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My research interests
focus on exploring question at the interface of population, community and
evolutionary ecology. Specifically, I am interested in understanding the
causes of life-history variation both within and among species as well as
the consequences of that variation to the outcome of community interactions.
I work in a number of lakes and ponds in Illinois and Michigan, and I find
that these habitats offer a superb opportunity for the study of a diverse
array of ecological and evolutionary questions. Not only are the boundaries
of lakes and ponds clearly defined for most planktonic organisms, but
remnants of past populations in the sediment (diapausing eggs and
microfossils) represent a long-term record of both species and genetic
diversity that can be accessed at any time. Microfossils have long been
used as a way to reconstruct past plankton assemblages, but the accumulation
of viable diapausing eggs or "egg banks" offers a living link between past
and present communities.
My current and past research projects are
described below. Graduate students in my lab are encouraged to develop their
own projects (with my help) in any area of ecology or evolution that I can
adequately advise. In other words, I do not require my students to work
specifically on my projects (or even on zooplankton), but they are more than
welcome to work at one of my field sites if they are so inclined.
Undergraduate students conduct laboratory and field projects using
populations located from my study sites in both the Champaign-Urbana area
and in Michigan. If you are an undergraduate interested in gaining research
experience and earning course credit in IB 390, please send me an email (caceres@life.uiuc.edu).
 Physical limnology for the parasite ecologist
Collaborators: Meg Duffy, Spencer Hall, Marianne Huebner, Sally MacIntyre,
Alan Tessier
Much of
my research is conducted in lakes and ponds in the vicinity of Michigan
State University's
Kellogg Biological Station. In one of my
current projects project, my collaborators and I
are focusing on the ecological interaction between a common microparasitic
fungus, its Daphnia host species, and the consequences to coexisting zooplankton and their
phytoplankton prey. To address this issue, we are combining aspects of
community ecology, physical limnology and epidemiological modeling.
Epidemics of this particular parasite only occur in these Daphnia
populations during fall, and the severity of epidemics varies among
lakes. We are examining the relative importance of physical factors (such as
the basin shape and the potential for mixing) and biological interactions in
determining the observed host-parasite dynamics.
Causes
and consequences of recombination
Collaborators: Mike Lynch, Justen Andrews, Jeffrey Boore, John
Colbourne, Elizabeth Housworth, Tom Little, Curt Lively, Barrie Robison, W.
Kelley Thomas, Mimi Zolan
I am
involved in a project headed by Mike Lynch at Indiana University that uses Daphnia as a model system to investigate the long standing
question in evolutionary biology: "Why sex and recombination?" The overall
goals of the project include: (1) development of high resolution genetic and
physical maps to provide a key resource for the remainder of the project;
(2) characterization of the genetic changes underlying and resulting from
the transition from meiotic to mitotic progeny production; (3) evaluation of
whether the mutation rate is affected by an absence of meiosis; (4) study of
the fates of nonsegregating alleles locked into asexual lineages, and a test
of the hypothesis that mutation load accumulates in the absence of
recombination; (5) evaluation of the extent to which recombination increases
vs. decreases the range of variation upon which natural selection acts; and
(6) tests of the hypothesis that host-parasite evolution drives the
evolution of recombination and sex. More information about the researchers
involved as well as the overall project can be found at the
Daphnia Genomics Consortium.
For this
project, my lab continues to focus on the same populations that I have been
studying since 1999 in collaboration with Alan Tessier (see below). For 12
population of Daphnia pulicaria, we have observed differences in the
annual investment in sexual reproduction (which is also differential
investment in dormancy). Several "high sex" and "low sex" populations are
included in different aspect of the project, both in my lab and at
Indiana. At Illinois, Cindy Hartway (post-doctoral fellow) and I are
exploring how among-lake differences in the risks experienced by the females
in the water column may contribute to the observed field patterns.
Population persistence and community assembly
In Illinois, I am using recently
constructed (50-100 yrs), lakes to address questions regarding how genetic
diversity, life-history variation and interspecific interactions influence
the persistence ability of populations, and consequently, the development of
planktonic communities. Dozens of lakes in Vermilion Co., IL were formed
within the past century when strip-mining created new basins. I have
collected sediment cores that extend to the formation of eight of these
lakes and used ephippia and other microfossils to record the colonization
sequence for cladoceran zooplankton in each lake. Despite different assembly
histories, the current cladoceran assemblages are quite similar among
lakes.
Because the lakes are so
young, the many of the diapausing eggs contained throughout the core are
still viable. When these eggs are removed from the
lake and hatched in the laboratory, they provide a living link to past
populations and communities. Now that we have the assembly sequences for
multiple lakes, we are in the process of extracting viable diapausing eggs
from different points in time to determine the relative importance of within
population (e.g., genetic diversity, life-history variation) versus among
population (e.g., competition, predation) processes in determining temporal
changes in species composition.
 Diapausing eggs
and the dynamics of plankton communities
Collaborator: Alan Tessier
In
our first collaboration, Alan and I explored a potential tradeoff
between Daphnia mortality risk in the water-column and diapause
investment (males and dormant eggs). We focused on 12 lake populations
of D. pulicaria around KBS. We found large differences among
lake populations in their investment in dormancy that was related to
the ability of populations to persist through the summer.
In general, populations
that experienced predictably low abundances in the active form
exhibited higher incidence of dormancy than did populations that
persisted in high abundance year round, but there were
exceptions. Laboratory studies showed strong clonal and population
genetic differences in male and ephippial production that mirrored
differences in field populations. Dormancy duration varied among lakes
in the field (from 4% to 55% egg hatching within the first year), but
was always >80% in the lab. Results from reciprocal transplant
experiments indicated that this variation is largely the result of
lake-specific environmental cues. Our results indicate considerable
among-lake variation in the risks for both the active and dormant
forms. It is the combination of these various risks that shape the
observed patterns. In these populations, investment in dormancy is
also an investment in sex. Hence, this among-lake variation that we
observed in diapause investment is also a gradient in sex investment.
I am continuing to pursue the causes and consequences of the variation
we observed in these populations with my current funding through the
FIBR grant (see above).
In
addition, by focusing on the relatively large grazer Daphnia
pulicaria, we can investigate how dormancy in a keystone species
influences the dynamics of the rest of the planktonic community. For
the past six years, we have been assessing the significance of
dormancy vs. over-wintering strategies on the spring plankton
succession (trophic biomass & CNP stoichiometry, daphniid food
quality) and zooplankton composition.
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Aquatic nuisance species:
Effects of invasive invertebrate predators on the food webs of the Great
Lakes
Collaborators: John Dettmers, Kim Schulz, Mark Teece, Allison Witt
We are using a variety
of techniques to assess the food-web consequences of exotic zooplankton
species in the Laurentian Great Lakes. In the past 15 years, two exotic
invertebrate predators, Bythotrephes (the spiny water flea) and
Cercopagis (the fish hook flea), have invaded the Great Lakes. Like most
zooplankton, these organisms are relatively small (<1cm in length) and
pelagic but are both key components of the food web. To date, the effects of
both Bythotrephes and Cercopagis on native invertebrate
predators and on fish remain poorly understood. We are examining
experimentally the interactions between the native and exotic invertebrate
predators and their prey. We also are using a combination of traditional
stable isotope analyses, novel fatty acid analyses, and gut content analyses
to provide a quantitative estimate of the relative importance of native and
exotic invertebrate predators as energetic sources or sinks for planktonic
fish in three of the Great Lakes and Lake Champlain. Although we have
completed all the field work for this project, we are continuing with
laboratory work and analysis. |
