Meeting Abstract
The gastropod shell is well-studied due to its preservation in the fossil record and interesting logarithmic coiling shape. In contrast to the typical coiled shell, a limpet-like shell morphology (no coil, apex of the shell central or slightly anterior, large aperture) has convergently evolved many times across the vast phylogeny of gastropods. With new genetic resources and developmental tools, we are able to investigate whether limpet-like lineages use similar or divergent developmental pathways to achieve their morphology. Several studies have implicated the morphogen dpp (BMP2/4 homologue) in shell coiling. dpp correlates with the direction of coiling in a heterobranch and is symmetrically expressed around the shell-secreting tissue in two patellogastropod limpets (Shimizu et al. 2013). Shimizu and colleagues hypothesize that changes in dpp activity result in differential cell proliferation that may underlie the numerous evolutionary transitions from coiled to limpet-like shells seen across Gastropoda. We are the first to investigate and functionally test this hypothesis in a caenogastropod (a speciose lineage) by using the developmental model Crepidula fornicata, the common slipper shell. Crepidula has a flattened limpet-like shell morphology, yet it does have a coil of less than one whorl. We hypothesize that because the shell has a right-handed coil, dpp expression will be higher on the right side of shell-secreting tissues. We characterize dpp expression in Crepidula using in situ hybridization from shell gland development through metamorphosis, and report effects of knocking down dpp signaling through the inhibitor dorsomorphin. We report a preliminary assessment of the role of cell proliferation in shell shape. Shell morphology was analyzed using a micro-CT scanner and geometric morphometrics.
