RESEARCH INTERESTS – Ecophysiology of
Animals (especially cryobiology)
Animals
living at mid and high latitudes encounter a range of stressful conditions
during the winter. Notable
factors challenging their survival include prolonged exposure to low temperature,
reduced food availability, dehydration in some specialized habitats, and
changes in habitat structure due to the presence of snow and ice. Specific problems encountered by
animals are shaped by where they live (aquatic vs. terrestrial settings) and
how they regulate body temperature (endotherm vs. ectotherm). My research explores how ectothermic
(cold-blooded) animals cope with subfreezing body temperatures during the
course of their overwintering.
This is a common event for a number of insect species and a few
species of frog. Freeze
tolerance is an adaptation that has evolved in a number of these
animals. It presents a
fascinating set of questions regarding how they are affected by the process
of tissue ice formation and what measures do they employ to survive an event
that is quickly lethal to many other animals. Below (left) you see a gray treefrog that was frozen for
about 2 days at -3 C, causing complete loss of its major systemic functions
(e.g. blood circulation). This
frog fully regained all bodily functions within a few hours after
thawing. A similarly frozen wood
frog is seen below (right), which also fully recovered upon thawing.
Frozen Gray Treefrog
Frozen Wood Frog
Freeze-tolerant
animals must cope with a variety of stresses when ice accumulates in their
body tissues. While some body
water remains in a liquid state, the amount of ice is substantial (+50% of
body water) and blood fails to circulate around the body. This renders oxygen delivery and
waste removal impossible in the frogs.
Anaerobiosis becomes the only means for energy support in the frogs. Insects are less compromised in their
ability to support metabolism during mild freezes because their tracheal
system continues to perform some level of respiratory gas exchange. The physiological consequences of
freezing are still quite profound in all freeze-tolerant animals, and they
experience lethal injury if they freeze at abnormally low temperatures or
they freeze for excessively long periods of time.
Most
freeze-tolerant animals control the extent of tissue freezing by adding
cryoprotective chemicals to their body fluids. These chemicals are common components like glycerol (seen
in many insects) and glucose (typical for most freeze-tolerant frogs), but
they reach levels that are 12s or even 100s of times more concentrated than
seen in typical animals.
Cryoprotectant molecules render less water freezable through
colligative means and they stabilize membranes and proteins. Other measures such as the production
of needed proteins are important to their ability to survive freezing and
thawing.
Student Research Supervision
I am very open to
involvement of undergraduate students in meaningful research projects in my
laboratory. Intensive
participation in scientific research is an important part of the
undergraduate experience for biology majors. Students learn firsthand how new knowledge is gained in
the discipline. In addition,
there is the opportunity to refine skills involved in data collection,
analysis, and interpretation.
The opportunity also exists for students to present their findings at
a scientific conference or coauthor papers in scientific journals. This then renders them more
competitive for admission into postgraduate programs in science and
medicine. One or two students annually
participate in research projects in my laboratory. Past participants include Michele Cutwa, Deborah Blakely,
Christine Edgar, Michael Elnitsky, Melissa First, Ed Fuchs, Alexa Harding,
Tom Heil, Janet Huang, Amanda Johnson, Adrienne Jones, Joseph Kefauver, Kerry
Kennedy, Diane Kuharsky, Christine Leszczynski, Becki Medwith, Ben Peffer, Matt
Rice, Sarah Robich, Chris Ten Eyck, and Alecia Welsh. Most students completed projects to
the point that they became coauthors on scientific papers in such journals as
the American Journal of Physiology (Tom Heil and Melissa First), American
Midland Naturalist (Becki Medwith and Christine Edgar), Copeia (Michele Cutwa
and Joe Kefauver), Canadian Journal of Zoology (Janet Huang and Matt Rice),
Environmental Entomology (Becki Medwith, Diane Kuharsky, and Christine
Leszczynski), Journal of Experimental Zoology (Adrienne Jones, Diane
Kuharsky, and Ben Peffer), Journal of Herpetology (Michele Cutwa), Journal of
Insect Physiology (Deb Blakeley) and Physiological Entomology (Chris Ten
Eyck). Because many questions
regarding the freeze tolerance of vertebrates and insects remain to be
addressed at a variety of levels of organization, my research program will
hopefully involve interested undergraduate students well into the
future. Lystina Kabay is
presently doing an independent study on the ice nucleating action of integument
features from caterpillars of the arctiid moths Pyrrharctia isabella and Hypercompe
scribonia.
Vertebrate Cryobiology
This is my longest
running area of study in the field of cryobiology. Past studies have focused on the freeze tolerance of frogs
with regard to the triggering of ice formation, dynamics of ice accumulation,
and the effects of freezing and thawing on systemic functions. Most notably, we found that the
cardiovascular and skeletal muscle systems are profoundly influenced by
freezing and thawing, that these frogs are highly susceptible to inoculative
freezing, that individual organs differ markedly in their capabilities to
supercool, and that endogenous proteins probably do not trigger spontaneous
freezing of frogs. Through
support from the National Science Foundation, recent studies examined the
interactive effects of freeze temperature and freeze duration on energy
metabolism, systemic functions, and organismal survival. The dependence of these parameters on
cryoprotectant (glucose) levels and total energy charge are major facets of these
studies. Some earlier work was done using NMR spectroscopy to gauge the
effect of freeze episodes on organophosphate levels and intracellular pH in
collaboration with Scott Kennedy (University of Rochester). My current research is exploring two
aspects of the ecophysiology of freeze-tolerant frogs. Studies are underway to characterize
the effects of nonlethal freezing on locomotor performance in order to
quantify the recovery process with regard to the intensity of freeze treatments
(duration and temperature).
These experiments have a comparative focus in examining three species
of freeze-tolerant frog – wood frogs Rana
sylvatica, spring peepers Pseudacris
crucifer, and gray treefrogs Hyla
versicolor. The latter
species has been intriguing to study since it makes use of glycerol as the
main cryoprotectant. Moreover, H. versicolor has a highly labile
mobilization response for glycerol that includes anticipatory (prefreeze)
production of this cryoprotectant under appropriate circumstances.
Insect Cryobiology
The overwintering biology of moths in
the family Arctiidae is the key focus of my current research on insects. Very little is known about their
overwintering biology despite several species in this family overwintering in
complex life stages (larvae/pupae).
Caterpillars of the Isabella Tiger Moth (Pyrrharctia isabella), which are commonly known as woolly bears,
are ideal for this work owing to their large body size permitting integrative
studies of responses ranging from the biochemical to organismal levels. This moth has a very broad geographic
distribution extending from the U.S. Gulf Coast to Labrador in Canada, which
causes woolly bears to experience a wide range of winter conditions as a
species. Caterpillars of the
Giant Leopard Moth (Hypercompe
scribonia – previously known as
Ecpantheria scribonia) are also included in these studies since it is a
close relative of the woolly bear but its distribution does not extend nearly
as far north as does the woolly bear.
My recent studies have investigated various aspects of caterpillar cryobiology
such as the cues triggering their mobilization of cryoprotectant, their
dynamics of energy utilization at low temperature, and their limits of freeze
tolerance. I am presently
investigating the impact of freeze conditions on water/ion homeostasis, the
dynamics of ice growth at the tissue level, and the underpinnings of
tissue/cellular injury when these caterpillars reach their tolerance
limits. Ecogeographic patterns
of cold hardiness in both species are also under investigation.
Woolly bear caterpillar (Pyrrharctia
isabella)
Giant leopard moth caterpillar (Hypercompe
scribonia)
Additional studies in recent years
addressed the influence of microclimate on the ecophysiology of
gall-inhabiting insects, especially the larvae of the goldenrod gallfly (Eurosta solidaginis). Third instar larvae of this dipteran
inhabit stem galls from July through April. Because the galls are exposed to the full effects of the
weather (heat, cold, drying, etc), these larvae have developed remarkable
abilities to cope with high temperatures, freezing, and desiccation. This research documented the effects
of temperature and moisture on the growth, metabolism, and survival of these
larvae.
Research
Techniques
Calorimetry,
cryomicroscopy, physiological recordings using computer assisted data
acquisition (Powerlab system), respirometry, and spectrophotometric
biochemical assays.
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