Ongoing projects
in Christian Schlötterer's laboratory
Microsatellite evolution
rDNA evolution
Identification
of local selective sweeps
Drosophila melanogaster
Cattle
Molecular
Evolution of Arabidopsis thaliana
Molecular Ecology
Conservation Genetics
Measuring
introgression in Austrian trout populations
Biodiversity
in European cattle breeds
Sperm competition
Biogeography of
Quercus
robur
Biogeography of
D.
melanogaster
Isolation
and characterization of genes involved in local adaptation
Social
structure of Latimeria chalumnae
Functional Genomics
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Molecular evolution
Microsatellite evolution
Microsatellites are a special class of repetitive
DNA. They consist of tandem repeats sized between 2-6 base pairs. Their
high polymorphism, codominance and PCR based analysis has made them one
of the most popular genetic markers. Microsatellites are used in behavioral
ecology, conservation genetics, phylogenetic studies and population genetics.
The wide spread use of microsatellites is, however, not matched with a
good knowledge of their mutation processes. The observed high mutation
rates of microsatellites, which range from 10-6-10-2,
are caused by a mutation mechanism called DNA slippage, which is specific
to microsatellites. We are interested in a further characterization of
their mutational behavior. In particular, we elucidate the factors which
are influencing the mutational behavior of microsatellites. To address
this question, we use a combination of several approaches including in
vitro experiments, population studies, genome surveys and E. coli
experiments.
rDNA evolution
The phenomenon of concerted evolution of tandemly
repeated sequences, such as the rDNA, was already described several years
ago: tandemly repeated sequences have very little sequence variation within
individuals/species, but normal levels of sequence divergence between species.
Since then, very little progress has been made form the phenomenology towards
a mechanism oriented explanation of the pattern and processes of concerted
evolution. We use the internal transcribed spacer (ITS), a largely unconstrained
region, to infer the pattern and rates of concerted evolution in two species:
D.
melanogaster and Q. robur.
Identification
of local selective sweeps
Drosophila melanogaster
It is well known that natural populations adapt to their
local environments. Thus, populations in different habitats are expected
to be subject to habitat specific selection regimes. The identification
of the genetic changes underlying these adaptations will not only contribute
to our understanding of the adaptation processes in natural populations,
but also provide the essential link between ecology and genetics. It is
extremely unlikely that the adaptation processes of natural populations
can be understood in laboratory experiments. In most cases the selective
advantages of advantageous alleles will be too small to be measured in
the laboratory. Therefore, we follow a novel screening strategy to identify
genomic regions involved in local adaptation. A large whole genome scan
based on polymorphic microsatellite loci is used to identify genes involved
in local adaptation. This battery of microsatellite loci is typed in our
collection of D. melanogaster populations which cover a wide range
of different habitats.
Cattle
Like in D. melanogaster, we use a microsatellite based
genome scan to identify genomic regions subjected to selection. Domestic
cattle offer the advantage, that some breeds, such as Holstein-Friesian,
have been exposed to a strong selection for milk production traits. Thus,
most of the adaptations to be identified should be associated with milk
production traits.
Molecular
Evolution of Arabidopsis thaliana
Arabidopsis thaliana is a predominantly selfing
plant and has been chosen as the genetic model organism for plants. This
provides an almost unique opportunity to compare observed pattern of variability
with theoretical predictions for selfing organisms. In collaboration with
Marie-Theres
Hauser, we are investigating natural variation at the GLABROUS1 locus
in A. thaliana ecotypes.
Molecular Ecology
Conservation Genetics
Measuring
introgression in Austrian trout populations
Austrian trout populations have been heavily stocked over
the past 100 years. The goal of our study is to identify populations that
show the least introgression from hatchery strains. More than 15 putatively
unstocked populations are surveyed. Based on mtDNA analysis we identified
several mtDNA haplotypes that are specific to Austrian populations. However,
most populations show substantial percentages of 'Atlantic haplotypes'
which are most likely the result of stocking. Because mtDNA is a very poor
marker to determine the degree of admixture of stocked populations, we
use several microsatellites to address this question in more detail.
Biodiversity in
European cattle breeds
Europe contains a large variety of different cattle breeds.
Some of these breeds, however, may possess genetic characters which, although
not presently used in a commercial context, may become economically important
in the future. Many breeds have been reduced to small numbers by changes
in economic practice, and decisions will be necessary regarding their management.
Such decisions can be made only if the genetic relationships within and
among breed stocks are characterized. We are interested in characterizing
biodiversity of European cattle breeds. Commercially important breeds are
studied as well as rare breeds. For a good inventory of cattle biodiversity,
we use sets of tightly linked and unlinked microsatellites as well as DNA
sequencing.
Sperm competition
The sexual conflict between males and females is particularly
well studied in D. melanogaster. During mating, males have been
shown to transfer sex peptides which, among other effects, result in a
reduced lifespan of D. melanogaster females. Females have two choices
to avoid the toxic effects of the seminal fluids. Either they reduce the
number of matings, or they develop a strategy to limit the toxicity of
the seminal fluid. Using microsatellite analysis to infer the number of
paternal genotypes in the offspring of freshly collected females we infer
the number of matings under natural conditions. Because populations were
found to differ in their mating strategies, we use these differences to
study the genetics of the sexual conflict in D. melanogaster.
Biogeography
of Quercus petraea and Q. robur
Refugial differentiation and routes of postglacial migration
are among major determinants of the patterns of molecular diversity in
a wide range of species in Northern Europe. In Quercus petraea
and
Q. robur the gradual colonization of Europe has resulted in a loss
of biodiversity measured by cpDNA and allozymes. We are currently using
microsatellites to measure variability in north-European populations (Ireland)
to obtain a fine grained picture about the colonization history and population
structure in Irish oaks.
Biogeography
of D. melanogaster
Despite being genetically well analyzed, very limited
information is available about the biogeography of D. melanogaster.
We use a set of microsatellite markers distributed over the entire genome
to infer the colonization history of D. melanogaster.
Isolation
and characterization of genes involved in local adaptation
It is well known that natural populations adapt to
their local environments. Populations in different habitats are expected
to be subject to habitat specific selection regimes. The identification
of the genetic changes underlying these adaptations will not only contribute
to our understanding of the adaptation processes in natural populations,
but also provide the essential link between ecology and genetics. It is
extremely unlikely that the adaptation processes of natural populations
can be understood in laboratory experiments. In most cases the selective
advantages of advantageous alleles will be too small to be measured in
the laboratory. Thus, we follow a novel screening strategy to identify
genomic regions involved in local adaptation. A large whole genome scan
based on polymorphic microsatellite loci is used to identify genes involved
in local adaptation. This battery of microsatellite loci is typed in our
collection of D. melanogaster populations which cover a wide range
of different habitats.
Social
structure of Latimeria chalumnae
The Coelacanth is the only living representative of a fossil
lineage of crossopterygian fish. As living fossils, they hold an important
evolutionary position in the early history of tetrapods. Coelacanths inhabit
lava slopes of volcanic islands in the Western Indian Ocean in around 200
m depth. We use microsatellite analysis to characterize their population
structure and mating behavior.
Functional Genomics
In the near future, the complete genomic DNA sequence will
be available for a wide range of eukaryotic organisms. To take full advantage
of the availability to the DNA sequence, it is mandatory to have a good
understanding of the functional importance of the various DNA regions.
Currently, several approaches are pursued to infer the function of genomic
sequences. Despite the importance of this work, it should be kept in mind
that the characterization of a single sequence stretch will always provide
an incomplete picture. Only if the functional differences of naturally
occurring alleles are considered in their genomic and environmental context,
will functional genomics match its high expectations.
Building upon the current genome projects, we use population
based genome scans to identify alleles with putative functional difference
between populations. The combination of this information with other currently
pursued approaches will provide further insight into the processes of adaptation
of natural populations to their environment. Of particular interest are
adaptation processes to population specific parasites and diseases.