Perspectives Online

Rapid evolution: CALS scientist’s work is quickly changing our understanding of ecology and evolution

Plant biologist Dr. Marc Johnson studies “the factors that influence the abundance, the distribution and the diversity of species within nature.”

Photos by Becky Kirkland
When it comes to thinking about how animals and plants influence the world around them, it’s tempting to imagine groups to be made up of genetically identical individuals. If there’s a group of common evening primrose in your backyard, well, you might expect those plants to host the same type of insects and the same number of insects as do the primroses around the corner. And you might expect that this will be the case today and tomorrow.

But populations aren’t homogenous, and they don’t stay the same over time. Each plant in a sexually reproducing species like the evening primrose is different from the next, and when taken together, these genetic differences can, over time, add up to big differences in the abundance and diversity of pests that feed on them.

Exploring those differences and their ecological influence is the heart of groundbreaking research conducted by Dr. Marc Johnson, a plant biologist who joined the College of Agriculture and Life Sciences’ faculty in 2009. His approach integrates natural history with lab and field experiments, along with diverse disciplines such as chemical ecology, quantitative genetics, molecular ecology and evolution, comparative biology and statistics.

For his contributions to a burgeoning new field of science known as community genetics, Johnson recently won the Young Investigator’s Prize from the American Society of Naturalists. The award recognizes outstanding research from early-career scientists.

Dr. Marc Johnson (left) and graduate students Rose Grinnan and Nash Turley are currently examining how global climate change could affect the interactions between insect pests and plants.
Photo by Becky Kirkland
Johnson will present his research findings at the society’s annual meeting in Portland, Ore., this June, and he’s also been invited to lecture at meetings across the globe – in Japan, England and the Netherlands.

“The reason why this research is exciting is because, in ecology, we are interested in the factors that influence the abundance, the distribution and the diversity of species within nature,” he explains. “Most ecologists have assumed that from an ecological standpoint, species are made up of homogenous sets of individuals and that the populations are evolutionarily static – they are unchanging.

“What I was able to show is that variation within species -- within a single plant species (and this applies to humans, to dogs, to insects, to any species you look at that contains genetic variation, which is virtually every living thing) -- has huge ecological consequences,” he says. “So genetic differences between two individuals can influence the diversity of insects on those plants, can influence which species they compete with and so on.

“And then as a result of these interactions, these plant populations can evolve -- and sometimes evolve very quickly, in a matter of just several generations -- so that the genetic composition of the population changes through time, and that leads to different associations with those species, different abundances of these insects and other plants,” he says.

Johnson reached this understanding through research he conducted with Dr. Anurag Agrawal at the University of Toronto, where he earned his Ph.D. in 2007.

Those studies yielded “some of the very first results [indicating] that genes can have these extended effects on communities of organisms and even on entire ecosystems,” Johnson says.

Today, ecologists are beginning to understand that this so-called community genetics research has important ramifications not just for plants and animals, but also for people, especially when it comes to agriculture and medicine.

Johnson cites two examples of the way rapid evolution of organisms has had a big impact on people: the way the tobacco budworm rapidly developed resistance to cotton engineered with the insect-killing Bacillus thuringiensis gene and the way that human flu strains continually evolve to overpower vaccines. {AUDIO 1: Hear Dr. Marc Johnson describe how interactions between organisms and rapid evolution have implications for agriculture | or read the transcript.}

In his own lab, Johnson and his colleagues – undergraduate and graduate students, technicians and post-doctoral fellows – are currently examining how the increased temperature and drought of global climate change could alter the interactions between insect pests and monoculture crops such as soybeans.

“If the genotypes that are conventionally used now are susceptible to changes in the environment that we will be experiencing, there might be existing varieties that we can use and plant instead,” he says. “This is something we are going to have to start understanding now if we want to be able to mitigate these stressors in the future.”

A desire to anticipate and help solve such significant problems drives Johnson’s research, as does an excitement about nature and science that was born during his childhood near Toronto, Canada. He says he spent many a day exploring the flora and fauna at the provincial park Presqu’ile, where his grandmother had a cottage. {AUDIO 2: Listen to Marc talk about his early fascination with natural history | or read the transcript.}

He went on to spend summers as a naturalist at Algonquin Provincial Park while he studied at the University of Guelph, then went on what he calls an around-the-world “Darwin trip” with a friend and soon-to-be wife. They started in England, working their way south and east – through the Pyrenees, to the Arabian desert, over to India and the Himalayas, then to Thailand, Hong Kong, New Zealand, Australia, Easter Island -- before finishing their journey at the Tierra Del Fuego archipelago at the southern tip of South America.

After returning, Johnson went on to the University of Toronto for his Ph.D. His goal: “discovering new knowledge that no one else has unearthed before.”

Later, through a post-doctoral fellowship at Duke University from 2007 to 2009, he began studying the ecological and evolutionary consequences of plant sexual reproduction – trying to understand how the variation in the ways in which plants reproduce can influence their ability to adapt to their parasites and evolve with them through time.

In research published in Proceedings of the National Academy of Sciences, Johnson and his colleagues discovered that sexually produced evening primrose plants withstand attacks from plant-eaters like caterpillars better than plant relatives that reproduce by themselves.

That research provides clues as to why sexual reproduction is so common, even when plants that reproduce asexually typically grow faster and out-compete sexually reproduced plants. {AUDIO 3: Hear more about Dr. Marc Johnson’s research on plant sex and its influence on plant and insect communities | or read the transcript.}

Johnson is also trying to understand how rapidly can evolution occur within natural plant populations and if the changes we see in the abundance of organisms around us from one year to the next can be due not only to factors such as environmental changes and predation but also to evolution within single plant populations.

“This is a very fast-moving, exciting new field,” Johnson says. “We still don’t know if what we are studying has general consequences in all natural and managed ecosystems, but if it does, it will have far-reaching implications. It’s now caught on in really a big way.”

-- Dee Shore