Ecology and Evolutionary Biology Commons^™

Consequences Of The Megafauna Extinction: Changes In Food Web Networks On The Edwards Plateau Across The Pleistocene-Holocene Transition, Quentin A. Smith Jr.

School of Biological Sciences: Dissertations, Theses, and Student Research

We are experiencing biodiversity loss due to climate change and human impacts, which is not only harmful to the environment but can also alter the composition of communities and interactions among species. The late Pleistocene experienced a loss of large-bodied mammals which resulted in significant changes in community structure due to changes in body size, diet, and species associations. The impact of these changes on species interactions and community structure across the Pleistocene-Holocene transition remains poorly understood. Using a robust data set of species composition, stable isotopes, body size, and climate variables, we constructed and compared ecological networks of mammal …

A Tale Of Two Genomes: The Complex Interplay Between The Mitochondrial And The Nuclear Genomes, Abhilesh S. Dhawanjewar

School of Biological Sciences: Dissertations, Theses, and Student Research

Mitochondria, the product of an ancient endosymbiotic event are pivotal to eukaryotic cells by synthesizing the majority of the cell’s ATP output. However, modern- day mitochondria are completely dependent on more than one thousand nuclear-encoded products for their function and the maintenance of their genomes. The fundamentally different ways in which the mitochondrial (mtDNA) and the nuclear (nucDNA) genomes are replicated and inherited lead to captivating coevolutionary dynamics between them. The aims of this dissertation are to investigate the coevolutionary dynamics between the mitochondrial and nuclear genomes at three distinct biological scales. At the organismal level, we use a Drosophila …

Discovering Novel Polyextremotolerant Fungi, And Determining Their Ecological Role Within The Biological Soil Crust Consortium, Erin Carr

School of Biological Sciences: Dissertations, Theses, and Student Research

The ecological niche of polyextremotolerant fungi within oligotrophic ecosystems such as biological soil crusts has not yet been determined. These fungi persist in locations where nutrients are depleted while simultaneously surrounded by autotrophic microbes such as algae and cyanobacteria. Yet it has not been shown that they are engaging in any exchange of nutrients the way lichens do. However, there is seemingly no other way for these fungi to obtain vital nutrients, such as carbon or nitrogen, other than from these microbes. Here we have isolated polyextremotolerant fungi from cold desert biological soil crusts which are a microbial biofilm that …

Prey Selection By Birds Of Prey, Anisha Pokharel

School of Biological Sciences: Dissertations, Theses, and Student Research

Prey selection is key to determine predator prey interaction and understanding the complexity of food web structure. In this thesis, we used two different approaches to understanding prey selection by North American birds of prey. Using a conventional method, in Chapter 1 we compared pellet analysis and trapping data to assess patterns of prey selection of barn owls in western Nebraska. Microtus spp. comprised 55.8% of the prey items in the barn owl’s diet. The proportion of several prey types in the diet were significantly different from the expected proportion based on trapping. This pattern may indicate barn owls actively …

Plant Mitochondrial Genome Evolution And Structure Has Been Shaped By Double-Strand Break Repair And Recombination, Emily Wynn

School of Biological Sciences: Dissertations, Theses, and Student Research

Plant mitochondrial genomes are large but contain a small number of genes. These genes have very low mutation rates, but genomes rearrange and expand at significant rates. We propose that much of the apparent complexity of plant mitochondrial genomes can be explained by the interactions of double-strand break repair, recombination, and selection. One possible explanation for the disparity between the low mutation rates of genes and the high divergence of non-genes is that synonymous mutations in genes are not truly neutral. In some species, rps14 has been duplicated in the nucleus, allowing the mitochondrial copy to become a pseudogene. By …

Condition-Dependent Life History Strategies, Shivani V. Jadeja

School of Biological Sciences: Dissertations, Theses, and Student Research

Many organisms evolve condition-dependent life history strategies to maximize their lifetime fitness in response to intrinsic and extrinsic processes. I investigated a sequentially flowering plant’s strategy to allocate resources to retain flowers versus grow existing basal fruits to a larger size, using the plant Yucca glauca. The sink strength hypothesis suggests basal fruits are nutrient sinks depriving distal flowers of resources and reducing their probability of retention. A low probability of retention of distal flowers can also be explained by the architectural effects hypothesis. This hypothesis posits inherent positional differences in structures along an inflorescence such as flower size …

Resource Allocation For Acorn Production: A Comparison Across Species Pairs Of Oaks With Contrasting Acorn Production Patterns And Water Use Strategies, Kyle A. Funk

School of Biological Sciences: Dissertations, Theses, and Student Research

Mast seeding, or masting, is a phenomenon where inter-annual seed production by individuals is synchronized across a population of plants. Masting is hypothesized to confer a selective advantage to plants by increasing rates of pollination or by decreasing rates of seed predation. Masting can also play a crucial role in ecosystem functioning as fluctuations in annual seed crops correspond with fluctuations in seed predator populations, which in turn have consequences that ripple throughout food webs. The mechanism(s) that causes masting is unresolved, but the high variability in seed production of masting plants is hypothesized to be caused, in part, by …

Nitrogen Addition And Ecosystem Functioning: Changes In Species Composition Leaf Traits Amplify Increases In Leaf Area Index And Canopy Chlorophyll, Anna R. Tatarko

School of Biological Sciences: Dissertations, Theses, and Student Research

Increased nutrient inputs can cause shifts in plant community composition and plant functional traits, both of which affect ecosystem function. We studied community- and species-level changes in specific leaf area (SLA), chlorophyll, leaf thickness, leaf toughness, plant height and leaf dry matter content (LDMC) in a full factorial nitrogen (N), phosphorus (P), potassium (K) fertilization experiment in a semi-arid grassland. Nitrogen was the only nutrient addition to significantly affect leaf functional traits, and N addition increased community weighted SLA by 19%, leaf chlorophyll content by 34%, height by 26%, and resulted in an 11% decrease in LDMC while leaf thickness …

Behavioral Plasticity Across Non-Social Contexts In Female Green Swordtails, Xiphophorus Hellerii, Lindsey M. Coit

School of Biological Sciences: Dissertations, Theses, and Student Research

Phenotypic plasticity is the ability of an individual to alter its phenotype in response to environmental change. Individuals that express plasticity in behavior can quickly respond to changes that occur in the environment. Therefore, individuals that exhibit behavioral plasticity can alter their behavioral expression to best match current environmental conditions. The degree and direction of behavioral plasticity may be influenced by variation in individual characteristics. Understanding how variation in individual traits affects behavioral plasticity, and, whether patterns of behavioral plasticity are consistent across behavioral contexts are important topics to explore as we try to better understand how plasticity evolves and …

The Plasticity Of Functional Traits In The Dipterocarps Of Borneo, Ju Ping Chan

School of Biological Sciences: Dissertations, Theses, and Student Research

Plasticity plays an important role in the adaptation of sessile organisms like plants to the environment. Plants have been shown to respond plastically in heterogeneous environments, with plants originating from more resource-diverse environments thought to display greater plasticity. There is also evidence that fast-growing species show greater plasticity, as acquisition of resources from resource flushes is greatly aided by faster adaptations. We tested these theories in a Bornean tropical rain forest among three soil specialization groups (clay specialists, sandy loam specialists, and generalists) using two treatments of soil (clay versus sandy loam) and two treatments of light (high versus low). …

Inter- And Intra-Individual Variation In Predator-Related Behavioral Plasticity Expressed By Female Green Swordtails (Xiphophorus Hellerii), Rachael A. Disciullo

School of Biological Sciences: Dissertations, Theses, and Student Research

Phenotypic plasticity is the ability of one genotype to express multiple phenotypes under variable environments. Behavioral plasticity is a type of phenotypic plasticity in which individuals adjust behavior in response to changes in environment. Often, behavioral plasticity is studied at the level of the population, rather than at the level of the individual. Further, few studies have considered the effect of individual traits, such as size and age, on the expression of behavioral plasticity, or, how individual plasticity may be correlated across different contexts. In this study, we used female green swordtails (Xiphophorus hellerii) to test the effects …

Proximate And Evolutionary Causes Of Sexual Size Dimorphism In The Crab Spider Mecaphesa Celer, Marie Claire Chelini

School of Biological Sciences: Dissertations, Theses, and Student Research

Animal species’ body sizes result from the balance between selection for survival and selection for reproduction. In species with sexual size dimorphism (SSD), this balance differs between females and males, resulting in distinct sizes despite similar constraints. I used an integrative approach to understand how sexual section, and differences in developmental trajectories and metabolic physiology, resulted in the female biased SSD of the crab spider Mecaphesa celer (Thomisidae). SSD in spiders is often assumed to be a consequence of selection for early male maturation, which should provide males with additional mating opportunities. My results allow us to discard mate …

The Joint Effect Of Phenotypic Variation And Temperature On Predator-Prey Interactions, Jean P. Gibert

School of Biological Sciences: Dissertations, Theses, and Student Research

Understanding the factors underpinning to food web structure and stability is a long-standing issue in ecology. This is particularly important in a context of global climate change, where rising environmental temperatures may impact the way species interact, potentially leading to changes in food web structure and to secondary extinctions resulting from cascading effects. In order to understand and predict these changes, we need to hone our comprehension on the way predators and their prey interact. Recent studies suggest that, in order to do so, we need to focus on the traits controlling those interactions, such as body size. Mean body …

Population And Morphological Changes In American Kestrels Through Space And Time, Teresa E. Ely

School of Biological Sciences: Dissertations, Theses, and Student Research

A once common raptor, the American kestrel (Falco sparverius) has experienced population declines in the last two decades throughout North America. Many hypotheses exist about the decline, including mortality from West Nile virus, rodenticide poisoning, climate change, an increase in predators, and core habitat loss or degradation, which could influence food availability. Food availability is key to raptor survival and reproduction, and changes in food availability throughout the year can have lifelong effects on size and body condition. Here we examine how morphology, specifically mass and wing chord, has changed at seven migration sites throughout North America as …

Expansion Of The Chlorovirus Genus By Studies On Virus Natural History And Chlorella Host Metabolism, Cristian F. Quispe

School of Biological Sciences: Dissertations, Theses, and Student Research

Inland waters cover about 2.5 percent of our planet and harbor huge numbers of known and unknown microorganisms including viruses. Viruses likely play dynamic, albeit largely undocumented roles in regulating microbial communities and in recycling nutrients in the ecosystem. Phycodnaviruses are a genetically diverse, yet morphologically similar, group of large dsDNA-containing viruses (160- to 560-kb) that inhabit aquatic environments. Members of the genus Chlorovirus are common in freshwater. They replicate in eukaryotic, single-celled, chlorella-like green algae that normally exist as endosymbionts of protists in nature. Very little is known about the natural history of the chloroviruses and how they achieve …

Plasticity In Female Mate Choosiness: A Result Of Variation In Perceived Predation Risk And The Interaction Of Female Age And Male Density, Ashley Atwell

School of Biological Sciences: Dissertations, Theses, and Student Research

In many species, female mate choices can be a strong source of sexual selection. Females often prefer a certain male phenotype, and this can be due to benefits females gain from mating with preferred males. However, such benefits can sometimes be outweighed by the cost of searching for a preferred male. These costs and benefits often change concomitantly with changes in environmental (e.g., predator abundance and conspecific density) and internal factors (e.g., female age). Thus, female mate choosiness (the degree to which preferences for certain males are expressed) should often be plastic. Plasticity in female mate choosiness may be complicated …

The Equitable Contributions Of Environment, Management And Restoration Status On Grassland Diversity And Composition, Raeann C. Powers

School of Biological Sciences: Dissertations, Theses, and Student Research

Plant composition is controlled by a combination of environmental, biotic, historical and management factors. Although there has been much focus on restoring grassland diversity, it is unclear which factors and/or interactions of factors are constraining diversity in grasslands and the relative influences of different factors. We measured soil fertility, soil texture, grazing intensity, fire frequency and plant cover in 694 plots, located within 33 remnant and restored fields in managed grasslands in the central Great Plains. Using univariate (general linear model) and multivariate (PERMANOVA) analyses, we identified significant factors and their relative contributions to plant richness, evenness, floristic quality index …

Stress Responses And Energy Storage In Drosophila Melanogaster Selected For Resistance To A Gram-Positive Bacillus Cereus Spores, Zhen Hu

School of Biological Sciences: Dissertations, Theses, and Student Research

A survival response study was carried out by using D. melanogaster and the opportunistic pathogen B. cereus as the agent of selection. The spores of B. cereus, a gram-positive bacteria that can cause the human pathogen disease, were applied in our artificial laboratory selection. Selected lines were treated with B. cereus spores. Wound control lines were punctured with a needle dipped into sterile H₂O. Control lines did not apply any treatment. Three different environmental treatments were used within each line type (autoclaved spores of B.cereus, sterile H₂O and no treatment). The autoclaved spores were …

Costs Of Female Mating Behavior In The Variable Field Cricket, Gryllus Lineaticeps, Cassandra M. Martin

School of Biological Sciences: Dissertations, Theses, and Student Research

Female animals may risk predation by associating with males that have conspicuous mate attraction traits. The mate attraction song of male field crickets also attracts lethal parasitoid flies. Female crickets, which do not sing, may risk parasitism when associating with singing males. If parasitism risk is sufficiently high, it may affect the evolution of female mating behaviors. In this dissertation, I explore the interaction between the female variable field cricket, Gryllus lineaticeps, and the parasitoid fly, Ormia ochracea. To begin, I investigated whether female parasitism risk resulted from being near singing males. I found that females can become …

The Roles Of Phenotypic Plasticity And Genotypic Specialization In High Altitude Adaptation, Danielle M. Tufts

School of Biological Sciences: Dissertations, Theses, and Student Research

In vertebrates living at high altitude, arterial hypoxemia may be ameliorated by reversible changes in the oxygen-carrying capacity of the blood (regulated by erythropoiesis) and/or changes in blood–oxygen affinity (regulated by allosteric effectors of hemoglobin function). These hematological traits often differ between taxa that are native to different elevational zones, but it is often unknown whether the observed physiological differences reflect fixed, genetically based differences or environmentally induced acclimatization responses (phenotypic plasticity). Here, we report measurements of hematological traits related to blood–O₂ transport in populations of deer mice (Peromyscus maniculatus) that are native to high- and low-altitude …

The Origin And Molecular Evolution Of Two Multigene Families: G-Protein Coupled Receptors And Glycoside Hydrolase Families, Seong-Il Eyun

School of Biological Sciences: Dissertations, Theses, and Student Research

Multigene family is a group of genes that arose from a common ancestor by gene duplication. Gene duplications are a major driving force of new function acquisition. Multigene family thus has a fundamental role in adaptation. To elucidate their molecular evolutionary mechanisms, I chose two multigene families: chemosensory receptors and glycoside hydrolases. I have identified complete repertoires of trace amine-associated receptors (TAARs), a member of chemosensory receptors, from 38 metazoan genomes. An ancestral-type TAAR emerged before the divergence between gnathostomes (jawed vertebrates) and sea lamprey (jawless fish). Primary amine detecting TAARs (TAAR1-4) are found to be older and have evolved …

Predation And Behavioral Plasticity In Green Swordtails: Mate Choice In Females And Exploratory Behavior In Males, Andrew J. Melie

School of Biological Sciences: Dissertations, Theses, and Student Research

Two studies were carried out with green swordtails, Xiphophorus helleri, to investigate the effect of predation on swordtail behavior, and to determine how behavioral plasticity operates in both a mate choice and an anti-predator context. Male green swordtails vary in colorful conspicuous traits, e.g. the colorful dorsal fin and sword. Female swordtails have a preexisting bias for males with a sword, and prefer long-sworded males to short-sworded males, but this preference is plastic. The first study examined predator-related plasticity in the behavior of males differing in size. Smaller males showed greater behavioral plasticity; they were more active in the absence …

Spontaneous Male Death And Monogyny In The Dark Fishing Spider Dolomedes Tenebrosus Hentz, 1843 (Araneae, Pisauridae), Steven K. Schwartz

School of Biological Sciences: Dissertations, Theses, and Student Research

Male animals typically attempt to mate with multiple females in order to increase their reproductive success. In some species, however, males instead invest in fertilizing the eggs of a single female. Monogyny (male monogamy) is found in a diverse assemblage of taxa, and recent theoretical work reveals that a male-biased sex ratio can favor the evolution of this relatively rare mating system. We integrate this theoretical framework with field observations and laboratory experiments involving the sexually size dimorphic fishing spider, Dolomedes tenebrosus. Results from mating trials revealed a novel form of self-sacrifice behavior where males spontaneously die when they …

Foraging Challenges: Unsuitable Prey And Limited Information, Travis M. Hinkelman

School of Biological Sciences: Dissertations, Theses, and Student Research

Food acquisition is a complicated task. The profitability of potential food items depends on numerous factors, including the spatial distribution, probability of detection and capture, and suitability of the food. Animals faced with such challenges can use relatively simple mechanisms to maximize foraging efficiency. However, mechanisms that maximize foraging efficiency under some ecological conditions (e.g., prey scarcity) may produce ostensibly suboptimal behavior under different ecological conditions (e.g., prey abundance). In the work presented here, we explore two facets of foraging: (1) consuming unsuitable prey, and (2) searching for resources with limited information about resource location. To explore the consequences of …

Gene Duplication And The Evolution Of Hemoglobin Isoform Differentiation In Birds, Michael T. Grispo

School of Biological Sciences: Dissertations, Theses, and Student Research

The majority of bird species co-express two functionally distinct hemoglobin (Hb) isoforms in definitive erythrocytes: HbA (the major adult Hb isoform, with α-chain subunits encoded by the α^A-globin gene) and HbD (the minor adult Hb isoform, with α-chain subunits encoded by the α^D-globin gene). The α^D-globin gene originated via tandem duplication of an embryonic α-like globin gene in the stem lineage of tetrapod vertebrates, which suggests the possibility that functional differentiation between the HbA and HbD isoforms may be attributable to a retained ancestral character state in HbD that harkens back to a primordial, …

Herbivory Affects Patterns Of Plant Reproductive Effort And Seed Production, Natalie M. West

School of Biological Sciences: Dissertations, Theses, and Student Research

Insect herbivory can have a major influence on plant reproduction, and potentially drive selection for strategies that reduce or resist herbivore effects. I used a combination of field experiments and ecological modeling to examine how modifications in the patterns and timing of reproductive investment might ameliorate the consequences of herbivore damage for plant reproduction. I performed experiments to examine how changes in reproductive effort after apical damage and reduction of insect herbivory affected seed production in two thistles native to Nebraska. I then used field data to parameterize a life history model predicting the resource allocation among buds and size …

Life History Tradeoffs And Phenotypic Plasticity: The Tale Of A Flight Polyphenic Field Cricket, Chandreyee Mitra

School of Biological Sciences: Dissertations, Theses, and Student Research

Most organisms are resource limited. Such limitations can result in tradeoffs between life history traits -- any traits that affect survival or reproduction. Flight polyphenic field crickets are thought to be a classic example of such a life history tradeoff, in which individuals tradeoff investment in flight capability and investment in reproduction. This polyphenism results from the interaction of two morphological traits: wing morphology (short or long) and flight muscle morphology (functional pink or non-functional white), and is affected by both genes and the environment. I examined life history traits of a flight polyphenic field cricket, Gryllus lineaticeps. First, …

The Complexities Of Wolf Spider Communication: Exploring Courtship Signal Function In Rabidosa Rabida, Dustin J. Wilgers

School of Biological Sciences: Dissertations, Theses, and Student Research

Evidence of signal complexity is seemingly pervasive across animal communication systems. Exploring signal function may provide insight into how these displays evolved and are maintained. This dissertation examines the courtship signal function in a grassland wolf spider. Rabidosa rabida lives in an extremely complex environment, and males use complex displays incorporating both visual and seismic modalities. Using several approaches I provide insight into the content and efficacy of the various signal components, as well as how variation in these displays influence female mating decisions in isolation and combined.

First, I manipulated male and female body condition using diet quantity manipulations …

Multilocus And Parametric Analyses Of The Evolutionary History Of The Amazonian Peacock Cichlids, The Genus Cichla (Teleostei: Cichlidae), Stuart Willis

School of Biological Sciences: Dissertations, Theses, and Student Research

Accurate knowledge of species boundaries and species phylogeny are fundamental to testing hypotheses of recent evolutionary processes, but the estimation of these partitions is challenging due both to inherent confusion about what is being estimated as well as the data available to estimate them. Using multilocus data from mtDNA, microsatellites, and nuclear locus sequences of over 1100 individuals, we delimited eight separately evolving species of Cichla rather than the 15 described. Among species we found evidence of rare but widespread introgressive hybridization, while within these species we observed evidence of long-term gene exchange and constrained evolutionary trajectories. In most cases …

Ecological Effects Of Virus-Resistant Transgenic Squash, Holly R. Prendeville

School of Biological Sciences: Dissertations, Theses, and Student Research

Two ecological risks associated with the use of transgenic crops include the effects of transgene products on non-target organisms and the effects of a transgene after it moves from crops into a wild plant population. In work presented here, we specifically investigate the ecological risks of virus-resistant transgenic squash. We observed pollinator behavior to determine if pollinators are affected by nontarget effects of the virus-resistant transgene. We found that pollinator behavior did differ between conventional and virus-resistant transgenic squash due to pleiotropic effects of the transgene. This difference in pollinator behavior can affect plant mating patterns, thereby affecting crop-wild hybridization …