Thesis (Ph.D.)--University of California, San Francisco, 2008. / Source: Dissertation Abstracts International, Volume: 69-06, Section: B, page: 3428. Adviser: Arnold R. Kriegstein.

Thesis (Ph.D.)--Lehigh University, 2008. / Adviser: Murray Itzkowitz.

<p> Sex determination in leatherback sea turtles is directed primarily by the temperatures a clutch experiences during the middle third of development. Warmer temperatures tend to produce females will cooler temperatures yield males. Nest temperatures can vary spatially and temporally. During the 2010 and 2011 nesting seasons, this study estimated the hatchling sex ratio of leatherback sea turtles on Sandy Point National Wildlife Refuge (SPNWR), St. Croix, U.S. Virgin Islands. I measured sand temperatures from May- August and across the spatial range of leatherback nesting habitat. I spatially interpolated those temperatures to create maps that predicted temperatures for all nests incubating on SPWNR. Nest temperatures were also directly measured and compared with predicted nest temperatures to validate the prediction model. Sexes of dead-in-nest hatchlings and full term embryos were used to confirm the sex-temperature response. The model showed that microclimatic variation likely impacts the production of both sexes on SPNWR.</p>

<p> Communication facilitates almost every social interaction between organisms and this communication is especially important for mate acquisition. Anuran amphibians are an excellent model system to study mate choice behaviors and sexual selection. In this work I recorded male calls of the spring peeper, <i> Pseudacris crucifer</i>, between two populations (Maryland and Louisiana) and analyzed call parameters such as frequency, duration, and rise and fall time. I found differences in the frequency and the frequency sweep of the calls. I conducted choice experiments to test female mating preferences in the Louisiana population and found a preference for longer calls over short calls. Females did not express a preference for frequency, frequency sweep, or local (LA) versus foreign (MD) calls. I also conducted multimodal signaling experiments on the t&uacute;ngara frog, <i>Physalaemus pustulosus</i>. I used natural calls and a robotic t&uacute;ngara frog to determine how females assess different signal modalities (auditory versus visual). I tested previously established attractive calls against unattractive calls, paired with the robo-frog and inflating vocal sac, to see if the visual stimulus would modulate the attractiveness of the call. The presence of the vocal sac did not make the unattractive call more attractive. The vocal sac may have important implications for localization in a more complex environment but here, it did not act as a mate attracting signal. This study provides the ground work necessary for multimodal signaling in spring peepers and for complex sensory environment choice tests in the t&uacute;ngara frog.</p>

Chloroplast protein degradation during senescence is delayed in autophagy mutants

<p> Microbial biofilms on leaf litter can assimilate nutrients, thus altering the elemental composition (i.e. stoichiometric composition) of detritus. Aquatic macroinvertebrates consuming stoichiometrically-altered detritus may increase, decrease, or not change growth rates depending upon their body stoichiometry. Invertebrates with high body phosphorus (P) can allocate more P to rRNA, increasing protein production and growth. Thus, if diet nutrient limitation is alleviated, high P invertebrates are expected to increase growth rates. Conversely, low P invertebrates might not respond or decrease growth rates, due to the metabolic costs of eliminating excess nutrients. Diptera from two families were used in growth studies and fed either maple or oak leaves with different levels of carbon:phosphorus (C:P) to determine if diet P influenced growth rates and body stoichiometry of these high P organisms. </p><p> <i>Tipula abdominalis</i> from the family Tipulidae, were hypothesized to increase growth and consumption rates, and decrease body C:P as diet C:P decreased. It was also hypothesized that the proportion of consumed material composed of a particular element used in growth would increase (GGE), and that the diet ratio at which neither C or P is limiting, and at which maximum growth would occur, would decrease as diet C:P decreased (TERC:P). It was observed that <i>T. abdominalis</i> growth and consumption varied based on leaf type and elemental composition. <i>Tipula abdominalis</i> fed oak had high growth (5.4% day-1) and consumption (1.98mg mg tipulid-1 day-1) compared to maple diets, while individuals fed maple increased growth (2.6 to 5.0% day-1) and consumption (1.1 to 2.1mg mg tipulid-1 day-1) across treatments as maple C:P decreased. <i>Tipula abdominalis</i> were overall homeostatic in body stoichiometry. Contrary to expectations, GGEs decreased as diet C:P decreased, maintaining stoichiometric homeostasis. Also, current TER calculations were not representative of observed growth rates. Thus, results indicate that leaf stoichiometry and leaf type interact to influence growth rates. </p><p> Three genera of Chironomidae (<i>Chironomus, Polypedilum, Micropsectra </i>) were fed a gradient of diet C:P to determine if there are differences in taxon-specific growth responses to changes in diet stoichiometry. It was hypothesized that genera with higher body P would increase growth more than genera with lower body P, and that body P in high P genera would increase as they consumed more dietary P. The three genera had different growth responses to decreased diet C:P that did not appear to be influenced by organism body stoichiometry or diet stoichiometry. <i>Chironomus</i> fed maple and oak and <i>Micropsectra</i> fed maple had similar growth rates (17.5% day^-1), while having significantly different body C:P, 141 and 249 for <i>Chironomus</i> fed oak and maple, respectively, and 359 for <i>Micropsectra</i> fed maple. Despite similarities in diet C:P ranges (1000 to 8000), <i>Chironomus</i> and <i> Polypedilum</i> had different growth responses: <i>Chironomus</i> had high growth, while <i>Polypedilum</i> fed maple did not grow and lost mass (- 4.8% day^-1), and Polypedilum fed oak exhibited relatively low growth rates (5.9% day^-1). Leaf type and genus identity appear to be important factors in determining growth response. However, most Dipterans in this study either increased growth or had no response to dietary P enrichment. Understanding how organism genus identity interacts with leaf type and leaf stoichiometry to influence growth rates will allow more accurate predictions of community changes in nutrient enriched systems. </p>

<p> Movement presents a unique challenge for snakes (suborder Serpentes), which utilize limbless locomotion to move in terrestrial and aquatic environments. Lateral undulation, the fastest and most commonly used type of snake locomotion, has been extensively studied in both contexts due to its prevalence in the animal kingdom. However, the effects of speed on locomotor kinematics have only been studied in aquatic conditions. During swimming, snakes are known to increase speed by increasing wavelength and amplitude while maintaining constant frequency. Additionally, amplitude in aquatic environments increases from the anterior to the posterior regions of the body. The mechanism for increasing speed in a terrestrial context is unknown, despite the fact that the majority of snakes reside in terrestrial areas. Therefore, I compared terrestrial locomotor kinematic data with existing aquatic swimming data to determine whether kinematic differences exist for increasing speed in different environments. In this study, Eastern Garter Snakes, <i>Thamnophis sirtalis </i> (<i>n</i>=4), were filmed utilizing lateral undulation at two different speeds with 120fps high-speed video. I examined speed effects on locomotion by conducting detailed comparisons of key kinematic and performance variables including wavelength, amplitude, frequency and segmental angles of the waves created during lateral undulation.</p><p> The speed effects of terrestrial locomotion were found to differ from aquatic locomotor pattern in wavelength; the mean wavelength observed in our terrestrial trials increased significantly as speed increased. Other variables, including frequency, amplitude and growth of amplitude from head to tail, exhibited similar patterns to aquatic locomotion. This study provides insight into the mechanisms by which snakes generate locomotor complexity from a simple body plan.</p>

<p> We have used the <i>C. elegans</i> primordial gonad to understand how stem cells assemble into a niche during development. The <i>C. elegans </i> primordial gonad contains two somatic gonad precursor cells (SGPs) and two primordial germ cells (PGCs). The primordial gonad assembles during embryogenesis when PGCs and SGPs come together adjacent the intestine. </p><p> As a first step in understanding niche assembly, we investigated how PGCs move to the site where the primordial gonad forms. PGCs and somatic cells move into the interior during gastrulation. Because somatic cells require transcription to ingress whereas PGCs are transcriptionally quiescent, we hypothesized that somatic cells might push or pull the PGCs into the embryo. We used videomicroscopy to identify cells that contact the PGCs, and used laser killing to determine if the contacting cells are required for PGC ingression. The PGCs are surrounding by adjacent mesodermal cells and internal endodermal cells. We found that the only contacting cells necessary for PGC ingression were the endodermal cells, which ingress into the embryo an hour before the PGCs. Killing or altering the fate of the endodermal cells prevented PGC ingression but not ingression of other somatic cells. Using fluorescent membrane markers and live imaging, we showed that PGCs and endodermal cells maintain contact throughout gastrulation, and that endodermal cells move dorsally as PGCs ingress form the ventral surface. PGCs express high levels of E-cadherin/HMR-1, and knocking down E-cadherin/HMR-1 caused PGCs to detach from endodermal cells and remain on the surface of the embryo. Finally, we show that the enrichment of HMR-1 protein in the PGCs is not due to transcriptional upregulation, but is instead due to an increase in protein expression mediated by the hmr-1 3' UTR. We propose that PGCs upregulate E-cadherin/HMR-1 to maintain tight adhesion with endodermal cells, which pull the PGCs into the embryo and position them at the site of primordial gonad assembly. Our results highlight the importance of germ cell - gut interactions during development and of E-cadherin-mediated adhesion in niche formation.</p>

<p> Invasive tamarisk has many impacts in freshwater systems including increasing soil salinity, decreasing water content, and causing a shift in food web structure. Tamarisk species originally introduced to the US have hybridized and have been documented invading salt marsh systems in San Diego County, California. The main goals of this study were to determine the impacts of tamarisk within a salt marsh and among genetic types of tamarisk. Amplified Fragment Length Polymorphism was used to determine genetic identity of each individual salt-marsh invading tamarisk. Abiotic impacts depended on microhabitat, as did tamarisk tree morphology, and infauna community composition. Tamarisk altered abiotic factors in the upland and upstream microhabitats and altered infauna community composition in the marsh microhabitat. 17.8% of trees were hybrids of <i> T. ramosissima</i> x <i>T. chinensis.</i> The remainder were pure <i>T. chinensis.</i> Tamarisk genetic identity did not influence abiotic factors, although invertebrate diversity was lower beneath pure <i> T. chinensis</i> than the hybrid. The tamarisk invasion was not an <i> in-situ</i> hybridization and had the most pervasive impact on the infauna in the marsh microhabitat.</p>

<p> Bur oak (Quercus macrocarpa Michx.) savannas of the Great Plains have long been reported to be disappearing and/or progressing to other vegetative schemes. These losses are directly relatable to the arrival of European settlers and their subsequent suppression in natural prairie fires, along with the introduction of domestic livestock. A preliminary investigation of the floristic composition within remaining oak savannas of Custer County, Nebraska was conducted as a base means of documenting plant diversity within the remaining savannas of central Nebraska. The point-centered quarter method was used to determine species, density, relative density, frequency, relative frequency, dominance, relative dominance, and importance values (IV). The Swedish-increment boring method was applied to woody vegetation to document tree ages and compositional change in the savanna over time. Exclusion cages on oak seedlings, vegetative and soil sampling were also utilized. Results indicated a bleak future for the remaining savannas of Nebraska. Bur oak averaged an importance value of 159.10 out of 300.00, leaving a substantial portion of the importance values divided among several fire-sensitive species. The majority of bur oaks sampled were distributed among the higher size classes, indicating a low rate of recruitment. Age class distributions further support this conclusion with a minuscule number of oaks younger than 25 years of age and the majority of the species recorded over 100 years of age. Seedling survivability tests during summer months produced low survivorship (3.13%) due to drought and large/small mammal herbivory. Winter testing displayed similar results. Vegetation sampling indicated high percentages of exposed till and weedy plant species, indicating a long history of abuse. Soil tests resulted in significant differences in phosphorus and zinc concentrations. As oak recruitment failings continue on a near global scale, more research should be conducted to assist in the conservation and management of these vital ecosystems.</p>