Research Report from the Yale School Forests
Amphibian Accomplishments
vol. 1, issue 1: February 2013
Research Highlights
• While roadside conditions were detrimental to all salamanders,
roadside-adapted individuals fared 25% better than forest salamanders under roadside conditions
• Roadside and forest salamanders fared equally well under forest
conditions
• Compared populations were separated by just hundreds of yards,
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 as part of their
response to landscape development. 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
Photo © Carl Zimmer
Photo © Carl Zimmer
advantage in conditions of road runoff toxicity. 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 demonstrating that vertebrates can
adapt to roads 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
• Global environmental change 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