Molluscs, such as snails, mussles, oysters and squid, are a group of animals that have enjoyed incredible evolutionary success for more than 540 million years. An international team of researchers from the University of Göttingen, the University of Bourgogne and the Museum of Natural History in Paris has now proposed that one of the reasons for this evolvability lies in the modularity of the tissue that forms the molluscan shell.
Press release No. 104/2018
Evolvability through modularity – an ancient design principle
International team of researchers characterizes the genetic map of molluscan shell formation
(pug) Molluscs, such as snails, mussles, oysters and squid, are a group of animals that have enjoyed incredible evolutionary success. Since their origins in the pre-Cambrian more than 540 million years ago, they have been able to adapt to an impressive range of habitats. An international team of researchers from the University of Göttingen, the University of Bourgogne and the Museum of Natural History in Paris has now proposed that one of the reasons for this evolvability lies in the modularity of the tissue that forms the molluscan shell. The results were published in Gigascience.
In terms of numbers of species, molluscs are second only to the arthropods – insects, spiders, crabs and beetles. Over the last 540 million years, molluscs have evolved shells that display amazing variation in shape, size, pigmentation and structure from the nano- to the macro-scale. The shells of all snails, oysters and bivalves is fabricated by a complex network of genes and proteins that scientists are only beginning to understand.
The researchers first identified a suite of largely novel genes involved in shell formation in a particular species of freshwater snail. They then set about mapping where these genes were expressed within the shell-forming tissue, the mantle. The results were striking in that almost all of the genes could be categorized into one of five zones within the mantle tissue that likely determine the properties of the different layers within the shell itself.
“This modular arrangement would allow for different species of mollusc to manipulate the features of one particular shell layer, for example the outer-most pigmented layer, or the inner-most pearlescent layer, without necessarily influencing the other layers and to more efficiently respond to evolutionary pressures,” says Professor Daniel J. Jackson, leader of the study and the research group “Evolution of the Metazoa” at Göttingen University. “This kind of modularity of body parts is also seen in arthropods, and it is widely believed to be one of the reasons we have so many insects, spiders and crustaceans.”
While the general morphology of the shell-forming mantle tissue has long been known for a large number of molluscs, this is the first time a large-scale proteomic, transcriptomic and spatial expression survey of shell-forming genes has been applied to any species of mollusc. The researchers are now looking forward to working more in-depth with the results in order to understand how the moluscan shell is actually built.
Original publication: Ines Herlitze et al. Molecular modularity and asymmetry of the molluscan mantle revealed by a gene expression atlas. GigaScience 2018. Doi: 10.1093/gigascience/giy056.
Prof. Dr. Daniel J. Jackson
University of Göttingen
Faculty of Geoscience and Geography
Goldschmidtstraße 3, 37077 Göttingen
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