Quantitative measures and 3D shell models reveal interactions between bands and their position on growing snail...

Area of Science:

• * Evolutionary Biology
• * Developmental Biology
• * Malacology

Background:

• * Gastropod shells preserve ontogenetic changes in shape, color, and banding patterns.
• * Qualitative scoring limits understanding of mechanisms controlling fine variation in inherited shell characters.
• * Snail shell banding offers insights into population genetics and developmental processes.

Purpose of the Study:

• * To investigate the mechanisms controlling quantitative variation in gastropod shell banding patterns.
• * To understand how individual bands are placed and interact during shell growth.
• * To establish a quantitative method for analyzing shell shape and banding patterns.

Main Methods:

• * Empirical measurement of quantitative variation in *Cepaea* snail shells.
• * 3D modeling of shell shape and banding patterns using ShellShaper software from 2D photographs.
• * Comparative analysis of banded shells versus shells lacking specific bands.

Main Results:

• * Absence of individual bands has minor but significant impacts on the position of remaining bands.
• * Shell growth rate is uniform, except in the region below the lowermost band.
• * Wider bands in *Cepaea* are not an artifact of increased shell growth; they originate wider and grow at a similar rate.
• * 3D models derived from 2D images accurately reflect empirical measurements.

Conclusions:

• * The genetic locus controlling band presence/absence primarily acts after band positioning is established.
• * Wider bands are determined by initial width rather than differential growth rates.
• * A validated 3D modeling method is established for quantitative studies of shell banding variation, growth parameters, and morphometrics.
• * Future research linking banding phenotype to biomineralization pathways can illuminate mollusc shell diversity.