Adaptive radiation along a benthic/pelagic ecological axis in North America’s most diverse, endemic clade of freshwater fishes

Eastern North America is unparalleled throughout the temperate world in terms of freshwater fish biodiversity. A monophyletic group of approximately 250 cyprinid fishes, known as the open posterior myodome (OPM) clade, dominates the fish species richness in the freshwater ecosystems of this region. In this dissertation, I explore the influence of eco-evolutionary divergence along a benthic/pelagic habitat axis on the generation of this hyper-diverse group of fishes. My three chapters work synergistically to address the question: Did a historical shift from benthic to pelagic habitats by OPM cyprinids represent the invasion of an open adaptive zone and result in the simultaneous bursts of phylogenetic and ecological diversification that signify an adaptive radiation? In Chapter I, I perform the first gene tree/species tree analysis on OPM species to reconcile discordance between previous phylogenetic hypotheses as it relates to inferring the history of benthic and pelagic habitat transitions in the group. I then construct the most thoroughly sampled OPM phylogenies to date in Chapter II. Using these large-scale phylogenies and habitat-use data, I conducted ancestral state reconstructions to trace the history of benthic to pelagic habitat use during the history of the clade. I then performed lineage through time and diversification rate analyses that suggested that a period of accelerated lineage diversification followed the initial shift from benthic to pelagic habitats in the OPM radiation. In Chapter III, I recovered a significant evolutionary relationship between jaw protrusion angle (JPA) and preferred foraging height in the water column between 15 co-occurring OPM taxa. I also recovered evidence for a burst of morphological disparification in a number of individual muscoskeletal characters that are evolutionary correlated with JPA after the major benthic to pelagic shift inferred in Chapter II. Overall, the results from this dissertation suggest that an early shift from benthic to pelagic habitats in OPM cyprinids represented the invasion of an open adaptive zone and was followed by a period of rapid phylogenetic and eco-morphological evolution as species diverged to exploit vertically segregated sub-zones throughout the water column. Taken together, these results are likely the most robust evidence for an adaptive radiation to date

Geographic and Temporal Diversification Patterns in the Barcheek Darter Species Group

The purpose of this study was to investigate geographic and temporal diversification patterns in the barcheek darter species group. Specifically, my two questions were “Is there geographical structure of alleles or haplotypes within currently recognized species that is suggestive of unrecognized, or cryptic, species diversity within the clade?” (geographic diversification pattern) and “How old are inter- and intraspecific divergence events in the evolutionary history of the clade?” (temporal diversification pattern). A three gene dataset from 159 barcheek individuals of two mitochondrial coding regions, cyt b and ND2, along with a nuclear intron, S7, was analyzed using parsimony and Bayesian phylogentic methods to answer the first question. Divergence times were estimated using fossil calibration of this Bayesian phylogeny in order to answer the second question. Three barcheek species were found to have significant population structure suggestive of cryptic species diversity. E. basilare in particular was recovered as being comprised of five reciprocally monophyletic clades endemic to each of the major tributaries to the upper Caney Fork River. Inter- and intraspecific divergence events were found to be relatively old in the clade, nearly all pre-Pleistocene, with a crown node age estimated at 12.68 mya. These results are discussed in light of the present understanding of the tempo of diversification in the darter radiation

Compounding the Results: The Integration of Virtual Worlds With the Semantic Web

Over the past 20 years, governmental use of Web-base information and technologies has continually expanded taking advantage of the Web's vast, ever- expanding volumes of browser-accessible information. Now, it infuses two new technologies, the first one espousing a world where semantic-powered applications become knowledgeable assistants for Web users. The second new technology takes a perceivably flat two-dimensional approach to presenting current Web-content and adds a three-dimensional perspective to the presentation. Welcome to the Semantic Web as seen through the eyes of a Virtual World participant, an environment where Web users no longer are browsing for information that is largely static, where Web users interact through their proxies (avatars) query applications (Web agents) soliciting them to collect, filter, verify, correlate and present answers to their queries often in a more visually palatable three-dimensional format. Following a brief overview of these two technologies, this article presents several of the key force drivers behind their evolution and the benefits gleaned from their collective use. Further discussion identifies new methods for visualizing semantic content in virtual worlds. Finally, as with any technological evolution, the merge of these two technologies brings on a whole new set of challenges from a Web userÕs perspective as well as perspectives from technology developers both in academia and government

Explosive diversification following a benthic to pelagic shift in freshwater fishes

BACKGROUND: Interspecific divergence along a benthic to pelagic habitat axis is ubiquitous in freshwater fishes inhabiting lentic environments. In this study, we examined the influence of this habitat axis on the macroevolution of a diverse, lotic radiation using mtDNA and nDNA phylogenies for eastern North America\u27s most species-rich freshwater fish clade, the open posterior myodome (OPM) cyprinids. We used ancestral state reconstruction to identify the earliest benthic to pelagic transition in this group and generated fossil-calibrated estimates of when this shift occurred. This transition could have represented evolution into a novel adaptive zone, and therefore, we tested for a period of accelerated lineage accumulation after this historical habitat shift. RESULTS: Ancestral state reconstructions inferred a similar and concordant region of our mtDNA and nDNA based gene trees as representing the shift from benthic to pelagic habitats in the OPM clade. Two independent tests conducted on each gene tree suggested an increased diversification rate after this inferred habitat transition. Furthermore, lineage through time analyses indicated rapid early cladogenesis in the clade arising after the benthic to pelagic shift. CONCLUSIONS: A burst of diversification followed the earliest benthic to pelagic transition during the radiation of OPM cyprinids in eastern North America. As such, the benthic/pelagic habitat axis has likely influenced the generation of biodiversity across disparate freshwater ecosystems. doi: 10.1186/1471-2148-13-27

Design and fabrication of instrumented composite airfoils for a cryogenic wind tunnel model

Two instrumented horizontal stabilizers and one instrumented vertical stabilizer were designed and fabricated for testing on the Pathfinder 1 (PF-1) Transport Model in the NASA Langley Research Center's National Transonic Facility (NTF). Two different designs were employed: the horizontal stabilizer utilized a metal spar and fiberglass overwrap and the vertical stabilizer was made of all fiberglass. All design requirements were met in terms of design loads, airfoil tolerances, surface finish, orifice hole quality, and proof-of-concept tests. Pressure tubing installation was found to be easier for these concepts as compared to methods used in conventional metallic models. Ease of repair was found to be a principal advantage in that some fabrication problems were overcome by reapplying fiberglass cloth and/or epoxy to damaged areas. Also, fabrication costs were judged to be lower when compared to the more conventional design fabrication costs

Aero-Heating of Shallow Cavities in Hypersonic Freestream Flow

The purpose of these experiments and analysis was to augment the heating database and tools used for assessment of impact-induced shallow-cavity damage to the thermal protection system of the Space Shuttle Orbiter. The effect of length and depth on the local heating disturbance of rectangular cavities tested at hypersonic freestream conditions has been globally assessed using the two-color phosphor thermography method. These rapid-response experiments were conducted in the Langley 31-Inch Mach 10 Tunnel and were initiated immediately prior to the launch of STS-114, the initial flight in the Space Shuttle Return-To-Flight Program, and continued during the first week of the mission. Previously-designed and numerically-characterized blunted-nose baseline flat plates were used as the test surfaces. Three-dimensional computational predictions of the entire model geometry were used as a check on the design process and the two-dimensional flow assumptions used for the data analysis. The experimental boundary layer state conditions were inferred using the measured heating distributions on a no-cavity test article. Two test plates were developed, each containing 4 equally-spaced spanwise-distributed cavities. The first test plate contained cavities with a constant length-to-depth ratio of 8 with design point depth-to-boundary-layer-thickness ratios of 0.1, 0.2, 0.35, and 0.5. The second test plate contained cavities with a constant design point depth-to-boundary-layer-thickness ratio of 0.35 with length-to-depth ratios of 8, 12, 16, and 20. Cavity design parameters and the test condition matrix were established using the computational predictions. Preliminary results indicate that the floor-averaged Bump Factor (local heating rate nondimensionalized by upstream reference) at the tested conditions is approximately 0.3 with a standard deviation of 0.04 for laminar-in/laminar-out conditions when the cavity length-to-boundary-layer thickness is between 2.5 and 10 and for cavities in the depth-to-boundary-layer-thickness range of 0.3 to 0.8. Over this same range of conditions and parameters, preliminary results also indicate that the maximum Bump Factor on the cavity centerline falls between 2.0 and 2.75, as long as the cavity-exit conditions remain laminar. Cavities with length-to-boundary-layer-thickness ratio less than 2.5 can not be easily classified with this approach and require further analysis

The labor market regimes of Denmark and Norway – one Nordic model?

The literature on the Danish and Norwegian labor market systems emphasizes the commonalities of the two systems. We challenge this perception by investigating how employers in multinational companies in Denmark and Norway communicate with employees on staffing changes. We argue that the development of ‘flexicurity’ in Denmark grants Danish employers considerably greater latitude in engaging in staffing changes than its Nordic counterpart, Norway. Institutional theory leads us to suppose that large firms located in the Danish setting will be less likely to engage in employer–employee communication on staffing plans than their Norwegian counterparts. In addition, we argue that in the Danish context indigenous firms will have a better insight into the normative and cognitive aspects to flexicurity than foreign-owned firms, meaning that they are more likely to engage in institutional entrepreneurialism than their foreign owned counterparts. We supplement institutional theory with an actor perspective in order to take into account the role of labor unions. Our analysis is based on a survey of 203 firms in Norway and Denmark which are either indigenous multinational companies or the subsidiaries of foreign multinational companies. The differences we observe cause us to conclude that the notion of a common Nordic model is problematic