Theses and Dissertations at Montana State University (MSU)
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Item Hybridization and invasiveness in Eurasian watermilfoil (Myriophyllum spicatum): is prioritizing hybrids in management justified?(Montana State University - Bozeman, College of Agriculture, 2021) Hoff, Hannah Katherine; Chairperson, Graduate Committee: Ryan Thum; Ryan A. Thum was a co-author of the article, 'Hybridization and invasiveness in Eurasian watermilfoil (Myriophyllum spicatum): is prioritizing hybrids in management justified?' submitted to the journal 'Invasive plant science and management' which is contained within this thesis.Hybridization can play an important role in the evolution of invasiveness. Eurasian watermilfoil (Myriophyllum spicatum L.) is a widespread aquatic invasive plant species that hybridizes with native northern watermilfoil (Myriophyllum sibiricum Kom.). Previous studies have found mixed evidence for whether hybrid watermilfoil (Myriophyllum spicatum x sibiricum) and pure M. spicatum differ in vegetative growth rate and herbicide response. While several studies have emphasized variation in these traits among M. spicatum x sibiricum genotypes, variation within M. spicatum has not been considered. Therefore, it is unclear how important genetic variation within M. spicatum, versus between M. spicatum and M. spicatum x sibiricum, is in influencing invasive traits and management outcomes. If M. spicatum x sibiricum genotypes are always more invasive than M. spicatum genotypes, simply distinguishing taxa may be sufficient for identifying lake management priorities; however, if significant phenotypic overlap is observed between taxa, distinguishing individual genotypes may be important for tailoring management strategies. We performed replicated trials of a vegetative growth and 2,4-D assay to measure clonal variation in growth rate and herbicide response of M. spicatum and M. spicatum x sibiricum. Our results indicate that M. spicatum x sibiricum exhibits higher average vegetative growth than M. spicatum, whether or not it is treated with 2,4-D. We did not observe interactions between taxon and treatment or between genotype and treatment. Despite differences between M. spicatum and M. spicatum x sibiricum in average vegetative growth, there was substantial overlap between taxa. For example, we found that the fastest-growing genotype of pure M. spicatum did not differ significantly in average growth from the fastest-growing M. spicatum x sibiricum genotype. The potential for overlap between these invasive Myriophyllum taxa suggests that distinguishing and characterizing genotypes may be more informative for management than simply distinguishing between M. spicatum and M. spicatum x sibiricum.Item Mechanisms of rainbow trout hybridization with native cutthroat trout in the Lamar River of Yellowstone National Park(Montana State University - Bozeman, College of Letters & Science, 2019) Heim, Kurt Conrad; Chairperson, Graduate Committee: Thomas E. McMahon; Thomas E. McMahon, Clint C. Muhlfeld, Brian D. Ertel and Todd M. Koel were co-authors of the article, 'Interspecific hybridization solves a phenological breeding mismatch for a nonnative invader' submitted to the journal 'Ecology' which is contained within this dissertation.; Thomas E. McMahon, Steven T. Kalinowski, Brian D. Ertel and Todd M. Koel were co-authors of the article, 'Invasive hybridization in a high-elevation stronghold: genetic status of Yellowstone cutthroat trout in the Lamar River of Yellowstone National Park' submitted to the journal 'Canadian journal of fisheries and aquatic sciences' which is contained within this dissertation.; Thomas E. McMahon, Brian D. Ertel and Todd M. Koel were co-authors of the article, 'Leveraging public harvest for genetic management: identification and exploitation of invasive hybrid trout in Yellowstone National Park' submitted to the journal 'Biological invasions' which is contained within this dissertation.Invasive hybridization--when invasive species interbreed with native species--is a pervasive conservation issue. Hybridization presents difficult management decisions and poses complex problems at the intersection of contemporary evolution, invasion biology, physiology, and landscape ecology. I examined the invasion scenario playing out in the Lamar River watershed of Yellowstone National Park where native Yellowstone cutthroat trout (YCT) are undergoing hybridization with introduced rainbow trout (RT). I first test the hypothesis that a breeding timing mismatch of an invasive species (i.e., RT often spawn far earlier than YCT, and eggs are scoured by snowmelt runoff) can be overcome by hybridization with a locally adapted native species, that spawn later (Chapter 2). I found support for this hypothesis. Spawning timing was strongly related to the degree of non-native admixture at the individual level, indicating that hybridization alters breeding timing in ways that could benefit hybrids. At the population level, hybrid spawning timing closely matched that of native taxa and was strongly correlated to stream flow conditions. Overall, these data suggest poorly matched spawning timing is unlikely to serve as a strong mechanism limiting invasive hybridization of YCT. Next, I mapped the spatial distribution of hybridization in the Lamar River watershed (Chapter 3). Many non-hybridized populations persist in the upper watershed, whereas a prominent source of RT in the lower watershed has likely contributed inordinately to the spread of introgression. Because hybridized populations occurred across a full range of environmental conditions, I do not predict that abiotic conditions (i.e., cold water, late-stream flow, high elevations, or small stream size) will prevent the spread of hybridization in the long-term. As such, management interventions are recommended in chapter 4 and 5. I developed a simple taxonomic key to identify hybrids and guide selective removal efforts (Chapter 4). Additionally, I used volunteer angler surveys to estimate that recreational anglers visiting the watershed (~10,000 per year) could likely harvest a substantial number of non-native trout that would contribute to genetic management goals. I conclude by providing recommendations for management and monitoring (Chapter 5).Item Genetic surveys in combination with laboratory studies on growth and response to herbicide can help design, evaluate, and optimize Eurasian watermilfoil management plans(Montana State University - Bozeman, College of Agriculture, 2018) Guastello, Paula Ropp; Chairperson, Graduate Committee: Ryan Thum; Ryan A. Thum was a co-author of the article, 'Mesocosm evaluation of Eurasian and hybrid watermilfoil response to endothall in Jefferson Slough, Montana' in the journal 'Journal of aquatic plant management' which is contained within this thesis.Eurasian watermilfoil (Myriophyllum spicatum) is a top priority for aquatic plant managers in the United States. Dense mats of Eurasian watermilfoil obstruct irrigation and recreational activities, while drastically reducing property values and potentially providing a habitat for disease-carrying mosquitos. Nuisance populations are generally managed through herbicide use. Eurasian watermilfoil is capable of both sexual and clonal reproduction, creating a unique opportunity for adaptation: sexual reproduction generates genetic variation within a population, then fit genotypes can propagate via clonal reproduction. Pure Eurasian watermilfoil is genetically diverse, and additional genotypes result from frequent hybridization with native northern watermilfoil (Myriophyllum sibiricum). Recent studies have shown that genetic variation in Eurasian watermilfoil populations may affect herbicide efficacy in managed populations. Given the variability in herbicide response, I propose conducting site-specific studies to evaluate the response of genotypes in a waterbody to evaluate and optimize management strategies. In my thesis, I evaluated the potential to control nuisance pure and hybrid Eurasian watermilfoil with endothall in a riverine environment (Jefferson Slough, Montana). Molecular genetic surveys indicated that only one genotype of each taxon was present throughout the slough. I first compared vegetative growth and endothall response of the hybrid and Eurasian genotypes in the greenhouse, where I did not identify a difference in endothall sensitivity. Next, I evaluated the efficacy of an operational endothall treatment in Jefferson Slough. Similar to the greenhouse study results, hybrid and Eurasian watermilfoil were reduced to the same average biomass seven weeks after operational endothall treatment. Taken together, the greenhouse and operational field treatment indicate that the genotypes in Jefferson Slough were similarly susceptible to endothall. However, vegetative growth differences may have important management implications over time. In the greenhouse, Jefferson Slough hybrids grew significantly more than Eurasian watermilfoil in the absence of endothall. Additionally, there was a qualitative shift towards higher frequency of hybrids where the taxa intermixed. These results suggest a relatively higher potential for re-growth of hybrids compared to Eurasian watermilfoil following treatment. Jefferson Slough hybrids may require additional treatment to achieve sufficient long-term control. In conclusion, I discuss integration of genetic surveys into management and research priorities.Item System analysis of the spread of introgressive hybridization in salmonid population through an agent-based simulation model(Montana State University - Bozeman, College of Agriculture, 2015) Della Croce, Patrick Lorenzo Davide; Chairperson, Graduate Committee: Geoffrey Poole; Geoffrey C. Poole, Robert A. Payn and Clemente Izurieta were co-authors of the article, 'Simulating the effects of stream network topology on the spread of introgressive hybridization across fish populations' in the journal 'Ecological modelling' which is contained within this thesis.; Geoffrey C. Poole and Gordon Luikart were co-authors of the article, 'Detecting and quantifying introgression in hybridized populations: simplifying assumptions yield overconfidence and uncertainty' submitted to the journal 'Molecular ecology resources' which is contained within this thesis.; Geoffrey C. Poole, Robert A. Payn and Robert E. Gresswell were co-authors of the article, 'Early detection of non-native alleles in fish populations: when sample size actually matters' submitted to the journal 'Fisheries' which is contained within this thesis.Using the specific example of introgressive hybridization between native cutthroat trout (Oncorhynchus clarkii sp., CTT) and introduced rainbow trout (O. mykiss, RBT), I have designed and developed an individual-based model that mimics the spread of introgressive hybridization in a river network inhabited by salmonids accounting for realistic population demographics, genetics, and stochasticity. As a tool capable of providing mechanistic explanations for observed patterns of introgression, the model is used in Chapter 2 to show that network bifurcations act as semi-permeable barriers to the spread of introgression across river network by decreasing (a) the rate of spread of non-native alleles and (b) the predictability of such spread. As a tool to test the effects of realistic population demographics and realistic mechanisms for the passage of alleles from one generation to the next the model is used in Chapters 3 and 4 to show that commonly used sampling and analysis methods greatly overestimate the power to detect and the precision to quantify introgression in populations.Item Inheritance of awnedness, kernel smoothness, kernel length, and reaction to two physiologic races of Tilletia in a spring wheat cross(Montana State University - Bozeman, College of Letters & Science, 1941) Smith, Orlie W.Item Assessment of reproductive isolation between Yellowstone cutthroat trout and rainbow trout in the Yellowstone River, Montana(Montana State University - Bozeman, College of Letters & Science, 2004) De Rito, Jr., James Nicholas; Chairperson, Graduate Committee: Alexander V. ZaleThe genomic extinction of Yellowstone cutthroat trout (Oncorynchus clarki bouvieri) has occurred throughout many parts of its historic range because of displacement and introgression with introduced rainbow trout (O. mykiss). However, fluvial cutthroat trout still retain their genetic integrity while co-existing with rainbow trout in the Yellowstone River drainage, Montana. I assessed whether spatial or temporal reproductive isolation, or both, occurs between these taxa. Time and place of spawning was determined by radio-telemetry of a total of 164 trout (98 cutthroat, 37 rainbow, and 29 cutthroat x rainbow hybrids) over three spawning seasons, from 2001 to 2003. Fish were telemetered in four areas of a 140-km segment of the mainstem Yellowstone River. Of the 164 radio-tagged fish, 73 (44 cutthroat trout, 15 rainbow trout, and 14 hybrids) were assumed to have spawned. Fifty-five (75.3%) of 73 radio-tagged fish that spawned used 16 tributaries, 17 (23.3%) used 7 river side channels, and 1 (1.4%) used the main channel of the Yellowstone River. The majority of fish that spawned (62%) used five spawning areas. These were used by 79% (N = 11) of hybrids, 61% (N = 27) of cutthroat trout, and 47% (N = 7) of rainbow trout that spawned. Spawning-area and spawning-reach overlap index values were high among all taxa. In contrast, mean migration and spawning dates of rainbow trout and hybrids were 5 to 9 weeks earlier than of cutthroat trout. Rainbow trout and hybrids began migrating and spawning in April and May when Yellowstone River discharges were lower and water temperatures were colder than discharges and temperatures during cutthroat trout migration and spawning in June and July. Spawningperiod overlap index values between rainbow trout and hybrids versus cutthroat trout were typically less than half the spatial overlap index values. Therefore, difference in time of spawning is likely the predominant mechanism eliciting reproductive isolation. Management actions focused on later spawning cutthroat trout in tributaries may enhance temporal reproductive isolation from rainbow trout and hybrids.Item Behavioral, ecological, and fitness consequences of hybridization between native westslope cutthroat trout (Oncorhynchus clarkii lewisi) and nonnative rainbow trout (O. mykiss)(Montana State University - Bozeman, College of Letters & Science, 2008) Muhlfeld, Clint Cain; Chairperson, Graduate Committee: Thomas E. McMahonAnthropogenic hybridization is one of the greatest threats to global biodiversity. Hybridization and introgression may lead to a loss of locally adapted gene complexes and ecological adaptations in native populations, yet these potential consequences have not been fully evaluated in nature. I investigated factors influencing the spread of hybridization between native westslope cutthroat trout (Oncorhynchus clarkii lewisi) and nonnative rainbow trout (O. mykiss) in the upper Flathead River system, Montana (USA) and British Columbia (Canada). The fundamental questions of my dissertation were: what are the behavioral, ecological, and fitness consequences of hybridization and what factors influence successful invasion of hybrids? First, I assessed the patterns of spawning between parental species and their hybrids and found that hybridization alters the spawning behavior of migratory westslope cutthroat trout, and is spreading via long distance dispersal of hybrids from downstream sources and some temporal overlap during spawning. Second, I describe for the first time how a wide range of levels of nonnative admixture affect fitness of cutthroat trout in the wild by estimating reproductive success in a recently invaded stream using parentage analysis with multilocus microsatellite markers. Small amounts of hybridization markedly reduced reproductive success, with fitness exponentially declining by ~50% with 20% nonnative genetic admixture. Finally, I evaluated the association of local-habitat features, landscape characteristics, and biotic factors with the spread of hybridization in the system, and found that hybridization increases in streams with warmer water temperatures, high land use disturbance and close proximity to the source of hybridization; however, none of these factors appeared sufficient to prevent further spread. These combined results suggest that hybrids are not only genetically different than westslope cutthroat trout but also have reduced fitness and are ecologically different, and that hybridization is likely to continue to spread if hybrid populations with high amounts of rainbow trout admixture are not reduced or eliminated. I conclude that extant aboriginal cutthroat trout are at greater conservation risk due to hybridization than previously thought and policies that protect hybridized populations need reconsideration.