Dissertation Research: The Macroevolutionary Consequences of a Neogastropod Adaptation

University Of Chicago, Chicago IL

Investigators

Abstract

0073248 Jablonski and Price Although evolutionary biologists have formalized the study of adaptation, few studies explain both why a trait is adaptive and ho--w it affects a lineage's history. Graduate student Rebecca Price, assisted by her adviser Dr. David Jablonski, addresses this issue in a study of fossil and living species of a group of gastropod molluscs of the Fasciolariidae. The neogastropods are an ideal focal taxon because they have high modern diversity, permitting the use of living animals to determine the functional significance of the character in question, and a rich fossil record directly to observe morphological changes through geologic time. The hypotheses under test concern the columellar folds, or plications on a gastropod shell's aperture, that traditionally are used as taxonomic characters, and that may function as adaptations, for example in body retraction to avoid predators, or in muscle attachment to increase speed of movement. Such functional adaptations may have affected rates and patterns of species diversification in different sublineages within the Fasciolariidae (Neogastropoda: Mollusca). This family has a rich fossil record, a range of fold morphologies, and, according to a preliminary phylogeny, has lost and added folds repeatedly. The student will use computed tomography (facilities made available at Argonne National Laboratory outside Chicago) to depict in 3-dimensions and quantify a series of characters that describe columellar fold morphology in ca. 100 samples in this family. To test that columellar folds are adaptive, and to evaluate some hypothetical functions, the student will (1) map each aspect of fold morphology onto an evolutionary tree to determine when it evolved, and (2) conduct a series of functional experiments at a marine station on shells with and without folds. The experiments are designed to improve our understanding of correlations between morphology and function, with the results extrapolated back on the phylogeny to track the 130 million years of fasciolariid history in functional terms.