Research Report from the Yale School Forests
Habitats, Habits and Heredity
vol. 1, issue 3: October 2013
Research Highlights
• Two ecologically-similar amphibian species distributed throughout New England show different patterns of movement and gene
flow across the same landscape
• Vernal pool amphibians of Connecticut forests show evidence of
rapid adaptation to a changing environment, suggesting the ability
to respond to gradual impacts of climate change
W
ildlife management decisions are often designed
to incorporate the ecological needs of a variety of
species, as is the case for New England’s amphibians.
Often considered among the most vulnerable of organisms, amphibians are portrayed as prone to rapid decline
in the face of changes in the environment and across the
landscape. However, recent research out of the YaleMyers Forest suggests that two of the region’s most
ubiquitous species, the spotted salamander (Ambystoma maculatum) and the wood frog (Rana sylvatica [syn.
Lithobates sylvaticus]) are neither as homogeneous nor as
slow to adapt as was thought.
In Dr. Jonathan Richardson’s doctoral research on the populations of wood frogs and spotted salamanders at the Yale-Myers Forest and across New England, he used measurements of
gene composition and flow to explore how quickly these amphibian populations adapt to environmental change and challenges. Using genetic techniques, Richardson’s work suggests
that these species respond to elements of landscape change very
differently, following divergent “circuitry” or pathways of gene
flow. In his 2012 Molecular Ecology publication, Richardson explains how landscapes can be compared to conductive surfaces,
where unsuitable habitats are assigned high costs in modeling
exercises, and are likened to surfaces that retard flows of electrical current. In these models, the “currents” hindered by these
high-cost areas are dispersal and gene flow, resulting in differential dispersal over varied landscapes.
Several landscape features were assessed for the cost
they pose to amphibian physical dispersal. Among these
were land cover, slope, wetland habitat, rivers, roads and
railroad lines. Gene flow across the region was higher
than expected for both species; however, each species
Photo by Jonathan Richardson
responded differently to these landscape characteristics,
a surprising result considering the ecological similarity
of these species. They require very similar habitat types
and exhibit similar life histories. Significant differences
were found in the degree to which each of these landscape features limits the physical dispersal of individuals
of the two species, such as salamanders’ greater avoidance of rivers or wood frogs’ higher resistance to roads.
Richardson’s findings are consistent with the hypothesis that physical limitation diminishes genetic flow
among sub-populations, which leads to greater genetic
structure but prevents the gene mixing generally needed
to adapt more rapidly to changes in the environment.
Certain life history attributes of spotted salamanders
may lead to their comparatively greater genetic structure, such as longer lifespan and higher fidelity to the
site where they were born, while wood frogs’ higher
connectivity between sub-populations leads to greater
adaptability in the face of landscape challenge or change.
Field experiments also showed that both species are able
to respond to environmental changes (e.g. changes in
canopy cover, pond temperature, predation) by rapidly
evolving to adapt to such shifts in their habitat. This
evolution can occur within several generations and in
the presence of gene flow from other populations with
dissimilar adaptations.
Management Implications
• Strategies designed to increase connections among populations need
to be tailored for individual target species to maximize impact
• Management for amphibian populations must adopt techniques to
slow rates of environmental change in order to allow for adaptation
of vernal pool amphibians
For more information: visit www.vernalpool.org or www.umaine.edu/vernalpools/
Visit the Yale School Forests page, environment.yale.edu/forests and click on Research.
Photo by Jonathan Richardson
Full article citations: Richardson, J. L. 2012. Divergent landscape effects on population connectivity in two co-occurring amphibian species. Molecular Ecology 21(18): 4437-4451.
Richardson, J. L., and M. C. Urban. 2013. Strong selection barriers explain microgeographic
adaptation in wild salamander populations. Evolution 21 (In Press).