Rapid Evolution of
Antipredator Responses
Do Pacific Treefrog Populations Differ in Their
Response to an Introduced Predator?
David Paoletti
Advisor:
Dr. Andrew Blaustein
Loss of Biodiversity
• Declining globally across all taxa
Amphibian Population Declines
Various Factors Contribute:
• UV radiation
• Disease
• Habitat Loss
• Pollution
• Over-harvesting
Oregon Spotted Frog
• Introduced Species
Introduced Species
Many plant and animal species have
become successfully established in
foreign environments.
Himalayan Blackberry
Cane Toad
Zebra Mussel
Introduced Species
Focal Species
Brook Trout
Pacific Treefrog
(Salvelinus fontinalus)
(Hyla regilla)
Antipredator Behaviors
Most amphibian larvae rely on waterborne
chemical cues to detect a potential
threat. Upon detection, an individual may
respond in several ways:
• Camouflage
• Refuge use
• Decrease in activity
Allopatric vs.
Sympatric Populations
Frogs
Fish
ALLOPATRY
Frogs+
Fish
SYMPATRY
Allopatric vs.
Sympatric Populations
Previous studies have shown that a
population may evolve to avoid a newly
introduced predator.
• Kiesecker and Blaustein, 1997
I Thought I Smelled
Something…
HYPOTHESIS:
Allopatric treefrog populations will not exhibit
antipredator behaviors.
Sympatric treefrog populations will recognize trout
as potential predators and thus change their
behavior accordingly.
Collection
H. regilla egg masses were collected
from natural populations in the
Cascade Mountains.
One from a lake
with brook trout
(allopatric).
One from a trout-free
habitat (sympatric).
Susan’s Pond
Three Creeks Lake
Trout-free habitat
Last stocked
in 1961
Experimental Design
Allopatric
Population
Sympatric
Population
Control Group
(No chemical cue)
Control Group
(No chemical cue)
Predator
Chemical Cue
Predator
Chemical Cue
Alternate
Chemical Cue
Alternate
Chemical Cue
Methods
•
•
15 minute acclimation period
Individuals spot-checked every ten
minutes for
two hours and
any change in
position
was recorded
Methods
Observations were conducted in a laboratory
setting. Activity levels for each group were
recorded and analyzed.
Predictions
Movement
ANOVA- P<0.001 cue effect
P=0.016 pop. effect
*
•Predator cue
significantly
decreased
movement
•Tadpoles from the
allopatric
population moved
significantly less
often
Distance
ANOVA- P<0.001 cue effect
P=0.05 pop. effect
*
•Both
populations
decreased
distance traveled
in the presence of
predator cues
•Tadpoles from the
allopatric
population traveled
less distance
Predicted Results
Actual Results
Conclusions
Sympatric AND allopatric populations reduce
activity in the presence of a predator
Treefrog populations exhibit antipredator
behaviors in the presence of a perceived
threat, regardless of prior experience
Rapid Evolution?
No evidence…
•Metapopulation
•Ancestral populations previously
exposed to predator
Acknowledgements
Howard Hughes Medical Institute
and Undergraduate Research,
Innovation, Scholarship and
Creativity (URISC)
Kevin Ahern and Andy Blaustein
Blaustein Lab:
Dr. Tiffany Garcia
Betsy Bancroft Anna Jolles
John Romansic Erin Scheessele