What's Behind the Amazing Marine Mollusk Shell Patterns?

Geneticists have identified the gene group responsible with the formation of amazing and beautiful shapes and color patterns on the inner side of the shell of many marine snails referred to as 'abalone'or "ear-shell" or "limpets".

A study had revealed that the shape and color patterns on the shell of any mollusk mirror the localized expression of specific genes in the mantle, a layer of skin situated just below the shell responsible with its development.

In a new study, geneticists have detected one particular gene that causes the appearance of blue dots on the shell of the mollusk. Australian and German researchers from the University of Queensland and the Department of Geobiology at the University of G�ttingen, analyzed gene expression in the tropical abalone Haliotis asinina.

They investigated 530 randomly-selected genes active in the mantle tissue of young ear-shells (image). 331 genes encoded proteins found in the mantle structure. Bioinformatics approach revealed that only 26% (85) of these genes secreted proteins from the shell.
22 of them were analyzed for the expression patterns. Each gene was active in a specific area of the mantle, being expressed in the formation of a specific layer, shape or coloration pattern of the shell. One gene in particular, Has-sometsuke, was very important in the expression of pattern maps precisely linked to pigmentation patterns in the shell. The gene was extremely active in the area of blue dots on the shell of the abalone.

Comparing Haliotis DNA fragments with the genome of another related snail, Lottia scutum, the geneticists discovered that genes behind the secreted mantle proteins, called "secretome", might be rapidly evolving genes. "The unexpected complexity and evolvability of this secretome and the modular design of the molluscan mantle enables the diversification of shell strength and design, and as such must contribute to the variety of adaptive architectures and colors found in mollusk shells." concluded the researchers.

Photo credit: Daniel Jackson