Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item MATING COSTS, MALE CHOICE DISPLACEMENT, AND THE EFFECTS ON HYBRIDIZATION AND SPECIATION IN THE HAWAIIAN CRICKET LAUPALA (SUBFAMILY:TRIGONIDIINAE)(2009) Jadin, Jenna; Shaw, Kerry L; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Contact zones between two closely-related species provide unique laboratories for studying the processes of speciation. This is because, within these zones, species barriers will be reinforced and speciation will reach completion, or the barriers will break down, causing the two species to become one. Which of these two alternatives will occur depends on the degree of genetic differentiation and behavioral isolation between the species. If there is significant and non-combinable genetic variation between species, but behavioral isolation between the two incipient taxa is incomplete and allows hybrid offspring to be produced, these hybrid offspring will have lower fitness relative to parental types and selection should act directly to eliminate those offspring and indirectly against parents with broad mating preferences or traits. If however the genetic architecture is similar and behavioral isolation is incomplete, the populations would be expected to turn into a hybrid swarm and eventually become one species. Patterns of behavioral isolation and genetic variation in several Laupala species pairs suggest that contact zones between closely related species are marked by conflicting patterns of behavioral isolation and genetic differentiation. Evidence also suggests that the complex courtship system of Laupala may allow male choice to play an important role in sexual selection and speciation. Therefore I tested several hypotheses about the genetic differentiation, sexual selection, and behavioral isolation in a contact zone between the closely-related and morphologically indistinguishable L. tantalus and L. pacifica species pair. First, by using the mitochondrial COI gene and AFLPs as genetic markers, I demonstrated that there appears to be mitochondrial DNA introgression between sympatric, but not allopatric congeners, which suggests contemporary hybridization in the contact zone. Next, I found that males experience post-mating resource-limitation and show a significant tendency to invest less into a second mating, however, their investment is dependent upon female size. Finally, I found that there is apparent displacement of male choice, decreased variation in spermatophore production, and asymmetrical mating isolation within the contact zone. This evidence all suggests that there is increased behavioral isolation in this contact zone, which may be consistent with a hypothesis of speciation by reinforcement. However, this evidence also suggests that male costs may result in male choice conflicting with other isolating mechanisms. If so, this study may be another putative case of reinforcement, or it may be an entirely novel report of conflicting selection pressures within a hybrid zone. I suggest that further studies are needed to measure hybrid fitness as well as to evaluate relative male and female mating costs within the complex mating system of this rapidly-diversifying genus.Item Assessment of local abundance, demographics, health and exploitation of Chesapeake Bay American eel(2009) Fenske, Kari Hammarsten; Wilberg, Michael J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Chesapeake Bay supports the largest U.S. harvest of American eel Anguilla rostrata, yet little is known about the underlying production rates sustaining harvests. Demographic attributes were compared between six sub-estuaries and with an unexploited population in the Hudson River. A mark-recapture experiment in the Potomac River yielded growth, abundance, and production estimates. Sub-estuaries characterized by lower salinity had a lower proportion of females, and American eels were older, slower growing and showed increased parasitism. Female American eels were larger, older, and had higher growth rates than other gender types. Local abundances were 10-fold higher in the Potomac River estuary in comparison to the Hudson River, but growth rates were similar. Mortality rates were twice as high as those in the Hudson River estuary. The production model indicated American eel recruitment and biomass decreased substantially during the past 20 years.Item COSTS AND BENEFITS OF COOPERATIVE INFANT CARE IN WILD GOLDEN LION TAMARINS (LEONTOPITHECUS ROSALIA)(2009) Siani, Jennifer Marie; Dietz, James M.; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In cooperative breeding species, nonbreeding individuals typically delay dispersal, forego reproduction and provide care to infants that are not their own. All caregivers must therefore balance infant demands against their own self-interests. In this dissertation I investigate the costs and benefits of cooperative infant care in wild golden lion tamarins (Leontopithecus rosalia) . In chapter 1, I examine what factors influence the distribution of infant care to clarify why helpers contribute care to infants. I find that reproductive status strongly influences infant caretaking patterns, with parents contributing significantly more infant carrying and food provisioning than helpers. Parental dominance in caretaking and the lack of variation in infant carrying or food transfers with caregiver age, sex or condition suggests that genetic relatedness dictates these caretaking decisions, with infant behavior also influencing food provisioning. In chapter 2, I investigate the effects of gestation and infant care on activity budgets and body mass to determine if infant care results in detectable short-term costs to caretakers. Tamarins are hypothesized to require assistance from nonreproductive helpers in raising offspring due to ecological (e.g. predation risk, foraging) and energetic costs of gestation and care of infants, usually twins. During gestation, reproductive females do not make behavioral changes that suggest an energy conservation strategy; however, all caregivers make behavioral changes while carrying infants to increase predator awareness and decrease energetic expenditure and are able to maintain a stable body mass throughout infant care. Cooperative infant carrying may allow individuals to balance energetic demands and mitigate predation risk, thus supporting the hypothesis that energetic costs have driven the evolution of cooperative caretaking. In chapter 3, I present the results of an acoustic playback experiment to determine the frequency and intensity of caregiver responses to infant begging vocalizations. Caregiver responses were influenced by reproductive status, sex, condition, experience, group size and activity level, but not familiarity or genetic relatedness. The variation in caregiver responses to infant vocalizations suggests that these responses are flexible and dynamic, shifting with changes in group composition and context and with individual reproductive status and physical condition.Item USE OF MOLECULAR TECHNIQUES TO ADDRESS THE EVOLUTION OF DISPLAY TRAITS IN THE PTILONORHYNCHIDAE AND OTHER PASSERIFORM SPECIES(2009) Zwiers, Paul; Borgia, Gerald; Fleischer, Robert; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Tests of hypotheses addressing the evolution of complex traits have greatly benefited from advances in the field of molecular genetics. Current molecular techniques allow for the identification of genetic variability, useful in estimating genetic relatedness and potentially explaining phenotypic variation. Here I use molecular data to address the evolution of complex traits within the Ptilonorhynchidae and other Passeriformes. My estimation of a bowerbird molecular phylogeny suggests two highly unlikely scenarios of complex trait evolution (i.e. polygyny, bower construction, decoration use, etc.); either polygyny and complex display traits evolved in parallel, or monogamy evolved from non-resource based polygyny, a transition for which no unambiguous examples could be found, and complex traits evolved once and were lost. Molecular evidence also supports the existence of four Sericulus species, dating the radiation to coincide with the upheaval of the central New Guinea mountain range, and suggests plumage coloration may be a labile trait within this group and therefore a poor indicator of species relatedness. Use of ultraviolet (UV) signals in birds is hypothesized to associate with the ability to see UV wavelengths, a trait with a well-documented genetic basis (replacements at key amino acid positions in the short-wavelength-sensitive 1 (SWS1) opsin pigment influence pigment sensitivity and potentially color discrimination). UV signal use may alternatively evolve to match the local light environment. Results from bowerbirds suggest extreme differences in UV reflectance are due to light availability and not differences in UV vision because amino acid sequences in the bowerbirds were nearly identical. Expanding upon this study, I compared SWS1 opsin gene sequences from 134 passeriform species and plumage UV reflectance measurements from 91 of these species. Results from the molecular data are unprecedented; replacements at five amino acid positions are predicted to have occurred nearly simultaneously, suggesting a constraint on UV vision evolution. Additionally, species reflect most intensely in wavelengths to which they are predicted to be sensitive. These results suggest a constraint on UV vision may also constrain the evolution of UV signals in the Passeriformes. These studies highlight the usefulness of molecular data when testing hypothesis of species and trait evolution.Item Active female sampling of male display predicts female uncertainty in mate choice(2009) Cendes, Linda Marie; Borgia, Gerald; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Information on how females use male display elements can be critical in understanding mate choice. Females often passively sample male displays, therefore female use of an element can be difficult to quantify. In satin bowerbirds, female tasting associated with male paint offers an opportunity to study how females actively assess of male display. In a preliminary study, I found that tasting was less common by females during courtships ending in copulation. This suggested that females with a greater proportion of tastes are less certain in their mate choice. I tested this hypothesis in several ways, and each indicated that a greater proportion of tasting was associated with measures suggesting mate choice uncertainty: visiting more times and more males, mating with multiple males, and switching among males. This active sampling behavior allows for examination of female assessment of a single component of male display and to predict certain female characteristics.Item HOW DENDRITIC ECOLOGICAL NETWORKS STRUCTURE THE DISTRIBUTION AND MOVEMENT OF STREAM SALAMANDERS(2009) Grant, Evan; Palmer, Margaret A; Nichols, James D; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Research in population biology is concerned with factors affecting the change in a population over time, including births, deaths, immigration and emigration. Despite the potential importance of dispersal, empirical data on movement are lacking in many systems. Hence, there is a large body of theory on dispersal that remains to be tested in real biological systems. In particular, many organisms exist in ecological networks with the complex geometry common to caves, plants and streams. This alternative network topology might influence population and community-level patterns and processes. Chapter 1 introduces the concept of the "dendritic ecological network," highlighting special properties and characteristics useful for understanding community and population-level processes. Of most interest for this dissertation is how the rigid spatial structure and branching topology may have implications for patterns of population distribution and the evolution of movement behaviour in stream organisms. In chapters 2 and 3, I investigate patterns of stream salamander distribution, which may be related to the spatial configuration of stream habitat branches. First, I determined the sampling methods suitable for estimating the probability a site is occupied by one of three stream salamander species. I then applied these methods to investigate occupancy patterns, in relation to stream spatial layout across two mid-Atlantic regions. I found that all three species have higher occupancy in streams with a confluent, firs-order stream, though the strength of this association seems to be related to life history characteristics. Finally, in chapters 4 and 5, I sought to identify movement pathways for larval, juvenile and adult Desmognathus stream salamanders. First, I tested my marking method on larval individuals, and found that the visual implant elastomer marks can be retained through metamorphosis. Then, using individual mark-recapture and multistate modeling, I found that stream salamanders move during the juvenile stage, with both an upstream-biased movement, and a proportionally large probability of moving overland to an adjacent stream reach. The chapters in this dissertation combine empirical investigations of the patterns and pathways of stream salamander movement. Taken together, they elucidate the underlying importance of dendritic ecological networks, and provide direct evidence of dispersal in stream salamanders.Item Effects of barrier perches and stocking density on the behavior, space use, and leg health of the domestic fowl (Gallus gallus domesticus)(2009) Ventura, Beth Ann; Estevez, Inmaculada; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The objective of this study was to discern whether providing enrichment in the form of barrier perches across a range of densities might improve leg and foot health and promote behavioral expression and more even use of space in broilers. To investigate this, 2,088 day-old broiler chicks were randomly assigned to one of three barrier treatments at one of three densities. Effects on behavior, space use, foot and hock health, tibia fluctuating asymmetry, fear and production were subsequently assessed. Higher densities appeared to compromise broiler welfare, seen by increased tibia length asymmetry, poorer foot and hock health, suppression of activity, increased disturbances, and decreased use of space. Conversely, barrier perches - particularly simple barriers - appeared to improve footpad quality, promote increased perching and activity, decrease aggression and disturbances, and improve use of the central pen space, all without negatively impacting production traits.Item NAKED GOBIES (GOBIOSOMA BOSC) AS INDICATORS OF OYSTER REEF RESTORATION SUCCESS(2009) Lederhouse, Terra Marie; Paynter, Kennedy T; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Naked gobies (Gobiosoma bosc) are the most abundant resident fish on oyster reefs in the Chesapeake Bay and serve as a critical trophic link between the benthic and pelagic communities. Their response to oyster restoration may therefore be a useful indicator of ecosystem functioning. Experiments were conducted from 2005-2006 in the Severn and Patuxent Rivers to determine the response of naked gobies to increasing availability of oyster substrate. Naked gobies and other resident macrofauna were collected from experimental oyster reefs, constructed using adult oysters of various densities, loose oyster shell, and ambient sediment. Naked goby abundance, length, dry weight, and biomass increased with the availability of oyster substrate and were positively correlated with the abundance of other resident macrofauna. Individual dry weight and biomass were greater on reefs with a high density of oysters than on control plots, and may therefore serve as important indicators of oyster reef habitat quality.Item THE DISTRIBUTION OF CALLINECTES SAPIDUS MEGALOPAE AT THE MOUTHS OF CHESAPEAKE AND DELAWARE BAYS: IMPLICATIONS FOR LARVAL INGRESS(2009) Biermann, Jeffery Lee; North, Elizabeth W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Transport of Callinectes sapidus (blue crab) megalopae from the continental shelf into estuaries may influence recruitment variability of this economically important species. This research seeks to determine the vertical distribution of C. sapidus megalopae near the mouths of Chesapeake and Delaware Bays, and thereby infer swimming behaviors that may influence ingress to these estuaries. Megalopae and physical conditions were sampled at locations from ~10 km inshore of the estuary mouths to ~40 km offshore in coastal shelf waters in September 2005 and 2006. Megalopae were present in greater abundance and at shallower depths during night compared to day at all locations, suggesting a diurnal effect on distribution within the estuary and on the continental shelf. Unlike previous studies, offshore distributions did not indicate surface oriented behavior. Within the mouth of Delaware Bay, limited evidence suggests that megalopae presence in the upper portion of the water column increases in response to nocturnal flood tides. Results suggest photoinhibited swimming near the mouths of Chesapeake and Delaware Bays. In context of previous laboratory studies, these findings indicate that estuarine chemical cues at very low concentrations may induce changes in megalopae behaviors and stimulate molting at least 40 km offshore of estuarine mouths. Results suggest wind-forcing and density-induced subtidal flow are more likely mechanisms for ingress to Chesapeake and Delaware Bays than tidal-transport.Item The effect of sperm mobility phenotype on fertility persistence in layer and broiler hens(2008) Baczynski, Kathleen; Estevez, Inmaculada; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Domestic fowl (Gallus gallus domesticus) were studied to identify accurate predictors of potential fertility in two lines of broiler breeder males along with fertility persistency in layer and broiler hens. Sixty-four Hy-Line layer and thirty-seven broiler breeder hens were AI with identical amounts of high or low mobility sperm from FG males. Morphological measurements were taken to determine relationships of these with semen volume, concentration, and mobility. We hypothesized that 1) semen quality would decline as males aged, 2) morphology would be positively correlated with semen quality, and 3) females AI with high mobility sperm would have a longer duration of fertility. Results revealed a significant age*line interaction for semen volume (p=0.0307), sperm concentration (p=0.0003), and sperm mobility (p=0.0405). Morphological measurements were correlated with different semen parameters in both lines. Fertility was positively correlated with semen quality. Sperm mobility influenced fertility in layer hens but not in broiler breeders.
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