Towards reconciliation of structure with function in plasmodesmata—who is the gatekeeper?
- Botha, Christiaan E J, Cross, Robin H M
- Authors: Botha, Christiaan E J , Cross, Robin H M
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:6497 , http://hdl.handle.net/10962/d1004493
- Description: Whilst the structure of higher plant plasmodesmata was first described by Robards (1963. Desmotubule—a plasmodesmatal substructure. Nature 218, 784), and despite many subsequent intensive investigations, there is still much that remains unclear relating to their ultrastructure and functioning in higher plants. We have examined chemically fixed plant material, and suggest that the conformational changes seen in plasmodesmatal substructure, particularly the deposition of electron-dense extra-plasmodesmal material, is linked to either manipulation of the hormonal balance (as in Avocado fruit), or of osmotic potential in leaf blade material. These changes result in the deposition of β 1,3-glucan (callose) at the neck region of these plasmodesmata. This electron-dense material is deposited at the neck region of plasmodesmata, and forms a collar-like structure. The formation of a collar is shown to be coupled with loss of lucence within the cytoplasmic sleeve. The formation of a collar at the plasmodesmatal orifice thus results in encapsulation and closure of the plasmodesmatal orifice. Closure of the orifice coincides with a loss of electron-lucence and a lack of resolution of the desmotubule. These ultrastructural changes are potentially significant and could contribute to, result in, or assist in the down-regulation of cell to cell trafficking via plasmodesmata.
- Full Text:
- Date Issued: 2000
- Authors: Botha, Christiaan E J , Cross, Robin H M
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:6497 , http://hdl.handle.net/10962/d1004493
- Description: Whilst the structure of higher plant plasmodesmata was first described by Robards (1963. Desmotubule—a plasmodesmatal substructure. Nature 218, 784), and despite many subsequent intensive investigations, there is still much that remains unclear relating to their ultrastructure and functioning in higher plants. We have examined chemically fixed plant material, and suggest that the conformational changes seen in plasmodesmatal substructure, particularly the deposition of electron-dense extra-plasmodesmal material, is linked to either manipulation of the hormonal balance (as in Avocado fruit), or of osmotic potential in leaf blade material. These changes result in the deposition of β 1,3-glucan (callose) at the neck region of these plasmodesmata. This electron-dense material is deposited at the neck region of plasmodesmata, and forms a collar-like structure. The formation of a collar is shown to be coupled with loss of lucence within the cytoplasmic sleeve. The formation of a collar at the plasmodesmatal orifice thus results in encapsulation and closure of the plasmodesmatal orifice. Closure of the orifice coincides with a loss of electron-lucence and a lack of resolution of the desmotubule. These ultrastructural changes are potentially significant and could contribute to, result in, or assist in the down-regulation of cell to cell trafficking via plasmodesmata.
- Full Text:
- Date Issued: 2000
Analysis of chromameter results obtained from corticosteroid-induced skin blanching assay: comparison of visual and chromameter data
- Schwarb, Fabian P, Smith, Eric W, Haigh, John M, Surber, Christian
- Authors: Schwarb, Fabian P , Smith, Eric W , Haigh, John M , Surber, Christian
- Date: 1999
- Language: English
- Type: text , Article
- Identifier: vital:6426 , http://hdl.handle.net/10962/d1006562
- Description: In a Guidance document, the American FDA recommends the use of a Minolta chromameter rather than the human eye for the quantitative assessment of the pharmacodynamic blanching response produced by topical application of corticosteroids. The purpose of this study was to compare the appropriateness of the human eye and two models of chromameter for the estimation of skin blanching, in terms of the quality of the data generated by each method. The corticosteroid-induced skin blanching from four different betamethasone 17-valerate cream formulations was compared in a typical human skin blanching trial. The optimized assay methodology routinely practised in our laboratories was utilized. The blanching responses were assessed visually by three trained, independent observers and recorded by two chromameters (Minolta model CR-200 and model CR-300). The topical availability of the four creams was determined using visual scoring and chromameter measurements. All data were manipulated in such a manner as to produce a blanching response versus time profile from which AUBC analysis could be performed. Good correlation was observed between the visual assessments made by three independent observers. In contrast, moderate correlation was determined between visual, CR-200 and CR-300 measurements. Surprisingly, no direct linear relationship between the AUBCs produced by the two chromameters was observed indicating that the quality of the data obtained from the two instruments may not be equal. This investigation also indicated that the use of the chromameter is not completely objective. Visual scoring and chromameter measurement produce data sets that differ in quality. Each procedure needs to be validated and investigators have to be trained for both visual assessment and the operation of the chromameter, particularly with regard to the manipulation of the measuring head of the instrument.
- Full Text:
- Date Issued: 1999
- Authors: Schwarb, Fabian P , Smith, Eric W , Haigh, John M , Surber, Christian
- Date: 1999
- Language: English
- Type: text , Article
- Identifier: vital:6426 , http://hdl.handle.net/10962/d1006562
- Description: In a Guidance document, the American FDA recommends the use of a Minolta chromameter rather than the human eye for the quantitative assessment of the pharmacodynamic blanching response produced by topical application of corticosteroids. The purpose of this study was to compare the appropriateness of the human eye and two models of chromameter for the estimation of skin blanching, in terms of the quality of the data generated by each method. The corticosteroid-induced skin blanching from four different betamethasone 17-valerate cream formulations was compared in a typical human skin blanching trial. The optimized assay methodology routinely practised in our laboratories was utilized. The blanching responses were assessed visually by three trained, independent observers and recorded by two chromameters (Minolta model CR-200 and model CR-300). The topical availability of the four creams was determined using visual scoring and chromameter measurements. All data were manipulated in such a manner as to produce a blanching response versus time profile from which AUBC analysis could be performed. Good correlation was observed between the visual assessments made by three independent observers. In contrast, moderate correlation was determined between visual, CR-200 and CR-300 measurements. Surprisingly, no direct linear relationship between the AUBCs produced by the two chromameters was observed indicating that the quality of the data obtained from the two instruments may not be equal. This investigation also indicated that the use of the chromameter is not completely objective. Visual scoring and chromameter measurement produce data sets that differ in quality. Each procedure needs to be validated and investigators have to be trained for both visual assessment and the operation of the chromameter, particularly with regard to the manipulation of the measuring head of the instrument.
- Full Text:
- Date Issued: 1999
Cicadas (Hemiptera, Homoptera: Cicadoidea) of Mkomazi
- Villet, Martin H, Van Noort, Simon, Packer, M
- Authors: Villet, Martin H , Van Noort, Simon , Packer, M
- Date: 1999
- Subjects: To be catalogued
- Language: English
- Type: text , book chapter
- Identifier: http://hdl.handle.net/10962/442756 , vital:74030 , ISBN , https://doi.org/10.1046/j.1472-4642.2001.00094.x
- Description: The cicadas are a group of insects belonging to the order Hemiptera which comprises a diverse range of insects including the bugs, leafhoppers, aphids, scale insects etc. The Hemiptera are characterised by specialised mouth parts that are adapted for piercing and sucking up sap from host plants or animal juices from their prey. All cicadas are plant feeders and can be extremely camouflaged when sitting and feeding on a branch, although the males give themselves away by their persistent, often high pitched calls.
- Full Text:
- Date Issued: 1999
- Authors: Villet, Martin H , Van Noort, Simon , Packer, M
- Date: 1999
- Subjects: To be catalogued
- Language: English
- Type: text , book chapter
- Identifier: http://hdl.handle.net/10962/442756 , vital:74030 , ISBN , https://doi.org/10.1046/j.1472-4642.2001.00094.x
- Description: The cicadas are a group of insects belonging to the order Hemiptera which comprises a diverse range of insects including the bugs, leafhoppers, aphids, scale insects etc. The Hemiptera are characterised by specialised mouth parts that are adapted for piercing and sucking up sap from host plants or animal juices from their prey. All cicadas are plant feeders and can be extremely camouflaged when sitting and feeding on a branch, although the males give themselves away by their persistent, often high pitched calls.
- Full Text:
- Date Issued: 1999
Description of adult and larva of Ichnestoma pringlei n. sp. (Coleoptera: Scarabaeidae Cetoniinae), with notes on its biology and ecology
- Perissinotto, Renzo, Smith, Tamara J, Stobbia, P
- Authors: Perissinotto, Renzo , Smith, Tamara J , Stobbia, P
- Date: 1999
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/453815 , vital:75289 , https://doi.org/10.1080/03946975.1999.10539390
- Description: There are at present 10 described species in the primitive genus Ichnestoma Gory and Percheron 1833. These are all phylogenetic and geographic relicts of high evolutionary and conservation interest. The discovery of a new species, I. pringlei n. sp., and the first description of a larva (third instar) of this genus are reported here. New information is also presented on their life-cycle and on the dependence of their activities on rainfall patterns, particularly in the semi-arid region of the Karoo. In this region, larvae seem to take 2 years to complete growth and metamorphosis since they feed only after major rainfall events, while remaining inactive and deep underground during dry periods. Adults emerge from their cocoons only after summer rains of at least 15 mm. They lack functional mouth parts and are unable to feed. Their life span is only 3–5 days. Because females are completely flightless and unable to disperse, species of the genus are extremely vulnerable to environmental degradation. It seems likely that they may play a key role in the decomposition of dead plant matter, especially in dry and clay-rich soils where other primary decomposers are scarce.
- Full Text:
- Date Issued: 1999
- Authors: Perissinotto, Renzo , Smith, Tamara J , Stobbia, P
- Date: 1999
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/453815 , vital:75289 , https://doi.org/10.1080/03946975.1999.10539390
- Description: There are at present 10 described species in the primitive genus Ichnestoma Gory and Percheron 1833. These are all phylogenetic and geographic relicts of high evolutionary and conservation interest. The discovery of a new species, I. pringlei n. sp., and the first description of a larva (third instar) of this genus are reported here. New information is also presented on their life-cycle and on the dependence of their activities on rainfall patterns, particularly in the semi-arid region of the Karoo. In this region, larvae seem to take 2 years to complete growth and metamorphosis since they feed only after major rainfall events, while remaining inactive and deep underground during dry periods. Adults emerge from their cocoons only after summer rains of at least 15 mm. They lack functional mouth parts and are unable to feed. Their life span is only 3–5 days. Because females are completely flightless and unable to disperse, species of the genus are extremely vulnerable to environmental degradation. It seems likely that they may play a key role in the decomposition of dead plant matter, especially in dry and clay-rich soils where other primary decomposers are scarce.
- Full Text:
- Date Issued: 1999
On the life history of a cyprinid fish, Labeo cylindricus
- Weyl, Olaf L F, Booth, Anthony J
- Authors: Weyl, Olaf L F , Booth, Anthony J
- Date: 1999
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125408 , vital:35780 , https://doi.10.1023/A:1007543319416
- Description: Fishes of the genus Labeo are widely distributed throughout Africa and consist of at least 80 species which comprise 16.4% of the African cyprinid ichthyofauna (Reid 1985). Most labeo species are also commercially important throughout the African continent, having contributed significantly to various fisheries. Their roe (sensu caviar) is often harvested as an additional bycatch (Skelton et al. 1991). Despite their obvious importance, the few studies that have investigated aspects of their life history have been conducted on the larger commercial species (Lowe 1952, Mulder 1973, Balon et al. 1974, Potgieter 1974, Baird 1976, Tomasson et al. 1984, van Zyl et al. 1995).
- Full Text:
- Date Issued: 1999
- Authors: Weyl, Olaf L F , Booth, Anthony J
- Date: 1999
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125408 , vital:35780 , https://doi.10.1023/A:1007543319416
- Description: Fishes of the genus Labeo are widely distributed throughout Africa and consist of at least 80 species which comprise 16.4% of the African cyprinid ichthyofauna (Reid 1985). Most labeo species are also commercially important throughout the African continent, having contributed significantly to various fisheries. Their roe (sensu caviar) is often harvested as an additional bycatch (Skelton et al. 1991). Despite their obvious importance, the few studies that have investigated aspects of their life history have been conducted on the larger commercial species (Lowe 1952, Mulder 1973, Balon et al. 1974, Potgieter 1974, Baird 1976, Tomasson et al. 1984, van Zyl et al. 1995).
- Full Text:
- Date Issued: 1999
Abundance and trophodynamics of Euphausia crystallorophias in the shelf region of the Lazarev Sea during austral spring and summer
- Pakhomov, Evgeny A, Perissinotto, Renzo, Froneman, P William
- Authors: Pakhomov, Evgeny A , Perissinotto, Renzo , Froneman, P William
- Date: 1998
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/480895 , vital:78491 , https://doi.org/10.1016/S0924-7963(98)00046-3
- Description: An investigation to estimate the seasonal changes in feeding habits in relation to the energy budget of Euphausia crystallorophias was carried out during austral spring and summer 1994/95 in the shelf region of the Lazarev Sea.
- Full Text:
- Date Issued: 1998
- Authors: Pakhomov, Evgeny A , Perissinotto, Renzo , Froneman, P William
- Date: 1998
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/480895 , vital:78491 , https://doi.org/10.1016/S0924-7963(98)00046-3
- Description: An investigation to estimate the seasonal changes in feeding habits in relation to the energy budget of Euphausia crystallorophias was carried out during austral spring and summer 1994/95 in the shelf region of the Lazarev Sea.
- Full Text:
- Date Issued: 1998
Problems in rural transformation in South Africa specifically in the land reform arena:
- Antrobus, Geoffrey G, Fraser, Gavin C G, Tapson, D R
- Authors: Antrobus, Geoffrey G , Fraser, Gavin C G , Tapson, D R
- Date: 1998
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/143035 , vital:38195 , https://www.infona.pl/resource/bwmeta1.element.agro-article-dc77672d-7269-4641-bf99-605eaa5fe369
- Description: Problems in rural transformation in South Africa specifically in the land reform arena
- Full Text:
- Date Issued: 1998
- Authors: Antrobus, Geoffrey G , Fraser, Gavin C G , Tapson, D R
- Date: 1998
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/143035 , vital:38195 , https://www.infona.pl/resource/bwmeta1.element.agro-article-dc77672d-7269-4641-bf99-605eaa5fe369
- Description: Problems in rural transformation in South Africa specifically in the land reform arena
- Full Text:
- Date Issued: 1998
Spatial and temporal variability in recruitment of intertidal mussels around the coast of southern Africa
- Harris, Jean M, Branch, George M, Elliot, Bridget L, Currie, Bronwen, Dye, Arthur H, McQuaid, Christopher D, Tomalin, Bruce J, Velasquez, Claudio
- Authors: Harris, Jean M , Branch, George M , Elliot, Bridget L , Currie, Bronwen , Dye, Arthur H , McQuaid, Christopher D , Tomalin, Bruce J , Velasquez, Claudio
- Date: 1998
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/447579 , vital:74658 , https://www.ajol.info/index.php/az/article/view/154717
- Description: Intensity of intertidal mussel recruitment was compared across a range of different spatial and temporal scales around the coast of southern Africa between June 1995 and October 1996. Comparison of the east and west coasts revealed significantly higher recruit densities on the west coast, corresponding to larger adult densities. This difference between the two coasts reflects biogeographic disparities in mussel species composition, growth rates and spawning intensities, oceanographic conditions and productivity. Significant spatial variations in recruitment were recorded between regions 100–1000 km apart and between localities 1–25 km apart. Results suggest that the influence of dispersal processes on recruitment patterns acts at a relatively small scale, and may affect the distribution and abundance of adults among shores only a few kilometres apart.
- Full Text:
- Date Issued: 1998
- Authors: Harris, Jean M , Branch, George M , Elliot, Bridget L , Currie, Bronwen , Dye, Arthur H , McQuaid, Christopher D , Tomalin, Bruce J , Velasquez, Claudio
- Date: 1998
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/447579 , vital:74658 , https://www.ajol.info/index.php/az/article/view/154717
- Description: Intensity of intertidal mussel recruitment was compared across a range of different spatial and temporal scales around the coast of southern Africa between June 1995 and October 1996. Comparison of the east and west coasts revealed significantly higher recruit densities on the west coast, corresponding to larger adult densities. This difference between the two coasts reflects biogeographic disparities in mussel species composition, growth rates and spawning intensities, oceanographic conditions and productivity. Significant spatial variations in recruitment were recorded between regions 100–1000 km apart and between localities 1–25 km apart. Results suggest that the influence of dispersal processes on recruitment patterns acts at a relatively small scale, and may affect the distribution and abundance of adults among shores only a few kilometres apart.
- Full Text:
- Date Issued: 1998
The biology of Tilapia rendalli and Oreochromis mossambicus (Pisces: Cichlidae) in a subtropical lake in Mozambique
- Weyl, Olaf L F, Hecht, Thomas
- Authors: Weyl, Olaf L F , Hecht, Thomas
- Date: 1998
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/446944 , vital:74572 , https://www.ajol.info/index.php/az/article/view/154744
- Description: This study of age and growth, reproduction and juvenile recruitment of Tilapia rendalli and Oreochromis mossambicus was undertaken in Lake Chicamba, a large, clear subtropical lake in central Mozambique. Sectioned otoliths were used to estimate age. Marginal zone analysis showed that annulus formation occurred during winter, in July and August. Maximum age estimates for T. rendalli and O. mossambicus were 16 and 10 years, respectively. Growth was described by the 3 parameter von Bertalanffy model as Lt= 238.74 (1-e-0,636 (1+ 00905)) mm TL for T. rendalli and Lt= 266.06 (1-e-0 70904 (1+ 0269)) mm TL for O. mossambicus. The length-at-50% maturity (Lm 50) of male T. rendalli was 218 mm total lenglh (TL) and 205 mm TL in females. In O. mossambicus the Lm 50 for males was 251 mm TL and for females 223 mm TL. Both species spawned throughout summer. Lake level was found to have no effect on spawning periodicity although recruitment was flood dependent.
- Full Text:
- Date Issued: 1998
- Authors: Weyl, Olaf L F , Hecht, Thomas
- Date: 1998
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/446944 , vital:74572 , https://www.ajol.info/index.php/az/article/view/154744
- Description: This study of age and growth, reproduction and juvenile recruitment of Tilapia rendalli and Oreochromis mossambicus was undertaken in Lake Chicamba, a large, clear subtropical lake in central Mozambique. Sectioned otoliths were used to estimate age. Marginal zone analysis showed that annulus formation occurred during winter, in July and August. Maximum age estimates for T. rendalli and O. mossambicus were 16 and 10 years, respectively. Growth was described by the 3 parameter von Bertalanffy model as Lt= 238.74 (1-e-0,636 (1+ 00905)) mm TL for T. rendalli and Lt= 266.06 (1-e-0 70904 (1+ 0269)) mm TL for O. mossambicus. The length-at-50% maturity (Lm 50) of male T. rendalli was 218 mm total lenglh (TL) and 205 mm TL in females. In O. mossambicus the Lm 50 for males was 251 mm TL and for females 223 mm TL. Both species spawned throughout summer. Lake level was found to have no effect on spawning periodicity although recruitment was flood dependent.
- Full Text:
- Date Issued: 1998
Learning from the people : participatory rural appraisal, geography and rural development in the 'new' South Africa
- Binns, Tony, Hill, Trevor R, Nel, Etienne L
- Authors: Binns, Tony , Hill, Trevor R , Nel, Etienne L
- Date: 1997
- Language: English
- Type: Article
- Identifier: vital:6675 , http://hdl.handle.net/10962/d1006649
- Description: Top-down rural development strategies in Africa have generally not succeeded in raising living standards among the rural poor. It is argued that inappropriate development strategies have stemmed from methodologies that fail to appreciate the whole picture in rural communities, and in particular ignore local people's perceptions, needs and understanding. Participatory Rural Appraisal (PRA) represents a significant step forward in the design of methodologies and a selection of these techniques is evaluated. Many PRA methods have much in common with the field research methods that have been used by geographers over many years to interpret people-environment relationships. A research investigation in Eastern Cape Province, South Africa, suggests that geographers could have an important role to play in this area of applied research and, in particular, in the context of post-apartheid South Africa there is an urgent challenge to be met in promoting rural development in poor, former black Homeland areas.
- Full Text:
- Date Issued: 1997
- Authors: Binns, Tony , Hill, Trevor R , Nel, Etienne L
- Date: 1997
- Language: English
- Type: Article
- Identifier: vital:6675 , http://hdl.handle.net/10962/d1006649
- Description: Top-down rural development strategies in Africa have generally not succeeded in raising living standards among the rural poor. It is argued that inappropriate development strategies have stemmed from methodologies that fail to appreciate the whole picture in rural communities, and in particular ignore local people's perceptions, needs and understanding. Participatory Rural Appraisal (PRA) represents a significant step forward in the design of methodologies and a selection of these techniques is evaluated. Many PRA methods have much in common with the field research methods that have been used by geographers over many years to interpret people-environment relationships. A research investigation in Eastern Cape Province, South Africa, suggests that geographers could have an important role to play in this area of applied research and, in particular, in the context of post-apartheid South Africa there is an urgent challenge to be met in promoting rural development in poor, former black Homeland areas.
- Full Text:
- Date Issued: 1997
Novas, eclipses and the English stage, 1598-1608
- Authors: Butler, Guy F
- Date: 1997
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/457738 , vital:75675 , https://hdl.handle.net/10520/AJA1011582X_6
- Description: In the sixteenth and early-seventeenth centuries very few kings, queens or councillors or, indeed, ordinary folk, made any important decisions without consulting their horoscopes. There is no reason to believe that Shakespeare was more sceptical about astrological prediction than his tough-minded Queen; but, even if he were sceptical, he could and did exploit his audience's susceptibility for dramatic ends. A reference to the stars could lift his action from the earthly to the cosmic. Astrological phenomena signalled the involvement of the Heavens with human affairs. In a sense, he and his fellow-dramatists had no option but to exploit the Heavens, because the canopy over half of the Elizabethan stage was referred to as 'the heavens.' It was adorned with paintings of the planets and the signs of the Zodiac. The heavens were built into his theatre, Let us start with eclipses of the sun and moon.
- Full Text:
- Date Issued: 1997
- Authors: Butler, Guy F
- Date: 1997
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/457738 , vital:75675 , https://hdl.handle.net/10520/AJA1011582X_6
- Description: In the sixteenth and early-seventeenth centuries very few kings, queens or councillors or, indeed, ordinary folk, made any important decisions without consulting their horoscopes. There is no reason to believe that Shakespeare was more sceptical about astrological prediction than his tough-minded Queen; but, even if he were sceptical, he could and did exploit his audience's susceptibility for dramatic ends. A reference to the stars could lift his action from the earthly to the cosmic. Astrological phenomena signalled the involvement of the Heavens with human affairs. In a sense, he and his fellow-dramatists had no option but to exploit the Heavens, because the canopy over half of the Elizabethan stage was referred to as 'the heavens.' It was adorned with paintings of the planets and the signs of the Zodiac. The heavens were built into his theatre, Let us start with eclipses of the sun and moon.
- Full Text:
- Date Issued: 1997
Patterns of sexual size dimorphism in African cichlid fishes
- Erlandsson, A, Ribbink, Anthony J
- Authors: Erlandsson, A , Ribbink, Anthony J
- Date: 1997
- Language: English
- Type: Article
- Identifier: vital:7135 , http://hdl.handle.net/10962/d1011778
- Description: Although the Cichlidae is a well-studied family of African fishes, the evolution of sexual size dimorphism (SSD) and its relation to life-history, behaviour, feeding and habitat have not been comparatively examined. The investigation of SSD reported here was based on a study of the scientific literature. Prerequisites to such studies are records of maximum size of adult males and females. Disappointingly few authors published such measurements, so the data are fewer than anticipated given that the cichlids are such a species-rich group. Now that this omission has been noted, it is hoped that investigations of the future will include information on maximum size of adults of both sexes. Data from 215 species showed great variation in the degree and direction of SSD, without any really strong trends being evident. In the majority of species, males were larger than females or there was no size difference between the sexes. In 10% (21 species), females were larger than males. All of these are lacustrine, tend to live in deep water, often over muddy substrata and to feed to a greater extent than expected on non-defendable food sources. The degree of SSD increases with increasing body size in species where males are the larger sex and decreases in species where females are the larger In territorial species, in which competition between territorial males is intensive, males are the larger sex. The expectation that polygynous cichlids would show a more marked degree of SSD than monogamous species was not met. Larger size in females (with one exception) occurs in mouthbrooding species only. Males are the larger sex in substratum brooders. It seems that the degree and direction of sexual size dimorphism in cichlids is a consequence of a balance of natural and sexual selection, but there is a need to increase the sample size to understand the interplay of these selection pressures and to establish the validity of the emerging trends.
- Full Text: false
- Date Issued: 1997
- Authors: Erlandsson, A , Ribbink, Anthony J
- Date: 1997
- Language: English
- Type: Article
- Identifier: vital:7135 , http://hdl.handle.net/10962/d1011778
- Description: Although the Cichlidae is a well-studied family of African fishes, the evolution of sexual size dimorphism (SSD) and its relation to life-history, behaviour, feeding and habitat have not been comparatively examined. The investigation of SSD reported here was based on a study of the scientific literature. Prerequisites to such studies are records of maximum size of adult males and females. Disappointingly few authors published such measurements, so the data are fewer than anticipated given that the cichlids are such a species-rich group. Now that this omission has been noted, it is hoped that investigations of the future will include information on maximum size of adults of both sexes. Data from 215 species showed great variation in the degree and direction of SSD, without any really strong trends being evident. In the majority of species, males were larger than females or there was no size difference between the sexes. In 10% (21 species), females were larger than males. All of these are lacustrine, tend to live in deep water, often over muddy substrata and to feed to a greater extent than expected on non-defendable food sources. The degree of SSD increases with increasing body size in species where males are the larger sex and decreases in species where females are the larger In territorial species, in which competition between territorial males is intensive, males are the larger sex. The expectation that polygynous cichlids would show a more marked degree of SSD than monogamous species was not met. Larger size in females (with one exception) occurs in mouthbrooding species only. Males are the larger sex in substratum brooders. It seems that the degree and direction of sexual size dimorphism in cichlids is a consequence of a balance of natural and sexual selection, but there is a need to increase the sample size to understand the interplay of these selection pressures and to establish the validity of the emerging trends.
- Full Text: false
- Date Issued: 1997
Plasmodesmatal frequency in relation to short-distance transport and phloem loading in leaves of barley (Hordeum vulgare). Phloem is not loaded directly from the symplast
- Botha, Christiaan E J, Cross, Robin H M
- Authors: Botha, Christiaan E J , Cross, Robin H M
- Date: 1997
- Language: English
- Type: Article
- Identifier: vital:6504 , http://hdl.handle.net/10962/d1005928
- Description: We investigated the phloem loading pathway in barley, by determining plasmodesmatal frequencies at the electron microscope level for both intermediate and small blade bundles of mature barley leaves. Lucifer yellow was injected intercellularly into bundle sheath, vascular parenchyma, and thin-walled sieve tubes. Passage of this symplastically transported dye was monitored with an epifluorescence microscope under blue light. Low plasmodesmatal frequencies endarch to the bundle sheath cells are relatively low for most interfaces terminating at the thin- and thick-walled sieve tubes within this C3 species. Lack of connections between vascular parenchyma and sieve tubes, and low frequencies (0.5% plasmodesmata per μm cell wall interface) of connections between vascular parenchyma and companion cells, as well as the very low frequency of pore-plasmodesmatal connections between companion cells and sieve tubes in small bundles (0.2% plasmodesmata per μm cell wall interface), suggest that the companion cell-sieve tube complex is symplastically isolated from other vascular parenchyma cells in small bundles. The degree of cellular connectivity and the potential isolation of the companion cell-sieve tube complex was determined electrophysiologically, using an electrometer coupled to microcapillary electrodes. The less negative cell potential {average -52 mV) from mesophyll to the vascular parenchyma cells contrasted sharply with the more negative potential (-122.5 mV) recorded for the companion cell-thin-walled sieve tube complex. Although intercellular injection of lucifer yellow clearly demonstrated rapid (0.75 μm s-1) longitudinal and radial transport in the bundle sheath-vascular parenchyma complex, as well as from the bundle sheath through transverse veins to adjacent longitudinal veins, we were neither able to detect nor present unequivocal evidence in support of the symplastic connectivity of the sieve tubes to the vascular parenchyma. Injection of the companion cell-sieve tube complex, did not demonstrate backward connectivity to the bundle sheath. We conclude that the low plasmodesmatal frequencies, coupled with a two-domain electropotential zonation configuration, and the negative transport experiments using lucifer yellow, precludes symplastic phloem loading in barley leaves.
- Full Text:
- Date Issued: 1997
- Authors: Botha, Christiaan E J , Cross, Robin H M
- Date: 1997
- Language: English
- Type: Article
- Identifier: vital:6504 , http://hdl.handle.net/10962/d1005928
- Description: We investigated the phloem loading pathway in barley, by determining plasmodesmatal frequencies at the electron microscope level for both intermediate and small blade bundles of mature barley leaves. Lucifer yellow was injected intercellularly into bundle sheath, vascular parenchyma, and thin-walled sieve tubes. Passage of this symplastically transported dye was monitored with an epifluorescence microscope under blue light. Low plasmodesmatal frequencies endarch to the bundle sheath cells are relatively low for most interfaces terminating at the thin- and thick-walled sieve tubes within this C3 species. Lack of connections between vascular parenchyma and sieve tubes, and low frequencies (0.5% plasmodesmata per μm cell wall interface) of connections between vascular parenchyma and companion cells, as well as the very low frequency of pore-plasmodesmatal connections between companion cells and sieve tubes in small bundles (0.2% plasmodesmata per μm cell wall interface), suggest that the companion cell-sieve tube complex is symplastically isolated from other vascular parenchyma cells in small bundles. The degree of cellular connectivity and the potential isolation of the companion cell-sieve tube complex was determined electrophysiologically, using an electrometer coupled to microcapillary electrodes. The less negative cell potential {average -52 mV) from mesophyll to the vascular parenchyma cells contrasted sharply with the more negative potential (-122.5 mV) recorded for the companion cell-thin-walled sieve tube complex. Although intercellular injection of lucifer yellow clearly demonstrated rapid (0.75 μm s-1) longitudinal and radial transport in the bundle sheath-vascular parenchyma complex, as well as from the bundle sheath through transverse veins to adjacent longitudinal veins, we were neither able to detect nor present unequivocal evidence in support of the symplastic connectivity of the sieve tubes to the vascular parenchyma. Injection of the companion cell-sieve tube complex, did not demonstrate backward connectivity to the bundle sheath. We conclude that the low plasmodesmatal frequencies, coupled with a two-domain electropotential zonation configuration, and the negative transport experiments using lucifer yellow, precludes symplastic phloem loading in barley leaves.
- Full Text:
- Date Issued: 1997
A review of estuarine ichthyology in South Africa over the past 50 years
- Authors: Whitfield, Alan K
- Date: 1996
- Language: English
- Type: text , Article
- Identifier: vital:7155 , http://hdl.handle.net/10962/d1011873
- Description: Progress in South African estuarine ichthyology between 1946 and 1995 is reviewed. The early estuary surveys of the 1950s and 1960s resulted in the compilation of species lists for individual systems, but contained very little biological or ecological information on fishes. These surveys were superseded by both autecological and synecological studies in the 1970s and 1980s, which yielded descriptive and process-orientated information on a wide variety of species. Estuarine research during the 1990s has focused increasingly at the community level, with several review papers on the life-history styles of groups of estuarine-associated fishes being published. The last decade has also seen the departure of a number of senior estuarine ichthyologists from the field. This decline in available expertise has coincided with increased demand for ichthyological information to be used in decision support systems for the wise management and conservation of estuaries. It is suggested that these demands be seen as a challenge, with studies being directed towards providing the type of information needed for the maintenance of vital ecological processes within these systems.
- Full Text: false
- Date Issued: 1996
- Authors: Whitfield, Alan K
- Date: 1996
- Language: English
- Type: text , Article
- Identifier: vital:7155 , http://hdl.handle.net/10962/d1011873
- Description: Progress in South African estuarine ichthyology between 1946 and 1995 is reviewed. The early estuary surveys of the 1950s and 1960s resulted in the compilation of species lists for individual systems, but contained very little biological or ecological information on fishes. These surveys were superseded by both autecological and synecological studies in the 1970s and 1980s, which yielded descriptive and process-orientated information on a wide variety of species. Estuarine research during the 1990s has focused increasingly at the community level, with several review papers on the life-history styles of groups of estuarine-associated fishes being published. The last decade has also seen the departure of a number of senior estuarine ichthyologists from the field. This decline in available expertise has coincided with increased demand for ichthyological information to be used in decision support systems for the wise management and conservation of estuaries. It is suggested that these demands be seen as a challenge, with studies being directed towards providing the type of information needed for the maintenance of vital ecological processes within these systems.
- Full Text: false
- Date Issued: 1996
Bleak future for multi-party elections in Kenya
- Authors: Fox, Roddy C
- Date: 1996
- Language: English
- Type: Article
- Identifier: vital:6683 , http://hdl.handle.net/10962/d1006681
- Description: With attention turning towards Kenya's second multi-party elections, due to be held before the end of 1997, it is imperative to look back to the flaws in the system which helped deliver President Daniel arap Moi and the Kenya African National Union (KANU) their victories in 1992. At present there is no sign of these defects being eradicated and the creation of new districts since then has demonstrated the Government's intention of enhancing an already biased structure. The underlying distribution of tribes and ethnic groups has had a fundamental impact on the electoral geography of Kenya, since they have controlled the delimitation of both the parliamentary constituencies and the administrative machinery of the whole country.
- Full Text:
- Date Issued: 1996
- Authors: Fox, Roddy C
- Date: 1996
- Language: English
- Type: Article
- Identifier: vital:6683 , http://hdl.handle.net/10962/d1006681
- Description: With attention turning towards Kenya's second multi-party elections, due to be held before the end of 1997, it is imperative to look back to the flaws in the system which helped deliver President Daniel arap Moi and the Kenya African National Union (KANU) their victories in 1992. At present there is no sign of these defects being eradicated and the creation of new districts since then has demonstrated the Government's intention of enhancing an already biased structure. The underlying distribution of tribes and ethnic groups has had a fundamental impact on the electoral geography of Kenya, since they have controlled the delimitation of both the parliamentary constituencies and the administrative machinery of the whole country.
- Full Text:
- Date Issued: 1996
Fifty years of ichthyology in Grahamstown
- Authors: Skelton, Paul H
- Date: 1996
- Language: English
- Type: text , Article
- Identifier: vital:7138 , http://hdl.handle.net/10962/d1011816
- Description: In July 1946, the fledgling Council for Scientific and Industrial Research (CSIR) awarded Dr J.L.B. (James Leonard Brierley) Smith of Rhodes University College a research fellowship of £800 to enable him to devote his energies to ichthyology. The university responded by providing accommodation, equipment and appointing Smith a research professor. These actions marked the beginning of what has become a major academic development in Grahamstown as represented by the J.L.B. Smith Institute of Ichthyology, the Department of Ichthyology and Fisheries Science (DIFS), and the Freshwater Fish Section at the Albany Museum. At present more than 40 people are employed in one way or other in these organizations, more than 20 of them professionals, in addition to whom there are 41 postgraduate students currently studying ichthyology or fisheries science through DIFS at Rhodes University. Altogether this represents a concentration of ichthyological expertise probably unmatched anywhere else in the world. It is opportune therefore to highlight a few of the more significant milestones in the history of ichthyology in Grahamstown and so illuminate some of the key factors behind this achievement.
- Full Text:
- Date Issued: 1996
- Authors: Skelton, Paul H
- Date: 1996
- Language: English
- Type: text , Article
- Identifier: vital:7138 , http://hdl.handle.net/10962/d1011816
- Description: In July 1946, the fledgling Council for Scientific and Industrial Research (CSIR) awarded Dr J.L.B. (James Leonard Brierley) Smith of Rhodes University College a research fellowship of £800 to enable him to devote his energies to ichthyology. The university responded by providing accommodation, equipment and appointing Smith a research professor. These actions marked the beginning of what has become a major academic development in Grahamstown as represented by the J.L.B. Smith Institute of Ichthyology, the Department of Ichthyology and Fisheries Science (DIFS), and the Freshwater Fish Section at the Albany Museum. At present more than 40 people are employed in one way or other in these organizations, more than 20 of them professionals, in addition to whom there are 41 postgraduate students currently studying ichthyology or fisheries science through DIFS at Rhodes University. Altogether this represents a concentration of ichthyological expertise probably unmatched anywhere else in the world. It is opportune therefore to highlight a few of the more significant milestones in the history of ichthyology in Grahamstown and so illuminate some of the key factors behind this achievement.
- Full Text:
- Date Issued: 1996
Late Devonian charophytes from the Witteberg Group, South Africa
- Gess, Robert W, Hiller, Norton
- Authors: Gess, Robert W , Hiller, Norton
- Date: 1995
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/72742 , vital:30106 , https://doi.org/10.1016/0034-6667(95)00007-8
- Description: The first record of Palaeozoic charophytes from southern Africa allows the establishment of two new genera to which are assigned four new species, Octochara crassa, O. gracilis. Hexachara setacea, and H. riniensis. Each species is represented by both vegetative and reproductive structures and suggested reconstructions are presented. Associated plant and animal remains, and the sedimentology and geochemistry of the containing rocks indicate that the charophytes probably grew in the shallow parts of a brackish coastal lagoon.
- Full Text: false
- Date Issued: 1995
- Authors: Gess, Robert W , Hiller, Norton
- Date: 1995
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/72742 , vital:30106 , https://doi.org/10.1016/0034-6667(95)00007-8
- Description: The first record of Palaeozoic charophytes from southern Africa allows the establishment of two new genera to which are assigned four new species, Octochara crassa, O. gracilis. Hexachara setacea, and H. riniensis. Each species is represented by both vegetative and reproductive structures and suggested reconstructions are presented. Associated plant and animal remains, and the sedimentology and geochemistry of the containing rocks indicate that the charophytes probably grew in the shallow parts of a brackish coastal lagoon.
- Full Text: false
- Date Issued: 1995
Patterns of distribution and conservation status of freshwater fishes in South Africa
- Skelton, Paul H, Cambray, James A, Lombard Amanda T, Benn, G
- Authors: Skelton, Paul H , Cambray, James A , Lombard Amanda T , Benn, G
- Date: 1995
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/447318 , vital:74610 , https://hdl.handle.net/10520/AJA00445096_904
- Description: The combined fish collection databases of the Albany Museum and the J.l.B. Smith Institute of Ichthyology are used to identify hotspots of endemism and threatened fish distributions in South Africa. Hotspots of fish species richness occur in the north-eastern lowveld sectors of South Africa and along the ecotone between the tropical/ subtropical and temperate faunal zones. Hotspots of endemic fish richness occur within both the tropical and temperate faunal regions, notably in the Olifants River system, Western Cape and in areas of high relief such as the Cape Fold Mountains, the Amatola-Winterberg (Eastern Cape), and the Drakensberg Escarpment (Kwazulu/ Natal-Eastern Transvaal). Threatened taxa are concentrated in the hotspots of endemic species richness which coincide largely with areas of major river conservation concern. There is limited scope for fish conservation within the ambit of formal (or informal) declared reserves, and the survival of the fauna depends on the success of river catchment conservation management. The value of museum collections in identifying areas of conservation concern for freshwater fishes is emphasized, and highlights the importance of well-preserved voucher specimens for biodiversity conservation.
- Full Text:
- Date Issued: 1995
- Authors: Skelton, Paul H , Cambray, James A , Lombard Amanda T , Benn, G
- Date: 1995
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/447318 , vital:74610 , https://hdl.handle.net/10520/AJA00445096_904
- Description: The combined fish collection databases of the Albany Museum and the J.l.B. Smith Institute of Ichthyology are used to identify hotspots of endemism and threatened fish distributions in South Africa. Hotspots of fish species richness occur in the north-eastern lowveld sectors of South Africa and along the ecotone between the tropical/ subtropical and temperate faunal zones. Hotspots of endemic fish richness occur within both the tropical and temperate faunal regions, notably in the Olifants River system, Western Cape and in areas of high relief such as the Cape Fold Mountains, the Amatola-Winterberg (Eastern Cape), and the Drakensberg Escarpment (Kwazulu/ Natal-Eastern Transvaal). Threatened taxa are concentrated in the hotspots of endemic species richness which coincide largely with areas of major river conservation concern. There is limited scope for fish conservation within the ambit of formal (or informal) declared reserves, and the survival of the fauna depends on the success of river catchment conservation management. The value of museum collections in identifying areas of conservation concern for freshwater fishes is emphasized, and highlights the importance of well-preserved voucher specimens for biodiversity conservation.
- Full Text:
- Date Issued: 1995
A comparison of the ichthyofaunas in two permanently open eastern Cape estuaries
- Whitfield, Alan K, Paterson, Angus W, Bok, Anton H, Kok, H M
- Authors: Whitfield, Alan K , Paterson, Angus W , Bok, Anton H , Kok, H M
- Date: 1994
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/447364 , vital:74618 , https://www.ajol.info/index.php/az/article/view/154297
- Description: The Kowie and Great Fish estuaries are situated less than 30 km apart, yet they differ considerably in terms of riverine inflow, turbidity, food resources and habitat availability. The ichthyofauna of the two estuaries were sampled using plankton, seine and gill nets. A greater ichthyofaunal richness (R) was recorded in the Kowie estuary and this is attributed to the wider range of habitats and greater degree of marine influence in this system. In contrast, all three sampling gears revealed an approximate 3:1 ratio between fish abundance in the Great Fish and Kowie estuaries.
- Full Text:
- Date Issued: 1994
- Authors: Whitfield, Alan K , Paterson, Angus W , Bok, Anton H , Kok, H M
- Date: 1994
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/447364 , vital:74618 , https://www.ajol.info/index.php/az/article/view/154297
- Description: The Kowie and Great Fish estuaries are situated less than 30 km apart, yet they differ considerably in terms of riverine inflow, turbidity, food resources and habitat availability. The ichthyofauna of the two estuaries were sampled using plankton, seine and gill nets. A greater ichthyofaunal richness (R) was recorded in the Kowie estuary and this is attributed to the wider range of habitats and greater degree of marine influence in this system. In contrast, all three sampling gears revealed an approximate 3:1 ratio between fish abundance in the Great Fish and Kowie estuaries.
- Full Text:
- Date Issued: 1994
Fishing Policy development consultative meeting
- FAWU
- Authors: FAWU
- Date: Dec 1994
- Subjects: FAWU
- Language: English
- Type: text
- Identifier: http://hdl.handle.net/10962/118446 , vital:34632
- Description: On 27 October 1994 we met at the Good Hope Centre with the purpose of launching a process for developing a fisheries policy. The call of the meeting was driven by the problems and the situation faced by Fisher folk. Communities in the coastal areas are starving and living under bad conditions. These resources are not utilised to address these problems at present as stated in the RDP. The present system creates conflict between individuals and between regions. Since the appointment of Mandla Gxanyana at the Good hope centre meeting lots of things have happened, consultation with regions, forums, organisation and individuals on how to take up this process and the formation of the committee. There was final agreement of bottom up approach. This approach encouraged region like Eastern Cape to take up the process and reported into the siting of the legislature of the Eastern Cape region. In KwaZulu Natal process of creating forum have started which include all the players. I hope this process will create a national Fishing Forum, which shall have committee in the different coastal communities, because RDP outline how our resource should be managed, that our communities are great pillar for the management of our resources.
- Full Text:
- Date Issued: Dec 1994
- Authors: FAWU
- Date: Dec 1994
- Subjects: FAWU
- Language: English
- Type: text
- Identifier: http://hdl.handle.net/10962/118446 , vital:34632
- Description: On 27 October 1994 we met at the Good Hope Centre with the purpose of launching a process for developing a fisheries policy. The call of the meeting was driven by the problems and the situation faced by Fisher folk. Communities in the coastal areas are starving and living under bad conditions. These resources are not utilised to address these problems at present as stated in the RDP. The present system creates conflict between individuals and between regions. Since the appointment of Mandla Gxanyana at the Good hope centre meeting lots of things have happened, consultation with regions, forums, organisation and individuals on how to take up this process and the formation of the committee. There was final agreement of bottom up approach. This approach encouraged region like Eastern Cape to take up the process and reported into the siting of the legislature of the Eastern Cape region. In KwaZulu Natal process of creating forum have started which include all the players. I hope this process will create a national Fishing Forum, which shall have committee in the different coastal communities, because RDP outline how our resource should be managed, that our communities are great pillar for the management of our resources.
- Full Text:
- Date Issued: Dec 1994