at a Snail's Pace
Zoologist studies marine snails
to answer questions about evolution
Zoology professor Elizabeth Boulding is answering
some big questions about evolution with the help of some
very tiny creatures.
For the past eight years, Boulding has been studying marine
snails native to Vancouver Island's West Coast to determine
if evolution could rescue a species from extinction, even
when that species is small in number and forced to adapt
"We wanted to investigate factors that determine whether
a population will adapt to change in the environment without
going extinct," she says. Boulding chose Littorina
subrotundata - snails that grow to be about three to
five millimetres in length - because they live in a rocky
and wave-exposed region with few predators and have smooth,
thin shells. She wanted to see if the snails would develop
thicker shells to resist predators if there was a sudden
But fooling with Mother Nature isn't easy. Boulding had
to introduce a predator and convince it to stick around
long enough to test her theory, then find a way to make
sure the snails ventured into dangerous territory.
"We simulated an invasion with purple shore crabs,"
says Boulding. Five times the size of the snails, the crabs
love to snack onthin-shelled creatures. "If the snails
have thicker shells, it makes them less preferable prey,"
she says. "We knew the snails would need to almost
double the thickness of their shells."
Boulding built "crab condos" out of cement to
give the crabs refuge, making it possible for them to live
in the wave-swept areas. "It took a few tries to come
up with the exact living conditions - very cold and wet
- that the crabs preferred."
She encouraged them to stay by ensuring their next meal
was never far away. "These are lazy crabs. They won't
leave their homes for long, so they only want to move about
two metres from their condos."
Boulding tethered snails to fishing line with waterproof
epoxy glue, making sure that some of the snails ended up
right near the crabs' "front doors."
"We tethered them at different distances so we could
make comparisons based on distance from the crab condos,"
Every May, Boulding makes the trip to Vancouver Island
to release another 90 crabs and collects the empty snail
shells, which are still attached to the fishing line. "You
can take one look at the shell fragment and tell what ate
it," she says. She brings the shells back to her Guelph
laboratory, where they are carefully measured and studied.
She also estimates snail migration between species that
have adapted to the crabs and those that have not using
molecular markers called microsatellites. The microsatellites
involve using DNA as biological tags on the snails. "High
migration from nearby populations that are not adapted to
crabs will prevent the snails from developing thicker shells,"
Based on her research, Boulding has developed a theoretical
model to help her predict whether the snails will evolve
enough to survive. This was an important step not only to
her research, but also for others in her field because the
model can be applied to any species.
"It isn't just for snails. Any time there's an invading
species, you can use this model to predict the effect on
a native species."
The model tells her that based on the findings thus far,
the snails should have increased their shell thickness enough
to survive, and more important, it should have become a
genetic trait, rather than something developed in just one
Boulding will have her first real chance to test her theory
and model predictions next summer, when she should have
a full 10 generations of snails to study and make comparisons.
"If we're lucky, we get two generations of snails
a year, and you really need 10 generations to see results."
Boulding, who joined the University of Guelph in 1993,
has published some of her findings from this project in
academic journals, including Heredity, Proceeding of
the Royal Society B, Marine Biology and the Journal
of Experimental Marine Biology and Ecology.
Her research is funded in part by a Premier's Research
Excellence Award and the Natural Sciences and Engineering
Research Council of Canada.