Evolving Before Our Eyes
Biologist Michael Kinnison studies contemporary evolution occurring
at rates that would make Darwin dizzy
Michael Kinnison doesn't expect
sympathy from UMaine friends and colleagues when he describes the rigors
of his fieldtrips to Trinidad.
Yes, it is a tropical island paradise. Yes, he sleeps in a hammock under
the stars on verdant slopes near the Caribbean nation's north coast.
Yes, there are colorful wild parrots and giant blue butterflies and
prawn-like delicacies known as "river lobsters."
But did he mention dengue fever and mosquitoes? Fungus and foot rot?
Flooding from jungle downpours? Poisonous snakes? Scorpions?
"Everything in Trinidad seems to bite," jokes the 33-year-old assistant
professor of biological sciences. "In fact, you can get bitten by
something different every day."
Not by guppies, however, and research into Trinidadian guppies (Poecilia
reticulata) is the reason Kinnison travels regularly to the exotic
locale off the coast of Venezuela. He plans to make three fieldtrips
this year, funded by a more than $399,000, four-year National Science
Foundation (NSF) grant.
It turns out that guppies — half-inch long, brightly colored inhabitants
of jungle rivers in Trinidad — are one of the best model systems for
research in an emerging discipline known as contemporary evolution, that
is tapping the toolbox of modern genetics to cast new light on classical
Darwinian theory and the role of "microevolution" in our world today. In
so doing, they stand to rewrite our perceptions of evolution and perhaps
even conservation strategies for endangered species like the Maine
Atlantic salmon.
Brought to popular attention by the Pulitzer Prize-winning book, The
Beak of the Finch (1994), contemporary evolution postulates that natural
selection and other evolutionary processes are ongoing and observable in
real time, not just frozen in the distant past, and that remarkable
changes can occur within a decade or less in such well-documented
subjects as guppies and Galapagos finches.
"The common perception of evolution is that it's ancient history, on
long time scales. Darwin doubted it was something you could ever
directly witness," says Kinnison. "But evolutionary history is being
written every day. We're finding in these organisms with very short life
cycles in the wild that evolution is something we can really measure."
His path to the field of evolutionary biology began in his native
Rochester, N.H., where he grew up fascinated by the worlds of water and
fish. "Fly-fishing, boating, swimming — you're always trying to imagine
what's going on beneath the surface," he says. "In a way, that's what
I'm doing today in science."
Kinnison's Ph.D. research at the University of Washington was a study of
contemporary microevolution using New Zealand chinook salmon. He has
since authored or co-authored more than 25 scholarly publications.
It was his interest in aquatic ecology and cold-water fish such as
salmon, trout and Arctic char that led Kinnison to the University of
Maine in January 2002, after a two-year postdoc at Dartmouth College. He
is still involved in UMaine-based research into wild salmon conservation
and serves as a statewide representative for the Maine Atlantic Salmon
Technical Advisory Committee.
The noisy political controversy surrounding the listing in November 2000
of wild salmon in eight Maine rivers for protection under the federal
Endangered Species Act involved some of the same scientific questions
that underlie Kinnison's guppy research, such as how the intermixing of
different populations of the same species affects adaptation and
survival in a changing environment. Although there remains uncertainty
about the degree of "wildness" among Maine salmon populations because of
past stocking efforts and interbreeding, Kinnison supports the listing.
"The bottom line is whether the trait variation that exists in these
salmon today is healthy and advantageous to their survival," he says.
"We need management strategies that take this into account. Should they
be maintained as separate populations, or should some mixing be
encouraged?" He describes trait variation as differences in
characteristics, like egg and body size, and growth rate.
This microevolution of genetic trait variation is at the heart of his
guppy studies, in particular a process known as "gene flow," or simply
the exchange of genes when different populations mix. Gene flow is often
viewed as impeding adaptation of populations to different environments,
but according to Kinnison "we actually know very little from an
empirical standpoint about the degree to which gene flow really limits
most natural populations."
"It is this uncertainty that has made it so difficult to judge the
impact of historic stocking efforts in salmon or to evaluate the
implications of human impacts on gene flow in many species of concern."
And gene flow is what Kinnison is pursuing in steamy Trinidad, by
looking at the very unendangered little Poecilia that populate waterways
in a remote northern area between the towns of Arima and Blanchisseuse.
The rivers he visits have colorful names like Marianne, Yarra, Aripo and
Quare. One base camp borders the famous Asa Wright Nature Centre and is
near the Simla estate, home of the late naturalist Charles William
Beebe.
Kinnison and colleagues — including scientists from UMaine, McGill
University, University of California, and Dalhousie University — usually
hang their hammocks on the South Slope near Arima, then drive daily up
and over the Northern Range mountains to arrive at the guppies' habitat:
short, narrow rivers that plunge from the heights over a series of
"barrier" waterfalls, with lots of pools along the way for fish
colonies.
"Below the falls, you have abundant predators; above the falls, few
predators," he says. "So we find that below, guppies are less bright.
Above, you've got the full range of colors: orange, red, green, blue,
black, silver. Below, they reproduce at a younger age. Above, they
mature at a larger size and an older age."
Gene flow kicks in, he explains, when guppies from above get swept into
a lower pool. "Let's say a bright-colored male arrives down below. Maybe
the females go crazy and he passes on his genes, or maybe he gets eaten
because he's so visible," says Kinnison. "What we actually see is that,
right below the waterfall, guppies are more like the ones above, then
less and less as you get farther away. The low predation guppies thus
appear to be getting their genes into the high predation population and
we hope to measure the fitness implications of this."
Using butterfly nets — "The local men all carry machetes, so they look
at us kind of funny" — the researchers capture individual guppies to
take measurements and "snip off a bit of fin for analysis, basically DNA
fingerprinting," he says. Part of his NSF-funded research involves
artificially changing the rate of gene flow in the guppies to help
quantify its evolutionary role in contemporary time.
Past studies, including research by David Reznick of the University of
California at Riverside and by Princeton University's Peter and Rosemary
Grant, have shown that contemporary evolution can occur in guppies — and
in Galapagos finches and some other species observed in isolated
habitats — in less than a decade in response to environmental pressures
and obeying the rules of Darwinian natural selection and sexual
selection. When enough variation occurs that once-similar populations
can no longer interbreed, a new species may be born.
"Microevolutionary processes can lead to big changes at rates never
imagined in Darwin's time, that's the revelation here," Kinnison says.
In addition to the guppy project in Trinidad and the conservation
genetics work with Maine Atlantic salmon, he and his students are
assessing trait variation among a dozen "relic" populations of Arctic
char in various Maine lakes. His pride and joy is a newly constructed
"guppy lab" in the basement of Murray Hall.
Kinnison also plans to develop a Web site to complement PBS' "Sex and
the Single Guppy" Web site, a popular tool that uses guppy research to
teach evolution.
"This is exciting science that people should know about," Kinnison says.
"Evolution is not just paleontologists digging up fossils anymore."
by Luther Young
March-April, 2004
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