Aquatic ecologist Ross Peterson pulls a trap from Enos Lake to search for the stickleback fish but the trap only contained the invasive crayfish, in Nanoose Bay, B.C., on May 18.Rafal Gerszak/The Globe and Mail
In a small, shallow lake on Vancouver Island, tucked in a pocket of undeveloped forestland, an evolutionary superstar has attracted the attention of cancer researchers, geneticists and evolutionary biologists.
But the unique population of three-spined stickleback in Enos Lake is in trouble, threatened by an invasive species.
The story of this tiny fish of no commercial value underscores why biodiversity matters.
The United Nations has recognized that Earth’s rapid loss of biodiversity is a twin emergency to climate change. In Canada, where one in five species is deemed to be at risk, the federal government launched consultations this spring to develop a national biodiversity strategy – a step toward meeting the country’s commitments to the UN to halt and reverse biodiversity loss by 2030.
Entrance to Enos Lake, which contains invasive crayfish, in Nanoose Bay, B.C.Rafal Gerszak/The Globe and Mail
It’s believed that saltwater stickleback were stranded in a string of lakes in British Columbia less than 12,000 years ago, after the last glaciation period.
In evolutionary terms, the fish adapted at lightning speed to their freshwater environment, and at least five lakes have been found where two distinct stickleback species co-existed for thousands of years. The benthic stickleback eats small aquatic animals and insect larvae off the lake bottom, while the limnetic stickleback occupies the upper layers of the water column, consuming zooplankton.
The two species were so different that they didn’t interbreed. Until, in Enos Lake, the environment changed.
The villain in this story, biologists suspect, is the introduction of signal crayfish to the lake in the 1990s. The crayfish disrupted the aquatic vegetation, altering the ecosystem and forcing the lake’s two genetically distinct stickleback populations, found nowhere else on Earth, to merge into a single hybrid swarm.
The swift adaptation makes the fish an excellent candidate for research purposes. But the factors that make them unique – the just-right conditions that allowed them to evolve – also make them vulnerable to change. At Enos Lake, even the fate of the new hybrid species is uncertain.
An invasive crayfish pokes its eyes above the water at Enos Lake in Nanoose Bay, B.C.Rafal Gerszak/The Globe and Mail
During a recent visit, Ross Peterson, a biologist who is part of the volunteer corps monitoring the Lake and its special fish, pulled up live traps he’d set the day before. The traps were full of crayfish of all sizes – but not a single stickleback.
The crayfish “are reproducing quite well,” he said ruefully, as he watched one climb up the side of the trap, threatening to topple over the top edge. He lowered the trap so it could tumble gently back into the lake – killing it would be futile. “We tried for a summer to trap the hell out of the crayfish and we weren’t making a dent. There are tens of thousands now,” he said.
The signal crayfish was likely introduced by humans, possibly as a food source – they taste like lobster.
Katie Peichel, an evolutionary geneticist who has worked with U.S. cancer researchers on the Enos Lake stickleback, says the fish are of interest because they can rapidly change form, function and behaviour, allowing for genetic studies that can be measured in a span of years. (On average, it takes two million years for a single ancestral species to split into two new species or evolve into a secondary species.)
Dr. Peichel and her colleagues have looked to the stickleback to study complex genetic traits in order to shed light on the genetic networks at play in diseases such as cancer.
The hybrid population in Enos Lake is helpful to science, she says, but she wishes she’d had a chance to study the two separate populations before they lost their distinct characteristics. “We lost a pair of the youngest species on Earth,” she said in an interview. “These stickleback species pairs provide such a rare opportunity to observe the formation of new species in ‘real time’ and have provided us with important new insights.”
Aquatic ecologist Ross Peterson shows a trap while searching for stickleback fish.Rafal Gerszak/The Globe and Mail
Before she took up her current post as head of the Institute of Ecology and Evolution at the University of Bern, Dr. Peichel was at the Fred Hutchinson Cancer Center in Seattle, where she studied the Enos Lake hybrid population to understand the genetic architecture that underlies adaptation to different environments.
“We took advantage of this unfortunate situation to try and learn something about the genetics of divergence between the species,” she said.
At last count, Canada had 873 critically imperilled species. Some are well-known – even iconic – such as the Southern Resident killer whales. But even species that are not cute or majestic need protection.
“When many people think about biodiversity, they think of large and charismatic animals, like pandas or elephants,” Dr. Peichel noted. “But these little fish that most people don’t really think about or care about have a key role in their ecosystems, and loss of diversity in these little fish can have a big impact on the overall ecosystem.”
Officially, the species pair in Enos Lake have not been declared extinct because Canada’s species at risk registry moves slowly. The fish were listed as endangered in 2005, but at that point it was already too late. The federal status listing acknowledged as much: “Although it is possible that a small number of genetically-pure fish still exist in the lake, the ongoing presence of an invasive crayfish, and associated habitat degradation, continue to place this species at a high risk of extinction.”
In practice, they are extinct, said Dolph Schluter, whose work earned him the Crafoord Prize in biosciences – the equivalent of the Nobel prize in this field – earlier this year. The judges recognized him as one of the world’s leading authorities on ecology’s role in how species arise and diversify.
Dr. Schluter, a professor of zoology at the University of British Columbia, runs a lab that includes two rooms of fish tanks, as well as 20 outdoor ponds, devoted to three-spined stickleback – limnetic, benthic and many hybrids. Here, he was able to answer evolutionary questions first raised in Charles Darwin’s On the Origin of Species, showing how a species can develop its own unique characteristics in nature.
“The stickleback turned out to be a wonderful system for addressing those questions,” he said. The stickleback species pairs are the most interesting to evolutionary biologists, but of the five lakes where such pairs were found, only three remain. The pair in Hadley Lake on Lasqueti Island have also been wiped out by an invasive species.
Dr. Schluter plans to return to Enos Lake in September as part of a team that will take core samples from the lake bottom, hoping to trace the genetic history of the stickleback back to the time they first arrived as a marine fish trapped in fresh water.
“We’re going to look for spines and DNA from stickleback that died prior to the crayfish invasion, and weaving back through time, through the sediments down to the marine layer, to see if we can actually find stickleback bones and even stickleback DNA from those times, to give us a better picture of how the pairs formed.”
At Enos Lake, Mr. Peterson worries about the future. He sees the stickleback as a world treasure – but one that can easily be lost. He has worked to raise awareness in the local community about the need to restore the lake for its long-time inhabitants, but the competition for resources is tough. He points to a pamphlet with an endangered furry creature on the cover. “The Vancouver Island marmot gets all the attention – and why not? They are cute,” he said. The stickleback, decidedly, are not.
“But how many are we going to lose before we push the panic button?”
Justine Hunter