Evolution Commons^™

Sexual Di(Et)Morphism: Using Experimental Evolution To Test Whether Resource Partitioning Promotes Divergence Of The Sexes In Drosophila Melanogaster, Owen A. Jamieson

Theses and Dissertations (Comprehensive)

Sexual dimorphism has been a long-studied phenomenon in the field of evolutionary biology. Usually, these differences in morphology, physiology and/or behaviour between the sexes are studied through the parsimonious lens of sexual selection. However, there are natural history cases where this lens does not seem applicable. Some species show sex specific morphological traits whose presence may not be due to a direct benefit to reproduction, but a difference in how each sex interacts with the environment and differing selective pressures from the environment on either sex. Darwin even brought up examples of this kind of dimorphism and pondered their existence, …

A Geometric Morphometric Analysis Of Acetabular Shape Variation Across Bat Families, Jordan L. Huff

Electronic Theses and Dissertations

Bats are the only mammals capable of powered flight, and research is concentrated on this adaptation. Their non-flight locomotion has received comparatively little attention. Previous studies show that non-flight locomotor behaviors vary across families. Members of Pteropodidae are efficient climbers but cannot effectively walk, whereas Phyllostomidae and Vespertilionidae are better at terrestrial locomotion but show reduced arboreal capabilities. The non-flight locomotion of Hipposideridae and Rhinolophidae is less understood, although rhinolophids exhibit limited terrestrial locomotion. This study examined whether differences in locomotor behavior are associated with variation in acetabular morphology. A geometric morphometric analysis of acetabular shape was conducted across multiple …

Pickleweed In The Disappearing Marsh: Population Genetics & Metal Accumulation In Salicornia Depressa, Alice Kaisla

Graduate Doctoral Dissertations

Salicornia is a genus of succulent halophytes found in salt marshes around the world. Salicornia species have a remarkably high tolerance for heavy metal pollution and have been shown to accumulate high concentrations of heavy metals in their tissue under experimental conditions. As a result, they are both a useful system for studying evolution in polluted coastlines and a potential candidate for use in phytoremediation. My research focuses on Salicornia depressa, known as pickleweed, a species commonly found in marshes along the heavily urbanized and industrialized New England coast. I investigate genetic diversity and population structure in S. depressa populations …

Investigating Cryptic Diversity In The Hawaiian Endemic Plant, Psychotria Mariniana (Rubiaceae), Uyen Thi Hoang Nguyen

Master's Theses

Islands, with their isolation and steep environmental gradients, serve as natural laboratories for studying speciation. Molecular phylogenetic and population genetic methods utilizing Next-Generation Sequencing (NGS) have revolutionized our ability to document patterns of genetic divergence and diversity. Cryptic diversity, genetically distinct populations that were previously unrecognized as unique, and cryptic speciation, where divergent genetic populations may be deserving of status as unique species, have been observed in many taxa. The Hawaiian Islands provide an ideal setting for studying divergence and speciation due to their extreme isolation, known ages, and volcanic origin. Previous work has investigated the evolutionary relationships of the …

Structure And Diversity Of Play Behavior In Juvenile Belding's Ground Squirrels, Paul O'Driscoll Ii

Master's Theses

Play behavior is ubiquitous among juvenile mammals and can promote motor, social, and cognitive development, providing multiple adaptive benefits to young animals in some cases. The structure of play can be linked to the benefits it confers on individuals. I evaluated the structure of play in juvenile Belding’s ground squirrels (Urocitellus beldingi), a species for which multiple adaptive benefits of play have been identified. I compared juvenile play in U. beldingi to adult sexual and aggressive behavior to determine and classify similarities between juvenile play and adult behavior. I evaluated diversity in the behaviors expressed during play interactions and diversity …

Quantifying Genetic Diversity In Nematode Feeding Rate, Jacob King

Honors Theses

Understanding how populations persist under changing environmental conditions is a central question in ecology and evolutionary biology. Variation in traits related to resource acquisition may play a key role in determining population survival when resources are limited or fluctuate over time. In this study, I investigated how variation in feeding-related traits influences population persistence using a combination of computational modeling and laboratory experiments. I developed a stochastic, individual-based consumer–resource model to simulate population dynamics across varying levels of trait variance and resource regimes. Across 60,000 simulated populations, increased trait variation consistently reduced extinction risk and extended persistence time, although the …

Polydactyl Precursors: Insights Into Early Tetrapod Locomotion From Polydactyl American Alligators, Trevor P. Brewington

All Theses

Several of the earliest tetrapod lineages exhibited polydactyl limbs, with seven or eight digits per limb rather than the typical five or fewer seen in extant lineages. How these digit configurations might have been used during terrestrial locomotion is unclear, given the lack of living models in which their performance can be studied and limited evidence from fossil trackways. However, polydactyly occasionally appears in natural populations of American alligators (Alligator mississippiensis), animals with body plans that broadly resemble those of early tetrapods. To test how polydactyl limbs similar to those of early tetrapods might have functioned on land, …

Shape Variation In The Mandible Of The Borophagine Canids And Implications For Predatory Behavior, Benjamin Neavear

Theses, Dissertations and Culminating Projects

The borophagines are an extinct lineage of canids that inhabited North America for more than 20 million years. This group included genera such as Aelurodon, Borophagus, and Epicyon. Borophagines are commonly referred to as “bone-crushing dogs” because their skull morphology converged with that of extant hyenas, predators capable of consuming bone. The purpose of this study was to determine whether convergence was present in the mandible, an anatomical structure strongly correlated with feeding behavior, particularly in the genera Aelurodon and Borophagus. It was hypothesized that most borophagine taxa possessed mandibular shapes similar to those of hyenas. Numerous mandibular characters were …

Morphological Variation Of Lingual Glands In Wild American Alligator (Alligator Mississippiensis) Populations, Benjamin Angalet

Master's Theses

American alligators (Alligator mississippiensis) inhabit diverse aquatic ecosystems including freshwater wetlands, swamps, and estuarine rivers. As apex predators, their physiological resilience has implications for ecosystem stability and long-term conservation. With projected sea-level rise and increasing saltwater intrusion into coastal freshwater habitats, understanding the osmoregulatory capacity of alligators is increasingly important. Unlike marine-tolerant crocodilians such as the saltwater crocodile (Crocodylus porosus), which possess specialized salt-secreting lingual glands in addition to renal and cloacal mechanisms, the morphology and physiological significance of lingual glands in wild American alligators remain poorly understood. This study examined lingual gland morphology and plasma …

The Hitchhiker's Guide To The Host: Fleas And The History Of Pikas In North America, Josh Pletcher

All NMU Master's Theses

Parasite phylogenetics can offer windows into the cryptic evolutionary history of hosts, often highlighting events that are not recorded by the phylogenetics of the host. Pikas (small lagomorphs) host a diverse parasite community comprising endoparasites (e.g., coccidians, nematodes, and cestodes) and ectoparasites (e.g., fleas and mites). Phylogenetic analysis of pika endoparasites has revealed pikas evolved in Asia and colonized North America in two waves, and that contact between these two pika lineages allowed parasites to be transferred from one lineage to another and to survive the extinction of their original host. To uncover these cryptic histories, understanding the biogeography of …

Ontogeny And The Effects Of Perinatal Stress In The First Immature Skeleton Of Teleoceras Aepysoma (Perissodactyla, Rhinocerotidae), Joe Gajewski

Electronic Theses and Dissertations

Recovery of an immature fossil rhinoceros (Teleoceras aepysoma) skeleton (ETMNH 32999) from the Gray Fossil Site in Tennessee offers the first insights into the ontogeny of the species. ETMNH 32999 is interpreted to be a subadult male in an age class equivalent to ~17-20% of potential lifespan. Comparative analyses support the hypothesis that subadults of related taxa are typically ~91% of average adult size in most dimensions. However, certain cranial dimensions are substantially lower than expected in ETMNH 32999, averaging only ~74% of the average conspecific adult. Such departure from typical growth rates is suggested to be attributable …

Sex Or Survival: Does Wounding Elicit A Somatic Reproductive Tradeoff In Narnia Femorata Males?, Lillian E. Burbulis

Departmental Honors & Graduate Capstone Projects

Animals must partition resources into different life history traits resulting in tradeoffs because resources are finite. A tradeoff is the allocation of resources to one trait over another. Theory states that energy is allocated in a hierarchical fashion. For example, somatic maintenance should be a higher priority than reproduction, resulting in more resources being allocated to somatic maintenance compared to reproductive traits. The metabolic investment hypothesis states that energy must follow a hierarchical order prioritizing somatic maintenance over reproduction. Another hypothesis for energy allocation is the terminal investment hypothesis. This hypothesis states that energy will be allocated to reproduction over …

Not Just Static: Evolutionary Throughlines In The Female Voice, Maria Hand '26

Honor Scholar Theses

Vocal communication is essential for many forms of human interaction and discourse. As such, the human voice has been the subject of extensive scientific research in a variety of contexts, including that of potentially evolved characteristics. Researchers have long studied the various changes that occur in direct relation to hormonal shifts across the ovulatory cycle, but one particularly interesting facet of this research is the voice. There are numerous acoustic parameters that are highly socially salient, and thus an ideal means with which to study potential ovulatory cycle related changes. Studies of this subject additionally provide further insight into the …

Evolution Of Antibiotic Responses During Chronic P. Aeruginosa Infections In The Human Lung, David Frank Ritz

Dartmouth College Ph.D Dissertations

Typical antibiotic susceptibility testing (AST) of microbial samples is performed in homogeneous cultures in batch environments, which does not account for the highly heterogeneous and dynamic nature of antibiotic responses. The most common mutation found in P. aeruginosa lineages evolved during chronic cystic fibrosis infections in the human lung, a loss of function of repressor MexZ, increases basal levels of multidrug efflux MexXY, but does not increase resistance by traditional minimal inhibitory concentration (MIC) assays. Here, we use single cell microfluidics to show that P. aeruginosa’s response to aminoglycosides is highly heterogeneous, with only a subpopulation of cells surviving exposure. …

The Presence Of Predators Moderates Evolutionary Responses Of Trinidadian Killifish To A Novel Parasite, Anne E. Christian

Biology Dissertations

The Healthy Herds Hypothesis suggests the idea that prey populations derive a benefit from their predators: predators reduce the exposure of their prey to infectious disease, both by limiting prey population densities and by eliminating sick individuals. Much research has focused on the balancing effect that predators have on ecosystems. There is a current need for research into whether these effects cause evolutionary shifts in prey populations, where strong predation pressure prevents prey species from evolving physiological tolerance or resistance to infectious agents. Parasites especially often have rapid effects on host evolution, due to exploitative interactions.

I seek to address …

Stress And Reward Interactions In Substance Use Disorder: An Evolutionary Mismatch Framework, Nicholas L. Castrucci

Honors Theses and Capstones

Substance use disorder (SUD) is a major public health concern characterized by compulsive substance use despite adverse consequences. While contemporary models emphasize biological, psychological, and environmental contributors, stress- and reward-related systems are often examined in isolation. This review integrates these systems within an evolutionary mismatch framework to examine how chronic stress exposure and repeated substance use increase vulnerability to addiction. Stress and reward systems are evolutionarily conserved but may become chronically dysregulated under modern conditions characterized by persistent psychosocial stressors and highly potent rewarding stimuli. This is associated with converging neuroadaptations across stress and reward circuitry, resulting in altered affective …

The Impacts Of Wing-Flashing By Northern Mockingbirds On Foraging, Parental Care, And Reproductive Success, Anna R. Starman

Undergraduate Honors Theses

Foraging efficiency may be enhanced by flashing patches of white wing and tail feathers and has been documented in several avian species. Northern Mockingbirds (Mimus polyglottos, NOMO) exhibit this “wing-flashing” (WF) behavior while foraging, during displays, and in response to predators. In NOMOs, WF has been hypothesized to increase foraging success, but previous findings are inconclusive. To further investigate the biological role(s) of WF behavior in NOMOs, the ventral surface of white primary feathers of male NOMOs were artificially darkened, and the foraging and provisioning rates of undarkened (control) males and their mates were compared. While foraging, undarkened …

Equid Major Histocompatibility Complex (Mhc) Evolution & Genome Organization, Lauren C. Johnson

Theses and Dissertations--Veterinary Science

The evolution of modern horses has a well-documented fossil record and has long been of interest to the genetics community. Although non-caballine equids (e.g. zebras, donkeys, and asses) can hybridize with horses, the resulting offspring are typically infertile. Despite these reproductive barriers, genomic analyses reveal regions of high sequence similarity among equid species. This dissertation investigates the role of historical introgression in the evolution of modern Equus species. The first chapter re-evaluates earlier findings derived from a limited horse population and a single reference genome. The variants of the identified regions were pushed through Ensembl’s Variant Effect Predictor to assess …

Analysis Of Alternative Oxidase In Non-Angiosperm Plants, Anissa M. Francis

Theses and Dissertations (Comprehensive)

Alternative oxidase (AOX) is a mitochondrial terminal oxidase that provides an alternative pathway for electron transport, allowing plants to maintain respiratory flexibility under environmental stress conditions. While AOX has been extensively studied in angiosperms (flowering plants), little is known about its distribution and conservation in non-angiosperms. Based on gaps identified in the literature, this thesis investigated the distribution of AOX across non-angiosperm plant lineages. Although AOX is present in many green algae and is therefore considered to be an ancient protein that originated before the existence of non-angiosperm plants, it remains unclear whether the protein is uniformly distributed across these …

Sex In Plants: Birth, Death, And Trying To Survive In Changing Climates, Elena M. Meyer

Theses and Dissertations

Plant mating systems are key determinants of fitness. Angiosperms exhibit a wide variety of reproductive strategies, including self-fertilization (or selfing), outcrossing, and mixed mating. It has been estimated that up to 43% of plant species are capable of selfing, and selfing has been hypothesized to provide reproductive assurance where opportunities for mating may be limited, such as in marginal environments. However, questions regarding the overall distribution of selfing rates across angiosperms, the maintenance of mixed mating in the face of inbreeding depression, and the impact of self-fertilization on diversification rates remain incompletely resolved. Here, we explore the dynamics of self-fertilization …

Phylogeography, Fungal Host Specificity, And Fitness In The Corallorhiza Maculata Species Complex, Hana Thixton-Nolan

Graduate Theses, Dissertations, and Problem Reports (ETD)

Mycoheterotrophic plants exploit fungi for most or all nutritional needs, providing a compelling system to address the evolutionary consequences of genome reduction, population-level variation, and germination requirements. I am using the widespread Corallorhiza maculata species complex to address questions of genomic variation, fungal host specificity, morphological variation, and germination requirements across the broad geographic range from Mexico to northern North America. This complex contains C. bulbosa, C. macrantha, and C. mertensiana, the latter with three varieties (maculata, occidentalis, and mexicana). These taxa vary in flowering time, floral morphology, and fungal associations. However, the degree …

How Semiflightless Birds Adapt: A Survey From Barú, Costa Rica, Eli P. Laloudakis

Scripps Senior Theses

When we think of birds, we think of flight. Because of this, scientific research often focuses on how birds evolved flight and how their wings function during flight. However, not all birds can fly or fly well, as wings wax and wane on developmental, seasonal, and evolutionary time scales (Dial and Heers 2021). Consequently, rudimentary wings can be found in developing birds, secondarily flightless or semiflightless birds, birds that undergo simultaneous molts, and extinct theropods with “protowings” (structures that preceded fully functional wings). Secondarily flightless and semiflightless birds often evolve where there is no/low predation, abundant year-round food supply, and …

Overview And Methods Of Molecular Paleontology: A Review, Shelby Touchstone

Williams Honors College, Honors Research Projects

Molecular paleontology—the study of ancient biomolecules preserved in fossils and sediments, including ancient DNA, lipids, and proteins—has motivated researchers since the 1950s, inspiring both scientific inquiry and broader cultural imagination. Think Jurassic Park. This honors thesis presents a comprehensive review of the history, current state, and methods of the field of molecular paleontology. Drawing on peer-reviewed literature and scholarly resources accessed through databases such as EBSCO and Bierce library, this review examines key techniques such as Next Generation Sequencing and amino acid racemization and will go over limitations and controversies in the field. It will also explore potential new …

Dosage Sensitivity And The Evolution Of Dosage Compensation: Tests Of The Insensitive Sex Chromosome Hypothesis In Flour Beetles, Shana Pau

Biology Dissertations

Sex chromosome evolution generates imbalances in gene dosage that can disrupt gene expression and organismal function. These imbalances are often resolved through dosage compensation mechanisms, yet the factors that drive the emergence and diversity of these systems remain poorly understood. This dissertation addresses a central question in evolutionary genomics: what governs the evolution of dosage compensation?

Focusing on dosage sensitivity as a potential driver, I evaluate the Insensitive Sex Chromosome Hypothesis (ISCH), which predicts that chromosome-wide compensation is more likely to evolve in genomic contexts that are not depleted of dosage-sensitive genes. Using flour beetles (Tribolium spp.) as a …

A Review Of Mockingbird Song, Jacqueline Milander

Student Theses

The northern mockingbird (Mimus polyglottos) is known for its large repertoire and highly versatile song patterns.  It is a frequent mimic that is thought to continue learning sounds from its environment for the duration of its life.  Utilizing available song studies, this is a comprehensive review of northern mockingbird song, including learning, mimicry, repertoires, song dependence on seasonal cyclicity, and song function, particularly interspecific territoriality. While much discussion has surrounded the idea that northern mockingbirds engage in interspecific territoriality and that vocal mimicry functions in intersexual selection, this review provides new insight into the possibility that latitudinal differences among populations …

Exploring Factors Mediating White-Nose Syndrome In Little Brown Bats, Carly R. Trujillo

Graduate Theses/Dissertations

The little brown bat (Myotis lucifugus) has experienced drastic population declines across North America due to the recent disease white-nose syndrome (WNS). Previous studies have identified putatively adaptive alleles (PAAs) that may give individuals a greater likelihood of survival. However, there could be geographic-specific adaptation, creating different adaptive landscapes. Additionally, there may be energetic trade-offs between disease survival and reproductive output, and it is not clear what the long-term survival outcomes for the species may be as a result. Long-term evolutionary outcomes are unclear because this species has a lifespan exceeding the arrival of WNS and is difficult …

Homoplasy Of Maxillary Orthognathism In Derived Homo, Jared Jordan

Graduate Studies Theses and Dissertations 2026

The evolution of the orthognathic condition in the genus Homo represents a monumental transition toward the facial morphology of modern humans from that of earlier hominins, but the phylogenetic positioning of this transformation remains poorly understood. This study investigated temporal trends in maxillary and mandibular prognathism in the genus Homo, and whether maxillary and mandibular shortening in East Asian H. erectus and later East Asian Middle Pleistocene Homo (e.g., Homo longi) represent independent derivations of orthognathic morphology, thereby making orthognathism a homoplasy in the genus Homo. Using a sample of roughly 109 cranial and mandibular specimens spanning …

Population Structure Analysis Of Four Basal Higher-Attines Using Bioinformatic Approaches, Gabriel Mcdanield

Biology Theses

Metapopulations within the family Formicidae are unique among other animals due to the large colonies they build, and the mating strategies required to fertilize a specialized reproductive caste that will often produce young for the life of the colony. One group of ants, the fungus-gardeners (tribe Attini). The population structure of North American non-leafcutting, fungus-gardening ants has been understudied, especially in the southwest of the United States. Additionally, not much is known about their dispersal biology, so the dynamics of dispersal of these species and how they affect population structure is likewise not well known. To shed light on the …

Phylogenetic Comparative Vocal Evolution, Casper W. Buchanan

Master's Theses

Vocal learning is a trait unique to humans, bats, cetaceans, primates, and birds (Jarvis & Nottebohm, 1997; McComb & Semple, 2005; Wilbrecht & Nottebohm, 2003). Although there has been extensive research on vocal learning in songbirds, parrots are an even closer proxy to human learning, as they are social, intelligent, and lifelong learners, with some having repertoires of over 300 sounds (Benedict et al., 2022; Péron et al., 2011; Thomsen et al., 2019; Toft & Wright, 2015). Elevated vocal learning can be attributed to the need for parrots to have strong communication skills through the sharing of information over foraging, …

Using Rattlesnake Venom To Model Complex Trait Evolution Across Ecological And Evolutionary Scales, Samuel R. Hirst

USF Tampa Graduate Theses and Dissertations

A central challenge in evolutionary biology is understanding how genetic variation leads to phenotypicdiversity, particularly for complex traits that strongly influence fitness. Traits form the substrate of natural selection, but it is genes, that are inherited across generations. To fully understand the evolutionary process, we must therefore connect the molecular basis of trait variation with the evolutionary outcomes of such traits.

For relatively simple traits, the genotype–phenotype relationship is well understood. Classic systems, such as coat color in beach mice or toxin resistance in garter snakes, have provided effective examples of how relatively few loci underlie conspicuous adaptive differences across …