Biology Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/2749

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DIMETHYSULFONIOPROPIONATE (DMSP) AND DMSP-LYASE IN CNIDARIAN ALGAL SYMBIOSES
(2010) Yost, Denise Marie; MITCHELMORE, CARYS L; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Dimethylsulfoniopropionate (DMSP) is a multifaceted sulfur compound produced by several groups of marine phytoplankton, macroalgae and higher plants. Additionally, DMSP cleaving enzymes (most of which are thought to be DMSP-lyases) are known to exist in many species of marine phytoplankton, macroalgae and bacteria. Endosymbiotic dinoflagellate microalgae (genus Symbiodinium) of reef-building corals produce high intracellular levels of DMSP. The existence of DMSP-lyase(s) in Symbiodinium was, until recently, unknown. The function(s) of the DMSP/DMSP-lyase system in cnidarian-algal symbioses is poorly understood. Chapter one introduces coral symbioses, DMSP and the potential roles of the DMSP/DMSP-lyase system in cnidarian-algal symbioses. Chapter two describes the first evidence for in vivo DMSP-lyase activity in several isolated Symbiodinium strains, revealing varying levels of DMSP and DMSP-lyase activity. These results prompted further characterization of Symbiodinium DMSP-lyases. Enzyme assay optimization and substrate kinetics experiments found the measured activity of DMSP-lyase enzymes to be affected by permeabilization buffers, pH, temperature and potential oxidative stress effects (chapter three). Prior to investigations of field-collected intact corals, methods for DMSP analyses were optimized in the laboratory to address the inherent complexities of the coral holobiont. This work compared several preparation techniques for the analysis of particulate (algae only, DMSP_p) and total (coral tissue and algae, DMSP_t) DMSP in several species of stony corals (chapter four). Field-collected corals in chapter five showed DMSP_p and DMSP_t responses when exposed to the oxidative stressor, copper. The second field study (chapter six) describes how DMSP_p and DMSP_t concentrations within five prominent Bermudian corals changed with water depth. Finally, chapter seven presents a synthesis examination of the potential functional attributes and significance of the DMSP/DMSP-lyase system in cnidarian-algal symbioses. The factors influencing variable DMSP production and accumulation as well as differences in DMSP-lyase activity are discussed in light of methodological limitations, the biology and physiology of symbiont and coral, Symbiodinium phylotype and environmental variables. The results of this research highlight the existence of DMSP-lyases in Symbiodinium and provide insight into the partitioning of DMSP in cnidarian-algal symbioses, furthering our understanding of the production and potential turnover of DMSP while recognizing the limitations inherent in such investigations.
A comparative analysis of sperm storage in six brachyuran superfamilies: mating behavior, ecological variation and phylogenetic patterns
(2010) Rodgers, Paula Jane; Reaka, Marjorie L; Hines, Anson H; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
While life history traits are shaped by allometric, phylogenetic, environmental and behavioral factors, few comparative studies of brachyuran life history patterns have considered sperm storage traits as important components of reproductive strategies. To understand the evolutionary forces selecting for sperm storage and their interactions with other life history traits, I (1) used controlled laboratory experiments and field mating observations to examine variation in male sperm transfer patterns, (2) sampled variation in female reproductive output and sperm storage for two species across a latitudinal gradient, (3) conducted a survey of life history traits across a broad range of brachyuran taxa, and (4) used phylogenetic analyses to identify patterns in the evolution of life history traits in brachyurans. From mating experiments and observations on five species, I found that males transfer more sperm with longer than shorter copulation durations and that variation in copulation duration was shaped by differences in the species' ecologies. Latitudinal surveys of two species with contrasting mating systems identified seasonal and geographical variation in female reproductive output. While the variation in most reproductive traits could best be explained at smaller spatial scales, a sperm storing species, Callinectes sapidus became sperm limited at low latitudes. From a comparative survey of male and female life history traits across 61 species of brachyurans, I found that allometry, phylogeny and mating strategies explained much of the variation in life history traits. Using rigorous phylogenetic techniques, male life history traits showed more plasticity across the phylogeny than female traits suggesting male traits may be influenced more by behavioral and environmental factors. After correcting for phylogenetic signals, species with larger male sperm stores had larger amounts of sperm stored by the female. In summary this dissertation illustrates the importance of partitioning variation in mating behavior, phylogeny, environmental factors and allometry when examining the evolution of life history traits in brachyurans.
RELATIONSHIPS BETWEEN LARVAL MORPHOMETRICS AND SETTING EFFICIENCY IN THE EASTERN OYSTER, CRASSOSTREA VIRGINICA
(2009) Vlahovich, Emily Ann; Meritt, Donald W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
In oyster hatcheries, the decision to move larvae from rearing tanks to setting tanks is based on physical and behavioral characteristics. These criteria can suggest conflicting action and a more reliable method may result in higher spat production. I observed hatchery reared Crassostrea virginica larvae, beginning with larvae retained on a 200 µm sieve. Aliquots of larvae were measured or placed in a setting vessel, and the remaining were returned to the culture cone daily. Each day had an associated setting efficiency, loss, and set of larval morphometrics, including shell height and length and eyespot diameter. Day was most strongly correlated with setting efficiency. Eyespot diameter was moderately correlated with setting efficiency, and shell morphometrics were weakly correlated with setting efficiency. I estimated daily spat production, which peaked on day 2. These results suggest spat production may be increased by altering current hatchery methods to consider eyespot diameter or days past retention on a 200 µm sieve when deciding to place larvae in setting tanks.
CRITICAL PATCH SIZES AND THE SPATIAL STRUCTURE OF SALT MARSH COMMUNITIES
(2009) Martinson, Holly Marie; Fagan, William F; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The size, connectivity, and quality of habitat patches can have multifaceted impacts on species and communities. In this dissertation, I combined a multi-year field survey, manipulative field experiments, and a literature review to investigate how spatial structure influences species and their trophic interactions in fragmented habitats. For all empirical work, I used as a study system the arthropod assemblage found on patches of the salt marsh grass Spartina patens. In Chapter 1, I conducted seven surveys of habitat patches over three years to examine the effects of patch size, connectivity, and local environmental conditions on a guild of specialist sap-feeding herbivorous insects and their natural enemies. I found striking differences among species in the effects of both patch size and connectivity, which led to differences in species' relative abundances and trophic structure among these patches. In Chapter 2, I manipulated host plant quality and predator density to experimentally examine mechanisms that might structure this arthropod community. I found that positive responses of herbivores to experimentally-elevated patch quality were limited by dispersal constraints and that predation by abundant generalist spiders may constrain the spatial distribution of certain species. Investigating systems beyond the marsh, I conducted a literature review and analysis in Chapter 3 wherein I examined whether the spatial structure of habitats generally influences trophic interactions. From the literature, I identified 171 studies of trophic interactions in fragmented habitats and found that the influence of fragmentation and related variables on the occurrence or strength of trophic interactions was largely predictable based on the habitat affinity of interacting species. With this dataset, I also identified key gaps in the fragmentation literature, including a heavy bias towards the study of two-species interactions. Therefore, in Chapter 4 I took advantage of my data from the salt marsh to identify how, in addition to the two-species interactions of parasitism and egg predation, more complex food web interactions might depend on variation in the size of habitat patches. Overall, my findings show that variation in patch size can have varied, but predictable, effects on patch occupancy, population density, and interactions between species in fragmented habitats.
An RNA:DNA-based index of growth in juvenile Atlantic menhaden (Brevoortia tyrannus): laboratory calibration and field assessment
(2009) Edwards, Jason Lee; Miller, Thomas J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Atlantic menhaden (Brevoortia tyrannus) is an ecologically and economically important species in the mid-Atlantic coastal ecosystem. Its population dynamics are influenced by growth and survival during juvenile occupancy in estuarine nursery habitats. Therefore, quantifying production of potential nursery areas is important to understanding population processes and defining essential fish habitat for this species. Based on laboratory growth experiments, an RNA:DNA-based growth model was developed for young-of-the-year menhaden. The temporal response of RNA:DNA to changes in feeding condition was also quantified in the laboratory. Results of these investigations indicate RNA:DNA as a reliable tool for estimating recent growth and condition in relation to habitat residency. RNA:DNA-based estimates of growth were combined with site-specific abundance estimates to evaluate the spatiotemporal variability in production of potential menhaden nursery habitats. Site-specific production estimates exhibited high spatiotemporal variability suggesting menhaden utilize a mosaic of habitats to promote production, rather than specific sites consistently generating high levels of production.
Breaking the A-P axis: Evolution of diverse asexual reproduction strategies in Convolutriloba acoels
(2009) Sikes, James M.; Bely, Alexandra E.; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The defining characteristic of the Bilateria is the presence of a distinct head end and tail end, which defines the anterior-posterior (A-P) axis, a feature that is established during embryogenesis and generally remains unaltered during the lifetime of an organism. While a few bilaterians have evolved asexual reproduction strategies that allow them to subdivide the A-P axis, acoels in the genus Convolutriloba have an unparalleled ability to alter the A-P axis during modes of transverse fission, longitudinal fission, and reversed polarity budding. Convolutriloba acoels thus offer an exceptional opportunity to investigate the mechanisms that allow for the radical modification of an already established A-P body axis and to explore the evolution and development of diverse asexual reproduction strategies among related species. In this study, I reconstruct the evolutionary history of asexual reproduction in the Convolutriloba and compare the diverse modes of asexual reproduction at the level of body-wall musculature, nervous system development, and cell proliferation while also exploring the regenerative potentials of tissues across species with different modes of asexual reproduction. In addition, I further explore the unusual process of A-P axis reversal that occurs during reversed polarity budding in C. retrogemma through studies of body patterning and regeneration. The results of these analyses suggest that a rich developmental toolkit of regenerative abilities, including the ability to utilize both epimorphosis and morphallaxis, to regenerate all parts of its body even from a small fragment, and to produce bifurcated A-P axes were present in the ancestor of the Convolutriloba allowing for the evolution of A-P axis modifications unlike any other bilaterian group. This toolkit along with the evolution of a seemingly unpatterned zone of tissue within the body of C. retrogemma capable of generating new anterior axes appear to have allowed this species to evolve the ability to form reversed A-P axes during budding.
Environmental conditions in winter and their ecological and evolutionary consequences for American redstarts (Setophaga ruticilla)
(2008-11-21) Studds, Colin Eastman; Inouye, David W; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
I used both observational and experimental approaches to assess the causes of nonbreeding habitat quality and to evaluate their ecological and evolutionary consequences for a Neotropical-Nearctic migratory bird, the American redstart (Setophaga ruticilla). Relative to control birds overwintering in second-growth scrub, redstarts experimentally upgraded from scrub to mangrove forest incorporated mangrove stable-carbon isotope signatures, maintained mass over winter, departed earlier on spring migration, and had higher apparent annual survival. Significantly higher arthropod biomass on upgrade territories implicated food availability as a proximate mechanism of habitat quality. Food availability, body condition, and spring departure schedules also depended on nonbreeding season rainfall. Food availability in mangrove was higher than in scrub in three of four years, allowing birds in this habitat to maintain superior body condition and depart earlier on spring migration. Abundant rainfall in a single year led to abnormally high food availability in scrub and early departure of birds in both habitats, suggesting both the amount and timing of rainfall influenced nonbreeding performance. Habitat occupancy and annual variation in rainfall had significant consequences for natal dispersal and selection through annual survival. Stable-hydrogen isotope ratios (δD) in feathers of immature birds captured again as adults indicated that habitat use in the first nonbreeding season interacted with spring phenology on temperate breeding grounds to influence the distance traveled on the first spring migration and direction of natal dispersal. In contrast, adults showed site fidelity between breeding seasons, suggesting nonbreeding conditions did not affect breeding dispersal and that migration distance becomes fixed later in life. Patterns of δD also revealed directional selection for short migration distance to southern breeding areas, a pattern that was nearly twice as strong in scrub compared to mangrove. During dry winters, redstarts experienced stabilizing selection on departure dates and directional selection for short migration. In years of high rainfall, birds experienced correlational selection favoring late departure when in good body condition. Thus, occupancy of moist habitats and years of high rainfall relaxed selection against late departure and longer migration. Collectively, these findings emphasize the need to understand how events throughout the annual cycle interact to shape fundamental biological processes.
Characterization of the Role of the fem genes in the Sex Determination Pathway of Caenorhabditis briggsae
(2008-08-11) Hill, Robin; Haag, Eric S; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
In the genus Caenorhabditis, self-fertile hermaphrodites in C.elegans and C.briggsae evolved from females by developing the ability to generate a limited number of self sperm. The fem genes are crucial for spermatogenesis and the sperm-to-oocyte switch in C.elegans hermaphrodites. RNAi results of the fem genes in C.briggsae hermaphrodites differed from results in C.elegans, suggesting regulation of germ line sex determination pathway differs between the two species. To more definitively address this possibility, and to further investigate the role of the fem genes in the sex determination pathway of C.briggsae, deletion mutants of Cbr-fem-2 and Cbr-fem-3 were generated and characterized. Double Cbr-tra-1;Cbr-fem-2 and Cbr-tra-1;Cbr-fem-3 were also generated to further characterize the role of the fem genes and their relationship to tra-1. Our results show that while the somatic role of the fem genes have been conserved in both species, their germline role differs. Males of both species require the fem genes for somatic development and to suppress oocyte production. However, C.briggsae hermaphrodites do not require the fem genes for spermatogenesis or the sperm-to-ooycte switch. The double mutant analysis results suggest that, unlike C.elegans, Cbr-tra-1 remains epistatic to the Cbr-fem genes in the germline sex determination system in C.briggsae. While there is overall similarity in phenotypic categories between the double mutants, the percentages within each category differs. The double tra-1;fem3 mutant phenotype differs significantly from the single tra-1 mutant, suggesting a role for Cbr-fem-3 in regulating Cbr-tra-1 activity. A previously undescribed Emo phenotype was also discovered in both single and double mutants in C.briggsae and in C.elegans tra-1 mutant alleles e1099 and e1781. The overall results of this study are consistent with the convergent evolution of hermaphroditism within the genus Caenorhabditis and suggest considerable genetic flexibility in this developmental pathway.
The adaptive significance and prevalence of courtship feeding in Hawaiian swordtail crickets
(2008-06-04) deCarvalho, Tagide; Shaw, Kerry; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Males of many insect species feed their partner during courtship and mating. Studies of male nutrient donation in various systems have established that nuptial feeding has evolved mostly through sexual selection. Although there is extensive diversity in form, the function of nuptial gifts is typically limited to either facilitating copulation or increasing ejaculate transfer, depending on the time at which the gift is consumed by females. Unlike other insects, the Hawaiian swordtail cricket Laupala (Gryllidae: Trigonidiinae) exhibits serial transfer of nuptial gifts. Males transfer multiple spermless 'micro' spermatophores over several hours before mating at the end of the day (i.e. before the transfer of a single sperm-containing 'macro' spermatophore). By experimental manipulation of male microspermatophore donation, I tested several hypotheses pertaining to the adaptive significance of nuptial gifts in this system. I found that microspermatophore transfer improves insemination, by causing the female reproductive tract to take in more sperm. This result reveals a previously undocumented function for premating nuptial gift donation among insects. Enhanced sperm transfer due to microspermatophore donation may represent male manipulation or an internal mechanism of post-copulatory choice by females. I also performed experimental manipulation of male photoperiod to investigate how time and gender influence nuptial gift production and mating behavior. I found that the timing of mating is limited in males but not females and that the time of pair formation has consequences for the degree of nuptial gift donation, which suggests that both mating timing and microspermatophore number is important for male reproductive success. Finally, I observed the mating behavior of several trigonidiine taxa for a comparative analysis of sexual behavior and found that other genera also utilize spermless microspermatophores, which suggests that microspermatophore donation may be a common nuptial gift strategy among swordtail crickets. The elaborate nuptial feeding behavior of Hawaiian swordtail crickets prior to mating represents a newly discovered strategy to increase male insemination success rather than mating success. Based on this unexpected result, it is worth exploring whether courtship behaviors in other cricket or insect mating systems have also evolved to increase sperm uptake.
Mechanism and evolutionary significance of the loss of melanin pigmentation in the cave fish Astyanax mexicanus.
(2008-05-27) Hixon, Ernest R; Jeffery, William R; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The regressive evolution of traits such as eyes and pigmentation is common among cave organisms. As a model to study regressive evolution, I have used the teleost Astyanax mexicanus, which consists of eyed and pigmented epigean forms and many populations of cave-dwelling forms that have lost those traits. This study investigates the mechanism for the loss of melanin production, from the origin of chromatophores from the neural crest to the synthesis of melanin within the melanocyte. I show that cavefish retain a migratory population of neural crest derived cells that are tyrosinase positive and respond to exogenous signals as expected of a melanocyte. I then propose that the regressive evolution of melanin pigmentation is a selectively evolved trait that provides for an excess of dopamine, supported by the near two-fold increase in dopamine in cavefish brains, quantified via HPLC analysis. This study suggests that regressive evolution sometimes occurs via selection.

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