Meeting Abstract

128.6  Tuesday, Jan. 7 14:45  Foregut development in predatory caenogastropods: Common developmental trajectories despite changing life histories HOOKHAM, B.K.**; PAGE, L.R.; University of Victoria bhookham@uvic.ca

Caenogastropods experienced an impressive adaptive radiation, with the evolution of new feeding strategies a prominent theme. The ancestral feeding condition is herbivorous grazing, whereas the derived condition is predatory feeding with a proboscis and complex foregut, as shown by neogastropods. Previous research has looked to development to explain how the proboscis and derived foregut of predators evolved. In species with indirect development, the definitive foregut arises from an anlage of undifferentiated cells embedded within the ventral wall of the larval foregut. At metamorphosis, the larval mouth and distal foregut are destroyed, the definitive foregut takes its place, and a new mouth is formed. These developmental novelties allow for development of the adult foregut without disruption of larval feeding and ensure the adult foregut is ready for use immediately after metamorphosis. The developmental pattern observed in indirect developing species (e.g. Nassarius mendicus) suggests how predatory feeding may have evolved; however, a similar developmental pattern was not identified in a direct developing caenogastropod (Nucella lapillus). By means of histological sectioning and 3D reconstructions, I identified a larval foregut and anlage of the definitive foregut in the direct developing species Nucella lamellosa. In N. lamellosa, like the indirect developing species, the anlage gives rise to the definitive foregut and at metamorphosis the distal larval foregut is destroyed. The developmental innovation that facilitated the evolution of predatory feeding in indirect developing caenogastropods is also apparent in a direct developing species, which strongly suggests that the proboscis and complex foregut of predators evolved in a common ancestor with indirect development.