Meeting Abstract
Mollusc shells are a prime example of “endless forms most beautiful” and exhibit many diverse and complicated patterns. Shells are formed by the mantle, which lines the opening of the shell (aperture), secreting the necessary components for biomineralization. Great strides have been made in recent years in understanding the molecular processes involved in secreting the calcium carbonate shell. The patterns of shell shape and sculpture have been modeled extensively, but whether these models reflect the biological reality is unclear. Nothing is known about how the process of shell secretion is modified to yield different patterns of shell sculpture. Here I study: What aspects of the mantle changes to produce different shell sculpture? Nucella ostrina has plastic shell sculpture, varying from strong spiral ribs to a smooth shell. The ability to produce ribs arises from a single gene, two allele polymorphism. Examining the mantle of ribbed and smooth snails using histology, TEM, 3d reconstructions, histochemistry, and in situ hybridizations, I show that simple changes in the dimensions of the mantle epithelium correlate with ribs in the shell. Alternative hypotheses such as ultrastructural changes in the epithelium were tested and rejected. Thus shell ribbing is formed by a corrugated mantle epithelium; in a rib, the region secreting shell material is longer, producing a thicker shell than the intervening inter-rib regions, while a smooth shell has a smooth-edged, uniform mantle. These results support general conclusions from the modelling literature that relatively few parameter changes can account for many of the diverse shell shapes seen in molluscs. Furthermore this work is a first step in understanding how snails grow shell sculpture, and can be built upon to explain more elaborate and diverse forms.
