Meeting Abstract
The gastropod shell has evolved diverse forms and is well preserved in the fossil record, inspiring a century of research on the rules that guide shell coiling. To understand how selection has shaped the diversity of shell forms over time, we must link models of morphology to the shell’s underlying genetic basis. Shimizu et al. (EvoDevo 2013, 4:15) noted that dpp (BMP2/4 homolog) expression was enriched in the direction of shell coiling in the shell gland of pond snails, but was expressed equally around the gland in limpets, a lineage of gastropods characterized by their secondarily derived non-coiling shells. Shimizu and colleagues hypothesize that changes in dpp activity may underlie the numerous evolutionary transitions from coiled to limpet-like shells seen across Gastropoda. To test for the generality of this mechanism, dpp needs to be examined in a variety of gastropod lineages. We evaluate dpp in the developmental model system Crepidula fornicata (the common slipper shell), which belongs to Caenogastropoda, a species-rich branch of gastropods that have not yet been examined for dpp expression. Like the distantly related non-coiling limpets of Shimizu et al.’s 2013 study, Crepidula has convergently evolved a flattened limpet-like shell morphology, yet it does have a coil of less than one whorl. Due to its intermediately coiled morphology, informative phylogenetic position, and wealth of molecular tools, we decided to use Crepidula to further investigate the role of dpp in shell coiling. In this study, we characterize dpp expression using whole mount in situ hybridization from the earliest stages of shell gland development through later growth of the larval shell. Over these stages, we also characterize dpp activity using immunohistochemistry of its activated signal transducer pSMAD1/5/8. Future work will carry out functional tests and expand analysis to other gastropod lineages.
