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No description available.

Call number: LD2668 .T4 1979 J32 / Master of Science

Thesis (MSc)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Physiological diversity in insects was investigated in terms of gas exchange patterns and metabolic rate. Since the majority of hypotheses that propose to explain the occurrence of Discontinuous Gas Exchange Cycles (DGCs) are adaptive, the possibility of adaptation was explored in two ways. First, since repeatability is one of the three prerequisites for natural selection, and rarely tested in insects, the repeatability of gas exchange characteristics and metabolic rate were tested in a Perisphaeria sp. cockroach. Four major gas exchange patterns were recognized and these patterns were found to be extremely variable within this species. However, repeatability was still generally high for the majority of the gas exchange characteristics and metabolic rate. Moreover, between individual variability generally accounted for a large proportion of the variance, supporting the repeatability findings. Therefore, both metabolic rate and gas exchange patterns might indeed be adaptive traits in this Perisphaeria sp. cockroach. Second, the distribution of the three gas exchange patterns (DGCs, cyclic and continuous) across the insect phylogeny was investigated. Data were extracted from the literature and gas exchange patterns for eight insect orders, representing mainly the endopterygotes, were measured. Using standard respirometry techniques, data for a total of ten additional orders were added, which represented both apterygote orders, six exopterygote orders and two endopterygote orders that were previously uninvestigated. In addition, four of the five adaptive hypotheses were tested by investigating the occurrence of DGCs in winged or wingless insects, subterranean and non-subterranean insects, and insects from mesic and xeric environments. Results indicate that DGC has evolved at least five times in the insects and that the cyclic gas exchange pattern is likely to be basal. No support was found for the chthonic, hybrid and oxidative damage hypotheses, while DGCs were associated with xeric environments. This analysis provides some support for the hygric hypothesis. In addition the prediction of the fractal network model for metabolic scaling which states that both intra- and interspecific scaling coefficients should be identical and equal to 0.75, was tested. Three species of polymorphic worker ants were used to determine the intraspecific scaling coefficient. Data from the literature were added to provide metabolic rate information on 42 species of the Formicidae. The interspecific scaling coefficient was determined in several ways: the traditional method (Ordinary Least Squares regression models), with the two respirometry techniques analyzed separately or in combination (e.g. open and closed system), and using phylogenetic independent contrasts with the same sets of data. Intraspecific coefficients were significantly different from 0.75. The slope of the interspecific regression obtained using Ordinary Least Squares regression models was not significantly different from 0.75. However, when phylogenetic relatedness was accounted for the slope differed significantly from 0.75. Therefore, the fractal network model was not supported by these findings, since slope values are not equal and also not statistically equivalent to 0.75. Overall, variability of both metabolic rate and gas exchange patterns in insects is higher than generally suggested by the literature. These findings provide much scope for future work. / AFRIKAANSE OPSOMMING: Hier word die fisiologiese diversiteit van insekte ondersoek in terme van hul gaswisselings patrone asook hul metaboliese tempo. Die oorgrote meerderheid van die hipoteses wat voorgestel is om die onstaan en bestaan van Diskontinue Gaswisseling in insekte te verklaar, is op ‘n evolusionêre grondslag gebaseer. Vir hierdie rede word die moontlikheid van Diskontinue Gaswisseling as ‘n aanpassing op twee maniere ondersoek. Herhaalbaarheid is een van die voorvereistes van aanpassing (in terme van evolusie) en dit is tot dusver slegs ‘n paar keer in insekte getoets is. Daarom word die herhaalbaarheid van die gaswisselings komponente, asook die metaboliese tempo hier in ‘n Perisphaeria sp. kokkerot ondersoek. Vier hoof gaswisselings patrone is geidentifiseer en die bevinding was dat die patrone geweldig kan varieer binne hierdie spesie. Ten spyte hiervan was die herhaalbaarheid steeds hoog vir die oorgrote meerderheid van die gaswisselings komponente asook vir die metaboliese tempo. Verder het die variasie tussen individue tot ‘n groot proporsie van die totale variasie bygedra, wat die betekenisvolheid van die hoë herhaalbaarheid beklemtoon. Dus, beide metaboliese tempo sowel as gaswisselings komponente kan moontlik as ‘n aanpassing beskou word in hierdie kokkerot. Tweedens, die verspreiding van die drie gaswisselings patrone (Diskontinue Gaswisseling, siklies en kontinu) in die insekte is ondersoek. Gaswisselings patrone vir agt van die dertig insek ordes is vanuit die literatuur verkry, alhoewel dit meestal verteenwoordigend van die Endopterygota is. Data vir tien additionele ordes wat nog nooit voorheen ondersoek is nie is bygevoeg, insluitende beide die ordes van Apterygota en ses ordes van die Exopterygota, asook twee ordes van die Endopterygota. Verder is vier van die vyf hipoteses met betrekking tot aanpassing ondersoek deur die teenwoordigheid van Diskontinue Gaswisseling in gevleuelde en ongevleuelde insekte, ondergrondse en bogrondse insekte, asook insekte van gematigde en droeë omgewings te ondersoek. Resultate dui aan dat Diskontinue Gaswisseling ten minste vyf keer onafhanklik in insekte onstaan het en dat die sikliese patroon heel moontlik basaal is. Die resultate bied geen ondersteuning vir die hipoteses wat gegrond is op gaswisseling in ondergrondse omgewing of oksidasie beskerming nie. Daar is wel ondersteuning vir die hipotese aangaande die rol van water verlies in die onstaan en onderhoud van Diskontinue Gaswisseling. Additioneel is daar ondersoek ingestel na die verwagting wat deur die fraktale netwerk model vir metaboliese glyskale gestel word, wat lui dat beide die binne- sowel as tussen-spesies koëffisiënte identies aan mekaar en gelyk aan 0.75 sal wees. Drie polimorfiese mier spesies is gebruik om die binne-spesies koëffisiënt te bepaal. Data vanuit die literatuur is hier bygevoeg en sodoende was informasie vir 42 mier spesies van die Formicidae beskikbaar. Verskillende metodes is gebruik om die tussen-spesies koëffisiënt te bepaal: die tradisionele metode (sg. “OLS”-regressie), met die twee tegnieke om metaboliese tempo te bepaal (bv. oop en geslote sisteem metodes) apart asook saam, en deur gebruik te maak van filogeneties onafhanklike vergelykings vir dieselfde datastelle. Die binne-spesies koëffisiënte was almal betekenisvol verskillend van 0.75. Die tussen-spesies regressie waar gebruik gemaak is van ‘n “OLS”-regressie model was nie betekensivol verskillend van 0.75 nie. Met filogenetiese verwantskappe egter in ag geneem, het die koëffisiënt wel betekenisvol verskil van 0.75. Dus word die fraktale netwerk model nie ondersteun deur hierdie studie nie, aangesien die koëffisiënte nie indenties aan mekaar is nie, en ook statisties verskil van 0.75. In die algemeen is die variasie in metaboliese tempo sowel as gaswisselings patrone aansienlik hoër as wat afgelei kan word uit die literatuur. Hierdie bevindinge stel ‘n basis vir heelwat verdere werk in die toekoms.

No description available.

Among the South African Thysanura, the order Lepismatoidea has spread over the whole sub-continent, while all except one species of the order Machiloidea are confined to the discontinuous forest belt which lies below the escarpment of the inland plateau. The Machiloidea are not , however, strictly confined to the actual forests within their geographical region, some species invading regions of considerable aridity. Investigations on the ecology, water relations and orientation behaviour of a representative species of each order have been carried out. These have revealed that: (i) the physical conditions in the typical niche of the Machiloidea are extremely stable, whereas those in the habitat of the Lepismatoidea are subject to some considerable fluctuation. (ii) the Lepismatoidea are more resistant to desiccation than the Machiloidea; in both cases this resistance is due in part to physical barriers in the cuticle and partly to an active metabolic process. (iii) the Machiloidea rely on their eversible vesicles, situated on the abdominal coxosternites, for the uptake of water which cannot be drunk, such as a thin film of water or soil capillary water. (iv) the Lepismatoidea are able to absorb water from a subsaturated atmosphere. (v) the behavioural responses of both in respect of humidity, temperature, light and gravity, are such as to keep them in conditions within the range of their physiological limitations. From these results it is concluded that the Machiloidea can survive outside the shelter of forests, provided that water is readily available in some form in which it can be absorbed by the animals. The general implications of the results are such as to permit the erection of an hypothesis explaining the distribution of the Thysanura in South Africa in terms of t he availability of wate. The results also lead to speculations on the evolution of the Pterygota.

The epicuticular wax layer prevents excessive loss of body water in most insects. The innermost layer of the wax is an oriented monolayer, offering the greatest resistance to the movement of water molecules across the cuticle. Several workers have shown that this oriented monolayer undergoes phase transition at a certain temperature and that the loss of water increases rapidly above this temperature which is now known as transition temperature. Other researchers deny a sharply defined transition point and claim that loss of water increases exponentially with temperature. The controversy includes Corixids. This work was carried out in an attempt to study the water relations of Cenocorixa expleta (Hungerford) in dry air. An apparatus was built to pass dry air over a single insect at constant speed and temperature. Measurements were made of the evaporation rate and the temperature of the cuticle, using copper-constantan thermo-couples made from 47 s.w.g. wires. In one series of experiments, the insects were pre-treated by immersion in water or surfactant solutions of various temperatures before their evaporation rates were measured in dry air of 20 G. Adult C. expleta have a transition point which lies near 30 C but composite evaporation/temperature curves do not show it. The evaporation rates in dry air are slightly temperature-dependent below, and highly temperature-dependent above transition. When caused by high temperature air, transition appears to be reversible: the insects regain waterproofness at approximately 25 C. To prove or disprove the existence of a transition point it is necessary to measure the evaporation rates of an individual insect over the entire temperature range. Phase transition and loss of waterproofness can also be caused by water of 30 C to 35 C. In this case the effect is irreversible. Detergent solutions of sub-transition temperatures remove a small fraction of waterproofing agent, possibly the non-oriented portion of the wax layer. The presence of the transition phenomenon in G. expleta, i. e., the fact that these insects lose their waterproofing, suddenly at approximately 30 G, and the fact that they lose this waterproofing permanently if it is caused by high temperature water, may limit their successful survival in small water bodies and thus their distribution. / Land and Food Systems, Faculty of / Graduate

Previous studies of selective reabsorption in insect excretory system have concentrated almost exclusively on the rectum, while the role of the ileum has been assumed to be minor. The properties and control of solute and fluid transport in two segments of the hindgut, the ileum and rectum, from the desert locust (Schistocerca gregaria) have been studied and compared in vitro using everted sac and flat sheet preparations. Everted sacs of locust ileum transported fluid from the lumen side to hemocoel side over a 5 h period at near constant rates of 3.0 to 3.5 μL-h⁻¹-ileum⁻¹ and tissue volume did not change. Inhibition by azide indicated metabolic dependence of fluid transport. Fluid absorption occurred against osmotic concentration differences of up to 600 mosmol. Fluid transport was stimulated by cAMP, both nervous and glandular lobes of corpus cardiacum (CC), and fifth ventral ganglia (VG) in a dose-dependent manner. All stimulants caused ilea to absorb against larger osmotic concentration differences than unstimulated sacs. The ileal absorbate remained hyperosmotic to the luminal saline under all conditions and stimulants increased absorbate osmolality. Unstimulated fluid transport was supported at 50% of control levels by any one of Na+, K+, or CI⁻. Stimulation of fluid transport by CC or VG was dependent on CI⁻ and maximal stimulation occurred when the Na+:K+ ratio was 1:1. Cyclic AMP, CC and VG all stimulated Na+,K+ and CI⁻ absorption across everted ileal sacs. This is the first direct demonstration that Na+ reabsorption is controlled in insect excretory systems. Stimulation resulted in a decrease in absorbate HCO₃⁻ levels and pH concurrently with an increase in absorbate CI⁻ levels. Stimulation of fluid transport was associated with a 3-fold increase in transepithelial potential (hemocoel negative) suggesting stimulation of electrogenic anion (CI⁻) movement to the hemocoel. Net Na+ absorption occurs largely by electroneutral active transport. NH₄+/Na+ exchange may account for one-third of stimulated net Na+ flux. Extracts from both CC and VG stimulated fluid, K+, and CI⁻ transport across everted rectal sacs, but only a small stimulation of Na+ flux was observed which was an order of magnitude less than that observed for stimulated ilea (0.4 versus 5.1 μequiv-h⁻¹ -cm⁻²). Unlike the rectum, the ileum did not transport proline transepithelially and ileal fluid transport was not stimulated by increasing concentrations of proline in the bathing saline. Rectal fluid transport was stimulated 50% by increasing external proline concentration from 1 to 80 mM. Stimulation of rectal fluid transport by proline also occurred in the absence of Na+, K+, and CI⁻ and occurred against larger osmotic concentration differences. These results are consistent with previous reports of a high capacity transport system for proline in locust rectum. The presence of anion-stimulated ATPase and Na+,K+-ATPase in locust hindgut was also investigated. Anion-stimulated ATPase activities were observed in microsomal fractions of both rectum and ileum. Microsomal fractions from both tissues had enriched specific activities of several plasma membrane marker enzymes and decreased activities of two mitochondrial markers as compared to homogenate enzyme activities. Na+,K+-ATPase activity was 20-fold higher in the rectum than in the ileum, associated with the greater development of the basolateral membrane in the rectum. Overall the results suggest that ion and fluid reabsorption in the locust ileum is much more important in the excretory process than previously supposed. Moreover, this reabsorption was shown to be under neuroendocrine control. / Science, Faculty of / Zoology, Department of / Graduate

The cellular mechanism and regulation of KC1 reabsorption across the rectum of the desert locust Schistocerca gregaria has been studied using tracer fluxes, ion-sensitive microelectrodes, and electrophysiological techniques. Serosal addition of 1 mM cAMP stimulates transepithelial short- circuit current (I[sub=SC]) and net Cl absorption (J[sub=net;sup=Cl] ) 10-fold, increases transepithelial potential (V[sub=t]) 4-fold, and reduces transepithelial resistance (R[sub=T]) by 40-65%. The properties of locust Cl transport are not consistent with NaCl cotransport models proposed in other epithelia: i) Cl is absorbed from nominally Na-free saline, ii) there is no correlation between trace amounts of Na contamination and the rate of Cl transport, iii) exposure to cAMP increases ³⁶Cl influx across the apical border into rectal tissue without affecting ²²Na influx, iv) Cl-dependent I[sub=SC] is not inhibited by 1 mM ouabain (2 h) or 1 mN furosemide (1 h), v) J[sub=net;sub=Cl] is not affected when the apical Na electrochemical gradient is reduced by 85%, and vi) there is no relationship between Na and Cl net electrochemical gradients across the apical membrane. Cl/HCO₃ exchange is also unlikely since i) Cl-transport is electrogenic, ii) J[sub=net;sub=Cl] is insensitive to CO₂⁻ and HCO₃⁻ removal, and iii) Cl-dependent I[sub=SC] is not inhibited by 1 mM SITS or 1 mM acetazolamide after 1 h exposure. The cAMP-stimulated system is Cl-selective: Cl >> Br >> I,F,SCN,P0₄,SO₄.C₂H₃O₂,urate. The halide sequence suggests a site having high field strength. Cl-dependent I[sub=SC] is inhibited by low mucosal pH and high osmotic pressure. J[sub=net;sub=Cl] obeys Michaelis-Menten-type kinetics. Mucosal K increases both the K[sub=m] and V[sub=max] of transepithelial Cl absorption (K[sub=a] = 5.3 mM K). The active step in J[sub=net;sub=Cl] is at the apical membrane because net entry of Cl occurs against a large, unfavourable electrochemical gradient. Serosal cAMP and mucosal K directly stimulate the active step since both of these agents cause simultaneous increases in J[sub=net;sub=Cl] and the electrochemical potential opposing CI entry. Passive K transport in the mucosa-to-serosa direction is favoured across apical and basal membranes. Most K absorption (~84%) is electrically coupled to active CI transport under open-circuit conditions, however a small active component is apparent during exposure to cAMP. The response of V[sub=T] to transepithelial salt gradients depends strongly on the direction of the gradients, suggesting that locust rectum is a "tight" epithelium. Intracellular current and fluorescent dye injections reveal strong coupling between rectal cells. Flat-sheet cable analysis indicates that locust rectum becomes "tighter" during cAMP exposure, when transcellular conductance increases from 60 to 95% of the total tissue conductance. cAMP increases apical membrane K conductance and basal membrane CI conductance. K permeability is inhibited by high (physiological) K and osmotic concentrations. The driving force of CI transport is calculated by two independent methods and the results are interpreted in terms of an equivalent electrical circuit model for KCl reabsorption across locust rectum. / Science, Faculty of / Zoology, Department of / Graduate