In 1963, armed with a crowbar and curiosity, Robert Paine started an experiment that changed how we think about ecosystems. At a series of tide pools on the Washington coast, the young University of Washington ecologist pried up orange and purple starfish, Pisaster ochraceus, and hurled them into Mukkaw Bay.
The loss of that single species transformed the tidepools. Mussels that were a favorite food of the starfish took over, crowding out many other species. The insights led Paine to coin the term “keystone species” to describe a critical species that can determine the fate of an entire ecosystem, like the central keystone that keeps an arch from collapsing. The idea has played a pivotal role in understanding ecosystems, such as the way the eradication of wolves around Yellowstone National Park led to a surge in grazing by elk that wiped out willow populations and eroded stream ecosystems. It underscores, in an age of mass extinctions, how the loss of even a single species can wreak havoc.
Now, a group of scientists have taken the insight to even a smaller level. They’ve found what they call a keystone gene. While the results come from a laboratory, it underscores the potential ecological risks from the loss of biodiversity, even within a species.
“Our findings show that the current loss of genetic diversity may have cascading effects that lead to abrupt and catastrophic shifts in the persistence and functioning of terrestrial ecosystems,” says Matt Barbour, a researcher at University of Zurich in Switzerland who helped lead the research.
To see how subtle genetic differences within the same species might resonate through an entire ecosystem, scientists in Zurich and the University of California, Davis turned to a lab rat of the plant world, Arabidopsis thaliana, also known as mouse-ear cress or thale cress. The tiny, spindly plant with delicate flowers is often considered a weed and can be found sprouting from such unlovely places as the cracks in a sidewalk.
But for scientists, the hardy plant has several advantages. It is widely used in plant research as a model organism and has been dissected down to the genetic level. It is also a popular food among aphids, putting it at the bottom of a sequence of relationships between different species.
In this case, Barbour and the other researchers capitalized on these relationships by creating miniature ecosystems in small containers simplified to just four organisms: the plant, two aphids that feed on the plant, and a parasitic wasp that lays its eggs on aphids.
To test the effect of a single genetic change in the plant, they took four different strains of the Arabidopsis, each with a single difference in a part of its genetic code that influenced production of chemicals that can repel aphids. Each of those variants is found in nature as well. They then created 60 mini-ecosystems in small mesh-walled boxes, each with different combinations of plants.
All of these little worlds changed as the scientists followed their progress for roughly four months. In some cases, all the insects starved and vanished. In other cases, one of the two aphid species disappeared. In still others, the system gradually broke down until just the plant and an aphid species was left.
When the researchers sifted through the patterns of extinctions, one feature stood out. Ecosystems with a version of the plant in which a single gene (AOP2) was turned off were much less likely to witness an extinction. The extinction rate fell by 29% when a plant with the disabled AOP2 gene was present, the researchers reported last week in Science.
It turns out that in addition to being involved in production of plant-defense chemicals, the gene also influences the plant’s growth rate. With the gene inactivated, the plant grew faster, enabling it to better keep up with demands placed on it by the aphids, the researchers found.
While a controlled laboratory is a far cry from the messy world and its intricate food webs, the researchers note their findings show that even a difference in a single gene can have far-reaching consequences.
The findings demonstrate the potential importance of combing genetic and ecological tools for understanding how genetic changes might influence the fate of ecosystems, the authors write, It also underscores the dangers of losing genetic variation within a species as its numbers shrink, or the potential for impacts from introducing organisms with a genetic tweak that turns out to be significant. That gene, after all, could turn out to be a keystone much like Paine’s starfish.
Barbour, et. al. “A keystone gene underlies the persistence of an experimental food web.” Science. Mar. 31, 2022.
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