Consider transgenerational effects when assessing toxicity

In ecotoxicological research, we study how toxic chemicals entering the environment can affect plants, animals, and entire ecosystems. To understand how those contaminants harm organisms, we generally start with experiments conducted in a safe laboratory environment. In these laboratory experiments, different organisms are exposed to different concentrations of the environmental contaminant of interest. We use this approach to establish safety thresholds, as it allows us to understand at which concentration the pollutant harms organisms. 

These experiments where we study the direct exposure of an organism to a toxic chemical are a crucial and important part of developing safety standards. However, a new research article published by our own Rebecca Osborne, a PhD student in Prof. Ryan Prossers lab, shows that it is not only important to examine organisms that are in direct contact with the toxin, but also how the offspring of those organisms are affected. They were especially interested in offspring that didn’t come in direct contact with the toxin but were only exposed via their parents.

Rebecca discovered that freshwater snails exposed to the environmental contaminant copper before reproducing had “kids” that were much less tolerant to copper than “kids” born to snails that were never exposed to copper. This is a really important finding, as it shows that we might underestimate the negative effects of some toxic contaminants when we only look at the direct effects and ignore, what we call the transgenerational effect. 

Copper is only considered an environmental contaminant if it appears in higher concentration. At smaller concentrations, copper can be beneficial to organisms. However, if the concentration of copper is above normal background levels, it becomes harmful to the environment and can cause significant damage to organisms. Copper enters waterways via different pathways. Some of the main sources of copper pollution are mining, road water run-off, and wastewater effluents. Copper is also a common ingredient in fertilizers and pesticides. Sometimes, it is also directly applied to lakes or streams to kill algae and or unwanted mussels and snails. 

The organism that was used in this research is the File Ramshorn snails (Planorbella pilsbryi). It’s a small freshwater snail that inhabits lakes and slow-moving streams in south-central Canada and northern United States. This snail species is a hermaphrodite, which means, each individual has male and female genitalia. Freshwater snails and other related species are playing an important role in aquatic ecosystems. Not only are they important food for other aquatic organisms but also some bird species such as waterfowl. In addition to being food for many organisms, they also break down plant material into nutrients while eating. 

In this experiment, freshwater snail adults were exposed to different levels of coppers. Several snails died when exposed to the highest copper concentration, but none of them died in any of the tanks with lower concentrations of copper. The study also found that the snails exposed to higher levels of copper took significantly longer to produce eggs compared to the snails in lower copper concentrations. 

After the week-long exposure to copper, these adult snails were given a recovery period in clean water for ten days. During that time, they produced offspring. These offspring were never directly exposed to copper, as they were born while their mother was recovering in clean water. Rebecca Osborne and her co-authors found was that those snails that were born in clean water but to parents that were exposed to an environmental contaminant, copper in this case, were indeed negatively affected. Most visibly, those offspring had a very low tolerance for copper. This shows an important example of a transgenerational effect, an effect where offspring are harmed via their parents' exposure to a contaminant.

These transgenerational effects are fascinating and not too well understood, especially for freshwater snails. There are several different possible mechanisms that could cause this transfer of effects onto offspring. In this case, the authors speculate that most likely the cause is that the parents needed a lot of energy to resist the copper and were therefore not able to invest as much of their resources into producing the offspring, leaving the offspring more vulnerable to environmental contaminants. 

These findings are highlighting the importance to consider transgenerational effects for future ecotoxicological studies. Neglecting transgenerational effects in ecotoxicological research could mean that we are underestimating the effects of contaminants. Whereas this study uses copper and snails, the authors suggest that those transgenerational effects are important to consider for other organisms and other environmental contaminants as well. 

Citation: Osborne, R. K., Gillis, P. L., & Prosser, R. S. (2020). Transgenerational effects of copper on a freshwater gastropod, Planorbella pilsbryi. Freshwater Mollusk Biology and Conservation, 23(1), 42-54.

You can find the original research article following this link: https://bioone.org/journals/Freshwater-Mollusk-Biology-and-Conservation/volume-23/issue-1/fmbc.v22i2.2020.42-54/Transgenerational-Effects-of-Copper-on-a-Freshwater-Gastropod-Planorbella-pilsbryi/10.31931/fmbc.v22i2.2020.42-54.full

If you have any questions about our research contact sescomms@uoguelph.ca and if you have specific questions about this article, contact Prof. Ryan Prosser directly via email: prosserr@uoguelph.ca