Mountain Scholar :: Browsing by Author "Ghalambor, Cameron K., advisor"

Browsing by Author "Ghalambor, Cameron K., advisor"

Now showing 1 - 10 of 10

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
Body size, first year breeding, and extra-pair paternity in an island endemic, the Island Scrub-Jay
(Colorado State University. Libraries, 2014) Desrosiers, Michelle A., author; Angeloni, Lisa M., advisor; Ghalambor, Cameron K., advisor; Funk, W. Chris, committee member; Sillett, T. Scott, committee member; Crooks, Kevin R., committee member
Body size is a fundamental characteristic that shapes all aspects of an organism's biology. The advantages of large body size may include increased probability of territory acquisition, a critical component of fitness for species that require a territory to breed. Large body size, an indicator of quality, may also be advantageous to males in acquiring mates, including matings outside of a pair bond. Such advantages could be especially important in island systems because habitat saturation may result in strong intra-specific competition for territories, and females may be especially motivated to seek large extra-pair mates to increase the body size of their offspring. We tested the role of body size in determining the ability of an island-endemic bird, the Island Scrub-Jay, Aphelocoma insularis, to acquire a territory and breed in their first spring, as well as to sire extra-pair offspring. We compared the body size of individuals that obtained a territory and bred to those that did not, as well as the body size of social fathers to the extra-pair sires to whom they lost paternity. We found that large body size was important in the siring of extra-pair young. However, body size did not predict the ability of male or female Island Scrub-Jays to acquire a territory and breed in their first year. We suggest that year-to-year variation in environmental conditions and chance may be more important than a large body size or weapon performance in early territory acquisition. Our study provides evidence for a mechanism, specifically female preference for a large body size in males, that supports the observed rates of extra-pair paternity, and demonstrates the general difficulty, even for individuals with a relatively large body size, of acquiring a territory as a yearling in an island system with saturated habitat.
Open Access
Demography and parental investment in orange-crowned warblers: testing life history theory
(Colorado State University. Libraries, 2012) Sofaer, Helen R., author; Ghalambor, Cameron K., advisor; Noon, Barry R., committee member; Sillett, T. Scott, committee member; Webb, Colleen T., committee member
Understanding the diversification of life history strategies is a major goal of evolutionary ecology. Research on avian life history strategies has historically focused on explaining variation in clutch size, and most studies have tested whether this variation can be explained by variation in a single ecological factor, such as food availability or mortality risk. However, relatively few studies have evaluated whether the causes of variation within populations are distinct from or similar to the causes of variation between populations. In my dissertation, I compare the life history strategies of orange-crowned warbler (Oreothlypis celata) populations and study the causes of variation in clutch sizes, incubation behavior, nestling provisioning rates, nestling growth rates, and breeding phenology. I tested alternative hypotheses for the ecological causes of divergent life histories, and assessed the consequences of these different reproductive strategies for parents and offspring. My results indicate that no single ecological factor can explain life history variation either within or between populations. Instead, life history and behavioral traits differ in their sensitivities to different ecological factors, and while differences between nearby populations can reflect plastic responses to ecological variation, populations that are more geographically and evolutionarily distant can differ in both their responses to ecological variation and in the consequences of variation in parental behavior for offspring growth and development.
Open Access
Eco-physiological drivers of geographic range limits in two closely related euryhaline fish species
(Colorado State University. Libraries, 2021) Marshall, Craig Anthony, author; Ghalambor, Cameron K., advisor; Angeloni, Lisa M., advisor; Myrick, Christopher A., committee member; Earley, Ryan L., committee member
A fundamental goal in evolutionary ecology is to understand the problem of why species occur in some environments and not others. Indeed, a general pattern in nature is that many organisms occupy only a subset of the total range of the environments they are physiologically capable of tolerating. Theory suggests that the abiotic environment can constrain the distributions of species, but testing the relative roles of different mechanisms in shaping species distributions has proven to be a major challenge for both plants and animals. In fish, salinity tolerance is a defining factor in shaping the ranges of many species. Nonetheless, the influence of salinity tolerance on patterns of dispersal and local adaptation are understudied for most species. Euryhaline fishes are capable of acclimating to a wide range of salinities, yet may exhibit a preference for a particular salinity. For example, previous work in euryhaline teleosts indicates that crossing a salinity gradient typically results in increased oxygen uptake, energetic costs, and activation of the stress response. Thus, plastic or evolved tolerance to increased salinity might come at the expense of fitness-related traits (i.e., locomotion, feeding, mate acquisition, etc.), but few studies have investigated the potential for such trade-offs. Maintaining ionic and osmotic homeostasis in the face of a salinity change is critical for survival, but also energetically costly. Efficient osmoregulation relies primarily on the gills, but the process is complicated given that freshwater and saltwater fishes differ in the direction of ion transport through the gill epithelia. Thus, proper restructuring of the gills is fundamental to surviving a salinity transition. This plastic response has been observed in euryhaline fishes, however there is intra- and interspecific variation in the timescale of this process. The endocrine system plays a significant role in salinity acclimation, and in euryhaline teleosts salinity exposure increases the concentration of circulating plasma cortisol to facilitate osmoregulation. Previous work indicates that cortisol is involved in promoting structural changes in both fresh and saltwater gills, but its role in osmoregulation and adaptation differs between the two types. Thus, comparisons of cortisol concentrations can provide insight into the roles of local adaptation and plasticity for euryhaline fishes that exist along a salinity gradient. On the island of Trinidad, the euryhaline guppy (Poecilia reticulata) is confined to freshwater whereas the closely related swamp guppy (Poecilia picta), co-exists with the guppy in freshwater, but also spans into brackish and saltwater. To understand this pattern, we employed an integrative approach to investigate the mechanisms and potential trade-offs that may exist upon exposure to increased ambient salinity as a result of seasonal and daily tidal fluctuations. We examined the effect of a gradual salinity increase on sustained swimming (UCRIT) for P. reticulata and burst swim performance for P. reticulata and P. picta by estimating salinity performance curves (SPCs) using field collected fish. We mimicked the same salinity challenge in the lab and measured the ability of lab reared P. reticulata and P. picta to maintain internal osmolality. In addition, we used a novel method to quantify differences in circulating cortisol levels in P. picta allowing us to infer whether populations along the salinity gradient track stable versus variable salinity levels by adjusting their cortisol levels. Our experiments revealed that P. reticulata can maintain sustained swimming performance across a broad range of salinities and achieves peak performance at the isosmotic point, confirming its euryhaline ability. In contrast, both P. reticulata and P. picta initially experience a drop in burst swimming performance when exposed to salinity challenge, but are able to acclimate over time to higher salinities and re-establish their performance. However, this acclimation response occurs much more quickly in P. picta compared to P. reticulata. The slower acclimation response of P. reticulata could potentially make them more vulnerable to predation risk when they attempt to become established in brackish water, thus contributing to their ranges being restricted to freshwater in Trinidad. Cortisol analyses along the salinity gradient provide support for P. picta having the ability to plastically increase circulating cortisol levels in response to daily fluctuations in salinity. Overall, these results demonstrate how understanding the physiological responses to salinity can inform which mechanisms do and do not contribute to distribution patterns in nature.
Open Access
Evolutionary underpinnings of microgeographic adaptation in song sparrows distributed along a steep climate gradient
(Colorado State University. Libraries, 2021) Gamboa, Maybellene Pascual, author; Ghalambor, Cameron K., advisor; Funk, W. Chris, advisor; Sillett, T. Scott, committee member; Wolf, Blair O., committee member; Hufbauer, Ruth A., committee member; Morrison, Scott A., committee member
Understanding how evolutionary processes interact to maintain adaptive variation in natural populations has been a fundamental goal of evolutionary biology. Yet, despite adaptation remaining at the forefront of evolutionary theory and empirical studies, there remains a lack of consensus about the evolutionary conditions that enable adaptation to persist in natural populations, especially when considering complex phenotypes in response to multivariate selection regimes. In my dissertation, I disentangle the evolutionary mechanisms that shape adaptive divergence in song sparrows (Melospiza melodia) distributed along a climate gradient on the California Channel Islands and nearby coastal California. First, I found evidence that climate, and neither vegetation nor selection for increased foraging efficiency, likely drive adaptive divergence in bill morphology among insular populations. Second, I used an integrated population and landscape genomics approach to infer that bill variation is indicative of microgeographic local adaptation to temperature. Lastly, I tested whether the distinct climate gradient facilitates adaptative divergence in other thermoregulatory traits and found evidence to support environmental temperatures result in fixed population differences in many complementary phenotypes, including plumage color, feather microstructure, and thermal physiology. Collectively, these results find support for microgeographic climate adaptation in a suite of complex phenotypes and demonstrate the utility of integrative approaches to infer local adaptation in natural populations. Finally, by developing a more holistic understanding of climate adaptation in natural populations, my results inform conservation management of this species of special concern.
Open Access
Habitat use, territoriality, and parental behavior of orange-crowned warblers (Oreothlypis celata)
(Colorado State University. Libraries, 2010) Yoon, Jongmin, author; Ghalambor, Cameron K., advisor; Angeloni, Lisa Marie, committee member; Doherty, Paul F., 1970-, committee member; Sillett, Terence Scott, 1966-, committee member
To view the abstract, please see the full text of the document.
Open Access
Intra- and interspecific variation along environmental gradients: adaptation, plasticity, and range limits
(Colorado State University. Libraries, 2012) Torres Dowdall, Julián R., author; Ghalambor, Cameron K., advisor; Angert, Amy L., committee member; Fausch, Kurt D., committee member; Poff, N. LeRoy, committee member; Thomas, Stephen, committee member
Understanding the processes underlying patterns of intraspecific variation, and how these processes in turn shape the distributional limits of species is a fundamental goal of evolutionary ecology. The study of species distributed along environmental gradients provides a framework for testing how changing conditions lead to local adaptation, phenotypic plasticity, and ultimately shape distributional limits. Yet, environmental gradients are complex, being composed of a diversity of abiotic and biotic factors that act on individual species and shape the interactions between them. Thus, empirical studies aimed to understand patterns of intraspecific divergence and interspecific diversity need to evaluate the effects of both abiotic and biotic factors varying along gradients. Evolutionary ecologists have become increasingly interested in trying to understand the costs and limits to trait variation along environmental gradients and what factors prevent species from evolving larger geographic ranges. Theory predicts that species distributed along environmental gradients should track conditions through local adaptation or adaptive phenotypic plasticity, and that a disruptive factor along the gradient (e.g. increase in the steepness of the gradient, the presence of a competitor, etc.) could result in the formation of distribution limits as conditions become unsuitable for populations persistence. Empirical studies analyzing large-scale patterns of phenotypic variation have provided support for the formation of clines in response to environmental gradients. However, less evidence has accumulated for the formation of such patterns at local scales and clear disruptive factors leading to distributional limits remain elusive. My dissertation takes an evolutionary ecological perspective to understand how environmental gradients shape patterns of variation within and between species. Here, I attempt to understand how abiotic and biotic factors interact to drive patterns of phenotypic variation. To approach this question, I used as a study system two closely related, ecologically similar, and parapatric species of poeciliids distributed along rivers on the island of Trinidad, West Indies. In the first part of this dissertation, I focus on the patterns of intraspecific variation in the Trinidadian guppy (Poecilia reticulata) along a predation risk gradient. I used this species to explore the spatial scale at which local adaptation occurs (Chapter 1), and to investigate the role of adaptive phenotypic plasticity in allowing species to track local optima (Chapter 2). I found that local adaptation in Trinidadian guppies occurs at a smaller spatial scale than previously shown. My results also suggest that adaptive plasticity plays an important role in allowing Trinidadian guppies to track local optima along a gradient of predation risk. Furthermore, I found divergence in patterns of plasticity between Trinidadian guppy populations adapted to low- or to high-levels of predation pressure. My results suggest that this difference in adaptive phenotypic plasticity evolved as a by-product of adaptation to local environmental conditions. In the second part of my dissertation I change my focus from patterns of intraspecific variation to patterns of interspecific variation along environmental gradients. I examine how the Trinidadian guppy and its sister species, the swamp guppy (P. picta), are distributed along a complex environmental gradient in lowland rivers of Trinidad (Chapter 3), and performed a series of experiments aimed to determine what factors drive their distributions (Chapter 4). As Trinidadian rivers approach the ocean, several factors change in comparison to upstream localities, including changes in productivity, physicochemical conditions, and community composition. I found that the Trinidadian guppy and the swamp guppy show an overlapping parapatric distribution along the interface between brackish-freshwater in the lowland rivers of Trinidad. The swamp guppy is usually found in downstream sections of the rivers, both in fresh- and brackish water. On the other hand, the Trinidadian guppy is only found in freshwater, dropping off abruptly at the brackish-freshwater interface. Field and laboratory experiments suggest that brackish water environments are physiologically stressful for the two study species, as survival and growth rate in this environment were lower compared to that observed in freshwater. Also, these experiments indicate that the Trinidadian guppy is competitively dominant over the swamp guppy across all salinity conditions. Thus, I showed that asymmetric competition limits the competitively subordinate swamp guppy to the harshest end of the salinity gradient, and that stressful salinity conditions limits the dominant Trinidadian guppy to the less stressful freshwater end of the gradient.
Open Access
Microgeographic divergence in a single-island endemic: evolutionary patterns and conservation implications
(Colorado State University. Libraries, 2014) Langin, Kathryn M., author; Ghalambor, Cameron K., advisor; Crooks, Kevin R., committee member; Funk, W. Chris, committee member; Morrison, Scott A., committee member; Sillett, T. Scott, committee member
Understanding the processes that generate biological diversity is the central goal of evolutionary biology. Geographic isolation has traditionally been viewed as the primary scenario favoring evolutionary divergence. However, there is growing appreciation for the role of ecological variation and natural selection in driving adaptive differentiation, even in the absence of geographic barriers to gene flow. My dissertation tests for microgeographic patterns of local adaptation within one of the most range-restricted bird species in North America, the Island Scrub-Jay (Aphelocoma insularis). The species is restricted to Santa Cruz Island in southern California, USA, where it occurs in a diversity of habitat types within its narrow (250 km2) geographic range. Remarkably, I found that Island Scrub-Jays in three separate stands of pine habitat had longer, narrower bills than those in oak habitat, a pattern that mirrors adaptive differences between allopatric populations of the species' mainland congener (A. californica). Adaptive divergence was not constrained by genetic diversity, even though Island Scrub-Jays had much lower levels of neutral genetic diversity than A. californica. Genetic data indicate that Island Scrub-Jays in pine habitat were more closely related to individuals in adjacent oak habitat than to individuals in other pine stands, indicating that each pine stand can be considered an independent case where adaptive divergence has been maintained in the face of some gene flow with adjacent oak birds. Morphological differences were not abrupt across the pine-oak boundary, as bill length declined gradually with distance from pine habitat, a clinal pattern that is also consistent with a scenario of divergence-with-gene flow. Individuals mated non-randomly with respect to bill length within the population, which may be due to a combination of (1) isolation-by-distance (localized dispersal) across the landscape and spatial autocorrelation in bill morphology, and (2) assortative mating at a more local scale based on bill morphology or correlated acoustic signals. These findings provide strong support for the notion that microgeographic patterns of local adaptation may be more common than is currently appreciated, even in mobile taxonomic groups like birds. They also underscore the importance of conserving Island Scrub-Jays across the entire island in order to preserve the species' full range of biological diversity and to facilitate adaptive responses to future environmental changes.
Open Access
The evolutionary ecology of aquatic insect range limits: a mechanistic approach using thermal tolerance
(Colorado State University. Libraries, 2018) Shah, Alisha Ajay, author; Ghalambor, Cameron K., advisor; Funk, W. Chris, advisor; Poff, N. LeRoy, committee member; Clements, William H., committee member
Understanding the effect of climate variability on species physiology and distribution is a longstanding and largely unresolved challenged in evolutionary ecology with important implications for vulnerability to climate change. My dissertation is focused on understanding the effects of temperature on physiological traits and genetic population structure of aquatic insects, to better understand the mechanisms that underlie their elevation range distributions. For my first chapter, I tested the hypothesis proposed by Dan Janzen in 1967, that temperate mountain species should have broad thermal tolerances thus allowing them to disperse easily across elevation, unhindered by the novel temperatures they encounter. On the other hand, tropical species should exhibit narrower thermal tolerances in response to the stable climate they experience. They should be physiologically challenged to disperse and be restricted to a narrow elevation range distribution. I measured critical thermal limits (CTMAX and CTMIN) and thermal breadth (difference between CTMAX and CTMIN) in several phylogenetically related temperate (Colorado) and tropical (Ecuador) aquatic insect species. I found that, as predicted, species that encounter wider stream temperature ranges, such as temperate species and high elevation tropical species, have broader thermal breadths compared to their tropical and low elevation relatives. Next, I tested how plastic the critical thermal maximum (CTMAX) response was in a subset of aquatic insects. Greater acclimation ability is thought to allow species to withstand the large temperature fluctuations associated with different seasons. Implicit in Janzen's hypothesis, is the assumption that temperate species have greater acclimation ability compared to tropical species. My experiments revealed that temperate and high elevation tropical mayfly species had greater acclimation ability compared to their relatives. However, we found no differences in acclimation capacity in stoneflies. Temperature may therefore not affect all species equally, and species acclimation ability may be a result of other factors such as body shape and evolutionary history. I then measured a third trait, metabolic rate, to investigate how it varies with temperature in temperate and tropical mayflies. Metabolic rate is arguably one of the most important traits for species because it determines the amount of energy an animal has available for its activities. I found that metabolic rates vary between temperate and tropical mayflies, and that temperatures away from a certain optimum are stressful and sometimes lethal for tropical but not temperate mayflies. Finally, I linked thermal tolerance to dispersal by correlating gene flow among populations with pairwise differences in the physiological trait CTMAX. Analyses revealed that there was lower gene flow (higher FST) among populations in Ecuador than among populations in Colorado. Within Ecuador, differences in CTMAX were highly correlated with maximum stream temperature, which was found to best explain tropical mayfly genetic structure. In Colorado, no environmental or physiological variable was found to explain population structure. Our results indicate, as Janzen predicted, that temperature can act as a significant barrier to dispersal among tropical populations but not in temperate ones. Thermal sensitivity measured as CTMAX was also correlated with FST but was not significant. As a whole, the results from my research lend support to Janzen's hypothesis and suggest that temperature plays an important role in determining range limits of aquatic insect species through its effect of thermal tolerance traits. While this research addresses long standing questions in ecology and evolution, it also has conservation implications. Most importantly, as the effects of global climate change augment, the thermally sensitive tropical species from this study system are at particular risk for extreme population declines or even extinction.
Embargo
The genomics of habitat-linked microgeographic adaptation in an island endemic bird
(Colorado State University. Libraries, 2024) Cheek, Rebecca G., author; Ghalambor, Cameron K., advisor; Funk, W. Chris, advisor; Sillett, T. Scott, committee member; Aubry, Lise M., committee member
A fundamental goal of evolutionary biology is to understand the mechanisms that maintain adaptive diversity. This dissertation focuses on the interplay of two key evolutionary mechanisms - natural selection and gene flow. While natural selection is often portrayed as a driving force of adaptive evolution, gene flow is assumed to disrupt selection by introducing maladapted alleles into locally adapted populations. Yet this paradigm is beginning to shift as a growing appreciation for the role gene flow may play in concert with natural selection to facilitate adaptative divergence. I explore this interaction of selection and gene flow in island scrub-jays (Aphelocoma insularis), a highly mobile bird experiencing local adaptation at a microgeographic scale. First, I demonstrated that observed differences in bill morphology between pine-oak ecotones are likely genetically based despite overall limited population genetic structure. Second, I found that the genetic underpinnings of divergent bill morphologies are highly parallel at higher genetic levels, which is indicative of selection acting on shared, but highly polygenic, molecular pathways. Finally, I tested alternate dispersal mechanisms potentially impacting patterns of limited gene flow and found evidence for sex-biased natal habitat preference shaping limited dispersal. Collectively, these results show how gene flow can enhance adaptive divergence at microgeographic scales.

Browsing by Author "Ghalambor, Cameron K., advisor"

Results Per Page

Sort Options