Completing Darwin's work on evolution by unlocking the mysteries of how natural selection drives the origin of new species.
"The diversity of life is the most astonishing thing to happen in the universe since the Big Bang, and we need to understand it better if we hope to preserve it."
Dolph Schluter stands atop the craggy outpost of a twenty-metre high clifftop, his gaze intently focused on the waves below him. From his vantage point, he can see the fishing boat that has come to take him off Los Hermanos, a remote island in the Galapagos archipelago. But it's not much use. The seas are too rough and the steep shoreline of the jagged volcanic rock would smash to pieces any boat that attempted to dock.
Behind him, two of his colleagues are frantically packing data books — their most precious cargo — into airtight plastic bags. Everyone is hungry. They've run out of food, and after one failed attempt to get off the island the day before, they can't afford to wait any longer.
Days earlier, Schluter, his fellow PhD student Trevor Price, and their field assistant Steven "Spike" Millington came to Los Hermanos to study small, brown birds called finches. Upon landing, Schluter and Price swam ashore when a huge surge of water picked them up and knocked them flat on their backs. Price walked away with a few nicks and scratches, still with his rope in hand, but the wave dragged Schluter along the barnacle-covered shore, scraping up his back pretty badly. He still has the scars to prove it.
Even with his banged-up back, Schluter knew he had a job to do. He and Price scrambled to the clifftop, high above a small rocky ledge at the water's edge below. Price handed the rope to Schluter, offered a little nod, and leapt into the waters below. From the ledge, Price unpacked the boat and tied up all the equipment they would need, including mist nets, data books, binoculars, and even a do-it-yourself surgery guide in case of an emergency, such as a ruptured appendix. Along with the gear, was several days' worth of food rations: tinned wieners, crackers, tea bags, drinking water, and a box of eggs. Schluter hauled this all onto the island even though his back was in a terrible state--and he didn't break any of the eggs.
Now, after a successful period of research on the island, Schluter stares down at the choppy seas. The memory of that painful landing is fresh in his mind, and the healing wounds sting in the salty air as he gauges how he'll get down off the cliff. The scratching sounds of the calling finches ring in his ear, and he's concentrating feverishly. Price, however, has no time for calculated thought. He takes a running start and throws himself off the cliff once more, plunging with a splash into the white-capped waves below. "Trevor is a maniac," Schluter mutters to himself.
Schluter and Millington quickly lower all the equipment and the invaluable data logs down from the cliff, but by now the small ledge is awash. Price dangles the data books and binoculars on the ends of bamboo mist net poles, and extends them as far as he can, just managing to reach the waiting arms of the boat's hired fishermen. All the other gear, though, Price tosses as far as he can, and the fishermen scramble frantically to bring it all aboard. Everything is soaked; everything that is, except for the data books, thankfully. Now, with all the equipment aboard the boat, not much remains: just Schluter and Millington.
"Do you want to jump first or shall I?" asks Schluter, with a slight tremble in his voice.
"I can't jump," whispers Millington. "I don't know how to swim."
"There might be no other choice," says Schluter, resignedly.
If he has to jump, Millington doesn't want to break his glasses. So he hands them to Schluter, who ties them up, eases them down towards Price below, and then tosses the rope as well. Millington, however, is now in no state to jump. Schluter realizes he's going to need the rope again to help Millington descend from the cliff, and he yells to Price to swim ashore once more. No small feat in the turbulent seas, but the daredevil Price doesn't bat an eyelash at the idea. With the rope once again in hand, Schluter ties up Millington, and, together with Price, they lower their half-blind field assistant down to the awaiting boat below. Now, only Schluter and Price are left on the island.
"Last one in the water is a rotten egg," shouts Price, as he hurls his body off the cliff for a third time. From the waters below, he then starts taunting Schluter, the lone remnant of human life on Los Hermanos, to jump. Schluter is nervous. All the fishermen below are waiting for him, watching, and they're growing impatient to leave the dangerous, choppy waters of the island's edge.
Not wanting to be outdone by Price, Schluter tightens his body, stretches out his arms, and dives head first, breaching the turbulent seas with barely a splash.
Dolph Schluter grew up in Dorval, in the southwestern part of the island of Montreal. His parents immigrated to Canada from the Netherlands, though he says his roots are a mixture of Dutch with German, French, and English. Even as a young child, Schluter was keen to study animals. He remembers summers spent camping in northern Vermont where he would stalk the long grasses trying to catch jumping mice. His very first "experiment" was to set up a baited box with a piece of string to trap birds, "just to get up close and be able to watch them," he says.
In his teen years, Schluter maintained a small beetle collection, and was a keen birdwatcher. At school, Schluter collected leftover rat skeletons from his biology classes and repeatedly dissected and reassembled them to understand how all the bones fit together. He even saved up enough pocket money running a paper route to buy a small fishing boat, and he spent the summers of his youth fishing on Lac St-Louis off the west coast of Montreal.
Schluter could read before he was old enough to start kindergarten, so it was always assumed that he would go to university, even though no one in his family had ever done so. Because of his interest in animals, he decided to attend Guelph University, as it had the best veterinary school in the country. At Guelph, however, he became more interested in his natural history and biology classes, and quickly switched his degree to wildlife management.
To fund his studies, Schluter spent his summers working for his undergraduate mentor, Ron Brooks, a wildlife biologist who studied snapping turtles in Algonquin Park. After graduating in 1977, Schluter had a job lined up to survey mammals in the Albertan Athabasca tar-sands. He was all ready to go, but just before leaving Guelph he went to a talk given by Bob Montgomerie, now a professor at Queen's University, about the foraging behaviour of hummingbirds. "I was blown away," he says. "I was fascinated by the idea of really working on big ideas, rather just studying the basic biology of a species."
He abandoned his surveying job, and began graduate studies with Peter Grant at the University of Michigan, Ann Arbor. His PhD research involved studying the Galapagos finches to understand how competition for food shapes the evolution of beak size differences between finch species. After graduating in 1983, Schluter held short post-doctoral positions, first at the University of California, Davis, and then at the University of British Columbia (UBC). Ever since, he's worked as a professor of zoology at UBC, and now holds a Canada Research Chair and is a Fellow of the Royal Societies of London and Canada.
In 2005, Schluter spearheaded the construction of a new Biodiversity Research Centre at UBC, where he served as director until 2007. The centre supports more than 50 researchers and houses a public museum dedicated to the study of biodiversity.
Writer: Elie Dolgin
When Charles Darwin stepped ashore on the Galapagos Islands in 1835, he encountered a group of small, brown birds called finches. He didn't think much of the birds at the time, but back in his office in London, as his ideas about evolution were taking shape, Darwin realized that the finches he had collected were all related to each other yet differed in their beak size and overall shape. Writing in his memoir, The Voyage of the Beagle, he speculated on how that could have happened, noting: "One might really fancy that, from an original paucity of birds in this archipelago, one species had been taken and modified for different ends."
Darwin was on to something.
Darwin "was remarkably insightful, but he was never able to test any of his ideas" about natural selection and the origin of species, says Schluter. So, as a PhD student Schluter did just that. In the late 1970s, he followed in Darwin's footsteps to the Galapagos Islands to test how and why different species of finches became modified for different ends.
The process by which one species gives rise to multiple species exploiting different niches is now known as adaptive radiation, as opposed to other more common patterns of evolution in which a single species changes through time without splitting into many forms. In the case of the finches — which earned the nickname "Darwin's finches" — a single species from mainland South America migrated to the rocky Galapagos, where it diversified into 14 species with distinctive beaks specialized for different diets on different islands: seeds, insects, flowers, and even seabird blood.
Much of Schluter's early work focused on what happens when two ecologically similar species compete for resources. A common outcome of this clash is that the two species evolve to be more different and occupy different niches when they co-exist than when they live alone. Schluter demonstrated this phenomenon, known as "character displacement," in two seed-eating species of Darwin's finches: the small ground finch, Geospiza fuliginosa, and the medium ground finch, G. fortis.
Schluter discovered that on islands where only one species was found, the finches' beaks were fairly similar and intermediate in size. But on the island of Santa Cruz where both species overlapped, the smaller ground finches had smaller beaks and the medium ground finches had larger beaks. Character displacement is now recognized as a universal feature of adaptation, and is known to occur in a wide range of organisms including birds, fish, mammals, reptiles, insects, and plants.
Schluter also helped resolve how the 14 different Darwin's finch species are related to each other. He compared aspects of the birds' body shapes and showed that the oldest species are all insect-feeders, whereas the youngest ones dine on seeds. Because the mainland ancestor of all the Galapagos finches was a seed-eater though, Schluter could show that ancient seed-eating birds must have gone extinct, but that the diet re-evolved on the islands where seeds were abundant.
Adaptive radiation is only part of the puzzle of how species are formed. To maintain separate species once organisms begin to diverge, ecologically distinct forms must choose not to mate with one another, or if they do mate, their DNA must be different enough that hybrid offspring are sick or sterile. This "reproductive isolation" is the hallmark of speciation. According to Schluter, how this occurs in nature is one of the deepest questions in biology. And yet, it is one for which he has made considerable inroads.
"When I took [Schluter] on as a graduate student I had no doubt he had exceptional potential," says Schluter's former mentor, Peter Grant, an evolutionary biologist at Princeton University. "[Schluter] is talented in several ways. First, he has a knack of going to the heart of a problem, and bringing considerable quantitative skills to bear on its solution. Second, he is imaginative, infectiously enthusiastic, and an excellent communicator."
Darwin's finches were a good system to study speciation in action. But Schluter wanted an organism that he could manipulate experimentally to test many of his outstanding questions. So when Schluter started up his own lab at UBC, he swapped to studying a group of fish called three-spined sticklebacks. "I started working on the sticklebacks," he says, "so I could start to address these questions in a system in which experiments were possible." It also didn't hurt that the fish lived a bit closer to home — the sticklebacks Schluter studies are found in the lakes and coastal waters of British Columbia.
A single marine type of stickleback occurs in the salty Pacific waters, but in a few freshwater BC lakes, the 5-cm sticklebacks are found in two different forms, known as benthic and limnetic. The benthics are short-bodied, wide-mouthed, poorly armoured fish that feed on insects at the shallow lake margins; the limnetics, on the other hand, are slender-bodied, narrow-mouthed, well-armoured, open lake predators of zooplankton. In the lab, the two forms can mate, but they remain genetically distinct in the wild because their behaviours are so different that they rarely interbreed.
One of the "most glorious features" of sticklebacks for understanding speciation, says Schluter, is that the two forms have independently arisen four times in inland lakes in BC in a period spanning just 10,000 years. "What hits you over the head when you look at these things is just how similar are the events in which two ecologically differentiated species have formed," he says. "In each case, virtually the same series of adaptations is present."
Schluter has taken the different benthic and limnetic forms back to his lab to show experimentally that reproductive isolation also evolves repeatedly. Although he found that benthic and limnetic sticklebacks usually refused to mate together, two benthics or two limnetics that evolved in complete isolation in different lakes were compatible and content breeders. "Repeatedly we see the same mechanism of reproductive isolation evolve in lock step with adaptation to their environment," says Schluter.
How do the fish repeatedly evolve the same adaptations? "Natural selection is the only process that can do that," he says.
Adaptive radiation in beak size and shape in the Darwin's finches. Hereditary relations between the different kinds of finches are determined by DNA markers in the genes. Diets are indicated by shading as follows: seeds (black), insects (white) and vegetation (shaded). The pie at the centre provides an estimate of the diet of the last common ancestor of all species with the area of portions giving relative support for the three diet states.
How can the ordinary processes of natural selection and genetic fluctuations through time result in reproductive isolation, such that animals cannot mate or have only sterile offspring? Schluter says: "We know the process of natural selection is involved but not how it accomplishes what it does. What genes do it? Are mating incompatibilities an incidental byproduct of changed body size?"
Schluter, D. The ecology of adaptive radiation. Oxford University Press, Oxford, UK, 2000.
Grant, P. R., and B. R. Grant. How and why species multiply: The radiation of Darwin's finches. Princeton University Press, 2007.
--Writer: Elie Dolgin
According to Schluter you need a passion for natural history to get a career in evolutionary biology, but there are plenty of jobs. Examples include environmental monitoring, consulting, and professions such as veterinary medicine. He also suggests careers in physiology, medicine, laboratory technical jobs, and the many career possibilities in third world development projects involving animals and people.
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