Darwin’s Fishing Net: Manipulating Complex Ecosystems
by Guest Blogger,
Tyler Kokjohn, Ph.D.
In an effort to protect fisheries, laws and treaties require trawlers to use nets with a mesh big enough to allow smaller, presumably young fish, to escape. The basic idea is simple; capture and eat the big fish, but let the young ones live to reproduce and replenish the stock. That is logical, but the evidence suggests that practice is not only failing, but in combination with overfishing it is doing something perverse; fish are growing more slowly, reaching sexual maturity earlier and, due to smaller sizes, producing fewer eggs (1).
Picture Darwin’s fishing net capturing the big ones, but always letting the little fish escape. Using it over and over again, perhaps to a point of overfishing, is a powerful un-natural selection which leaves a fish population with proportionately more small fish. Some escapees may be young, growing fish, but some might be small sized adults. Do this enough and over a long period of time the net effect could favor small fish reproduction to the point that waters become populated with significantly smaller fish. Scientists hoping to conserve fisheries may have unwittingly engineered declines in the average body size and condition of commercially harvested species.
Living systems are dynamic, more than a little mysterious and unpredictable. We often discover how complex living systems really work by observing them in action or perturbing them with sometimes disastrous consequences. Consumption of methylmercury present in food can produce a severe neurological disease syndrome (2). Methylmercury present in aquatic environments increases in concentration (bioaccumulated) as it flows up the food chain, sometimes reaching toxic levels as was the case with Minamata disease. Named for the geographic locale of first recognition in Japan, this horrific disease outbreak was the result of disposing mercury-laden industrial waste into the bay that served as an important source of seafood for nearby residents.
There are some good reasons why we do not fully grasp how natural ecosystems work. Part of the problem is we do not exactly know what is in them. Microbiologists examining natural environments using gene probe methods that can reveal bacteria without having to grow (culture) them discovered only a small proportion of the microbial universe is known to science (3) a situation scientist David Stahl likened to going into the Amazon Basin for the first time. The majority of microbes, the entities that control the most fundamental aspects of ecosystem function on our planet, are unknown to us. The fact is we do not understand life on our planet and cannot produce even a rudimentary roster of the critical players. Assumptions, predictions and extrapolations do not always survive when theory is confronted with the complex realities of living systems.
Gene drives, constructions that are able to automatically spread themselves and cargo DNA throughout entire populations of organisms, have created concern because of the possibility they might damage ecosystems. However, no one knows how well gene drives will actually perform in natural environments. And there could be factors such as spontaneously arising mutations that might inhibit their activities (4, 5). The idea that future ecosystem engineers might capitalize on factors impairing gene drive activity to keep them under firmer control is interesting. In theory, if damping factors are effective they might help defuse objections to releasing gene drives, a strange situation where it becomes permissible to use a devicebecause it won’t work well for long. It remains to be seen if using impaired gene drive methods to achieve public health goals like halting mosquito-borne virus disease for example would be practical or economically sustainable.
It is important to note that gene drive technology has immense promise but is still hypothetical. So is the concept of drive damping. Scientists are now eagerly sorting out the realities as to how gene drives work and perhaps fail to work. Given the limitations in our knowledge and the fact that complex living systems are often unpredictable and surprising and we should perturb ecosystems with care.
(1) B. Borrell. 2013. A Big Fight Over Little Fish. Nature, 31 January 2013. http://www.nature.com/news/ocean-conservation-a-big-fight-over-little-fish-1.12325
(2) K. M. Rice et al. 2014. Environmental Mercury and Its Toxic Effects. J. Prev. Med. Public Health 47(2):74-83. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3988285/
(3) R. F. Service. 1997. Microbiologists Explore Life’s Rich, Hidden Kingdoms. Science, 21 March 1997, [275(5307):1740]. http://science.sciencemag.org/content/275/5307/1740.full
(4) T. H. Saey. 2016. Seeing the Upside in Gene Drives’ Fatal Flaw. Science News, 15 July 2016. https://www.sciencenews.org/article/seeing-upside-gene-drives-fatal-flaw
(5) R. L. Unckless et al. Evolution of Resistance Against CRISPR/Cas9 Gene Drive. bioRχiv11, June 2016. http://biorxiv.org/content/biorxiv/early/2016/06/11/058438.full.pdf