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dc.contributor.authorPowell, Matthew G.en_US
dc.description.abstractPaleontological documentation of hybridization events has the potential to address a multitude of evolutionary and paleobiological issues unanswerable by purely biological means. However, previous studies of modern hybrids suggest that their morphology is often insufficient for their reliable discrimination. This study analyzes the morphology of an extant, genetically-identified Mercenaria spp. (Bivalvia: Veneridae) hybrid zone using Bookstein coordinates and multivariate methods to answer two questions: (1) can hybrid Mercenaria spp. individuals be identified based on morphology alone, and (2) would a Mercenaria spp. hybrid zone be recognizable in the fossil record?

Multivariate statistical procedures (principal components analysis, canonical variate analysis, etc.) using Bookstein coordinates demonstrate that, within the hybrid zone, hybrid individuals cannot be identified due to extreme overlap with the parental taxa. The hybrid zone as a whole, however, can be identified by comparison with pure-species populations sampled from outside the hybrid zone. Hybrid zones occupy parental species morphospace plus intermediate morphospace. The technique of using multiple pure-species populations to establish species morphospace is introduced to control for processes that may also result in morphological intermediates at ecological time scales (dimorphism, ecophenotypy, and geographic variation). Four alternative causal explanations of morphological intermediates through geological time (primary intergradation, uncoupled genetic and morphological divergence, time-averaged evolving populations, and developmentally instable populations) are evaluated. A literature survey strongly suggests that neither time-averaging nor developmental instability is occurring at the beginning of a lineageâ s evolutionary history, and that hybridization may be much more extensive than paleontological data suggest.

dc.publisherVirginia Techen_US
dc.rightsI hereby grant to Virginia Tech or its agents the right to archive and to make available my thesis or dissertation in whole or in part in the University Libraries in all forms of media, now or hereafter known. I retain all proprietary rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation.en_US
dc.subjectHybrid Zonesen_US
dc.titleMorphometric Characterization of a Mercenaria spp. (Bivalvia) Hybrid Zone: Paleontological and Evolutionary Implicationsen_US
dc.contributor.departmentGeological Sciencesen_US of Scienceen_US Polytechnic Institute and State Universityen_US
dc.contributor.committeechairKowalewski, Michalen_US
dc.contributor.committeememberBambach, Richard K.en_US
dc.contributor.committeememberTurner, Bruce J.en_US

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