A
note to prospective graduate students:
I
am currently accepting new graduate students interested in topics
related to plant ecology, life history evolution, or evolutionary
ecology. The faculty and graduate students within the Ecology and
Evolution Program at UVA are a very lively and interactive group
and one of our major strengths is in plant evolutionary ecology.
Students in my lab have the opportunity to design projects either
tangentially related to my current projects or using a study system
of their own choice. Please contact me by email if you are interested
in applying.
A
note to prospective undergraduate students:
There
are opportunities in my lab for both paid undergraduate research
assistant positions and for independent study for academic credit.
Paid research assistants gain experience working on my projects
on the field, greenhouse, and in the lab. In addition to part-time
positions in the semester, I hire several full-time students for
the summer field season. I also have had several recent graduates
working full-time in my lab to gain research experience before applying
to graduate school.
Current
Research Projects:
The
projects in my lab focus on life history evolution and the limitations
of natural selection. Graduate student projects range from research
into the consequences
of selection across different life stages, to
plasticity responses across the life cycle and to factors limiting
selection at species ranges.
Click
for links to the research of current
and former lab members
I also have
a large ongoing project to study the demography of aging. Aging
can be quantified as either an increase in mortality as individuals
in a population get older, or as a decline in physiological functioning.
Humans clearly show aging but most other species do as well. For
evolutionary biologists, aging presents a paradox because it is
phenomenon that is clearly disadvantageous to individuals yet natural
selection is ineffective at removing it from populations. Several
questions then arise: First, how universal is aging? Is it found
in natural populations? Is it found in plants?; Secondly, if a species
is identified that can escape aging, what unique biological features
allow it to do so?
One major
project in my lab is a long-term investigation into the patterns
of mortality and aging in a natural plant population. We have established
a large experimental field population of Plantago lanceolata that
consists of individuals of known age and genotype. Approximately
30,000 individuals have been followed throughout their life cycle
and the age-specific patterns of mortality, reproduction, size,
growth, and disease have been measured. The oldest individuals in
this experiment are now eight-years old and recent results have
shown that older individuals have significantly higher mortality,
relative to younger cohorts, during times of stress (Roach
et al. 2009). This pattern of demographic aging, which was demonstrated
through an age-by-environment interaction, is one of only a few
examples of aging in a natural population. We have also demonstrated
age-independent mortality that depends not only on abiotic factors,
such as temperature and cumulative precipitation, but also on biotic
factors such as reproduction and size (Roach
and Gampe 2004). Current projects are quantifying the age-specific
patterns of reproduction and size and investigating the characteristics
of the oldest-old survivors in this experimental population.
We have also used Plantago lanceolata to test the adaptive benefits
of iteroparity and semelparity in this short-lived polycarpic perennial
(Shefferson
and Roach 2009). Our results showed that plants experienced
variable numbers of reproductive years, but one or two years were
most common (~46.7% of the population reproduced only once). The
probability of flowering at least once prior to death was determined
strongly by extrinsic, environmental or intrinsic but environmentally-influenced
variables, including early-life size, cohort, and block, but also
varied with a number of interactions involving paternal lineage.
The number of reproductive years contributed significantly to fitness
in this system, more so than all other variables tested, although
most of the variation in relative fitness may be attributed to ultimately
environmental influences. We suggest that the high proportion of
each cohort composed of plants reproducing only once may be due
to environmental constraints on either growth or size. Such environmental
influences, particularly on early life size, may result in small
but important indirect effects on fitness. These results are consistent
with previous work that showed that if different cohorts experience
different ecological and selective histories, then variation in
patterns of mortality and reproduction that may be due not only
to age but also to the history of individuals within the population
(Roach
2003). Relationships between traits across different life stages
must be taken into consideration if we want to understand the dynamics
of reproduction and mortality within a population.
New models
for the study of aging are critical because they can lead us to
question established theories and paradigms. This work on plant
aging has led us to recognize that there are many plant species,
and some animal species such as lobster and corals, that show indeterminate
growth, and these patterns of growth may lead to violations of critical
assumptions of the evolutionary theories of senescence. In collaboration
with colleagues from the Max Planck Institute for Demographic Research
we developed a model that showed that negative senescence may be
found in indeterminate-growth species for which size and fecundity
increase with age (Vaupel
et al. 2004).
In a more
ecological context, spatial location is critical for plants because
they cannot move. In this experiment with Plantago lanceolata, we
planted individuals in the field in a regular grid design. This
allowed us to assign a coordinate to every individual and thus to
identify its exact location relative to other plants in the population.
We are now asking questions about the scale of micro-environmental
change across our experimental field. For example, are the locations
in the field that are favorable for juvenile growth also favorable
for adult reproduction? Or, are different spatial locations better
for traits at different life stages? We also know the exact location
of the parents that we dug up from this field before we transplanted
them to the greenhouse to make the seeds for these experimental
plants. With this information we are now asking questions such as:
Do offspring located relatively close to the site from where one
of their parents was located perform better than their siblings
located farther from the parental site? In other words, is there
any evidence for local adaptation in this population of P. lanceolata?
