PhD, University of Cincinnati, 2024, Arts and Sciences: Biological Sciences

Oxygen is a basic necessity of life for nearly all species. However, owing to environmental or medical conditions, the required concentration of oxygen to maintain metabolic demand may not be available. Interestingly, while some species struggle with even modest changes to oxygen concentration, others can withstand large fluctuations including periods of extremely low oxygen (hypoxia). Fishes inhabit nearly all aquatic environments, inclusive of well- and poorly- oxygenated conditions, making them especially suitable to study the effects of hypoxia. However, the evolutionary mechanisms that enabled these traits to arise are relatively unknown. The blind Mexican cavefish, Astyanax mexicanus, presents a unique model to study both adaptations to hypoxia as well as the underlying evolutionary mechanisms. This species is comprised of two morphotypes, an ‘ancestral-surrogate' surface morphotype that resides in well-oxygenated lakes, rivers, and streams of northeastern Mexico and the southwest United States, and an obligate cave-dwelling morphotype found in numerous distinct caves throughout the limestone karst of northeastern Mexico that are likely hypoxic. This drastic environmental shift prompted the necessity to adapt to the harsh conditions within caves. While many cavefish traits have been characterized, adaptations to hypoxia have received very little attention. In this dissertation, I aimed to begin to characterize traits in cavefish that may confer adaptive advantages to living in hypoxic conditions. First, we discuss empirical measurements of dissolved oxygen as well as the environmental features that likely contribute to the hypoxic condition of caves. We then investigated morphological changes to red blood cells that enable a higher concentration of hemoglobin protein in circulation. Subsequently, we set out to determine how individual hemoglobin orthologs are regulated to contribute to the aggregate increase of hemoglobin protein. Additionally, we revealed une (open full item for complete abstract)

Committee: Joshua Gross Ph.D. (Committee Chair); Stephanie Rollmann Ph.D. (Committee Member); Brian Carlson Ph.D. (Committee Member); Michael Booth Ph.D. (Committee Member); Daniel Buchholz Ph.D. (Committee Member) Subjects: Biology

PhD, University of Cincinnati, 2018, Arts and Sciences: Biological Sciences

The vertebrate skull has undergone dramatic morphological changes across evolutionary history. While the cell lineages and genes involved in cranial development are well conserved across vertebrates, the precise mechanisms involved in facial patterning giving rise to diverse features remain largely uncharacterized. Further, the cranium is made up of multifarious tissues making up the nervous, vascular, visual, muscular and skeletal systems. The putative interactions between these tissues during development and their involvement in facial patterning are presently unclear. The complex nature of the cranium poses a challenge in modeling cranial development. Natural animal systems, particularly those evolving under extreme environmental pressures, provide the opportunity to advance our understanding of how the changes to the skull arise in nature. As a consequence of life in complete darkness, the blind Mexican cavefish has evolved extensive morphological changes within the cranium, such as complete loss of the eyes. Cavefish also harbor numerous bony alterations and asymmetries within the craniofacial complex. In contrast, cavefish have dramatically expanded their sensory system, increasing the number of both tastebuds and mechanoreceptor neuromast organs within the cranium. In this dissertation, I first determine when during life history, cranial malformations and asymmetries arise in cavefish. Next, I characterize the developmental mechanisms involved in abnormal cranial bone formation in cavefish. Finally, I describe interactions between bone development and sensory organs within the cranium. The dichotomy between sensory expansion and abnormal bone development establishes cavefish as an excellent and integrative model system for understanding the biological processes involved in craniofacial patterning. The results presented here inform on mechanisms of craniofacial evolution across vertebrates, as well as provide insight into etiologies of cranial malformations wi (open full item for complete abstract)

Committee: Joshua Gross Ph.D. (Committee Chair); Daniel Buchholz Ph.D. (Committee Member); Elke Buschbeck Ph.D. (Committee Member); Donna Carlson Jones Ph.D. (Committee Member); Stephanie Rollmann Ph.D. (Committee Member) Subjects: Biology

PhD, University of Cincinnati, 2015, Arts and Sciences: Biological Sciences

The natural world reflects profound biodiversity in every corner of the globe. These phenotypes range from wing spot variation for camouflage in butterflies, to protective armored plates in marine stickleback fish, to extravagant mating displays in peacocks. For many phenotypes, the “selective”?benefit is self-evident. However, some forms of phenotypic evolution?are less obvious, such as regressed or “lost” characters, since it can be difficult to determine the association between a? discarded trait and a selective advantage. Cave-dwelling animals such as the blind Mexican cavefish, Astyanax mexicanus, serve as excellent models to investigate regressive evolution. The surface form is extant, allowing for direct comparisons between river- and cave-dwelling conspecifics. Cavefish likely evolved from an “ancestral” surface-dwelling form, which invaded the caves of Northeastern Mexico. As a consequence of roughly 3 million years in darkness, these remarkable cavefish lost their coloration. Moreover, the recurrent loss of pigmentation in geographically isolated populations renders this system ideal for investigating the broader changes mediating regressive evolution in nature. To investigate these fundamental questions, we utilize an integrative approach to characterize genetic mechanisms contributing to coloration loss in nature. For this, we aimed to describe multiple genetic components – simple traits, complex characters and global changes in gene expression – that may contribute to regressive pigmentation. Although some simple traits (albinism and brown) have been characterized, the roles of cis-regulatory mutations affecting these single locus traits have not been described. We investigated populations of cavefish that harbor “brown” yet depict an intact coding sequence. We discovered many sequence alterations present in the 5' putative promoter region of the causative locus Mc1r, some of which co-localized to highly conserved non-coding elements that may play a c (open full item for complete abstract)

Committee: Joshua Gross Ph.D. (Committee Chair); John Layne Ph.D. (Committee Member); Heather Norton Ph.D. (Committee Member); Kenneth Petren Ph.D. (Committee Member); Stephanie Rollmann Ph.D. (Committee Member) Subjects: Biology

Master of Science (MS), Bowling Green State University, 2010, Biological Sciences

When visual cues are poor or unavailable, animals often rely on a form of active sensing in which they produce their own signal energy to probe various features of the environment (e.g. echolocation by bats). In a different and less-understood form of active sensing, blind cavefish use their burst and coast swimming motions to generate flow signals that can be detected by the lateral line. The coast phase of the swimming cycle produces a relatively stable, dipole-like flow signal that is distorted when fish swim by nearby obstacles. In this study, we test the hypotheses that (a) blind cavefish have evolved behavioral specializations for active flow-sensing compared to their nearest sighted relatives (a morph of the same species) and (b) flow signal production is regulated by lateral line sensory feedback. We compared the swimming kinematics of blind and sighted morphs in response to a novel, dark environment - both before (T1) and after (T2) a 24-hr familiarization period and with and without a functional lateral line. There were two major findings of this study. The first was that the majority of burst-coast kinematic parameters exhibited no significant differences as a function of morph, familiarity with environment or lateral line functionality. Noteable exceptions included an increase in coast duration, coupled with a decline in swim cycle frequency after T2 for both morphs. The second major finding was that blind morphs exhibited a significantly higher incidence of swim cycles that formed part of a straight swimming trajectory. Both lateral line deprivation and familiarization in the arena led to significant declines in this number for blind, but not sighted morphs. Taken together, these results suggest that both morphs have inherited common neuroethological strategies for regulating burst-coast swimming kinematics, but that blind morphs differ significantly from sighted morphs in their swimming trajectories and in lateral line-enabled abilities to link swim cy (open full item for complete abstract)

Committee: Sheryl Coombs Dr (Advisor); Verner Bingman Dr (Committee Member); Moira van Staaden Dr (Committee Member) Subjects: Biology; Zoology

Master of Science (MS), Bowling Green State University, 2008, Biological Sciences

Mexican blind cavefish exhibit an unconditioned wall-following behavior in response to novel environments. Similar behaviors have been observed in a wide variety of animals, but the biological significance of this behavior and its evolutionary history are largely unknown. In this study, the behaviors of sighted river morphs and congenitally blind, cave-dwelling morphs of the same species, Astyanax fasciatus were videotaped during and after their initial introduction into a novel arena under dark (infrared) and visible light conditions. The swimming movements of fish in the experimental arena were tracked with an automatic image-tracking system to provide a post-hoc analysis of how the fish's swimming speed and position (distance and orientation) with respect to the arena walls varied over time. In response to the novel environment in the dark, both sighted and blind morphs exhibited wall-following behaviors with subtle but significant differences. Blind morphs swam more nearly parallel to the wall, exhibited greater wall-following continuity and persistence and reached maximum and stable swimming speeds (~1.5 BL/s) much more quickly than sighted morphs. In contrast, sighted morphs placed in the same novel, but well-lit environment exhibited dramatically different behaviors that consisted of either holding stationary positions near the wall for long periods of time or moving in and around the central region of the environment without moving along the walls. These results are consistent with the idea that both blind and sighted morphs have inherited primitive wall-following behaviors from their common sighted ancestor that serve an exploratory function under visually-deprived conditions. Under well-lit conditions, the proclivity of some sighted morphs to remain motionless near the wall of a novel environment suggests that near-wall preferences may also serve a protective function under some circumstances. It appears that wall-following behaviors of blind morphs rely m (open full item for complete abstract)

Committee: Sheryl Coombs PhD (Advisor); Robert Huber PhD (Committee Member); Paul Moore PhD (Committee Member) Subjects: Biology