Climate and pollution are changing characteristic of fish nature
Two studies published this week, one from the University of Michigan and the other from the Woods Hole Oceanographic Institution, show how nature is changing. The effects of pollution on fish and excess CO2 on plants and insects are changing those elements of nature.
In the study by researchers Rachel Vannette and Mark Hunter at the University of Michigan looked at how increased carbon dioxide in the atmosphere is affecting milkweed and subsequently monarch caterpillars. Milkweed produces heart poisons called cardenolides that discourage caterpillars and insects from chowing down on it.
Different genetic "families" of the common milkweed were studied in Northern Michigan.
"Specifically, we examined the response of milkweed plants to elevated carbon dioxide in terms of plant growth, asexual reproduction, and the production of chemical and physical defenses," Vannette said. Although all plants grew larger in response to elevated carbon dioxide, and all plant families showed similar growth and reproductive responses, plant families responded differently to elevated carbon dioxide in their production of chemical and physical defenses against plant-eating insects.
In particular, their production of heart poisons called cardenolides differed. While some plant families responded to elevated carbon dioxide by increasing cardenolide production, most decreased production—by as much as 50 percent
Plant eating species such as caterpillar’s choose what plants to eat by the amount of toxic substances like cardenolide. Those plants that reduced the production of cardenolide, shifted to physical defenses such as tougher leaves and an ability to quickly grow back after being eaten.
Taken together, the results provide evidence that in response to elevated carbon dioxide, genetically-based differences in plant defense mechanisms and the changing plant-insect interactions that result may influence how plants adapt to changing climate.
What these changes mean for monarch caterpillars is still unknown. However the ongoing research will be studying those effects as well.
Most fish populations were wiped out or contaminated. The Atlantic tomcod actually thrived due to a rapid evolutionary change. The fish developed a genetic resistance to the dangerous chemicals. A receptor gene called AHR2 changed so that it is missing “two of the 1,104 amino acids normally found in this protein.”
Although this kind of reaction has been seen when insects develop resistance to certain insecticides, and bacteria to antibiotics, “This is really the first demonstration of a mechanism of resistance in any vertebrate population,” said Isaac Wirgin of NYU’s Department of Environmental Medicine and leader of the study. Moreover, he said, the team has found that “a single genetic receptor has made this quick evolutionary change possible.”
The findings, reported online in the Feb. 17 issue of Science, provide a first look at “natural selection going on over a relatively short time, changing the characteristics of a population,” said WHOI Senior Scientist Mark E. Hahn, who, together with WHOI biologist Diana Franks, collaborated with Wirgin on the study. “It’s an example of how human activities can drive evolution by introducing stress factors into the environment.”
The two amino acids controlled the ability of the AHR2 receptor to bond to PCBS. The bond was weakened reducing the toxicity of the chemicals to the fish. Unfortunately for predators of the Atlantic tomcod, the PCBs that have accumulated in the fish are passed on to those who eat them. Atlantic tomcod are “prime prey” for striped bass. When the bass winds up on the dinner table the PCBs from the Atlantic tomcod wind up there too.
Although the evolutionary change may have helped the fish survive toxic levels of PCBs, it may have weakened its ability to respond to other dangers. As the Hudson River undergoes an “EPA-mandated cleanup”, the fish may find it difficult to survive a cleaner environment prompting further quick evolutionary changes.
“Hudson River tomcod have experienced rapid evolutionary change in the 50 to 100 years since release of these contaminants,” the researchers say in their paper. Added Wirgin: “Any evolutionary change at this pace is not a good thing.
Additionally, two studies published in Nature this week tied the increase in extreme weather events to global warming. Anthropogenic (man-made) climate change in the form of increased green house gases is increasing the chances of flooding.
The evolutionary changes we are seeing in our plant life and vertebrates like the Atlantic tomcod may only be samples of other changes that have not yet been studied or discovered. As we worry about the increase in extreme weather events and flooding that we are seeing world wide, we need to remember that those same events and are affecting other living creatures as well.
While we study the environmental and evolutionary changes that are happening around us, we can only wonder how they will eventually change us.
Photograph of Common Milkweed by Rachel Vannette. Photograph of Atlantic tomcod by (Mark Mattson, Normandeau Associates, Inc. Illustrations of AHR2 evolution by llustration by Jack Cook, Woods Hole Oceanographic Institution.
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