Zebra mussels as a model organism
Andreas Wanninger’s research interests revolve around the development and evolution of
organ systems (morphogenesis) – with a focus on neuromuscular systems in invertebrates.
The current FWF project is devoted to studying the roles of Hox and ParaHox genes in the
zebra mussel, Dreissena polypmorpha. Parallel to this effort, Dreissena will be established as
a model organism in the lab and the genome of this mollusk is currently being sequenced.
Andreas Wanninger, Head of the Department of Integrative Zoology
Professor Wanninger, what is your FWF project devoted to?
We are studying how the zebra mussel (Dreissena polymorpha) develops from the fertilized
egg to the mature adult. The investigation focuses both on key organ systems such as the
shell, musculature and nervous system as well as on the molecular level. We are specifically
focusing on those genes that are involved in determining the body axes (front-back, topbottom) and those participating in the development of the above-mentioned body
structures. Important in this respect are the so-called Hox und ParaHox genes that have
been preserved to such a degree during the course of evolution that they are present in the
vast majority of multi-cellular animals.
Data on the temporal and spatial expression of these genes are already available for
numerous organisms. Relatively little information is available on mollusks, which, among
other lesser-known groups, encompass mussels, snails and cephalopods. We do, however,
know that the Hox und ParaHox genes do not determine the body axes in cephalopods and
snails. Rather, they trigger the development of organ systems (for example the arm crown or
shells) and thus apparently assume completely different functions than they do in most
other multi-cellular organisms.
The zebra mussels are kept separately in glass containers in order to enable controlled
fertilization after spawning. © Sonia Rodriguez Monje
Studies and data on the Hox and ParaHox genes are missing entirely for mussels and clams –
a large and economically important group. Our efforts on Hox and ParaHox gene expression
in the zebra mussel is pioneering work that attempts to determine the developmental
processes in which these genes play a role.
Why have you specifically chosen zebra mussels as your study object?
Zebra mussels exhibit numerous interesting aspects, and we have initiated a range of
parallel projects devoted to studying this animal. For this purpose we have established a
working group composed, among others, of my PhD students Sonia Rodriguez Monje, who is
studying another important group of developmental genes, the Wnt genes, and André Luiz
de Oliveira, who is focusing on comparative transcriptomic analyses within the mollusks as a
whole. Other members include the postdoc Andrew Calcino who recently joined our lab and
who. One overarching goal is to establish the zebra mussel as a model organism in the lab.
Moreover, in cooperation with Thomas Rattei (Computational Life Sciences), we are
analyzing the transcriptomes of key developmental stages in zebra mussels, i.e., all the genes
that are active at a particular developmental stage of the zebra mussel. Parallel to this –
coordinated by Andrew Calcino – we are sequencing the genome of Dreissena in
cooperation with the Vienna Scientific Cluster (VSC).
The mussels are brought to the lab from their natural habitat, for example in the Danube.
© Sonia Rodriguez Monje
What approaches are you applying to study zebra mussels?
Spawning in males and females can be induced by a variety of methods, and we have been
successful to this end despite the lack of professional aquarium rooms. The subsequent
controlled fertilization of the eggs allows us to precisely date the developing embryos and
larvae, thus enabling the successive fixation of the developmental stages relevant for our
project. We are studying all developmental stages from the fertilized egg through the
various free-swimming larval stages until after metamorphosis of the animals into attached
bottom-dwellers. The aqualabs envisioned for the new Biocenter will further aid in
facilitating and streamlining this process in the future.
Veliger larva of Dreissena polymorpha. © Andrew Calcino
Zebra mussels are actually not a species native to Austria. What are the ecological and
economical repercussions of the spread of this invasive species?
That’s correct – zebra mussels were originally known from Russia and have spread via
shipping routes. They are now present almost everywhere on the European and North
American continent. Due to their massive reproductive output and their indirect lifecycle via
free-swimming larvae, the species can easily drift along waterways and rapidly establish
major populations. For example, studies from the early 1990s on the North American Great
Lakes reported massive declines in the native fish fauna. The explanation lies in the zebra
mussel’s extremely high filter-feeding efficiency: they can very quickly remove most of the
nutrients from the water column.
Moreover, the adult animals produce protein threads (so-called byssus threads) which
enable them to firmly attach to many different types of substrates. These threads, which the
bivalves can also detach, are very tear-resistant, making them a highly interesting
biomaterial with potentially high economic value. At the same time, it is precisely these
threads that enable zebra mussels to cause severe economic damage when they attach to
and block drinking water or wastewater pipes. This has major consequences, for example
when the impact involves the cooling water systems of nuclear power plants. Although we
are primarily focusing on evolutionary aspects, by decoding the genome of Dreissena and
applying all the studies we have now initiated, we hope to contribute to solving such
economical and ecological issues based on a molecular biology approach.
In the lab: Andrew Calcino, Sonia Rodriguez Monje, Andreas Wanninger
Website of the Department of Integrative Zoology:
https://zoology.univie.ac.at/people/staff/andreas-wanninger/