Throughout this course, we have frequently discussed how early life conditions can influence an organism later on in life. We have discussed this in a variety of different contexts, but one aspect we haven’t really touched on is disease risk. I have always been interested in how exposure to stressors in formative life stages of development may have enduring health effects. We have discussed how early-life stressors can alter an organism’s behavior later on in life. This altered behavior may have an impact on an organism’s ability to avoid infection, and in turn, increases their infection risk and/or tolerance. This is just one potential mechanism by which early-life exposure to stressors may influence disease risk later on in life.
A paper published in 2013 by Jason Rohr and colleagues entitled “Early-life exposure to a herbicide has enduring effects on pathogen-induced mortality” briefly discusses a variety of potential mechanisms by which early-life exposure to stressors may influence disease risk later on in life. The aim of their study was to test whether early-life exposure to a herbicide (atrazine) has immediate and/or long-term effects on Bd-induced mortality in amphibians. I find this paper particularly interesting because they also aimed to identify the mechanisms driving these effects. If you are interested in reading more about this study, I included a citation to the paper below.
There are several studies out there now looking at the impacts of a single environmental stressor on disease risk. Every organism gets sick at some point in their life. Thus, I think disease as a naturally occurring and anthropogenically induced stressor is an important component to research and think about. I find it particularly intriguing to think about questions that arise from the intersection in ecodevo, ecotox, and disease ecology.
I’m interested in understanding not only how a single environmental stressor, but rather multiple stressors interact with one another during development and the impact on carryover effects. We briefly touched on this in class this week, but we all know that amphibians experience multiple stressors during development under natural conditions. Many of these stressors we have discussed in class, yet we haven’t mentioned disease- a very prominent stressor for all organisms. My point being that there is a rather long list of potential stressors that a tadpole is exposed too during development. However, investigating and understanding the mechanisms driving these effects becomes much more complicated with exposure to multiple stressors. Even with unlimited resources, money, and time, it is still impossible to investigate and address all of the stressors one may experience under natural conditions. Looking at the impacts of a single or even two stressors in isolation is a good start, but it’s not the whole picture. I find myself frequently thinking about how we balance the natural conditions with what is logistically feasible. I do not have an answer as to how we should address this dilemma, but I think it is a really important component to consider in the field moving forward. Additionally, many papers I read (and the review we read for class this week by Thambirajah et al. 2019) state that additional studies need to be done examining the impacts of multiple contaminants or contaminant mixtures. I completely agree, however, few people (if any) address how to logistically accomplish this goal. If anyone has any ideas on how to conduct this sort of research, I would love to hear your thoughts and I eagerly welcome you to comment below!
Sources:
Rohr, J. R., Raffel, T. R., Halstead, N. T., McMahon, T. A., Johnson, S. A., Boughton, R. K., & Martin, L. B. (2013). Early-life exposure to a herbicide has enduring effects on pathogen-induced mortality. Proceedings. Biological Sciences / The Royal Society, 280(1772), 20131502.
Your post made me think of how invasive species can cause native species to be more susceptible to iridoviruses through stress. Pesticides as well, although they are usually found in the environment at levels that don't kill amphibians, the sublethal stress that they can cause I think is being overlooked, because studies have shown that they can be multipliers for the effects of other stressors like invasion, disease, or other processes that result in extirpation of a species. For example, a study by Rick Relyea in 2003 apparently showed that tree frogs exposed to the chemical carbaryl alone are resistant at certain levels but when the threat of predation is added as a factor to the same amount of carbaryl, the effects of carbaryl are up to 46x more lethal than they would be alone. Makes you think about the way we conduct environmental risk assessments and their potential to be flawed.
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