Research Report from the Yale School Forests
Amphibian Accomplishments
vol. 1, issue 1: February 2013
Research Highlights
• Roadside-adapted salamanders fared 25% better than forest salamanders under roadside conditions
• Roadside and forest salamanders fared equally well under forest
conditions
• Compared populations usually came from pools within a few
hundred meters of each other, indicating a high degree of adaptation over a small spatial gradient
R
esearch on woodland vertebrates at Yale-Myers Forest is
helping scientists understand the effect of human-caused
environmental pollution on species evolution. In his recent
doctoral work at Yale F&ES, biologist Steven P. Brady studied amphibian survivorship in pools near roads, contaminated
with road runoff containing salt (applied to reduce snow and
ice on roads) and chemicals like oil, gasoline and heavy metals
from the passage of vehicles. Compared to populations native
to pools deep within forests away from roads, those from roadside pools showed an intriguing difference.
Brady studied populations of two amphibian species: the
spotted salamander (Ambystoma maculatum) and the wood frog
(Rana sylvatica). To test species’ ability to adapt to changing
conditions, egg masses were collected from vernal pools deep
in the forest as well as from those along roadsides. In five years
of research Brady transplanted egg masses from roadside pools
to forested pools, and vice versa, followed by field observations
and a lab equivalent rearing the salamanders in swapped conditions. These efforts pursue two main questions: (1) what is
the effect of road adjacency on amphibians, and (2) are local
populations differentiated in their capacity to tolerate this effect
across a road proximity gradient?
In a study published in Scientific Reports last year,
Brady’s data demonstrates that spotted salamander populations showed a significantly different ability to cope with environmental stress presented by road runoff toxicity. While
all salamanders fared better overall in cleaner forest-pool conditions, individuals from roadside-adapted parents were 25%
better at coping with the toxicity in road-adjacent conditions
than those from forested pools. These findings confirm that
roadside-dwelling salamanders have some adaptation that confers a survivorship advantage in conditions of road runoff tox-
Photo credit © Carl Zimmer
Photo credit Steven Brady
icity. In some cases these eggs had come from pools only a few
hundred meters away from each other, so while the mechanism
responsible for this adaptation remains to be studied, Brady’s
research is also the first documented case that this vertebrate
evolution can happen over just a few generations and a relatively small spatial gradient.
Interestingly, the wood frog populations in Brady’s study,
though subjected to the same swaps and cross-conditioned
rearing, showed none of the same adaptation to the toxic conditions. Originating from and living in exactly the same pools
in the Yale-Myers Forest as the spotted salamanders in the
study, the wood frog populations are by contrast quite maladapted. For these animals, the inability to thrive under the
toxic influence of roads is inherited from one generation to
the next, showing none of the rapid evolutionary adaptation
demonstrated by the salamanders. As Brady writes, “That two
cohabiting species of amphibians differ so dramatically in their
responses highlights the need for precise, population-specific
approaches to understanding contemporary change. Together,
these results bring to light the fact that biological responses are
dynamic across small scales, and that both adaptive and maladaptive processes may often follow landscape alteration.”
Management Implications
• Species may evolutionarily respond to changing environmental
conditions faster than scientists had thought
• Species adaptation to change is not uniform, and can vary widely
across like species and small spatial scales
• Both adaptive and maladaptive responses may be induced following
landscape alteration
• A changing climate requires further research into differential adaptive responses of organisms
For more information:
Visit the Yale Forests page: environment.yale.edu/forests and click on Research.
EnvironmentYale coverage at environment.yale.edu/envy/stories and scroll down.
Full article citation: Brady, S. P. Road to evolution? Local adaptation to road adjacency
in an amphibian (Ambystoma maculatum). Scientific Reports. 2, 235 (2012). Available at
www.nature.com/srep/2012/120126/srep00235/full/srep00235.html