{"id":{"repo_id":"vt","oai_identifier":"oai:vtechworks.lib.vt.edu:10919/141159"},"canonical_url":"https://search.dev.ndltd.org/etd/vt/oai:vtechworks.lib.vt.edu:10919/141159","repository":{"repo_id":"vt","name":"Virginia Tech","base_url":"https://vtechworks.lib.vt.edu/oai/request"},"display":{"title":"Evolutionary Patterns of Avian Tetrodotoxin Resistance","abstract":"Beyond Arms Races: Evolution of Tetrodotoxin-Binding Sites in Avian Naᵥ Channels Tetrodotoxin (TTX) is a potent neurotoxin that blocks voltage-gated sodium channels (Naᵥ), inhibiting nerve and muscle function. Some species possess TTX as an anti-predator defense, and some predator species have evolved resistance to TTX via evolutionary changes in Naᵥ channels. TTX resistance is well known in reptiles and amphibians, but its occurrence in birds has been relatively unexplored. Examining how Naᵥ channels have evolved in birds offers a valuable way to contrast lineages shaped by selection imposed by encountering TTX-bearing prey (such as newts) with those that evolved without such pressure and to make generalizations about molecular evolution in this gene family. This thesis explores patterns of TTX resistance across nine Naᵥ channel paralogs (SCN1A–SCN11A) in 107 bird species. Phylogenetic analyses reveal a patchy distribution of resistance across the avian tree, with multiple independent gains and losses of resistance concentrated in cardiac and peripheral nervous system channels. These patterns resemble those seen in resistant reptiles. Previous work in reptiles also suggested that a vertebrate diet may either directly or indirectly lead to the evolution of TTX resistance in some Naᵥ channels. In birds, we found that although the correlation between diet and Naᵥ resistance was not statistically significant, four-state ARD models suggested a trend toward more frequent gains of resistance in vertivorous lineages than in non-vertivores. We found that TTX resistance evolved multiple times in the avian cardiac channel gene (SCN5A), raising the question of whether Naᵥ resistance evolves as a side effect of selection of some aspect of cardiac physiology. To test this idea, we used a database of avian heart rates, in which we tested for an evolutionary association between SCN5A resistance resting heart rate. We found no significant evolutionary correlation, instead, resistance appears to arise sporadically, possibly in response to lineage-specific pressures. This work presents the first comprehensive survey of TTX resistance in birds, indicating that even in lineages with low or zero toxin exposure, sodium channel evolution can follow complex and convergent pathways. Our results show that resistance arises in scattered bird lineages, including species with little or no exposure to TTX. Bird Naᵥ paralogs contain many of the same resistance-associated substitutions seen in squamates, implying a shared evolutionary toolbox of allowable changes; in birds, these substitutions appear in a patchy, transition-rich pattern that is not easily attributable to TTX exposure, highlighting background constraints and recurrent substitutions rather than a toxin-driven arms race.","abstract_html":"Beyond Arms Races: Evolution of Tetrodotoxin-Binding Sites in Avian Naᵥ Channels Tetrodotoxin (TTX) is a potent neurotoxin that blocks voltage-gated sodium channels (Naᵥ), inhibiting nerve and muscle function. Some species possess TTX as an anti-predator defense, and some predator species have evolved resistance to TTX via evolutionary changes in Naᵥ channels. TTX resistance is well known in reptiles and amphibians, but its occurrence in birds has been relatively unexplored. Examining how Naᵥ channels have evolved in birds offers a valuable way to contrast lineages shaped by selection imposed by encountering TTX-bearing prey (such as newts) with those that evolved without such pressure and to make generalizations about molecular evolution in this gene family. This thesis explores patterns of TTX resistance across nine Naᵥ channel paralogs (SCN1A–SCN11A) in 107 bird species. Phylogenetic analyses reveal a patchy distribution of resistance across the avian tree, with multiple independent gains and losses of resistance concentrated in cardiac and peripheral nervous system channels. These patterns resemble those seen in resistant reptiles. Previous work in reptiles also suggested that a vertebrate diet may either directly or indirectly lead to the evolution of TTX resistance in some Naᵥ channels. In birds, we found that although the correlation between diet and Naᵥ resistance was not statistically significant, four-state ARD models suggested a trend toward more frequent gains of resistance in vertivorous lineages than in non-vertivores. We found that TTX resistance evolved multiple times in the avian cardiac channel gene (SCN5A), raising the question of whether Naᵥ resistance evolves as a side effect of selection of some aspect of cardiac physiology. To test this idea, we used a database of avian heart rates, in which we tested for an evolutionary association between SCN5A resistance resting heart rate. We found no significant evolutionary correlation, instead, resistance appears to arise sporadically, possibly in response to lineage-specific pressures. This work presents the first comprehensive survey of TTX resistance in birds, indicating that even in lineages with low or zero toxin exposure, sodium channel evolution can follow complex and convergent pathways. Our results show that resistance arises in scattered bird lineages, including species with little or no exposure to TTX. Bird Naᵥ paralogs contain many of the same resistance-associated substitutions seen in squamates, implying a shared evolutionary toolbox of allowable changes; in birds, these substitutions appear in a patchy, transition-rich pattern that is not easily attributable to TTX exposure, highlighting background constraints and recurrent substitutions rather than a toxin-driven arms race.","abstract_has_math":false,"creators":["Shahnam, Cyrus Alexander"],"institution":"Virginia Tech","degree_name":"Master of Science","degree_level":"masters","degree_discipline":"Biological Sciences","degree_department":"Biological Sciences","school":null,"contributors":[],"advisors":[],"committee_chairs":["McGlothlin, Joel W."],"committee_members":["Uyeda, Josef C.","Moore, Ignacio T."],"year":2026,"date_issued":"2026-02-04","date_published":"2026-02-04","updated_at":"2026-07-22T22:19:33Z","subjects":["molecular evolution","toxin resistance","tetrodotoxin","voltage-gated sodium channel"],"languages":["en"],"rights":["In Copyright"],"rights_urls":["http://rightsstatements.org/vocab/InC/1.0/"],"identifier_entries":[{"key":"dc:identifier.other","label":"Dc Identifier Other","values":["vt_gsexam:45646"],"render_values":[{"text":"vt_gsexam:45646","href":null,"code":true}]}]},"links":{"outbound_url":"https://hdl.handle.net/10919/141159","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.committeechair","label":"Committee Chair","values":["McGlothlin, Joel W."]},{"key":"dc:contributor.committeemember","label":"Committee Member","values":["Uyeda, Josef C.","Moore, Ignacio T."]},{"key":"dc:contributor.department","label":"Department","values":["Biological Sciences"]},{"key":"dc:creator","label":"Author","values":["Shahnam, Cyrus Alexander"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2026-02-05T09:00:24Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2026-02-05T09:00:24Z"]},{"key":"dc:date.issued","label":"Date","values":["2026-02-04"]},{"key":"dc:publisher","label":"Institution","values":["Virginia Tech"]},{"key":"dc:type","label":"Dc Type","values":["Thesis"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Biological 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":["molecular evolution","toxin resistance","tetrodotoxin","voltage-gated sodium channel"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language.iso","label":"Language (ISO)","values":["en"]},{"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":["vt_gsexam:45646"]},{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://hdl.handle.net/10919/141159"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Beyond Arms Races: Evolution of Tetrodotoxin-Binding Sites in Avian Naᵥ Channels Tetrodotoxin (TTX) is a potent neurotoxin that blocks voltage-gated sodium channels (Naᵥ), inhibiting nerve and muscle function. Some species possess TTX as an anti-predator defense, and some predator species have evolved resistance to TTX via evolutionary changes in Naᵥ channels. TTX resistance is well known in reptiles and amphibians, but its occurrence in birds has been relatively unexplored. Examining how Naᵥ channels have evolved in birds offers a valuable way to contrast lineages shaped by selection imposed by encountering TTX-bearing prey (such as newts) with those that evolved without such pressure and to make generalizations about molecular evolution in this gene family. This thesis explores patterns of TTX resistance across nine Naᵥ channel paralogs (SCN1A–SCN11A) in 107 bird species. Phylogenetic analyses reveal a patchy distribution of resistance across the avian tree, with multiple independent gains and losses of resistance concentrated in cardiac and peripheral nervous system channels. These patterns resemble those seen in resistant reptiles. Previous work in reptiles also suggested that a vertebrate diet may either directly or indirectly lead to the evolution of TTX resistance in some Naᵥ channels. In birds, we found that although the correlation between diet and Naᵥ resistance was not statistically significant, four-state ARD models suggested a trend toward more frequent gains of resistance in vertivorous lineages than in non-vertivores. We found that TTX resistance evolved multiple times in the avian cardiac channel gene (SCN5A), raising the question of whether Naᵥ resistance evolves as a side effect of selection of some aspect of cardiac physiology. To test this idea, we used a database of avian heart rates, in which we tested for an evolutionary association between SCN5A resistance resting heart rate. We found no significant evolutionary correlation, instead, resistance appears to arise sporadically, possibly in response to lineage-specific pressures. This work presents the first comprehensive survey of TTX resistance in birds, indicating that even in lineages with low or zero toxin exposure, sodium channel evolution can follow complex and convergent pathways. Our results show that resistance arises in scattered bird lineages, including species with little or no exposure to TTX. Bird Naᵥ paralogs contain many of the same resistance-associated substitutions seen in squamates, implying a shared evolutionary toolbox of allowable changes; in birds, these substitutions appear in a patchy, transition-rich pattern that is not easily attributable to TTX exposure, highlighting background constraints and recurrent substitutions rather than a toxin-driven arms race."]},{"key":"dc:description.abstractgeneral","label":"General Abstract","values":["Beyond Arms Races: Background Evolution of Tetrodotoxin-Binding Sites in Avian Naᵥ Channels Many animals defend themselves with powerful toxins, and a few predators have evolved ways to survive eating them. One example is tetrodotoxin (TTX), a nerve poison found in pufferfish, newts, and other animals. TTX works by blocking tiny proteins in nerve and muscle cells that control electrical signals, often leading to paralysis or death. Snakes that eat toxic newts have evolved changes in these proteins that make them resistant to TTX. It is unclear whether other groups, such as birds, show similar patterns of resistance. In this study, I examined DNA from nine related genes that control electrical signaling (voltage-gated sodium channels) in 107 species of birds. These genes are different versions of the same basic channel, active in the brain, heart, and nerves throughout the body. I combined this genetic information with an evolutionary family tree of birds, data on diet, and measurements of heart rate. Using statistical models that account for shared ancestry, I traced when and where TTX-resistant versions of these genes appeared across the bird tree. TTX resistance in birds is not limited to a single group. Instead, resistance has evolved multiple times in different lineages and in several genes, especially those active in the heart and peripheral nervous system. These changes often occur at the same positions in the protein that have evolved resistance in snakes and other vertebrates, suggesting that evolution repeatedly reuses the same molecular steps. However, resistance was only weakly related to diet and showed no clear link to heart rate in the species for which data were available. Birds show many of the same genetic changes linked to toxin resistance as reptiles, but these changes occur inconsistently and are not clearly tied to toxin exposure, suggesting they arise from shared biological constraints rather than a direct evolutionary arms race. Studying these patterns helps us understand how vertebrate electrical signaling evolves across lineages, including when strong toxin-driven selection is present versus absent."]},{"key":"dc:description.degree","label":"Dc Description Degree","values":["Master of Science"]},{"key":"dc:format.medium","label":"Dc Format Medium","values":["ETD"]},{"key":"dc:title","label":"Title","values":["Evolutionary Patterns of Avian Tetrodotoxin Resistance"]}]}],"canonical_facts":{"dc:contributor.committeechair":["McGlothlin, Joel W."],"dc:contributor.committeemember":["Uyeda, Josef C.","Moore, Ignacio T."],"dc:contributor.department":["Biological Sciences"],"dc:creator":["Shahnam, Cyrus Alexander"],"dc:date.accessioned":["2026-02-05T09:00:24Z"],"dc:date.available":["2026-02-05T09:00:24Z"],"dc:date.issued":["2026-02-04"],"dc:description.abstract":["Beyond Arms Races: Evolution of Tetrodotoxin-Binding Sites in Avian Naᵥ Channels Tetrodotoxin (TTX) is a potent neurotoxin that blocks voltage-gated sodium channels (Naᵥ), inhibiting nerve and muscle function. Some species possess TTX as an anti-predator defense, and some predator species have evolved resistance to TTX via evolutionary changes in Naᵥ channels. TTX resistance is well known in reptiles and amphibians, but its occurrence in birds has been relatively unexplored. Examining how Naᵥ channels have evolved in birds offers a valuable way to contrast lineages shaped by selection imposed by encountering TTX-bearing prey (such as newts) with those that evolved without such pressure and to make generalizations about molecular evolution in this gene family. This thesis explores patterns of TTX resistance across nine Naᵥ channel paralogs (SCN1A–SCN11A) in 107 bird species. Phylogenetic analyses reveal a patchy distribution of resistance across the avian tree, with multiple independent gains and losses of resistance concentrated in cardiac and peripheral nervous system channels. These patterns resemble those seen in resistant reptiles. Previous work in reptiles also suggested that a vertebrate diet may either directly or indirectly lead to the evolution of TTX resistance in some Naᵥ channels. In birds, we found that although the correlation between diet and Naᵥ resistance was not statistically significant, four-state ARD models suggested a trend toward more frequent gains of resistance in vertivorous lineages than in non-vertivores. We found that TTX resistance evolved multiple times in the avian cardiac channel gene (SCN5A), raising the question of whether Naᵥ resistance evolves as a side effect of selection of some aspect of cardiac physiology. To test this idea, we used a database of avian heart rates, in which we tested for an evolutionary association between SCN5A resistance resting heart rate. We found no significant evolutionary correlation, instead, resistance appears to arise sporadically, possibly in response to lineage-specific pressures. This work presents the first comprehensive survey of TTX resistance in birds, indicating that even in lineages with low or zero toxin exposure, sodium channel evolution can follow complex and convergent pathways. Our results show that resistance arises in scattered bird lineages, including species with little or no exposure to TTX. Bird Naᵥ paralogs contain many of the same resistance-associated substitutions seen in squamates, implying a shared evolutionary toolbox of allowable changes; in birds, these substitutions appear in a patchy, transition-rich pattern that is not easily attributable to TTX exposure, highlighting background constraints and recurrent substitutions rather than a toxin-driven arms race."],"dc:description.abstractgeneral":["Beyond Arms Races: Background Evolution of Tetrodotoxin-Binding Sites in Avian Naᵥ Channels Many animals defend themselves with powerful toxins, and a few predators have evolved ways to survive eating them. One example is tetrodotoxin (TTX), a nerve poison found in pufferfish, newts, and other animals. TTX works by blocking tiny proteins in nerve and muscle cells that control electrical signals, often leading to paralysis or death. Snakes that eat toxic newts have evolved changes in these proteins that make them resistant to TTX. It is unclear whether other groups, such as birds, show similar patterns of resistance. In this study, I examined DNA from nine related genes that control electrical signaling (voltage-gated sodium channels) in 107 species of birds. These genes are different versions of the same basic channel, active in the brain, heart, and nerves throughout the body. I combined this genetic information with an evolutionary family tree of birds, data on diet, and measurements of heart rate. Using statistical models that account for shared ancestry, I traced when and where TTX-resistant versions of these genes appeared across the bird tree. TTX resistance in birds is not limited to a single group. Instead, resistance has evolved multiple times in different lineages and in several genes, especially those active in the heart and peripheral nervous system. These changes often occur at the same positions in the protein that have evolved resistance in snakes and other vertebrates, suggesting that evolution repeatedly reuses the same molecular steps. However, resistance was only weakly related to diet and showed no clear link to heart rate in the species for which data were available. Birds show many of the same genetic changes linked to toxin resistance as reptiles, but these changes occur inconsistently and are not clearly tied to toxin exposure, suggesting they arise from shared biological constraints rather than a direct evolutionary arms race. Studying these patterns helps us understand how vertebrate electrical signaling evolves across lineages, including when strong toxin-driven selection is present versus absent."],"dc:description.degree":["Master of Science"],"dc:format.medium":["ETD"],"dc:identifier.other":["vt_gsexam:45646"],"dc:identifier.uri":["https://hdl.handle.net/10919/141159"],"dc:language.iso":["en"],"dc:publisher":["Virginia Tech"],"dc:rights":["In Copyright"],"dc:rights.uri":["http://rightsstatements.org/vocab/InC/1.0/"],"dc:subject":["molecular evolution","toxin resistance","tetrodotoxin","voltage-gated sodium channel"],"dc:title":["Evolutionary Patterns of Avian Tetrodotoxin Resistance"],"dc:type":["Thesis"],"thesis:degree_discipline":["Biological Sciences"],"thesis:degree_level":["masters"],"thesis:degree_name":["Master of Science"],"thesis:institution_name":["Virginia Polytechnic Institute and State University"]},"updated_at":"2026-07-22T22:19:33Z"}