In the murky waters of a Seattle lake, a tiny fish challenges our understanding of evolution itself.
When we think of evolution, we imagine a slow, gradual process spanning millennia—dinosaurs becoming birds, early humans developing upright posture. But what if evolution could work in reverse? What if a species could rapidly revert to ancestral traits in response to environmental changes? This isn't science fiction; it's the remarkable story documented by evolutionary geneticist Catherine "Katie" Peichel and her team through studies of an unassuming little fish—the threespine stickleback.
The threespine stickleback (Gasterosteus aculeatus) might be small, but it's a superstar in evolutionary biology. These fish have diversified into countless forms across the Northern Hemisphere, particularly in their bony armor plating. Marine sticklebacks typically sport complete armor—a full suit of bony plates from head to tail—while their freshwater relatives often have reduced plating 4 .
Marine sticklebacks have full armor plating for predator protection.
Freshwater sticklebacks often have less armor for improved mobility.
This variation isn't just random; it's adaptive. Heavy armor provides protection against predators but comes at a cost of energy and mobility. When sticklebacks colonize safer freshwater environments, natural selection often favors less armor—or so biologists thought until Peichel's research revealed evolution could rapidly run in reverse .
The stage for this evolutionary drama was set not in a pristine wilderness, but in a polluted urban lake. Through the mid-20th century, Lake Washington in Seattle became increasingly polluted, with 20 million gallons of phosphorus-rich sewage pumped into its waters daily. The resulting algae blooms turned the water murky, limiting visibility to about 30 inches .
20 million gallons of sewage daily turned Lake Washington murky with only 30 inches visibility.
A $140 million cleanup effort transformed the lake, increasing visibility to 25 feet.
Improved water clarity changed predator-prey dynamics, favoring armored fish.
In this opaque environment, sticklebacks enjoyed relative protection from visual predators like cutthroat trout. With reduced predation pressure, natural selection favored the low-plated form common in freshwater populations. But then came the $140 million cleanup in the 1960s—one of the most expensive pollution-control efforts of its time .
As water clarity improved dramatically—eventually reaching 25 feet of visibility—the sticklebacks' world transformed. The very trait that had been advantageous now became a liability. Without the murky water's protection, poorly armored fish made easy targets for trout.
Peichel and colleagues tracked the sticklebacks' rapid adaptation by comparing historical data with contemporary samples. The results were stunning:
| Plate Morph | 1968 Percentage | 2000s Percentage | Change |
|---|---|---|---|
| Fully plated | 6% | 49% | +43% |
| Partially plated | Not reported | 35% | Not comparable |
| Low plated | 94% (combined) | 16% | -78% |
Table 1: Changes in Armor Plating in Lake Washington Sticklebacks (1968 vs. 2000s)
The shift was dramatic and rapid—in just 40 years (a blink of an eye in evolutionary time), the fully plated form had gone from rare to nearly half the population .
This rapid reversal was possible because of genetic variation maintained within the population. Peichel had previously identified the Eda gene as controlling armor plating during her postdoctoral work. This gene comes in two variants: one for complete plating and another for low plating .
Produces complete armor plating in marine environments.
Produces reduced armor plating in freshwater environments.
Even when the low-plated form predominated in the polluted lake, the complete-plating variant persisted in the population. When environmental conditions changed, natural selection could immediately act on this standing variation, favoring fish carrying the complete-plating variant.
"Having a lot of genetic variation in the population means that if the environment changes, there may be some gene variant that does better in that new environment than in the previous one, and so nature selects for it," Peichel explained. "Genetic variation increases the chance of overall survival of the species."
Peichel's stickleback research relies on integrating field studies with sophisticated genetic analyses. Here are key elements of their scientific toolkit:
| Tool/Material | Function in Research |
|---|---|
| Whole-genome sequencing | Identifies genetic variations associated with different traits |
| Microsatellite markers | Tracks population structure and gene flow |
| Eda gene markers | Specifically analyzes genetic variants controlling armor plating |
| Field sampling equipment | Collects fish from diverse habitats for comparison |
| Historical specimens | Provides baseline data for tracking changes over time |
Table 2: Research Reagent Solutions in Stickleback Evolutionary Genetics
Surprisingly, the Eda gene in sticklebacks has important implications for human health. In humans, mutations in this same gene cause ectodermal dysplasia, a group of more than 100 inherited disorders affecting skin, nails, hair, teeth, and sweat glands .
"There's probably a developmental correlation between these external structures in humans and the bony plates on the fish," Peichel noted. The stickleback research not only illuminates evolutionary processes but also provides insights into genetic pathways relevant to human disease .
Describes her work style as "organized"—schedules everything in iCal.
Hires good people and lets them pursue their ideas.
Recharges with running in the Swiss Alps, awake at 4 AM.
Catherine "Katie" Peichel brings a unique approach to her role as Professor at the University of Bern's Institute of Ecology and Evolution. She describes her work style as "organized"—so much so that she schedules everything in iCal, "If it's not in my iCal, I'm not going to do it." 3
Her leadership philosophy centers on empowering others: "Hire good people and then let them pursue their ideas. The best work in my lab has come from the great ideas of my postdocs and grad students." 3
When not unraveling evolutionary mysteries, Peichel recharges with long-distance running in the Swiss Alps. "Running frees my mind, and I have solved most of my scientific and personal problems while running," she shares. Her early morning routine—awake at 4 AM—helps her capitalize on when her brain works best 3 .
The Lake Washington stickleback study challenged several scientific assumptions. First, it demonstrated that reverse evolution can occur rapidly when environmental conditions change. Second, it questioned the primacy of "phenotypic plasticity"—the idea that organisms can change characteristics without genetic evolution—in explaining rapid adaptations .
Demonstrated that species can rapidly revert to ancestral traits.
Showed genetic evolution, not just plasticity, drives rapid change.
Peichel's ongoing research continues to explore how sticklebacks evolve, investigating questions of speciation and sex chromosome evolution. Her work established sticklebacks as a model for studying complex genetic traits, shedding light on genetic networks relevant to human diseases including cancer 3 .
The rapid evolutionary response documented in Lake Washington's sticklebacks offers a hopeful message in an era of environmental change. It suggests that some species may possess hidden genetic resources to adapt to changing conditions—if we preserve sufficient genetic diversity and if changes don't outpace evolutionary capacity.
As Peichel's research continues to reveal, the unassuming stickleback contains multitudes—holding secrets about evolution's past, present, and potentially, its future.