What these flowers can teach us about adapting to a human-altered world
This article was originally featured on The Conversation.
Human impact on global ecosystems can cause irreversible, severe, and widespread damage. However, life on Earth has evolved to face environmental challenges over 3.5 billion years. Could these same evolutionary forces allow life to continue in human-altered environments where it is not endangered?
Our most recent research shows that evolution seems inexorable during a biological invader, but then suddenly stalls after a century-long period of rapid adaptation . Understanding why this happens could help us manage biodiversity in the next century.
Natural selection can be a powerful force for evolutionary change in the face of environmental challenges. Galapagos finches evolve different beak sizes to feed on changing seed sources, over-harvested cod are maturing earlier and purple loosestrife plants flower earlier in response to shorter growing seasons in northern Ontario. Evolution has its limits.
For almost 20 years, I’ve studied how some species invade and thrive in new environments. I continue to work at Queen’s University with students and collaborators to study rapid evolutionary in nature .
A key theme in this work is the interplay of natural selection and evolutionary constraint.
Adapting to new environments requires new genetic variations. Natural selection can promote genes that increase survival and reproduction. Without new variants, adaptive evolutionary will stagnate.
Constraints are the reason related species share common traits, and the reason centaurs, mermaids and dragons exist only in mythology: no genes produce hooves or fish tails in humans, nor wings in large reptiles. Evolutionary constraints are the ultimate cause for extinction by limiting the options available for natural selection.
As a counterweight for natural selection, it’s surprising evolutionary constraints aren’t being studied as intensely. However, there are experimental tools to help.
Common garden studies
It involves the cultivation of genetically related individuals in an environment that allows for genetic differences in growth, development, and reproduction. Common garden experiments with purple loosestrife in our lab reveal a delicate dance of evolutionary constraint and natural selection.
Purple loosestrife, or Lythrum salicaria, is known for its attractive purple-pink flowers in invaded wetlands across Canada and the United States. Over the span of 150 years, this one species spread from Maryland to as far north as Labrador and Saskatchewan, and south to the Gulf of Mexico and southern California.
Purple losestrife has finite resources, just like other plants. Some genes produce more plants than others, while some make plants that bloom earlier. But no genes do both. This is a genetic constraint that prevents you from flowering earlier or growing bigger to gather more resources.
Plants that have more resources can produce more flowers and are more competitive. However, extra resources can be wasted if flowers cannot be produced in the right time of the season. This is because it is too cold to allow pollinators to visit and for seed development to take place. This delicate balance allows for optimal flowering times that track changes in the length and duration of the growing season.
How did natural selection and evolutionary constraints influence the flowering time for purple loosestrife in North America? Although we can’t travel back to the past, natural history collections offer a tangible connection to the past.
Dried specimens of purple loosestrife can be found in the Fowler Herbarium at Queen’s University and in dozens other herbarium collections throughout North America. Each specimen carefully preserved is recorded with the date and location of collection.
Using historical weather records, we reconstructed the local growing conditions of each specimen to computationally predict what each plant would look like if it were grown under uniform growing conditions–a virtual common garden.
No longer constrained by viable seed collections, we would use the virtual common garden to reconstruct 150 years of evolution across North America.
The results are stunning. The results are striking. In North America, earlier flowering evolves repeatedly in response to shorter growing season. After about a century, however, the rate of evolution seems slow. This is due to a trade-off between flowering times and size. This type of evolutionary stasis can also be observed in fossil records over longer timescales. This seems to be a common feature in evolution.
Constraints can be a reason to doubt that evolution will save species in stressful environments. However, constraints make evolution more predictable, at the least for the timescales that are most relevant to human civilization.
And this is just the beginning – a single species in a multitude. How does natural selection and constraint work in the case of invasive species or species in danger of extinction? Natural history collections allow us to understand the past and make predictions about the future. It’s high time they were given the attention they deserve.
Robert I. Colautti is an Assistant Professor in Biology and Canada Research Chair (Tier 2) in Rapid Evolution at Queen’s University, Ontario. Disclosure statement: Robert I. Colautti is funded by Queen’s University, Queen’s University and three federal granting agencies, NSERC (SHRC), CIHR.
The author of 5 books, 3 of which are New York Times bestsellers. I’ve been published in more than 100 newspapers and magazines and am a frequent commentator on NPR.