols to assure the most reliable results for all counties.

Popular Abstract

Can a water sample tell us if toads are present or not?

In Sweden and other countries in Europe, many toads and frogs are declining or at risk of declining. But how can we know that? This is because their numbers are monitored and reported to EU every 6th year. Monitoring of amphibians is usually done by counting number of calling males or the number of tadpoles in wetlands. However, for some species this may a bit tricky because they are not always calling or it may be difficult to count the tadpoles in the water if they cannot be seen. The tadpoles may also be difficult to identify to species level. I have investigated if small water samples from wetlands contained DNA from two toad species in Sweden. Today, environmental DNA also called eDNA can possibly be used as a compliment when searching for different species.

eDNA is DNA that originates from, for example, skin cells that the animal shed into the environment. A sample from the environment the species lives in therefore contains DNA if the species is present, and this DNA can be extracted in a laboratory. The endangered Natterjack toad (Epidalea calamita) breeds in small and shallow ponds during late spring and summer months, a water sample from these types of ponds can thus potentially reveal the presence of the species, even if the species is not there for the time of the monitoring.

In Sweden the Natterjack toad exist in 4 counties: Västra Götaland, Skåne, Blekinge and Halland. A total of 114 wetlands have been monitored in these counties during 2016 and 2017 by estimating the number of tadpoles. Additionally, a water sample was taken from each of the 114 wetlands in order to extract DNA from the Natterjack toad and the Common toad. I have compared the success between the traditional monitoring (counting tadpoles and calling males) with the detection success by eDNA, both in terms of the number of wetlands in which the species were found to be present, but also if both monitoring methods gave the same results.

The results from Västra Götaland was different from the other counties
In Västra Götaland conventional monitoring methods showed that the Natterjack toad occurred in 53 % of the visited wetlands whereas eDNA only showed that the toad occurred in 37 %. This is different from the other counties, where both monitoring methods showed that the toad occurred in 33 % of the visited wetlands. In Västra Götaland traditional monitoring gave different results compared to eDNA analyses. This means that even if the species had been observed during traditional monitoring, eDNA analysis did not necessarily confirm the observation. There are many potential reasons behind these regional differences between methods and patterns; one could be that the sites in Västra Götaland, are known to be affected by salt water from Kattegat - the DNA might be to degraded or diluted to be detected.

Overall, eDNA proved to be a useful tool in species identification, as field observations of both species of tadpoles was both confirmed and affirmed. Most importantly, eDNA also indicated the presence of the Natterjack toad at sites, where conventional methods would conclude it was absent. Even though the results are promising, site-specific protocols for collecting water samples for DNA extraction need to be developed.

Master’s Degree Project in Biology 30 credits 2018
Department of Biology, Lund University
Advisor: Per Nyström and Marika Stenberg
Advisors company Ekoll AB

• author: Blom, Lærke Breum
• supervisor: Marika Stenberg; Per Nyström
• organization: Degree Projects in Biology
• course: BIOM01 20171
• year: 2018
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 8938704
• date added to LUP: 2018-04-13 10:28:03
• date last changed: 2018-04-13 10:28:03