Scientists Turn Snails Into Slug-Like Creatures
ScienceDaily (Oct. 12, 2010) — Biologists have re-shaped the body design of snails. Exposure to platinum results in the formation of an internal shell instead of the normal external shell. During embryogenesis of the freshwater snail, Marisa cornuarietis, a time slot of just one or two days determines whether the animals form an outer shell or not. Reprogramming of the direction of growth of the molluscs´ shell-generating tissue during this sensitive phase prevents the development of the usual convoluted shell. In lieu thereof a small hollow cone grows inside the body -- similar to whats happens in squids.
Marisa transformed. (Credit: Heinz Köhler and Irene Gust, Universität Tübingen)
This new program has implications also for other organs: the gill is not located in a mantle cavity over the head, as usual, but rather no mantle cavity is formed at all and the gill remains at the posterior end of the visceral sac and floats freely in the water. These results which recently have been published in Evolution & Development by the group of Prof. Heinz Köhler and Prof. Rita Triebskorn from the Institute for Evolution and Ecology of Tübingen University, Germany, support the theory of 'macromutation'-based radical developmental shifts caused by modifications of signal transduction pathways which may have led to sudden body plan alterations during evolution.
+++++
Evolution & Development
Volume 12, Issue 5, pages 474–483, September/October 2010
Turning snails into slugs: induced body plan changes and formation of an internal shell
Raphaela Osterauer1, Leonie Marschner1, Oliver Betz2, Matthias Gerberding3,†, Banthita Sawasdee1, Peter Cloetens4, Nadine Haus5, Bernd Sures5, Rita Triebskorn1,6,
Heinz-R. Köhler1,*
Article first published online: 23 SEP 2010
DOI: 10.1111/j.1525-142X.2010.00433.x
Abstract
SUMMARY The archetypal body plan of conchiferan molluscs is characterized by an external calcareous shell, though internalization of shells has evolved independently in a number of molluscan clades, including gastropod families. In gastropods, the developmental process of torsion is regarded as a hallmark that is associated with a new anatomical configuration. This configuration is present in extant prosobranch gastropod species, which predominantly bear external shells. Here, we show that short-term exposure to platinum during development uncouples at least two of the processes associated with torsion of the freshwater snail Marisa cornuarietis. That is, the anus of the treated snails is located anteriorly, but the gill and the designated mantle tissue remains in a posterior location, thus preventing the formation of an external shell. In contrast to the prosobranchian archetype, platinum treatment results in the formation of a posterior gill and a cone-shaped internal shell, which persists across the lifetime. This first finding of artificially induced snail-slug conversion was also seen in the pulmonate snail Planorbarius corneus and demonstrates that selective alteration of embryonic key processes can result in fundamental changes of an existing body plan and—if altered regulation is inherited—may give rise to a new one.
+++++
Professores, pesquisadores e alunos de universidades públicas e privadas com acesso ao site CAPES/Periódicos podem ler gratuitamente este artigo da Evolution & Development e de mais 22.440 publicações científicas.
+++++
NOTA DESTE BLOGGER:
Pesquisa realmente incrível que merece a nossa atenção. Contudo, e aqui destaco, a pesquisa não tem nada a ver com a evolução. Razão? Exposição à platina durante um período crítico realmente converte a concha externa em um tipo de animal como este, e as reposições das guelras.
Os próprios pesquisadores disseram que isso não é, NOTA BENE, não é resultado de uma mutação genética, embora tenham afirmado que "regulação de gene está envolvida" ["gene regulation is involved"].
Conclusão? A experiência é um controle totalmente epigenético de um novo plano corporal. Todavia, a nova morfologia, que se espera de um fenômeno macroevolutivo, é completamente não hereditária.
Posso ver a cara de desapontamento da Galera dos meninos e meninas de Darwin...
Sobre os ombros de um gigante em biologia evolucionária...
