Die Embryonalentwicklung der Paradiesschnecke ... - TOBIAS-lib

Kapitel 1
in our experiments, a shell precursor is overgrown by ectodermal (mantle)
tissue (Kniprath, 1981; Page, 2000; Gibson, 2003). Particularly in extant
taxa of opisthobranchs, there is evidence for a stepwise reduction of the shell
(Wägele and Klussmann-Kolb, 2005) which is contradicting a hypothesis of
“macromutation”- based radical developmental shifts underlying body plan
modifications such as detorsion in these heterobranch gastropods. Nevertheless,
it is evident from our study that minimal changes in the blueprint for
molluscan ontogeny (or the corresponding signal transduction machinery of
the positional system) may lead to sudden body plan shifts. This observation
is consistent with the notion of modularity, the idea that a subset of variables
in a system may be changed independent of the remaining variables in the
system (Lipson et al., 2002) – in this case Pt leads to a drastic change during
early development to one part of the body without lethal consequences to
the whole organism.
We cannot exclude that similar, mutation-based body plan alterations
have contributed to the evolution of shell internalizations in several molluscan
taxa as we know them today.
Acknowledgements
The authors thank K.-H. Hellmer for technical assistance with the SEM, J.
Oehlmann for initially providing a M. cornuarietis stock, A. Dieterich for
help with tomography imaging, and R. Paxton and two anonymous reviewers
for critical comments on the manuscript. Studienstiftung des deutschen
Volkes and Landesgraduiertenförderung Baden-Württemberg are highly acknowledged
for financial support.
References
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