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: : publications : teaching
Schmidt Lab Web Page - http://paulschmidt.bio.upenn.edu evolutionary
ecology, ecological and evolutionary genetics My primary interest is examining the effects of variation in
the abiotic and biotic environment on the evolutionary dynamics
of specific phenotypes and genotypes in natural populations. This
research is broad in scope, incorporating methodologies from diverse
disciplines ranging from molecular and classical genetics to experimental
field ecology. Such a multidisciplinary approach can yield a more
comprehensive understanding of the interactions between genetic
and environmental variation and is readily applied to a variety
of organisms and ecological communities. Members of the laboratory
are encouraged to work in any organismal system that is well suited
to their particular interests. Currently our lab is working in
both the rocky intertidal in New England and fruit orchards along
the east coast of the U.S., “natural” habitats of the
introduced dipteran Drosophila melanogaster. environmental heterogeneity and selection in the intertidal
zone I am also investigating patterns of genetic and phenotypic variation
in four species of intertidal snail and their common introduced
predator, the green crab Carcinus maenas. As with barnacles, these
snails experience predictable variation in thermal stress and
predation intensity across various spatial scales. Furthermore,
the various snail taxa exhibit different life histories and have
distinct modes of larval dispersal, making very different predictions
regarding the genetic structure of populations and the potential
evolutionary responses to predation and thermal stress at small
vs. large spatial scales. Current and future projects in this
system include: 1) using hypervariable genetic markers to evaluate
genetic structure of crab and snail populations; 2) examining
the effects of variation in thermal stress and predation on the
distribution, abundance, and fitness of various shell phenotypes
and enzyme genotypes in the four snail species; and 3) the effects
of life history characteristics on the potential for local adaptation
to specific environmental regimes.
reproductive diapause in Drosophila melanogaster In many insect taxa, survivorship over extended and stressful
time periods is conferred by the expression of diapause (a neuroendocrine
mediated syndrome that is cued by token environmental stimuli,
causes reproductive arrest and is associated with increased longevity
and stress resistance). D. melanogaster was long believed to have
no seasonal response, but it is now known that adult females can
a) survive the winter season, b) exhibit reproductive diapause,
and c) that the expression of this dichotomous, fitness-related
trait is highly variable within and among natural populations.
The frequency of diapause incidence is strikingly clinal across
the latitudinal gradient in the eastern U.S., varying from approximately
35% in southern Florida to greater than 80% in New England populations.
Even in the absence of diapause-inducing cues, diapause and nondiapause
genotypes are phenotypically distinct for a variety of traits
including patterns of resource allocation, lipid content and starvation
resistance.
The “decision” to either diapause and postpone reproduction
or develop directly clearly has an impact on organismal fitness,
and variation for the diapause response may be of critical importance
to population dynamics and the evolution of life histories. I
am interested in examining whether diapause is a central component
of a series of traits involved in the adaptation of Drosophila
to temperate climates, and whether diapause variation reflects
a larger set of underlying pleiotropic and fitness correlated
traits associated with the same causal pathway. This series of
projects includes: 1) gathering basic ecological and natural history
data on resident D. melanogaster populations in temperate and
sub-tropical orchards as well as human-commensal populations in
urban settings; 2) using a combination of wild-caught and inbred,
laboratory evolved lines to evaluate what types of traits are
genetically correlated with both the ability to diapause (i.e.,
genotype) and the expression of diapause itself (i.e., the diapause
syndrome); 3) examining the dynamics of selection on and potential
adaptive significance of diapause in this species, using experimental
manipulations in both the field and laboratory; 4) evaluating
whether variation in diapause expression is associated with life
history tradeoffs and different patterns of resource allocation/energy
budgets; and 5) utilizing the tools of Drosophila genetics to
dissect the trait at the molecular level, evaluate the contribution
of candidate genes to phenotypic expression, and determine generalized
expression profiles of diapause and nondiapause lines under various
environmental regimes.
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