Has physical isolation resulted in genetically and phenotypically distinct watersnake and gartersnake populations on remote Lake Ontario islands?. Augustine, A. Ph.D. Thesis, February, 2026. ![Has physical isolation resulted in genetically and phenotypically distinct watersnake and gartersnake populations on remote Lake Ontario islands? [link]](https://bibbase.org/img/filetypes/link.svg "link")
Paper abstract bibtex Intraspecific divergence and speciation on remote marine islands are widely known. However, the processes that underly diversification on islands can occur at fine geographic scales as well, such as in islands in freshwater lakes. Dispersal-restricted organisms, such as snakes, inhabit islands throughout the North American Great Lakes, some of which are isolated from mainland populations by many kilometres of open water. I sought to test whether populations of northern water snake (Nerodia sipedon sipedon) and eastern garter snake (Thamnophis sirtalis sirtalis) on two small islands in eastern Lake Ontario ~12 km from the nearest mainland—Main Duck and Yorkshire Islands—are genetically and phenotypically distinct from mainland conspecifics. To assess island-mainland genetic divergence, I used genome-wide panels of single nucleotide polymorphism markers (SNPs) derived from reduced-representation sequencing. I also tested for differences in head morphology and body size among watersnake populations. My results show that insular populations of both species are indeed genetically distinct from their mainland counterparts, but that there are differences in overall genetic structure between the two species around eastern Lake Ontario, possibly related to differences in dispersal ecology and demographic history. In watersnakes, patterns of genetic differentiation appear to be largely related to the water currents of eastern Lake Ontario. In gartersnakes, island-mainland differentiation is more subtle, with a potential contact zone between more deeply diverged lineages southeast of the outlet of Lake Ontario into the St. Lawrence River. I did not find differences in head morphology independent of body size in watersnakes, but did find differences in snout-vent length (SVL) among island and mainland populations. Aside from yielding insights on the origins of snake populations endemic to small islands in the North American Great Lakes, my findings may be useful to conservation agencies, as they may decide to manage the island populations as distinct population segments, especially if future work demonstrates that these insular populations possess unique evolutionary histories or unique adaptive traits.
@phdthesis{augustine_has_2026,
title = {Has physical isolation resulted in genetically and phenotypically distinct watersnake and gartersnake populations on remote {Lake} {Ontario} islands?},
url = {https://hdl.handle.net/1974/36037},
abstract = {Intraspecific divergence and speciation on remote marine islands are widely known. However, the processes that underly diversification on islands can occur at fine geographic scales as well, such as in islands in freshwater lakes. Dispersal-restricted organisms, such as snakes, inhabit islands throughout the North American Great Lakes, some of which are isolated from mainland populations by many kilometres of open water. I sought to test whether populations of northern water snake (Nerodia sipedon sipedon) and eastern garter snake (Thamnophis sirtalis sirtalis) on two small islands in eastern Lake Ontario {\textasciitilde}12 km from the nearest mainland—Main Duck and Yorkshire Islands—are genetically and phenotypically distinct from mainland conspecifics. To assess island-mainland genetic divergence, I used genome-wide panels of single nucleotide polymorphism markers (SNPs) derived from reduced-representation sequencing. I also tested for differences in head morphology and body size among watersnake populations. My results show that insular populations of both species are indeed genetically distinct from their mainland counterparts, but that there are differences in overall genetic structure between the two species around eastern Lake Ontario, possibly related to differences in dispersal ecology and demographic history. In watersnakes, patterns of genetic differentiation appear to be largely related to the water currents of eastern Lake Ontario. In gartersnakes, island-mainland differentiation is more subtle, with a potential contact zone between more deeply diverged lineages southeast of the outlet of Lake Ontario into the St. Lawrence River. I did not find differences in head morphology independent of body size in watersnakes, but did find differences in snout-vent length (SVL) among island and mainland populations. Aside from yielding insights on the origins of snake populations endemic to small islands in the North American Great Lakes, my findings may be useful to conservation agencies, as they may decide to manage the island populations as distinct population segments, especially if future work demonstrates that these insular populations possess unique evolutionary histories or unique adaptive traits.},
language = {eng},
urldate = {2026-06-01},
author = {Augustine, Arjun},
month = feb,
year = {2026},
keywords = {Terrestrial Ecoregions (Wiken 2011)},
}
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I sought to test whether populations of northern water snake (Nerodia sipedon sipedon) and eastern garter snake (Thamnophis sirtalis sirtalis) on two small islands in eastern Lake Ontario ~12 km from the nearest mainland—Main Duck and Yorkshire Islands—are genetically and phenotypically distinct from mainland conspecifics. To assess island-mainland genetic divergence, I used genome-wide panels of single nucleotide polymorphism markers (SNPs) derived from reduced-representation sequencing. I also tested for differences in head morphology and body size among watersnake populations. My results show that insular populations of both species are indeed genetically distinct from their mainland counterparts, but that there are differences in overall genetic structure between the two species around eastern Lake Ontario, possibly related to differences in dispersal ecology and demographic history. In watersnakes, patterns of genetic differentiation appear to be largely related to the water currents of eastern Lake Ontario. In gartersnakes, island-mainland differentiation is more subtle, with a potential contact zone between more deeply diverged lineages southeast of the outlet of Lake Ontario into the St. Lawrence River. I did not find differences in head morphology independent of body size in watersnakes, but did find differences in snout-vent length (SVL) among island and mainland populations. Aside from yielding insights on the origins of snake populations endemic to small islands in the North American Great Lakes, my findings may be useful to conservation agencies, as they may decide to manage the island populations as distinct population segments, especially if future work demonstrates that these insular populations possess unique evolutionary histories or unique adaptive traits.","language":"eng","urldate":"2026-06-01","author":[{"propositions":[],"lastnames":["Augustine"],"firstnames":["Arjun"],"suffixes":[]}],"month":"February","year":"2026","keywords":"Terrestrial Ecoregions (Wiken 2011)","bibtex":"@phdthesis{augustine_has_2026,\n\ttitle = {Has physical isolation resulted in genetically and phenotypically distinct watersnake and gartersnake populations on remote {Lake} {Ontario} islands?},\n\turl = {https://hdl.handle.net/1974/36037},\n\tabstract = {Intraspecific divergence and speciation on remote marine islands are widely known. However, the processes that underly diversification on islands can occur at fine geographic scales as well, such as in islands in freshwater lakes. Dispersal-restricted organisms, such as snakes, inhabit islands throughout the North American Great Lakes, some of which are isolated from mainland populations by many kilometres of open water. I sought to test whether populations of northern water snake (Nerodia sipedon sipedon) and eastern garter snake (Thamnophis sirtalis sirtalis) on two small islands in eastern Lake Ontario {\\textasciitilde}12 km from the nearest mainland—Main Duck and Yorkshire Islands—are genetically and phenotypically distinct from mainland conspecifics. To assess island-mainland genetic divergence, I used genome-wide panels of single nucleotide polymorphism markers (SNPs) derived from reduced-representation sequencing. I also tested for differences in head morphology and body size among watersnake populations. My results show that insular populations of both species are indeed genetically distinct from their mainland counterparts, but that there are differences in overall genetic structure between the two species around eastern Lake Ontario, possibly related to differences in dispersal ecology and demographic history. In watersnakes, patterns of genetic differentiation appear to be largely related to the water currents of eastern Lake Ontario. In gartersnakes, island-mainland differentiation is more subtle, with a potential contact zone between more deeply diverged lineages southeast of the outlet of Lake Ontario into the St. Lawrence River. I did not find differences in head morphology independent of body size in watersnakes, but did find differences in snout-vent length (SVL) among island and mainland populations. Aside from yielding insights on the origins of snake populations endemic to small islands in the North American Great Lakes, my findings may be useful to conservation agencies, as they may decide to manage the island populations as distinct population segments, especially if future work demonstrates that these insular populations possess unique evolutionary histories or unique adaptive traits.},\n\tlanguage = {eng},\n\turldate = {2026-06-01},\n\tauthor = {Augustine, Arjun},\n\tmonth = feb,\n\tyear = {2026},\n\tkeywords = {Terrestrial Ecoregions (Wiken 2011)},\n}\n\n\n\n\n\n\n\n","author_short":["Augustine, A."],"key":"augustine_has_2026","id":"augustine_has_2026","bibbaseid":"augustine-hasphysicalisolationresultedingeneticallyandphenotypicallydistinctwatersnakeandgartersnakepopulationsonremotelakeontarioislands-2026","role":"author","urls":{"Paper":"https://hdl.handle.net/1974/36037"},"keyword":["Terrestrial Ecoregions (Wiken 2011)"],"metadata":{"authorlinks":{}},"downloads":0},"bibtype":"phdthesis","biburl":"https://bibbase.org/zotero/NAAtlas2024","dataSources":["qLjf8q88GSLZ5dAmC"],"keywords":["terrestrial ecoregions (wiken 2011)"],"search_terms":["physical","isolation","resulted","genetically","phenotypically","distinct","watersnake","gartersnake","populations","remote","lake","ontario","islands","augustine"],"title":"Has physical isolation resulted in genetically and phenotypically distinct watersnake and gartersnake populations on remote Lake Ontario islands?","year":2026}