Meeting Abstract

12.5  Sunday, Jan. 4  The role of Fgf8 in the origin of interdigital webbing in cetaceans COOPER, Lisa Noelle*; THEWISSEN, J.G.M.; NEOUCOM; NEOUCOM l.noelle.cooper@gmail.com

Cetaceans (whales, dolphins, and porpoises) evolved a soft-tissue flipper that encases the bony digits and generates lift during feeding maneuvers and locomotion. This flipper impedes individual digital movement and creates a smooth contour in which laminar flow of water may be maintained during locomotion. Although several studies have described embryonic development and adult variations in flipper shape, no studies have identified the genes and their associated proteins responsible for development of this structure. Utilizing bat wing membrane development as a comparison, this study aimed to identify the proteins active during flipper development by employing immunohistochemical techniques in embryos and fetuses of pantropical spotted dolphins (Stenella attenuata). Results indicate that, as in bats, dolphins exhibit fgf8 protein signals throughout the interdigital tissue. Within these tissues, fgf8 probably causes cell survival and proliferation, thereby inhibiting interdigital cell death. Based on the morphology of the metapodials and phalanges of the earliest fossil cetaceans (pakicetids), and their sister group (raoellids), it appears that these taxa possessed interdigital webbing. These fossils were recovered from sedimentary rocks indicating they inhabited freshwater streams that were rich in fine muds. Their webbing may have initially evolved as an adaptation for mud-based locomotion in the common ancestor to cetaceans and raoellids, but cetaceans later exapted the limb for aquatic locomotion by evolving a lift-generating hydrofoil.