Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
Browse
3 results
Search Results
Item Echolocation, high frequency hearing, and gene expression in the inner ear of bats(2017) Mao, Beatrice; Wilkinson, Gerald S; Moss, Cynthia F; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Bats are the only mammals capable of true flight, and are the second-most speciose mammalian radiation, represented by over 1200 extant species. Key to their evolutionary success was echolocation, which is a complex trait requiring specializations for vocalization, hearing, and echo processing. Because they rely on detecting and analyzing echoes that may return greatly attenuated relative to their outgoing calls, interference from non-target ‘clutter’ echoes poses a challenge for echolocating bats. Here, I demonstrate that the echolocating bat Eptesicus fuscus alters its echolocation behavior to ameliorate the impact of clutter echoes when tracking a moving target, and that the magnitude of its behavioral adjustments depended on the distance and angular offset of two symmetrically placed ‘distracter’ objects. Furthermore, I found that individual bats make different adjustments to their calls, call timing, or head movements, suggesting that multiple strategies for echolocating in clutter may exist. In my second chapter, I examined the expression patterns of hearing-related genes in juvenile bats. Biomedical research establishing the functional roles of hearing genes rarely examines gene expression beyond the early post-natal stage, even though high frequency hearing does not mature until late in development. I show that several key hearing genes implicated in human deafness are upregulated in juvenile bats relative to adults, or exhibit sustained upregulation through the developmental period corresponding to the maturation of echolocation behavior. In my third chapter, I review the evolution of high frequency hearing in mammals, focusing on echolocating bats and whales, which have independently evolved this complex trait. I provide an overview of recent studies that have reported molecular convergence in hearing genes among distantly related echolocators, and assert that the contribution of gene expression to hearing deserves further investigation. Finally, I argue that echolocators provide a unique opportunity to investigate the basis of high frequency amplification, and may possess mechanisms of hearing protection which enable them to prolong the use of echolocation throughout their long lives.Item FROM GENES TO BEHAVIOR: VARIATION IN THE VISUAL SYSTEMS OF LAKE MALAWI CICHLID FISHES(2011) Smith, Adam Ray; Carleton, Karen L; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Visual systems are ideal models for the study of sensory evolution. The cichlids of Lake Malawi possess an elaborated complex of genes (opsins) that encode chromatic visual pigments, which allows us to study the evolution and diversification of chromatic vision in great detail. In this dissertation, we investigated the molecular and behavioral properties of cichlid visual systems in order to more thoroughly understand the diversification of visual systems and the behavioral consequences of these changes. The work is organized into three research projects, with the following results: (1) Opsin gene sequence variation, with corresponding functional sensitivity changes, were found for the SWS1 (ultraviolet-sensitive), SWS2B (violet-sensitive), RH2Aβ (green-sensitive), and LWS (red-sensitive) opsin genes. Of the two genera profiled, each had two variable genes, suggesting that diversifying selection acts on different opsins in each genus. Furthermore, our data suggest that the variation in the SWS1 gene has arisen recently in Lake Malawi and is under rapid selection. (2) Intraspecific cone opsin gene expression variation was found in wild populations of multiple species. Expression variation was found primarily for the LWS and SWS1 genes, while the other genes were relatively consistent within species. This finding suggests that expression can be modulated by adding genes to what may otherwise be considered a species-specific expression pattern. Quantitative models suggested that this expression variation was not the result of environmental constraint. (3) Fish raised in different ambient developmental light environments had different cone opsin gene expression, primarily in the LWS opsin gene. These expression differences caused an increase in behavioral sensitivity in the optomotor response. Furthermore, analyses indicated that the OMR response is determined solely by the LWS cone pigment, rather than a complement of different cone types. Taken together, these findings shed new light on how visual systems diversify over short evolutionary time-scales, and the possible linkage of early determinants of visual sensitivities (opsin genes) and processes that directly influence speciation (behavior).Item PHYLOGENETIC RELATIONSHIP AMONG POLYMORPHIC OLIGOHYMENOPHOREAN CILIATES, WITH GENE EXPRESSION IN LIFE-HISTORY STAGES OF MIAMIENSIS AVIDUS (CILIOPHORA, OLIGOHYMENOPHOREA)(2007-11-29) Gebler, Glenn Frederick; Small, Eugene B.; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Class Oligohymenophorea is a monophyletic group possessing polymorphic taxa. Thus far, relationships within subclasses of oligohymenophorean ciliates and between polymorphic taxa within families are not well resolved. Here, nuclear small subunit rRNA (SSU rRNA) gene sequences from 63 representative taxa, including several polymorphic species, were used to construct phylogenies and test monophyly of the subclass Scuticociliatia and of the polymorphic taxa within the Oligohymenophorea. In addition, suppression subtraction hybridization (SSH) was used to test the hypothesis that genes are differentially expressed during microstome-to-macrostome and tomite-to-microstome transformation in the polymorphic scuticociliate Miamiensis avidus. Phylogenetic analyses confirmed monophyly of the subclasses Peritrichia and Hymenostomatia. The monophyletic scuticociliates encompassed most, but not all, taxa included in this study. The conditional acceptance of the hypothesis supporting monophyly of the Scuticociliatia was due to the ambiguous placement of three taxa, the apostome Anoplophrya marylandensis, the scuticociliate Dexitrichides pangi, and the peniculine Urocentrum turbo. The polymorphic trait most likely arose on at least four, and perhaps on as many as six, separate occasions within the oligohymenophorean ciliates. Several genes previously implicated in morphogenetic processes in eukaryotes were upregulated during microstome-to-macrostome transformation in M. avidus. Those genes were, elongation factor-1 alpha (Ef-1α), Constans, Constans-like TOC1 (CCT) transcription factor, a disulfide isomerase, heat shock protein 70, step II splicing factor (Slu7), U1 zinc finger protein, and WD40-16 repeat protein. A similar analysis for M. avidus undergoing tomite-to-microstome transformation identified genes previously linked to transformation processes in other protists: two cysteine protease genes lacking formal description (papain-family and XCP1 cysteine protease), two described cysteine protease genes, cathepsin B and cathepsin L, and one cysteine protease inhibitor (cystatin-1) gene. The roles of candidate genes for regulation of M. avidus life-history stages (Ef-1α for microstome-to-macrostome transformation; cathepsin B and cathepsin L for tomite-to-microstome transformation) were examined using pharmacological inhibition experiments. Drug treatments significantly reduced transformation of M. avidus microstomes into macrostomes within 6 h and prevented tomite-to-microstome transformation after 2.5 h. Results indicated that genes specifically linked to oral transformation in M. avidus are differentially expressed during microstome-macrostome and tomite-microstome transformation. Thus, this study used molecular techniques to understand the evolutionary history and development of polymorphism within the Oligohymenophorean ciliates.