Human Potassium channels

certain Indian coccids

South African marine ichthyofauna has remarkable diversity across a range of biogeographic zones from cold-temperate to subtropical. Two families stand out here, both with high diversity and high rates of endemism to the region, namely Sparidae and Clinidae. The Sparidae are of greater interest because of their commercial importance, and conversely, their conservation status. Several are listed as threatened by the IUCN. The Sparidae is also the family with the greatest plasticity in life history characteristics of any vertebrate family, as they include gonochorism, rudimentary hermaphrodites, and both kinds of sequential hermaphrodites. Life history characteristics are known determinants of the resilience of fish species to fishing, and more generally of their response, either positive or negative, to any form of disturbance. Life history characteristics of most of the species of Sparidae, in South Africa and worldwide, have been studied, particularly those of commercial and conservation importance. Omissions include those that are small, with little commercial importance. This is an oversight, as there is much to be learned about life history strategies by studying the full spectrum of variation in the family, and particularly those variants which produce numerically, and therefore ecologically, significant population sizes. In this thesis, I study the life history and parasite community of one of South Africa’s most abundant seabreams in separate chapters. In the last chapter I take a fresh perspective on life history variation among fishes, by comparing four sympatric seabreams to describe the several dimensions along which life history trade-offs can occur without the confounding influences of environment and phylogeny. Boopsoidea inornata (Castelnau, 1861) is endemic to South Africa. Eight hundred and seventeen fishes were sampled from four locations: False Bay, Struisbaai, Goukamma and Port Elizabeth from 2012 to 2014. They ranged in size from 130 to 310 mm fork length. The diet of B. inornata was investigated in False Bay and Struisbaai using Prey-Specific Index of Relative Importance (%PSIRI). B. inornata is an omnivore, with a preference towards small sand- and reef-dwelling prey and has only limited intake of algae and small fish. Age and growth were assessed using sectioned otoliths. A clear seasonal pattern of band formations deduced from the frequency of opaque margins show that B. inornata lay down one opaque and one transparent band per year. B. inornata is a small species (L∞= 222.7 mm) with high longevity (tmax= 37). It is a rudimentary hermaphrodite. The ovaries hold up to 8000 vitellogenic eggs, which equates to an average 19 eggs per gram of body mass. This value is low compared with other seabream species. B. inornata females spawn repeatedly during the year, although there is more spawning activity in spring, than in other months. The sex ratio is heavily skewed towards females (1:3.35). The presence of post-ovulatory follicles together with hydrated oocytes indicates that the species is an indeterminate batch spawner. Length at 50% maturity was calculated based on gonads collected throughout the spawning season. Females mature at 178 mm FL, compared to 185 mm FL for males. Female GSI greatly exceeds male GSI, and, together with the sex ratio, suggests a polygamous mating system. One hundred and fifty B. inornata were collected from False Bay, Struisbaai, Goukamma and Port Elizabeth to investigate associated parasite assemblages. Eighty six percent of the sample was infected by parasites. Parasites infecting B. inornata have never before been recorded. Nineteen parasite taxa were found infecting B. inornata across all localities and included myxozoan, monogenean, digenean, cestode, nematode, copepod and isopod representatives. Three species of digenean metacercaria showed high prevalence of infection in B. inornata across all four localities. These included a Stephanostomum sp. infecting the gill arches of 61%, and two unidentified digeneans. The unidentified digenean metacercariae- 2 was found in the kidneys and musculature of 59% of the total sample and the unidentified digenean metacercariae-1 was found infecting the hearts of 47% of the total sample. Overall parasite assemblages were significantly different amongst all localities, with no significant difference in parasite assemblages among size classes, age classes or sex within localities. Fish life history is affected by environmental and biological factors but is also constrained by phylogenetic influences on morphology and physiology. In an attempt to expose the nature and extent of life history trade-offs, I compared four closely related and sympatric seabreams, namely Spondyliosoma emarginatum, Pachymetopon blochii, Rhabdosargus globiceps and Boopsoidea inornata. I contend that only by eliminating or reducing as far as possible the effect of environment, habitat and phylogeny can we expose real trade-offs. Samples of each species were obtained in every season from the south-western Cape, South Africa, to obtain measures of total length, mass, gonadosomatic index and condition. S. emarginatum is a nest-guarding, short-lived, protogynous hermaphrodite. P. blochii is a resident, group-spawner, engaging in sperm competition. R. globiceps is a moderately long-lived migrant with a sex ratio of 1:1, that also engages in sperm competition over a short spawning season. B. inornata is a polygamous, long-lived resident with low annual fecundity, but a protracted spawning season. Although all four species are periodic strategists, life history trade-offs exist between several sets of variables, namely semelparity vs iteroparity, age-at-maturity vs maximum size, annual fecundity vs longevity, length of spawning season vs parental care, and length of spawning season vs migration. The efficiency of the sequential hermaphrodite strategy which allows every fish to spawn as a female until they are large enough to act as a male makes one question the rarity of this strategy. I argue that halving of the female life-span compromises the periodic strategy, and that hermaphroditism is at odds with migration. The latter rests on the assumption that the migrant social structure is based on cooperation, for feeding, defence and navigating in schools, whereas the hermaphrodite social structure is based on aggression and dominance hierarchies which requires residency and territoriality. No clear adaptive reason for the divergence among the sympatric species can be identified, although competition among the young is a candidate. This comparison reveals a wide range of options available to seabreams and shows how disparate life histories can be equally adaptive under identical conditions. More generally I have shown how a variety of life-history traits, such as migration, sex-ratio, reproductive strategy and somatic growth form interact to define a life-history.

Climate change and drought pose a major threat to agriculture and water resources globally and for rooibos (Aspalathus linearis (Burm. F.) R. Dahlgren) production in the Western Cape province of South Africa. Rooibos is adapted to the coarse, nutrient poor, acidic, well-drained, deep sandy soil of the Fynbos biome. The region has a Mediterranean climate, which is characterised by wet cold winters, with an average annual rainfall of about 375 mm, and dry summers. The growth of rooibos peaks in the summer months, implying a reliance on soil moisture. The current study aims to investigate the relationship between rooibos growth and soil moisture. The objectives of the study were: 1) to determine the effect of soil moisture on growth and evapotranspiration in rooibos under glasshouse conditions, 2) to adapt the CROPGRO model in DSSAT to simulate the shoot biomass yield of rooibos, using the rooibos CROPGRO model, 3) to investigate the effect of rooibos growth on soil moisture, and 4) to determine the effect of different levels of mulching and irrigation on rooibos yield and soil moisture. Some of the results obtained in the glasshouse study in Objective 1 and observational field data from the literature were used in the adaptation of the CROPGRO model. The glasshouse study was carried out at the University of Cape Town, using soils from Clanwilliam and Citrusdal sites to grow rooibos seedling for 16 weeks in pots before exposing them to drought treatments. The pots were arranged on trays in the glasshouse using a completely randomized design. Two drought treatments were used: moderate drought stress (MDS), set at 20% FC, and severe drought stress (SDS), during which watering was completely withdrawn, were applied to 10 pots per treatment per site. Data on plant growth, root morphology, evapotranspiration, soil moisture, chlorophyll fluorescence and leaves to determine chlorophyll and carotenoid concentration were collected from the plants in the glasshouse after 10 days of these drought treatments. The SDS plants were re-watered for 8 weeks for recovery, and together with the MDS and control plants were transferred into a growth chamber for measurement of gas exchange parameters and biomass. The CROPGRO model in DSSAT was adapted for rooibos by changing some parameters in a pigeon pea (Cajanus cajan L. Millspaugh) CROPGRO model. The adapted rooibos model was used to set up an experiment that compared the cumulative evapotranspiration and soil moisture from the rooibos field and bare soil under rainfed conditions. Also, in a simulation experiments, the model was used to determine the effect of three levels of mulching by means of wheat residue at 8000 kg/ha, 4000 kg/ ha and 2000 kg/ha and drip irrigation at 25.4mm and at 12.5mm once a week from December to March, both separately and in combination, on rooibos shoot biomass and soil moisture. The results from the glasshouse study showed a 40% decrease in biomass under MDS conditions for 12 weeks, while SDS plants could not survive beyond 10 days in the glasshouse. Root morphological features changed under severe drought stress, resulting in longer and thinner roots relative to the control plants. The reduced biomass accumulation under drought conditions was followed by reduced photosynthesis, stomata conductance, transpiration, and concentration of chlorophyll and carotenoids. Changes in both maximum quantum efficiency of photosystem II (Fv/Fm) and fluorescence quantum yield (Fq'/Fm') were observed in the later stages of the SDS plants (days 9 and 10) compared to the control plants but were unaltered in the MDS plants. The soil moisture correlated negatively with evapotranspiration and stomata conductance in control plants, while these relationships were absent in MDS plants. Changes in temperature in the glasshouse correlated positively with stomata conductance and transpiration in the control plants, but these correlations were also absent in MDS plants. However, changes in temperature correlated negatively with soil moisture in both the control plants and the MDS treated plants. The CROPGRO model in DSSAT was successfully adapted to simulate shoot biomass in rooibos under field conditions and the rooibos model had an agreement of 94% with observational shoot biomass under field conditions. Furthermore, the model simulated cumulative evapotranspiration in rooibos plants in the field, with an agreement of 56%. The simulated experiments showed that cumulative evapotranspiration from the rooibos field was 33% higher than that of bare soil, and showed that rooibos plants extract moisture from deep soil layers to a depth of about 2 m. Furthermore, rooibos growth in deep soil, and in mulched or irrigated treatments, produced higher shoot biomass than control plants. In deep soil, the simulated irrigated rooibos plants, which received 25.4 mm water weekly from December to March, produced a higher biomass yield than only rainfed or mulched plants. However, the combined treatments of mulching at 8000 or 4000 kg/ha and irrigation at 12.5 mm was similar to irrigation at 25.4mm. The average extractable soil moisture was greater in deep soil for all the treatments and control plants compared to shallow soil. Overall, the rooibos crop model shows that an increased supply of soil moisture enhances the production of biomass yield in rooibos in the field. Also, rooibos extracts moisture from a deeper soil layer, which enables it to hydrate its leaves and to transpire during the summer period for better growth and biomass production. Water loss through evapotranspiration was high in rooibos fields, and thus mulching of the plants would be beneficial for increased biomass production. However, even better rooibos yields were obtained when mulching was combined with irrigation. The glasshouse experiments showed a yield decrease of rooibos biomass by about 40% when the moisture supply was reduced by about 50% of the adequate conditions. The thinner and longer roots of rooibos, among other drought tolerance traits, most likely enable it to cope with low rainfall and drought conditions, which are prevalent in the Cederberg region of the Western Cape. The production of rooibos in the farms is prone to water loss through evapotranspiration, and thus soil moisture conservation technologies such as mulching would greatly enhance its biomass yield.

Data on the ciliate infestation of the alimentary tract of echinoids has been steadily growing. Work has been done on sea urchins from Bermuda, Tortugas, the east and west coasts of Japan, the coast of North Carolina; the coast of California, the Mediterranean Sea. and the North Sea. The present paper deals with the sea urchin Parechinus Angulosus, the only species of sea-urchin to be found along the southernmost parts of the coast of South Africa. Five species of ciliate have been found, of which three appear to be new species. All of these species belong to the order Holotrichida. Apart trom the ciliates found a red Rhabdocoele worm of the genus Syndesmus has been found. It lies in the perivisceral cavity attached to the outside of the intestine, and appears to be a new species. Many of the ciliates found in sea urchins are closely related to free-living species, and are fairly cosmopolitan in distribution. A careful consideration of taxonomic status and of geographical distribution should therefore result in considerable information regarding the origin of the endozoic habit.

The Acrothoracica of South Africa are reviewed for the first time, 50 years after the last publication on this group appeared. A new host category for acrothoracicans is described in Chapter 1, as Weltneria spinosa was collected from coralline red algae. This finding was not an isolated event, as this species was found inhabiting four different species of coralline algae across a range of sites up to 900 km apart. These are the first unequivocal records of living acrothoracicans burrowing into coralline red algae. Further inspections of coralline algae in this and other regions will likely reveal many more new host records and possibly new acrothoracican species. In Chapter 2 a systematic account and key to all known South African acrothoracicans are given, with each description accompanied by scanning electron microscopy, light microscopy and a distribution map. The number of known South African acrothoracicans is increased from four to eight species, as three new records and two undescribed species are added to the fauna, while one existing record is determined to be a nomen nudum. Chapter 3 examines patterns of distribution and host specificity. All species except one saw a range extension, some of which were > 500 km, while all species had additional hosts described. The species with the most hosts was W. spinosa, which was reported from 13 hosts that included gastropods, chitons and coralline red algae. South Africa thus now includes 11.27% of the world’s acrothoracican species, with 62.50% of these endemic. Moreover, 75% of South African acrothoracicans were endemic to specific provinces. However, these values are likely to change substantially as more sites are sampled both within the region and in neighbouring countries. In conclusion this dissertation shows that South Africa has more acrothoracican species, occupying more hosts across wider distributional ranges than previously thought. Although this study serves as a valuable baseline it should be expanded on through future sampling, specifically focusing on areas (Delagoa, Namaqua and offshore bioregions) and hosts (especially corals) not yet sampled in South Africa.

South Africa hosts plant species with a large variety of floral traits associated with different pollinator guilds. Suites of specialised floral traits associated with particular pollinators are known as pollination systems or syndromes. However, it is often uncertain how these pollination systems affect gene flow between plant populations, mating system outcome, and subsequent genetic health of plant species. Genetic variability is an important aspect in understanding the long-term survival of a species because excessive homozygosity, as a result of high amounts of inbreeding, may restrict a species’ long-term local adaptive potential. The African genus, Protea, is an ideal study system for exploring the evolution and maintenance of mating systems, because the pollination system for many species have been confirmed by pollinator exclusion experiments. The genus has several pollination systems including birds, insects and non-flying mammals. Comparative estimates of pollinators’ outcrossing abilities are rare and confined to bird and insect guilds. Furthermore, 10 microsatellite markers have been developed for the genus, but have not been used to assess the outcrossing abilities of various pollinators. This study thus had two aims: Firstly, to use microsattelite markers to estimate the outcrossing rates and subsequent genetic diversity of Protea species primarily pollinated by either birds (P. laurifolia and P. roupelliae), insects (P. caffra and P. simplex) or non-flying mammals (P. amplexicaulis and P. humiflora). Secondly, I aimed to understand how birds and non-flying mammal pollinators affect population connectivity and gene dispersal. This was done by comparing indirect estimates of gene flow in the therophilous, P. amplexicaulis, and ornithophilous, P. laurifolia. These estimates included population differentiation (G”st) between subpopulations and spatial genetic structuring within metapopulations of each species. I expected that less vagile pollinators, such NMP’s (non-flying mammal pollinators), would contribute the least to gene flow and cause high selfing rates and low genetic diversity within therophilous populations. Contrastingly, flying pollinators would be able to travel longer distances resulting in more genetic connectivity between plant populations. The high energetic demands and interplant movements of flying animals were predicted to result in high outcrossing rates in ornithophilous and entomophilous species. Non-flying mammal-pollinated (NMP) Protea species had high (> 0.8) and non-significantly different (p > 0.05) outcrossing rates relative to species pollinated by flying animals. Similarly, hand pollen supplementation experiments also revealed that small mammals were effective pollen vectors since P. amplexicualis individuals were not pollen limited. High multilocus outcrossing rates (> 0.80) may have resulted in all sampled Protea species exhibiting high levels of heterozygosity (> 0.7) and low levels of inbreeding. However, some of the outcrossing events were between kin (approximately 14 %), giving evidence for biparental inbreeding. Furthermore, the relationship between geographic distance and genetic distance was significant for sampled P. amplexicaulis individuals. In contrast, sampled P. laurifolia individuals were genetically similar across the landscape. This pattern was reflected in fine-scale (> 500 m) spatial genetic structuring in a sampled metapopulaton of P. amplexicaulis and a homogeneous distribution of P. laurifolia genotypes. Restricted gene dispersal recorded for P. amplexicaulis in this study may have been a result of the high levels of biparental inbreeding. It was not clear whether poor gene flow was primarily a result of restricted pollen dispersal created by NMP’s or restricted seed dispersal. Nevertheless, continuous limited gene dispersal between NMP populations may result in allopatric speciation over time. This provides a hypothesized reason as to why many of the therophilous Protea species are located in small and isolated populations. Additionally, there is a concern that restricted population size in combination with poor gene flow may lead to increased levels of inbreeding over time. This study provided the first evidence for localised gene dispersal, but high outcrossing rates, in NMP proteas.

Globally, freshwater fisheries are faced with numerous impacts that compromise fish populations. A knowledge and understanding of riverine fish movements are crucial for effective management and conservation of populations. However, there is a paucity of information about the spatial behaviour and ecology of wild and stocked cyprinids in floodplain rivers, especially under the influence of elevated flows. This study examined the factors affecting the lateral and longitudinal dispersal of juvenile and adult (wild and stocked) coarse fish in three lowland river catchments, namely the River Trent, the Yorkshire Ouse and the River Roding.A literature review was carried out to review the influence of floods on riverine ecosystem function and structure, and fish assemblage patterns. In unmodified lowland rivers, floods are characterized by lateral expansion onto floodplains resulting in high levels of habitat heterogeneity, essential for fish refuge, spawning, nursery and feeding. However, anthropogenic alterations to the flow regime and floodplain connectivity have had considerable detrimental impacts on fish populations. The main conclusion of the review was the need to restore and rehabilitate lowland rivers in an attempt to recover natural features or functionality. The effects of flood timing and magnitude were examined by sampling 0+ fish populations before, during and after floods in the Yorkshire Ouse, a constrained lowland river. Large numbers of eurytopic 0+ fishes were stranded on isolated floodplains when artificial levees ‘over-topped’ in summer (August). By contrast, backwaters provided refuge for high densities of 0+ eurytopic and rheophilic fishes. During floods, small fish were displaced or had lower survival. The results highlight the influence of flood timing on 0+ fish populations, the use of refuge areas and their importance of lowland river rehabilitation.In the River Trent, 0+ fish populations were sampled in the margins of the main river channel and in ten man-made floodplain waterbodies to evaluate the importance of variable connectivity between these habitats for rehabilitating the riverine-floodplain ecosystem. Fish assemblages compared favourably with studies on unmodified river reaches, i.e. succession of lotic-to-lentic habitat corresponded to a sequence of rheophilic-to-eurytopic-to-limnophilic fish species. Consequently it was concluded that the connection of man-made floodplain waterbodies to the river should incorporate variable, not just high, levels of hydrological connectivity into holistic riverine ecosystem management plans.Dual-Frequency Identification Sonar (DIDSON) was used to determine the influence of elevated flow on the lateral movements of adult fish between the Yorkshire Ouse and a marina (refuge habitat). Fish activity in the entrance was predominantly during daylight hours. Increased river flow resulted in significantly reduced fish movements, both towards and away from the marina, and fish presence in the entrance, except for larger fish (more than 30 cm) during the night. This study emphasised the importance of artificial floodplain waterbodies for adult cyprinid fish during winter months.The influence of environmental variation (flow and temperature) on movements of wild and stocked adult cyprinids is poorly understood, partially because of experimental difficulties. A laboratory study on PIT tagging individual juvenile cyprinids, identified that the method would be suitable for such investigations. In the River Roding, a combination of PIT and radio telemetry was used to compare habitat use, longitudinal movement (timing and direction), site fidelity and survival between wild populations and hatchery-reared fish. Wild cyprinids had high levels of ‘site fidelity’ but highly mobile individuals were present within the population, with movements positively correlated with temperature and flow. During elevated winter flows, wild fish occupied areas of reduced flow to reduce energy expenditure, but some fish performed exploratory movements. Movements of stocked fish were more frequent and longer than for wild fish, particularly just after release, possibly for exploratory purposes. Subsequently, movements of stocked fish were minimal, did not correlate with flow or temperature and the final distributions were more widely dispersed than found in wild fish. Importantly from a stocking perspective, stocked cyprinids had the behavioural and physiological ability to cope with elevated flows. However, differences in movements and habitat use between wild and stocked chub probably had consequences on survival.

Virulence (the harm to the host during infection) is the outcome of continuous coevolution between hosts and parasites. This thesis adds to a growing body of work on host-parasite interactions, and describes experiments that study the effects of variation in the genetic and the environmental contexts of infection. All of them focus on interaction between the planktonic freshwater crustacean Daphnia magna and a naturally occurring parasite, the spore-forming bacterium Pasteuria ramosa. I show that elevated minimum temperatures that facilitate parasite growth drive natural epidemics of this parasite. I also demonstrate that the expression of infection traits in P. ramosa is temperature-dependent in a genotype-specific manner [genotype-by-environment (GxE) interactions]. These GxE interactions could maintain polymorphism through environment-dependent selection. Next, I test if GxG interactions for infectivity can be altered by environmental variation (GxGxE interactions), and find that this trait is quite robust to thermal variation. Infectivity is also more important in determining parasite fitness relative to the production of transmission stages, highlighting the importance of considering natural infection routes, an aspect sometimes overlooked in studies of host-parasite systems. Another experiment under different food and temperature regimes showed evidence for environment-dependent virulence-transmission relationships, a fundamental component of virulence evolution models. Lastly, I show that variation in temperature does not increase the cost to the host of resisting infection.

Matrix attachment regions (MAR) are the sites on genomic DNA that interact with the nuclear matrix. A complex bipartite motif, the MAR recognition signature (MRS), has been proposed as a DNA sequence marker for MAR but its specificity and sensitivity remain unresolved. I describe here the distribution of the MRS in the genomes of a number of species from across animals and plants. The MRS is shown to have a distinctive, nonrandom distribution, with a particular relationship to genes. This relationship was studied in detail in the genome of Caenorhabditis elegans, revealing striking peaks of average MRS frequency in the regions flanking C. elegans genes. The occurrence of similar peaks in C. briggsae, Danio rerio, Arabidopsis thaliana, Drosophila melanogaster and Homo sapiens was also investigated. The nucleotide content in the vicinity of genes is examined and it too is shown to have striking peaks in regions surrounding genes. C. elegans genes associated with MRS were found to be significantly enriched for receptor activity annotations but not for some other features. Using this analysis of the genomic distribution of the MRS, the relevance of the MRS as a marker for MAR is discussed. The potential for MRS to play a functional role, as indicated by their peculiar frequency in the vicinity of genes, is also explored.