BIODIVERSITY AND ECOSYSTEM FUNCTIONING: EXPERIMENTAL TESTS USING ROCKPOOLS AS A MODEL SYSTEM

How anthropogenic changes to species composition and diversity are likely to affect the properties of the ecosystems of which they are an integral part, and by extension the goods and services humans derive from them, is a key question in ecology. Despite over a decade of vigorous empirical research and theoretical developments, there remain many unknowns. Using intertidal rockpools and laboratory marine mesocosrns, I used a variety of approaches to address several of these relatively poorly studied issues. In particular, the work presented here focused on the relative roles of species composition and richness, as well as the extent to which such effects are context-dependent. The first study (Chapter II) takes advantage of a successional gradient of macroalgal species composition and diversity resulting from the periodic addition of artificial rockpools to a coastal defense structure. The results show that the focal ecosystem properties (macroalgal biomass and productivity) were largely determined by species composition (and functional traits). Macroalgal species evenness, but not diversity, peaked at intermediate stages during the chronosequence, but no measure of diversity had a detectable influence on primary productivity. The results confirm the prediction that effects of species diversity will be outweighed by compositional changes during succession. I used an experimental approach in Chapters III to V, manipulating the composition and richness of intertidal molluscan grazers (Chapters III and V) and intertidal predatory crabs (Chapter IV) and measuring their effects on prey assemblages as focal ecosystem processes. In a 13-month field experiment (Chapter III) I found that effects on the composition and functioning of developing rockpool communities were determined by grazer composition, not the number of species. Laboratory mesocosm experiments show that the influence of species richness on ecosystem processes can be context-dependent. The effect of resource partitioning (of the multi-species prey assemblage) among predators was only detectable at high predator densities where competitive interactions between individual predators were magnified. A factorial experiment using the rate of algal consumption by molluscan grazers as a response variable, provides the first empirical test of the prediction that the balance between species richness and identity effects can be determined by the degree of spatial heterogeneity (Chapter V). Species identity had strong effects on homogeneous substrates, with the identity of the best-performing species dependent on the substrate. The strengths and limitations of the predominantly small-scale experimental approach employed here are discussed (Chapter VI)

Spring 1977

Thomas Jefferson (page 3) Herbicide Evaluation for Crabgrass Control--1976 (9) Fourty-Sixth Annual Turf Conference and First Industrial Show Program (10) Dollar Spot Fungicide Control Trial--1976 (13) All About Gardening (14) Herbicide Trials on Broadleaf Weeds and a Phytotoxicity Test--1976 (17) Helminthosporium Leaf Spot Fungicide Control Trial--1976 (17) Microbes--Cleaner-uppers for Polluted Waters (18

Are shark teeth proxies for functional traits? A framework to infer ecology from the fossil record

Modern sharks have an evolutionary history of at least 250 million years and are known to play key roles in marine systems, from controlling prey populations to connecting habitats across oceans. These ecological roles can be quantified based on their functional traits, which are typically morphological (e.g., body size) or behavioural (e.g., feeding and diet). Nonetheless, the understanding of such roles of extinct sharks is limited due to the inherent incompleteness of their fossil record, which consists mainly of isolated teeth. As such, establishing links between tooth morphology and ecological traits in living sharks could provide a useful framework to infer sharks' ecology from the fossil record. Here, based on extant sharks from which morphological and behavioural characteristics are known, the authors assess the extent to which isolated teeth can serve as proxies for functional traits. To do so, they first review the scientific literature on extant species to evaluate the use of shark dental characters as proxies for ecology to then perform validation analyses based on an independent data set collected from museum collections. Their results reveal that 12 dental characters have been used in shark literature as proxies for three functional traits: body size, prey preference and feeding mechanism. From all dental characters identified, tooth size and cutting edge are the most widely used. Validation analyses suggest that seven dental characters – crown height, crown width, cutting edge, lateral cusplets, curvature, longitudinal outline and cross-section outline – are the best proxies for the three functional traits. In particular, tooth size (crown height and width) was found to be a reliable proxy of all three traits; the presence of serrations on the cutting edge was one of the best proxies for prey preference; and tooth shape (longitudinal outline) and the presence of lateral cusplets were among the best indicators of feeding mechanism. Overall, the authors’ results suggest that in the absence of directly measurable traits in the fossil record, these seven dental characters (and different combinations of them) can be used to quantify the ecological roles of extinct sharks. This information has the potential to provide key insights into how shark functional diversity has changed through time, including their ecological responses to extinction events

The Ribosome Biogenesis Factor Nol11 Is Required for Optimal rDNA Transcription and Craniofacial Development in Xenopus

The production of ribosomes is ubiquitous and fundamental to life. As such, it is surprising that defects in ribosome biogenesis underlie a growing number of symptomatically distinct inherited disorders, collectively called ribosomopathies. We previously determined that the nucleolar protein, NOL11, is essential for optimal pre-rRNA transcription and processing in human tissue culture cells. However, the role of NOL11 in the development of a multicellular organism remains unknown. Here, we reveal a critical function for NOL11 in vertebrate ribosome biogenesis and craniofacial development. Nol11 is strongly expressed in the developing cranial neural crest (CNC) of both amphibians and mammals, and knockdown of Xenopus nol11 results in impaired pre-rRNA transcription and processing, increased apoptosis, and abnormal development of the craniofacial cartilages. Inhibition of p53 rescues this skeletal phenotype, but not the underlying ribosome biogenesis defect, demonstrating an evolutionarily conserved control mechanism through which ribosome-impaired craniofacial cells are removed. Excessive activation of this mechanism impairs craniofacial development. Together, our findings reveal a novel requirement for Nol11 in craniofacial development, present the first frog model of a ribosomopathy, and provide further insight into the clinically important relationship between specific ribosome biogenesis proteins and craniofacial cell survival

Seeing an exercise as a single mathematical object: using variation to structure sense-making

In this theoretical paper we take an exercise to be a collection of procedural questions or tasks. It can be useful to treat such an exercise as a single object, with individual questions seen as elements in a mathematically and pedagogically structured set. We use the notions of 'dimensions of possible variation' and 'range of permissible change', derived from Ference Marton, to discuss affordances and constraints of some sample exercises. This gives insight into the potential pedagogical role of exercises, and shows how exercise analysis and design might contribute to hypotheses about learning trajectories. We argue that learners' response to an exercise has something in common with modeling that we might call 'micro-modeling', but we resort to a more inclusive description of mathematical thinking to describe learners' possible responses to a well-planned exercise. Finally we indicate how dimensions of possible variation inform the design and use of an exercise

RPSA, a candidate gene for isolated congenital asplenia, is required for pre-rRNA processing and spleen formation in Xenopus

A growing number of tissue-specific inherited disorders are associated with impaired ribosome production, despite the universal requirement for ribosome function. Recently, mutations in RPSA, a protein component of the small ribosomal subunit, were discovered to underlie approximately half of all isolated congenital asplenia cases. However, the mechanisms by which mutations in this ribosome biogenesis factor lead specifically to spleen agenesis remain unknown, in part due to the lack of a suitable animal model for study. Here we reveal that RPSA is required for normal spleen development in the frog, Xenopus tropicalis. Depletion of Rpsa in early embryonic development disrupts pre-rRNA processing and ribosome biogenesis, and impairs expression of the key spleen patterning genes nkx2-5, bapx1 and pod1 in the spleen anlage. Importantly, we also show that whereas injection of human RPSA mRNA can rescue both pre-rRNA processing and spleen patterning, injection of human mRNA bearing a common disease-associated mutation cannot. Together, we present the first animal model of RPSA-mediated asplenia and reveal a crucial requirement for RPSA in pre-rRNA processing and molecular patterning during early Xenopus development

Increased hepatic oxidative metabolism distinguishes the action of Peroxisome proliferator-activated receptor delta from Peroxisome proliferator-activated receptor gamma in the ob/ob mouse.

BACKGROUND: The peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors and members of the nuclear receptor superfamily. The PPAR family consists of three members: PPARalpha, PPARgamma, and PPARdelta. PPARdelta controls the transcription of genes involved in multiple physiological pathways, including cellular differentiation, lipid metabolism and energy homeostasis. The receptor is expressed almost ubiquitously, with high expression in liver and skeletal muscle. Although the physiological ligands of PPARdelta remain undefined, a number of high affinity synthetic ligands have been developed for the receptor as a therapeutic target for type 2 diabetes mellitus, dyslipidemia and the metabolic syndrome. METHODS: In this study, the metabolic role of PPARdelta activation has been investigated in liver, skeletal muscle, blood serum and white adipose tissue from ob/ob mice using a high affinity synthetic ligand and contrasted with PPARgamma activation. To maximize the analytical coverage of the metabolome, (1)H-nuclear magnetic resonance ((1)H-NMR) spectroscopy, gas chromatography-mass spectrometry (GC-MS) and ultra performance liquid chromatography-mass spectrometry (UPLC-MS) were used to examine metabolites from tissue extracts. RESULTS: Analysis by multivariate statistics demonstrated that PPARdelta activation profoundly affected glycolysis, gluconeogenesis, the TCA cycle and linoleic acid and alpha-linolenic acid essential fatty acid pathways. CONCLUSIONS: Although activation of both PPARdelta and PPARgamma lead to increased insulin sensitivity and glucose tolerance, PPARdelta activation was functionally distinct from PPARgamma activation, and was characterized by increased hepatic and peripheral fatty acid oxidative metabolism, demonstrating the distinctive catabolic role of this receptor compared with PPARgamma

Coastal wetlands mitigate storm flooding and associated costs in estuaries

As storm-driven coastal flooding increases under climate change, wetlands such as saltmarshes are held as a nature-based solution. Yet evidence supporting wetlands' storm protection role in estuaries—where both waves and upstream surge drive coastal flooding—remains scarce. Here we address this gap using numerical hydrodynamic models within eight contextually diverse estuaries, simulating storms of varying intensity and coupling flood predictions to damage valuation. Saltmarshes reduced flooding across all studied estuaries and particularly for the largest—100 year—storms, for which they mitigated average flood extents by 35% and damages by 37% ($8.4 M). Across all storm scenarios, wetlands delivered mean annual damage savings of$2.7 M per estuary, exceeding annualised values of better studied wetland services such as carbon storage. Spatial decomposition of processes revealed flood mitigation arose from both localised wave attenuation and estuary-scale surge attenuation, with the latter process dominating: mean flood reductions were 17% in the sheltered top third of estuaries, compared to 8% near wave-exposed estuary mouths. Saltmarshes therefore play a generalised role in mitigating storm flooding and associated costs in estuaries via multi-scale processes. Ecosystem service modelling must integrate processes operating across scales or risk grossly underestimating the value of nature-based solutions to the growing threat of storm-driven coastal flooding

How Comprehensive and Efficient Are Patient-Reported Outcomes for Rotator Cuff Tears?

BACKGROUND: Increasing emphasis is placed on patient-reported outcomes (PROs) after common orthopaedic procedures as a measure of quality. When considering PRO utilization in patients with rotator cuff tears, several different PROs exist with varying levels of accuracy and utilization. HYPOTHESIS/PURPOSE: Understanding which disease-specific PRO may be most efficiently administered in patients after rotator cuff repair may assist in promoting increased patient and physician adoption of these useful scores. Using a novel assessment criterion, this study assessed all commonly used rotator cuff PROs. We hypothesize that surveys with fewer numbers of questions may remain comparable (with regard to comprehensiveness) to longer surveys. STUDY DESIGN: Systematic review. METHODS: Commonly utilized rotator cuff PROs were analyzed with regard to number of survey components, comprehensiveness, and efficiency. Comprehensiveness (maximum score, 11) was scored as the total number of pain (at rest/baseline, night/sleep, activities of daily living [ADLs], sport, and work) and functional (strength, motion/stiffness, and ability to perform ADLs, sport, and work) metrics included, along with inclusion of quality of life/satisfaction metrics. Efficiency was calculated as comprehensiveness divided by the number of survey components. RESULTS: Sixteen different PROs were studied. Number of components ranged from 5 (University of California at Los Angeles score [UCLA]) to 36 (Short Form-36 [SF-36], Japanese Orthopaedic Association score [JOA]). The Quality of Life Outcome Measure for Rotator Cuff Disease (RC-QoL) included all 5 pain components, while 7 PROs contained all 5 functional components. Ten PROs included a quality of life/satisfaction component. The most comprehensive scores were the RC-QoL (score, 11) and Penn (score, 10), and the least comprehensive score was the Marx (score, 3). The most efficient PROs were the UCLA, the Quick Disabilities of the Arm, Shoulder, and Hand score (QuickDASH), and Constant scores. The least efficient scores were the JOA and SF-36 scores. CONCLUSION: Many commonly utilized PROs for rotator cuff tears are lacking in comprehensiveness and efficiency. Continued critical assessment of PRO quality may help practitioners identify the most comprehensive and efficient PRO to incorporate into daily clinical practice