{"id":{"repo_id":"vt","oai_identifier":"oai:vtechworks.lib.vt.edu:10919/33094"},"canonical_url":"https://search.dev.ndltd.org/etd/vt/oai:vtechworks.lib.vt.edu:10919/33094","repository":{"repo_id":"vt","name":"Virginia Tech","base_url":"https://vtechworks.lib.vt.edu/oai/request"},"display":{"title":"Morphometric Characterization of a <i>Mercenaria</i> spp. (Bivalvia) Hybrid Zone: Paleontological and Evolutionary Implications","abstract":"Paleontological 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 <i>Mercenaria</i> spp. (Bivalvia: Veneridae) hybrid zone using Bookstein coordinates and multivariate methods to answer two questions: (1) can hybrid <i>Mercenaria</i> spp. individuals be identified based on morphology alone, and (2) would a <i>Mercenaria</i> 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 lineage's evolutionary history, and that hybridization may be much more extensive than paleontological data suggest.","abstract_html":"Paleontological 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 &lt;i&gt;Mercenaria&lt;/i&gt; spp. (Bivalvia: Veneridae) hybrid zone using Bookstein coordinates and multivariate methods to answer two questions: (1) can hybrid &lt;i&gt;Mercenaria&lt;/i&gt; spp. individuals be identified based on morphology alone, and (2) would a &lt;i&gt;Mercenaria&lt;/i&gt; 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 lineage&#x27;s evolutionary history, and that hybridization may be much more extensive than paleontological data suggest.","abstract_has_math":false,"creators":["Powell, Matthew G."],"institution":"Virginia Tech","degree_name":"Master of Science","degree_level":"masters","degree_discipline":"Geological Sciences","degree_department":"Geological Sciences","school":null,"contributors":[],"advisors":[],"committee_chairs":["Kowalewski, Michal"],"committee_members":["Bambach, Richard K.","Turner, Bruce J."],"year":2000,"date_issued":"2000-05-12","date_published":"2000-05-12","updated_at":"2026-07-22T22:19:27Z","subjects":["Morphometrics","Hybrids","Hybrid Zones","Paleontology"],"languages":[],"rights":["In Copyright"],"rights_urls":["http://rightsstatements.org/vocab/InC/1.0/"],"identifier_entries":[{"key":"dc:identifier.other","label":"Dc Identifier Other","values":["etd-05222000-15020012"],"render_values":[{"text":"etd-05222000-15020012","href":null,"code":true}]}]},"links":{"outbound_url":"http://hdl.handle.net/10919/33094","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.committeechair","label":"Committee Chair","values":["Kowalewski, Michal"]},{"key":"dc:contributor.committeemember","label":"Committee Member","values":["Bambach, Richard K.","Turner, Bruce J."]},{"key":"dc:contributor.department","label":"Department","values":["Geological Sciences"]},{"key":"dc:creator","label":"Author","values":["Powell, Matthew G."]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2014-03-14T20:38:01Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2014-03-14T20:38:01Z","2001-05-23"]},{"key":"dc:date.issued","label":"Date","values":["2000-05-12"]},{"key":"dc:publisher","label":"Institution","values":["Virginia Tech"]},{"key":"dc:type","label":"Dc Type","values":["Thesis"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Geological Sciences"]},{"key":"thesis:degree_level","label":"Degree Level","values":["masters"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Master of Science"]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["Virginia Polytechnic Institute and State University"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Morphometrics","Hybrids","Hybrid Zones","Paleontology"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:rights","label":"Dc Rights","values":["In Copyright"]},{"key":"dc:rights.uri","label":"Rights URI","values":["http://rightsstatements.org/vocab/InC/1.0/"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.other","label":"Dc Identifier Other","values":["etd-05222000-15020012"]},{"key":"dc:identifier.uri","label":"Identifier URI","values":["http://hdl.handle.net/10919/33094"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Paleontological 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 <i>Mercenaria</i> spp. (Bivalvia: Veneridae) hybrid zone using Bookstein coordinates and multivariate methods to answer two questions: (1) can hybrid <i>Mercenaria</i> spp. individuals be identified based on morphology alone, and (2) would a <i>Mercenaria</i> 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 lineage's evolutionary history, and that hybridization may be much more extensive than paleontological data suggest."]},{"key":"dc:description.degree","label":"Dc Description Degree","values":["Master of Science"]},{"key":"dc:title","label":"Title","values":["Morphometric Characterization of a <i>Mercenaria</i> spp. (Bivalvia) Hybrid Zone: Paleontological and Evolutionary Implications"]}]}],"canonical_facts":{"dc:contributor.committeechair":["Kowalewski, Michal"],"dc:contributor.committeemember":["Bambach, Richard K.","Turner, Bruce J."],"dc:contributor.department":["Geological Sciences"],"dc:creator":["Powell, Matthew G."],"dc:date.accessioned":["2014-03-14T20:38:01Z"],"dc:date.available":["2014-03-14T20:38:01Z","2001-05-23"],"dc:date.issued":["2000-05-12"],"dc:description.abstract":["Paleontological 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 <i>Mercenaria</i> spp. (Bivalvia: Veneridae) hybrid zone using Bookstein coordinates and multivariate methods to answer two questions: (1) can hybrid <i>Mercenaria</i> spp. individuals be identified based on morphology alone, and (2) would a <i>Mercenaria</i> 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 lineage's evolutionary history, and that hybridization may be much more extensive than paleontological data suggest."],"dc:description.degree":["Master of Science"],"dc:identifier.other":["etd-05222000-15020012"],"dc:identifier.uri":["http://hdl.handle.net/10919/33094"],"dc:publisher":["Virginia Tech"],"dc:rights":["In Copyright"],"dc:rights.uri":["http://rightsstatements.org/vocab/InC/1.0/"],"dc:subject":["Morphometrics","Hybrids","Hybrid Zones","Paleontology"],"dc:title":["Morphometric Characterization of a <i>Mercenaria</i> spp. (Bivalvia) Hybrid Zone: Paleontological and Evolutionary Implications"],"dc:type":["Thesis"],"thesis:degree_discipline":["Geological Sciences"],"thesis:degree_level":["masters"],"thesis:degree_name":["Master of Science"],"thesis:institution_name":["Virginia Polytechnic Institute and State University"]},"updated_at":"2026-07-22T22:19:27Z"}