Browsing by Author "Hoke, Kim L., committee member"

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Open Access
A tail of two fish: an integrative approach to understand how trade-offs and salinity influence two closely related euryhaline fish
(Colorado State University. Libraries, 2021) Mauro, Alexander Anthony, author; Ghalambor, Cameron K., advisor; Hoke, Kim L., committee member; Funk, W. Chris, committee member; Hufbauer, Ruth A., committee member
It is well understood that adaptive evolution can occur rapidly in nature and that anthropogenic climate change is causing - and will continue to cause - mass extinctions of the planet's biodiversity. These facts represent somewhat of a paradox: rapid adaptation can and does occur in nature, yet many populations are failing to adapt to environmental change. This dissertation lies at the interface of this paradox as it investigates the adaptive process. However, instead of investigating a case of adaptive success, it explores the mechanisms and circumstances underlying a case when evolution appears to be constrained. More specifically, it investigates how a trade-off between salinity tolerance and competitive ability contributes to an evolutionary range limit in Poecilia reticulata. It also investigates how salinity influences genetic variation in a more widespread fish, Poecilia picta.In chapter 1, a conceptual framework of trade-offs as evolutionary constraints that utilizes network/pathway thinking is presented. In chapter 2, it is experimentally shown that P. reticulata experiences a trade-off between salinity tolerance and competition with P. picta, that the trade-off is genetically based, and that it is indeed range limiting. In chapter 3 why this trade-off occurs at the physiological network level is investigated. It is shown that a negative relationship between salinity tolerance and competition arises because salinity exposure in P. reticulata results in the activation of hormonally mediated pathways in the brain associated with ion regulation and a decrease in aggression. Chapter 4 shifts the focus from P. reticulata to P. picta. to investigate how salinity influences the distribution of both neutral and adaptive genetic variation in a species that is found both freshwater and brackish water unlike P. reticulata. It is found that salinity can drive differentiation at putatively adaptive loci despite high levels of population connectivity in populations of P. picta.
Open Access
Evolution and plasticity of Trinidadian guppies in the field, the laboratory, and the classroom
(Colorado State University. Libraries, 2016) Broder, Emily Dale, author; Angeloni, Lisa M., advisor; Ghalambor, Cameron K., committee member; Hoke, Kim L., committee member; Whittemyer, George, committee member
A fundamental question in evolutionary biology is how organisms respond to new and changing environments. This question also has conservation implications in the face of human induced rapid environmental change, including invasive species, habitat loss, and climate change. In response to new or changing environments, populations may evolve genetic changes across generations, and individuals may also respond via phenotypic plasticity within a generation. We can use experimental methods and model systems to increase our understanding of the way that genes and the environment interact to shape phenotypes. The Trinidadian guppy is a small freshwater fish that exhibits phenotypic plasticity as well as rapid evolution in response to changes in the environment, namely changes in the predator community. We utilized experimental introductions and common garden experiments to investigate plasticity and evolution of cerebral laterality, genitalia, and mating behavior in guppies. Predation pressure is thought to select for a higher degree of cerebral laterality, or consistency in the partitioning of tasks between hemispheres of the brain. However, we found no difference in laterality between populations that evolved with high versus low levels of predation in the wild (Chapter 1). Instead, brothers reared with chemical predator cues were more highly lateralized than their brothers reared without cues, which is likely adaptive plasticity since a higher degree of laterality is associated with enhanced antipredator behavior. This study revealed the important but largely overlooked role of developmental plasticity in shaping cerebral laterality. Next, we took advantage of an experimental introduction of guppies from an environment with many predators to four replicate streams that contained few predators. In only 4-8 guppy generations, males in the introduced populations evolved shorter gonopodia for a given body size compared to the source population with high predation risk (Chapter 2). This suggests that longer gonopodia are advantageous in environments with predators, consistent with the hypothesis that longer genitalia facilitate forced copulations and allow males to circumvent female choice. We also measured male mating behavior using the same experimental introduction. In approximately 8-12 generations, we documented evolutionary changes in several mating behaviors, but these patterns were not consistent across populations (Chapter 3). We also found that low food levels during development reduced mating effort, but we found no evidence of developmental plasticity in response to predator cues in the rearing environment. Instead, we found an important role for contextual plasticity, a reversible and rapid response to the current situation, evident in behavioral changes with acute chemical cues of predation. Contextual plasticity is though to be especially important for behavioral traits allowing flexibility in response to rapidly changing conditions. This represents one of the few empirical studies designed to explore evolution, developmental plasticity, and contextual plasticity in the same experiment. The Trinidadian guppy is also a model system for science education, with locally adapted populations that provide an accessible example of evolution by natural selection. We created a hands-on authentic science program with live guppy experiments to teach evolution to middle school students (Chapter 4). Authentic science allows students to discover knowledge by conducting science as if they were practicing scientists, which should be particularly effective at teaching evolution, yet few programs have been developed. Students who participated in our program exhibited significant increases in both knowledge and acceptance of evolution. Our work with Trinidadian guppies documented patterns of evolution and plasticity in new environments for a series of traits using a powerful experimental framework. These experiments revealed a role for both genes and the environment in the way predation risk shapes cerebral laterality, genitalia, and mating behavior, suggesting that the relationship between plasticity and evolution is complex and likely depends on the trait being studied. We also demonstrated how the guppy system, and other organisms that exhibit local adaptation, can be used to develop engaging and effective authentic science programs to teach evolution to K-12 students.
Open Access
Evolutionary increase in genome size drives changes in cell biology and organ structure
(Colorado State University. Libraries, 2022) Itgen, Michael Walter, author; Mueller, Rachel Lockridge, advisor; Sloan, Daniel B., committee member; Hoke, Kim L., committee member; Zhou, Wen, committee member
The evolution of large genome size has been associated with patterns of phenotypic change in cell and organismal biology. The most fundamental of these is between genome size and cell size, which share a strong positive and deterministic relationship. As a result, increases in cell size alter the structure and function of the cell. Genome and cell size, together, are hypothesized to produce emergent consequences on development and physiology at the cellular and organismal level. My dissertation aims to better understand these patterns and identify potential mechanisms underlying these phenotypic changes. I test for the effects of genome and cell size on cell function, cellular physiology, and organ morphology by leveraging the natural variation in genome size found in salamanders (Genus: Plethodon). First, I show that transcriptomic data supports the predictions that large genome and cell size has functional consequences on cell biology. I also reject the hypothesis that large cell size is functionally linked to lower metabolic rate at the cellular level, but I provide transcriptomic evidence that cell size alters the metabolic state of cells. Finally, I show that genome and cell size drives morphological change in organ-specific ways in the heart and liver. I conclude that large cell size does not lower metabolic rate in salamanders. As an alternative, I propose that the evolution of low metabolic rate lifts the constraint of cell size, thus permitting the evolution of genome gigantism.
Embargo
Integrating genomics and telomere dynamics to understand climate adaptation in a migratory songbird
(Colorado State University. Libraries, 2025) Rodriguez, Marina D., author; Ruegg, Kristen C., advisor; Bailey, Susan F., committee member; Bay, Rachael A., committee member; Hoke, Kim L., committee member
Declines in avian species have become widespread due to numerous threats, including anthropogenic climate change. Migratory birds, which occupy multiple environments throughout their annual cycle, are particularly vulnerable. Understanding and predicting the response of migratory bird species to climate change is critical for targeted conservation efforts and the mitigation of further declines. A key factor in species resilience lies in their ability to genetically adapt to changing environments. Recent advances in conservation genomics have improved our ability to detect local adaptation and predict maladaptation to climate change in non-model species. In my dissertation, I test the overall hypothesis that integrating telomere dynamics and conservation genomics will allow for the identification and validation of fitness-related traits in studies of local adaptation. With this hypothesis, I aim to uncover potential mechanisms of local adaptation and assess the impacts of climate change on the yellow warbler (Setophaga petechia). In my first chapter, I link genetic, phenotypic, and environmental data with telomere length measurements to enhance our understanding of local adaptation and the effects of climate change in this species. In the second chapter, I combine models of genomic offsets with telomere data to validate the prediction that yellow warblers inhabiting regions with high genomic offset experience elevated physiological stress due to climate change. Finally, in my third chapter, I investigate local adaptation to the non-breeding grounds and test whether climate tracking reflects local adaptation across the annual cycle in this migratory species. Taken together, my doctoral research highlights the importance of understanding local adaptation to inform population responses to the changing climate. Importantly, this work represents the first demonstration of how integrating methodologies from modern genomics and assessment of biological measures of stress like telomeres can advance our knowledge of wild species' responses to environmental change and enhance conservation efforts.