1,720,958 research outputs found
Interactive effects of pH, temperature and exposure period on native and invasive mussels from the West Coast of South Africa
No full textGlobal warming and ocean acidification due to an increase in anthropogenic carbon dioxide can impact marine calcifying organisms. Shells of marine calcifying organisms protect their internal soft tissue and may be key in determining the susceptibility of marine calcifiers to these environmental stressors. To test this, the effects of pH, temperature, exposure period and their interactions on the performance of native and alien mussels with varying shell thickness was studied. Listed in order of decreasing shell thickness, I compared shell dissolution, shell growth, shell breaking force and condition index of Aulacomya ater, Choromytilus meridionalis (both native), Mytilus galloprovincialis and Semimytilus algosus (both invasive) found on the Western Cape coast of South Africa. Live mussels and bare shells were exposed to seawater temperatures of 14°C and 20°C set at two pH levels (7.5 and 8.0) for roughly 40 days. Live mussels were either exposed to aerial drying for four hours per day or fully submerged for the duration of the study. The results suggest that shell thickness determines the susceptibility of mussels to environmental stressors, in terms of shell dissolution and breaking force, but does not affect internal growth. Invasive mussels showed increased shell dissolution at low pH but their growth rates were unaffected. They also exhibited higher condition indices than native mussels under low pH and high temperatures. On the other hand, the thicker shelled native mussels showed no significant changes in shell dissolution among the treatments and exhibited increases in growth rates in low pH treatments. C. meridionalis, being cold water adapted, exhibited a reduction in condition index in high temperature treatments. The study indicates that native and invasive mussels have different compensatory mechanisms to respond to anthropogenic impacts. These mechanisms allow them to maintain their specific life history strategies under short term exposure to warming and acidification. It was also elucidated that mussels exposed to low temperature aerial conditions exhibit increased shell and tissue growth as periodic exposure minimises the deleterious effects of ocean acidification and warming. The findings suggest that native and invasive mussels respond differently to ocean acidification and warming depending on their specific physiologies and life history strategies
Growth-related gene expression in haliotis midae
Full text linkThesis (PhD (Genetics))--University of Stellenbosch, 2010.Includes bibliography.ENGLISH ABSTRACT: The slow growth rate of Haliotis midae impedes the optimal commercial production of this most
profitable South African aquaculture species. To date, no comprehensive effort has been made to
identify genes associated with growth variation in farmed H. midae. The aim of this study was therefore
to investigate growth variation in H. midae and to identify and quantify the expression of selected
growth-related genes. Towards this aim, molecular methodologies and cell cultures were combined as a
time-efficient and economical way of studying abalone transcriptomics and cell biology.
Modern Illumina sequencing-by-synthesis technology and subsequent sequence annotation were used
to elucidate differential gene expression between two sibling groups of abalone demonstrating
significant growth variation. Following transcriptome sequencing, genes involved in growth and
metabolism, previously unknown in H. midae, were identified. The expression of selected target genes
involved in growth was subsequently analyzed by quantitative real-time PCR (qPCR).
The feasibility of primary cell cultures for H. midae was furthermore investigated by targeting embryo,
larval and haemolymph tissues for the initiation of primary cell culture. Larval cells and haemocytes
could be successfully maintained in vitro for limited periods. Primary haemocyte cultures demonstrated
to be a suitable in vitro system for studying gene expression and were subsequently used for RNA
extraction and qPCR, to evaluate differential growth induced by bovine insulin and epidermal growth
factor (EGF).
Gene expression was thus quantified in fast and slow growing abalone and in in vitro primary
haemocyte cultures treated with different growth stimulating factors. The results obtained from
transcriptome analysis and qPCR revealed significant differences in gene expression between large and
small abalone, and between treated and untreated haemocyte cell cultures. Throughout in vivo and in
vitro qPCR experiments, the up-regulation of genes involved in the insulin signaling pathway provides
evidence for the involvement of insulin in enhanced growth rate for various H. midae tissues.
Besides the regulation of target genes, valuable knowledge was also gained in terms of reference genes,
during qPCR experimentation. By quantifying the stable expression of two genes (8629, ribosomal
protein S9 and 12621, ornithine decarboxylase) in various tissues and under various conditions, suitable
reference genes, that can also be used in future H. midae qPCR studies, were identified.
By providing evidence at the transcriptional level for the involvement of insulin, insulin-like growth
factors (IGFs) and insulin-like growth factor binding proteins (IGFBPs) in improved growth rate of H.
midae, the relevance of investigating ways to stimulate insulin/IGF release in aquaculture species was
again emphasized. As nutritional administration remains the most probable route of introducing agents that can stimulate the release of insulin-related peptides, continuous endeavours to stimulate abalone
growth through a nutritional approach is encouraged.
This is the first time next generation sequencing is used towards the large scale transcriptome
sequencing of any haliotid species and also the first time a comprehensive investigation is launched
towards the establishment of primary cell cultures for H. midae. A considerable amount of sequence
data was furthermore annotated for the first time in H. midae. The results obtained here provide a
foundation for future genetic studies exploring ways to optimise the commercial production of H.
midae.AFRIKAANSE OPSOMMING: Die stadige groeitempo van Haliotis midae belemmer die optimale kommersiele produksie van hierdie
mees winsgewende Suid-Afrikaanse akwakultuur spesie. Tot op hede is geen omvattende poging
aangewend om gene verwant aan groeivariasie in H. midae te identifiseer nie. Die doel van hierdie
studie was dus om groeivariasie in H. midae te ondersoek en om spesifieke groei-gekoppelde gene te
identifiseer en hul uitdrukking te kwantifiseer. Ter bereiking van hierdie doel is molekulêre metodes en
selkulture gekombineer as 'n en tydsbesparende en ekonomiese manier om perlemoen transkriptomika en
selbiologie te bestudeer.
Moderne Illumina volgordebepaling-deur-sintese tegnologie en daaropvolgende annotasie is gebruik
om verskille in geenuitdrukking tussen naby-verwante groepe perlemoen, wat noemenswaardige
groeivariasie vertoon, toe te lig. Na afloop van die transkriptoom volgordebepaling is gene betrokke by
groei en metabolisme, vantevore onbekend in H. midae, geïdentifiseer. Die uitdrukking van uitgesoekte
teikengene betrokke by groei is vervolgens ge-analiseer deur kwantitatiewe "real-time PCR" (qPCR). die lewensvatbaarheid van 'n primêre selkulture vir H. midae is ook ondersoek deur embrio, larwe en
hemolimf weefsels te teiken vir die daarstelling van primêre selkulture. Larweselle en hemosiete kon in
vitro suksesvol onderhou word vir beperkte periodes. Primêre hemosietkulture het geblyk 'n gepaste in
vitro sisteem te wees om geenuitdrukking te bestudeer en dit is vervolgens gebruik vir RNS ekstraksie
en qPCR, om differensiële groei, geïnduseer deur insulien en epidermale groeifaktor (EGF), te evalueer.
Geenuitdrukking is dus gekwantifiseer in vinnig- en stadiggroeiende perlemoen en in in vitro primêre
hemosiet selkulture wat behandel is met verskillende groei stimulante. Die resultate wat verkry is van
transkriptoomanalise en qPCR het noemenswaardige verskille in geenuitdrukking tussen groot en klein
perlemoen, en tussen behandelde en onbehandelde hemosiet selkulture uitgelig. Die op-regulering van
gene betrokke by die insulien sein-padweg, tydens in vivo en in vitro qPCR eksperimente, bied getuienis
vir die betrokkenheid van insulien in die verhoogde groeitempo van verskeie H. midae weefsels.
Benewens die regulering van teikengene is waardevolle kennis ook ingewin in terme van
verwysingsgene tydens qPCR eksperimentering. Deur die stabiele uitdrukking van twee gene (8629,
ribosomale proteien S9 en 12621, ornitien dekarboksilase) te kwantifiseer in verskeie weefsels en onder
verskeie kondisies is gepaste verwysingsgene, wat ook in toekomstige H. midae qPCR eksperimente
aangewend kan word, geïdentifiseer.
Deur getuienis vir die betrokkenheid van insulien, insuliensoortige groeifaktor en insuliensoortige
groeifaktor-bindingsproteïene by verbeterde groei van H. midae op transkripsievlak te bied, is die
toepaslikheid van bestudering van maniere om insulienvrystelling in akwakultuurspesies te stimuleer, beklemtoon. Aangesien voeding die mees waarskynlike roete is om middele wat insuliensoortige
peptiedvrystelling stimuleer daar te stel, word vogehoue pogings om perlemoengroei deur die regte
voeding te stimuleer, aangemoedig.
Hierdie is die eerste studie wat volgende generasie volgordebepaling (“next generation sequencing”)
gebruik vir die grootskaalse transkriptoom volgordebepaling van enige haliotied spesie. Dit is ook die
eerste keer dat ‘n omvattende ondersoek geloods word na die daarstelling van primêre selkulture vir H.midae. ‘n Aansienlike hoeveelheid volgorde data is ook vir die eerste keer geannoteer in H. midae. Die
resultate wat hier verkry is bied ‘n basis vir toekomstige genetiese studies wat maniere ondersoek om
die kommersiële produksie van perlemoen te optimiseer.Doctora
Doctoral writing for publication at a leading African university: publication patterns and pedagogies
No full textWriting-for-publication is a practice that doctoral students should acquire for
integration into international research culture. Publication rates and forms of
pedagogy supporting the development of publication skills for doctoral students,
however, remain inadequate worldwide. Limited data of doctoral student publication
from African universities is available in terms of publication patterns and pedagogies.
To gain insight into publication pedagogies, a top-publishing science department at
a leading African university was studied. A literature search was performed to find
journal articles linked to dissertations and the numbers and timing of publication
were documented. Supervisors and graduates from the sample were interviewed to
uncover educational strategies employed to support doctoral student publication.
Results indicate that the majority of the students published. Departmental culture
and a pedagogy of collaboration were highlighted as aspects encouraging students
to publish. These results indicate that, with appropriate educational strategies, PhD
students can be prolific publishers and thereby become integrated into research
cultures.Publisher's versio
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
An Intervention to Improve Academic Literacies in a First Year University Biology Course
Full text linkIn South Africa there are many students, especially those from previously underrepresented groups at university, who successfully gain access to university but do not succeed in completing their degree either within the prescribed time or at all. One of the barriers to student success at university is the difficulty these students have in accessing the literacy practices of the disciplines. Therefore, within a first year biology course at a South African University, an intervention that focused on the academic literacy practices in biology was introduced. The intervention was designed around the assignment of writing a lab report. This paper describes this intervention and how it impacted on one student\u27s journey from learning science at school to learning science at university. A literacy history interview and \u27talk around text\u27 interviews were used to assess the student\u27s experience of the intervention. Comparison of the student\u27s first and final drafts of the report revealed changes in the style and format of his writing. These changes in his report writing as well as in his attitude and motivation for writing the report were facilitated by a better understanding of the expectations of writing in university biology. This understanding was mediated largely through the modelling and deconstruction of the expected genre. This highlights not only the importance of providing first year students with examples of the genres they are expected to be writing but also the facilitation of their engagement with these new genres. Without these kinds of intervention many students are unlikely to gain access to disciplinary ways of learning and writing, which ultimately may lead to their exclusion from university
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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