Organisms that specialize in uncommon habitats are, by their very nature, inherently uncommon. Specialization has its advantages, namely reduced competition and predation, but it also incurs costs. Specialists often have small population sizes, narrow ranges, and fragmented habitat, all of which engender negative consequences on an evolutionary timescale. Herein, I examine benefits and costs of specialization in selenium-hyperaccumulating plants in the genus Astragalus (Fabaceae). These plants are disproportionately likely to be rare and of conservation concern. Thus, I optimized germination pretreatments for Astragalus species such that seed loss can be minimized during ex situ cultivation, and found that physical scarification is most effective in breaking hard-seed dormancy. Through analysis of soil in seleniferous habitats, I found that soil hydrology can rapidly deplete bioavailable selenium, potentially further reducing the habitat available for accumulators. To better understand the relationship between soil bioavailable selenium and plant performance, I subjected Astragalus species to a gradient of selenium concentrations in the greenhouse. Both non-accumulators and hyperaccumulators had less herbivory with increasing selenium concentrations, and also grew larger, despite the energetic cost of selenium uptake. One potential explanation for their larger growth is that selenium reduced inadvertent drought stress during the experiment, so I tested that hypothesis using a full factorial experiment of drought stress and selenium dosage. Although drought stress reduced lifespan and selenium extended it, there was no evidence that selenium ameliorated drought stress. As a case study of the potential population genetic consequences of specialization, I examined the genetic structure and diversity of two allopatric cryptic sister species of Astragalus. Despite known low pollen and seed dispersal and strong genetic isolation by distance, populations were relatively diverse and not substantially inbred. Additionally, the genetic data did not support a two-species arrangement, so I recommend the species be consolidated, although several populations are somewhat isolated and merit special conservation attention. In summary, hyperaccumulators derive ecological benefits from their specialization that outweigh its metabolic cost, but may suffer low connectivity between populations, if not necessarily inbreeding depression. Conservation efforts should thus focus primarily on minimizing threats to and preserving connectivity of specialist habitats.
","abstract_html":"<p>Organisms that specialize in uncommon habitats are, by their very nature, inherently uncommon. Specialization has its advantages, namely reduced competition and predation, but it also incurs costs. Specialists often have small population sizes, narrow ranges, and fragmented habitat, all of which engender negative consequences on an evolutionary timescale. Herein, I examine benefits and costs of specialization in selenium-hyperaccumulating plants in the genus <em>Astragalus</em> (Fabaceae). These plants are disproportionately likely to be rare and of conservation concern. Thus, I optimized germination pretreatments for <em>Astragalus</em> species such that seed loss can be minimized during <em>ex situ</em> cultivation, and found that physical scarification is most effective in breaking hard-seed dormancy. Through analysis of soil in seleniferous habitats, I found that soil hydrology can rapidly deplete bioavailable selenium, potentially further reducing the habitat available for accumulators. To better understand the relationship between soil bioavailable selenium and plant performance, I subjected <em>Astragalus</em> species to a gradient of selenium concentrations in the greenhouse. Both non-accumulators and hyperaccumulators had less herbivory with increasing selenium concentrations, and also grew larger, despite the energetic cost of selenium uptake. One potential explanation for their larger growth is that selenium reduced inadvertent drought stress during the experiment, so I tested that hypothesis using a full factorial experiment of drought stress and selenium dosage. Although drought stress reduced lifespan and selenium extended it, there was no evidence that selenium ameliorated drought stress. As a case study of the potential population genetic consequences of specialization, I examined the genetic structure and diversity of two allopatric cryptic sister species of <em>Astragalus</em>. Despite known low pollen and seed dispersal and strong genetic isolation by distance, populations were relatively diverse and not substantially inbred. Additionally, the genetic data did not support a two-species arrangement, so I recommend the species be consolidated, although several populations are somewhat isolated and merit special conservation attention. In summary, hyperaccumulators derive ecological benefits from their specialization that outweigh its metabolic cost, but may suffer low connectivity between populations, if not necessarily inbreeding depression. Conservation efforts should thus focus primarily on minimizing threats to and preserving connectivity of specialist habitats.</p>","abstract_has_math":false,"creators":["Statwick, Joseph M."],"institution":null,"degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":null,"degree_department":null,"school":null,"contributors":["Anna A. Sher, Ph.D.","Jennifer Ramp Neale","Scott Nichols","Robin Tinghitella"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2016,"date_issued":"2016-01-01T08:00:00Z","date_published":"2016-01-01T08:00:00Z","updated_at":"2026-07-24T02:03:35Z","subjects":["Selenium-hyperaccumulating plants","Population genetic consequences of specialization","Botany","Developmental Biology","Ecology and Evolutionary Biology","Evolution"],"languages":["en"],"rights":["Copyright is held by the author. User is responsible for all copyright compliance.
"],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://digitalcommons.du.edu/etd/1161","outbound_label":"Repository record","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Anna A. Sher, Ph.D.","Jennifer Ramp Neale","Scott Nichols","Robin Tinghitella"]},{"key":"dc:creator","label":"Author","values":["Statwick, Joseph M."]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.available","label":"Dc Date Available","values":["2017-02-17T08:00:00Z"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Ph.D."]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Selenium-hyperaccumulating plants","Population genetic consequences of specialization","Botany","Developmental Biology","Ecology and Evolutionary Biology","Evolution"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["Copyright is held by the author. User is responsible for all copyright compliance.
"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://digitalcommons.du.edu/etd/1161"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Organisms that specialize in uncommon habitats are, by their very nature, inherently uncommon. Specialization has its advantages, namely reduced competition and predation, but it also incurs costs. Specialists often have small population sizes, narrow ranges, and fragmented habitat, all of which engender negative consequences on an evolutionary timescale. Herein, I examine benefits and costs of specialization in selenium-hyperaccumulating plants in the genus Astragalus (Fabaceae). These plants are disproportionately likely to be rare and of conservation concern. Thus, I optimized germination pretreatments for Astragalus species such that seed loss can be minimized during ex situ cultivation, and found that physical scarification is most effective in breaking hard-seed dormancy. Through analysis of soil in seleniferous habitats, I found that soil hydrology can rapidly deplete bioavailable selenium, potentially further reducing the habitat available for accumulators. To better understand the relationship between soil bioavailable selenium and plant performance, I subjected Astragalus species to a gradient of selenium concentrations in the greenhouse. Both non-accumulators and hyperaccumulators had less herbivory with increasing selenium concentrations, and also grew larger, despite the energetic cost of selenium uptake. One potential explanation for their larger growth is that selenium reduced inadvertent drought stress during the experiment, so I tested that hypothesis using a full factorial experiment of drought stress and selenium dosage. Although drought stress reduced lifespan and selenium extended it, there was no evidence that selenium ameliorated drought stress. As a case study of the potential population genetic consequences of specialization, I examined the genetic structure and diversity of two allopatric cryptic sister species of Astragalus. Despite known low pollen and seed dispersal and strong genetic isolation by distance, populations were relatively diverse and not substantially inbred. Additionally, the genetic data did not support a two-species arrangement, so I recommend the species be consolidated, although several populations are somewhat isolated and merit special conservation attention. In summary, hyperaccumulators derive ecological benefits from their specialization that outweigh its metabolic cost, but may suffer low connectivity between populations, if not necessarily inbreeding depression. Conservation efforts should thus focus primarily on minimizing threats to and preserving connectivity of specialist habitats.
"]},{"key":"dc:format","label":"Dc Format","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["The Ecology and Evolution of Rare, Soil Specialist Astragalus Plants in the Arid Western U.S."]}]}],"canonical_facts":{"dc:contributor":["Anna A. Sher, Ph.D.","Jennifer Ramp Neale","Scott Nichols","Robin Tinghitella"],"dc:creator":["Statwick, Joseph M."],"dc:date.available":["2017-02-17T08:00:00Z"],"dc:description.abstract":["Organisms that specialize in uncommon habitats are, by their very nature, inherently uncommon. Specialization has its advantages, namely reduced competition and predation, but it also incurs costs. Specialists often have small population sizes, narrow ranges, and fragmented habitat, all of which engender negative consequences on an evolutionary timescale. Herein, I examine benefits and costs of specialization in selenium-hyperaccumulating plants in the genus Astragalus (Fabaceae). These plants are disproportionately likely to be rare and of conservation concern. Thus, I optimized germination pretreatments for Astragalus species such that seed loss can be minimized during ex situ cultivation, and found that physical scarification is most effective in breaking hard-seed dormancy. Through analysis of soil in seleniferous habitats, I found that soil hydrology can rapidly deplete bioavailable selenium, potentially further reducing the habitat available for accumulators. To better understand the relationship between soil bioavailable selenium and plant performance, I subjected Astragalus species to a gradient of selenium concentrations in the greenhouse. Both non-accumulators and hyperaccumulators had less herbivory with increasing selenium concentrations, and also grew larger, despite the energetic cost of selenium uptake. One potential explanation for their larger growth is that selenium reduced inadvertent drought stress during the experiment, so I tested that hypothesis using a full factorial experiment of drought stress and selenium dosage. Although drought stress reduced lifespan and selenium extended it, there was no evidence that selenium ameliorated drought stress. As a case study of the potential population genetic consequences of specialization, I examined the genetic structure and diversity of two allopatric cryptic sister species of Astragalus. Despite known low pollen and seed dispersal and strong genetic isolation by distance, populations were relatively diverse and not substantially inbred. Additionally, the genetic data did not support a two-species arrangement, so I recommend the species be consolidated, although several populations are somewhat isolated and merit special conservation attention. In summary, hyperaccumulators derive ecological benefits from their specialization that outweigh its metabolic cost, but may suffer low connectivity between populations, if not necessarily inbreeding depression. Conservation efforts should thus focus primarily on minimizing threats to and preserving connectivity of specialist habitats.
"],"dc:format":["application/pdf"],"dc:identifier":["https://digitalcommons.du.edu/etd/1161"],"dc:language":["en"],"dc:rights":["Copyright is held by the author. User is responsible for all copyright compliance.
"],"dc:subject":["Selenium-hyperaccumulating plants","Population genetic consequences of specialization","Botany","Developmental Biology","Ecology and Evolutionary Biology","Evolution"],"dc:title":["The Ecology and Evolution of Rare, Soil Specialist Astragalus Plants in the Arid Western U.S."],"thesis:degree_level":["Dissertation"],"thesis:degree_name":["Ph.D."]},"updated_at":"2026-07-24T02:03:35Z"}