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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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