By Fernando Gastón, Iturburu* and Lidwina, Bertrand*.
Endings are a great opportunity to reflect on past decisions. As both of us wrap up our PhDs in Ecotoxicology (Fernando at the National University of Mar del Plata and Lidwina at the National University of Córdoba, both in Argentina), we keep thinking of the questions we struggled with as students and the conclusions we reached. One of the biggest questions in our research was: is it better to work with native species or model organisms to examine research questions pertaining to aquatic environments in South America?
Model organisms are simple organisms expected to behave similarly to other organisms when exposed to potentially harmful chemicals. Traditional model species include zebrafish (Danio rerio), aquatic macrophytes of the Myriophyllum and Lemna genera and planktonic crustacean as Daphnia magna among others (Häder and Erzinger, 2018). Model species are well studied, so a lot is known about how to keep them happy and healthy in a laboratory setting. But, most benchmark testing for model organisms was developed in the northern hemisphere, particularly more socio-economically developed countries like the USA, China, Germany, UK, and Canada. Since different species are known to have different sensitivities to toxic compounds (Van der Oost et al., 2003), it is questionable whether or not model organisms can act as representative samples for environmental studies concerning environments in the southern hemisphere.
Our research was concerned with conducting experiments to understand the potential negative impacts of metals and pesticides on South American, particularly Argentinian, aquatic ecosystems. These chemicals can enter the environment from industrial activities such as metalworking, tanneries, litter bins, open sky mega-mining with tons of rocks extracted each year, and large- scale agricultural production which are all common throughout South America. We had several questions while designing our research experiments:
1- Are native species useful (like model ones) to assess environmental degradation through biomonitoring programs?
2- Are studies carried out using species from European or North American countries representative of the sensitivity of species present in ecosystems from others regions of the world?
3- Are the established guidelines developed with model organisms “good” enough to protect species from South American ecosystems?
4- Could we develop our own guidelines with native species?
We were ultimately swayed to using multiple local species (shown in Figures 1 and 2) because we believe, along with the experts of the OECD (Organization for Economic Co-operation and Development, 2002), that multiple indigenous test species provide more robust results for resolving regional environmental concerns. But this decision came with several advantages and disadvantages. Let’s start with the “worst” part of the story, the disadvantages of working with native species:
– The first problem is the absence or low availability of basic information about your object of study. Since no one else is studying them, there’s a lot more uncertainty in understanding how chemicals affect them. There is also little information about how to keep them healthy in a laboratory setting so it is hard to say if observations are caused by chemicals or just abnormal living conditions. Resolving this concern involves a lot of time, money, and resources (which are sparse when you’re a PhD student!) which can limit your experimental design and, sometimes, lead to make mistakes or to obtain non “suitable” results.
– Other problem arise when you try to publish your first paper and reviewer’s comments arrive in your inbox. Comments reflect great distrust in your results, even if standardized protocols were applied, because you are not using a model species. This leads some reviewers to doubt the usefulness of your research because is not a world recognized model and concern.
Figure 1- Australoheros facetus is a cichlid fish which inhabits the Parana’s basin in Brazil, Paraguay, Argentina, and Uruguay. It is a suitable and sensitive fish species to assess pesticides pollution in South American ecosystems. Ph: Fernando G. Iturburu.
But not everything is negative when you chose a native species to join you and your Ph.D. thesis for three or five years. Several advantages to using native species are:
– Usually, the “native” characteristic allows for better availability and accessibility to organisms for experimental tests. They don’t have to be shipped too far, and could even be collected close to your lab!
– You can avoid the introduction of exotic organisms into local waters when conducting field studies with foreign model organisms, which has the potential to cause serious ecosystems disorders.
– The lack of information about native species can also be considered a positive: ALL is new and the obtained information will improve the understanding of the sensitivity of these species and related ones, and how regional ecosystems would be affected in presence of pollutants. New biological mechanisms and responses can be found and published but, again, tips about how to communicate your research work are crucial! You must convince reviewers that non-model species results represent a novelty important for advancing global ecotoxicological knowledge.
– Results from native species studies would be considered for the selection of new, region-specific model species to use in the establishment of environmental guidelines of studied region, which could improve the protection of aquatic ecosystems.
When comparing results from our research to the existing body of literature, we found the advantages to outweigh the disadvantages. The literature describes that the LC50 (concentration at which 50 percent of organisms in a study exposed to a compound die) for the neonicotinoid insecticide imidacloprid in model fish is around 200 mg L-1 (IUPAC PPDB, 2018). Nevertheless, for the South American cichlid fish Australoheros facetus (Figure 1), we found that the LC50 value was much less: below of 10 mg L-1 (Iturburu et al., 2017)! Even more, this compound causes DNA damage from concentrations of 1 μg L-1 (Iturburu et al., 2018, remember that 1 microgram (μg) is a millionth part of 1 gram).
Figure 2- Palaemonetes argentinus represents a small decapod from water ecosystems of South America. Its sensitivity to pollutants exposure as well as its ecological relevance in trophic chains and, ecosystems, led to it being proposed as a possible bioindicator of environmental quality. Ph: Lidwina Bertrand.
We also found interesting results with respect to variability in sensitivity across organisms. For example, the Argentinean Environmental Water Quality Guidelines (AEWQG, 2003) recommends concentrations of the widely used insecticide chlorpyrifos (CPF) should not exceed 6 ng L−1 (being 1 nanogram, ng, a billionth part of one gram) for the protection of aquatic biota. This limit comes from experimental results with model species from others world regions. Nevertheless, the shrimp Palaemonetes argentinus (Figure 2) and the macrophyte Potamogeton pusillus showed significant response of studied biomarkers after 96hs of exposure at 3.5 ng L−1! In the case of the shrimp, several biomarkers responded significantly at 3.5 ng L−1 CPF, including metallothionein concentration (decreased), acetylcholinesterase (inhibited) and antioxidants enzymes (induced) activities; while in the macrophyte chlorophylls contents dropped in described conditions (Bertrand et al., 2016 and 2017). Usefulness of native species as bioindicators of water pollution was evidenced using them in river monitoring campaigns (Bertrand et al., 2018 a, b). So, all these results (and many others) which show that different species can still be affected at different concentrations of a chemical, even below an accepted limit, telling us that species selection in ecotoxicology testing is very important.
Thus, the native species have a lot of information to bring us, and from our place (and with all necessary considerations) we will continue to promote the use of these organisms to understand the possible effects of pollution in South American and others ecosystems. And maybe one day (who knows!), we will be able to have our own model species and guidelines.
Iturburu, Fernando Gastón obtained his Ph.D. in Biological Sciences at the National University of Mar del Plata, Argentina. His research focused on the effects of current use pesticides on two South American freshwater species: a cichlid fish (Australoheros facetus) and a macrophyte (Myriophyllum quitense). The thesis aimed to study different biomarkers of these organisms experimentally exposed to pesticides, as well as study factors which could modify the interpretation of these responses. As an ultimate goal, the project aimed to establish these organisms as freshwater bioindicators in South American aquatic ecosystems. Publications from PhD thesis can be found in:
Bertrand, Lidwina obtained her Ph.D. in Biological Sciences at the National University of Córdoba, Argentina. Her research focused on the usefulness of two South American native species, a small shrimp (Palaemonetes argentinus) and a rooted macrophyte (Potamogeton pusillus), as freshwater bioindicators. The thesis involved firstly the study of biomarkers responses in mentioned organisms exposed to environmentally relevant concentrations of pollutants (metal and pesticide) laboratory conditions. Experiments involved exposure concentrations lower than those suggested by Argentinean environmental guidelines. Finally, organisms were used in an active monitoring with the aim to analyze their sensitivity in sites with complex mixture of pollutants associated with different land uses in the Ctalamochita River Basin as a case of study. Publications from PhD thesis can be found in:
– AEWQG (Argentinean Environmental Water Quality Guidelines), 2003. Subsecretaria de Recursos Hídricos de la Nación, República Argentina.
– Bertrand, L., Monferrán, M.V., Mouneyrac, C., Bonansea, R.I., Asis, R., Amé, M.V., 2016. Aquat. Toxicol. 179, 72–81. http://dx.doi.org/10.1016/j.aquatox.2016.08.014
– Bertrand, L., Marino, D.J., Monferrán, M.V., Amé, M.V., 2017. Environ. Exp. Bot. 138, 139–147. https://doi.org/10.1016/j.envexpbot.2017.03.006
– Bertrand, L., Monferrán, M.V., Mouneyrac, C., Amé, M.V., 2018a. Chemosph. 206, 265–277. https://doi:10.1016/j.chemosphere.2018.05.002
– Bertrand, L., Monferrán, M.V., Valdés, M. E., Amé, M.V., 2018b. Env. And Exp. Bot. Under revision.
– Häder, D. P. and Erzinger, G. S., 2018. Bioassays: Advanced Methods and Applications. Elsevier. https://doi.org/10.1016/B978-0-12-811861-0.00031-0
– Iturburu, F.G., Zömisch, M., Panzeri, A.M., Crupkin, A.C., Contardo-Jara, V., Pflugmacher, S., Menone, M.L., 2017. Ecotoxicol. Toxicol. Chem. 36(3), 699-708. https://doi.org/10.1002/etc.3574.
– Iturburu, F.G., Simoniello, M.F., Medici, S., Panzeri, A.M., Menone, M.L., 2018. Bull. Environ. Contam. Toxicol. https://doi.org/10.1007/s00128-018-2338-0.
– International Union of Pure and Applied Chemistry (IUPAC). PPDB: Pesticides Properties DataBase. University of Hertforshire, Hatfield, Hertfordshire, UK. [cited 2018 April 19]. Available from: http://sitem.herts.ac.uk/aeru/iupac/atoz.htm.
– OECD (Organization for Economic Co-operation and Development). Testing guidelines. Available from: http://www.oecd.org/env/ehs/testing/
– van der Oost, R., Beyer, J., Vermeulen, N.P.E., 2003. Environ. Toxicol. Pharmacol. 13, 57–149, http://dx.doi.org/10.1016/S1382-6689(02)00126-6.