Erik Hom, associate professor of biology at the University of Mississippi, is using an $800,000 grant from the National Science Foundation to study the role of cooperation in evolution. Over the course of a year, Hom and his team will watch 1,000 generations of two species of yeast and algae evolve under different conditions. Photo by Kevin Bain/Ole Miss Digital Imaging Services
National Science Foundation-funded project tests repeatability, nature of evolution
by Clara Turnage
Researchers at the University of Mississippi are watching 1,000 generations of yeast and algae as they grow and change in real time to better understand how species evolve together.
The goal of the study is to understand how often and why evolution takes the same path. Answering these questions may help scientists predict evolution.
Erik Hom, Ole Miss associate professor of biology, and Sergey Kryazhimskiy, associate professor of ecology, behavior, and evolution at the University of California San Diego, are using funding from the National Science Foundation to test the roles that competition, cooperation, and the environment play in evolution.
“If you replay the tape, what happens?” Hom said. “Evolution is very much what we call a stochastic, or random, process, but it’s only random within certain constraints. Imagine if you roll dice; the number you land on is random. But it’s only random within the constraints of the number of faces on the die.
“What we’re asking is, ‘What are the genetic constraints that allow mutations to spread in populations? And why do they repeat?'”
The project will test these constraints by studying whether cooperation between organisms limits or expands the evolutionary pathways available to them.
The experiment centers on two microscopic organisms: yeast and alga. The alga uses carbon dioxide produced by the yeast to grow and replicate. In return, the alga provides a usable source of nitrogen that helps the yeast survive.
By altering the amount of nitrogen and carbon dioxide available in the two species’ lab-based ecosystem, the researchers can tailor the extent to which the yeast and alga need one another to live.
When those nutrients are plentiful, each can survive largely on its own. When they are scarce, the organisms must rely much more heavily on one another to live.
During the yearlong experiment, the researchers will be able to observe the yeast and algae through some 1,000 generations and identify how their genomes change depending on the extent to which they cooperate with or compete against one another.
“The goal isn’t to have one ‘winner’—this isn’t ‘Survivor,'” Hom said. “It’s to see how these microbes take on the challenge of surviving. It’s our job to tease out what’s common among them and what’s different, to see when they might use the same strategy and when they don’t.”
Although competition is often considered a primary driver of evolution, recent studies have found that cooperation plays a greater role than previously understood.
“We know that a lot of life depends on cooperation,” Kryazhimskiy said. “There are many cases we know of where different organisms work together to grow and thrive and a long-standing question in evolutionary biology is, ‘When and how cooperation evolves in the first place?’ The system that we’re working with can help investigate this question.”
Once collaboration begins between two species, more questions emerge: Do they evolve to help one another grow? Or does their imperative to survive supersede the need for cooperation, resulting in one species sabotaging another?
“If we force them to cooperate, you can imagine that it would be very difficult to break the cooperation,” Kryazhimskiy said. “But we have seen instances where a genetic mutation results in a ‘child’ that is much more competitive than its parent and produces less of the nutrient the partner needs.
“Eventually this trend could collapse the whole ecosystem because it’s producing less and less of the byproducts that both species need to survive.”
Better understanding when evolution follows predictable paths could help scientists anticipate how microbes respond to environmental pressures. That knowledge could inform scientific approaches to human problems such as antibacterial resistance, a global threat that occurs when bacteria do not respond to medicines.
“Bacteria are evolving, too,” Hom said. “Every time we pump in antibiotics, we are basically selecting for stronger mutations and resistance traits in the bacteria that remain. What if we instead thought, ‘Are there other solutions to do this?'”
If researchers understand how bacteria evolve, they can use therapeutics that are more difficult to resist, Kryazhimskiy said.
“When we produce a new drug that is going to kill a pathogen, one of the first questions should be, ‘How easy is it for the organism to evolve resistance?'” he said. “If it’s a single mutation, it’s very easy to evolve, and we can expect resistance in a few generations.
“It allows you to ask these more nuanced questions about the cost of resistance. Evolutionary prediction would ideally allow us to know the probability of these outcomes.”
This material is based on work supported by the National Science Foundation grant no. 2529576.
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