Beginsels en metodes vir die bepaling van die ouderdom van hominied fossiele en hulle vindplekke

Principles and methods used for the determination of the age of hominid fossils and their discovery sites Paleoanthropologists have an array of physical dating methods developed by researchers in the physical sciences. These techniques permit students of hominid evolution and associated culture to have increasing confidence that the evidence of past hominid morphology as expressed by the fossil finds is being placed in the correct chronological order. This article explains in a simple and straightforward way the evidence and logic that have led scientists to conclude that hominid fossils are not a few thousand years but at least several million years old. The main focus is on the 40Ar/ 39Ar technique, but other absolute dating techniques such as carbon-14, uranium-thorium-lead and radiocalcium are also reviewed. Relative dating methods are briefly discussed together with paleomagnetism (geomagnetism), optic stimulated luminescence and amino acids

Ghost crabs on a treadmill: Oxygen Uptake and Haemocyanin Oxygen Affinity

Ghost crabs Ocypode ceratophthalmus were exercised on a specially constructed treadmill. At a running speed of 13,3 cm s-1, most crabs ran for 2 h before getting fatigued. At this speed the oxygen consumption rate (MO2) was measured in time intervals for a total of 52 min. For exercised crabs the MO2 values are about eight times higher (28,5 ± 5.0 mmol l-1kg-1h-1 compared with the values (3,5 ± 0,4 mmol l-1kg-1h-1) for resting crabs. One hour after the exercising bout, the MO2 values were not back to normal resting values. The l-lactate levels in the haemolymph increase to 20,7 (± 4,8) mmol l-1 after 20 min exercise, whilst the pH decreases from 7,91 (± 0,05) to 7,71 (± 0,08). For resting crabs pre-branchial PCfe (venous) is 35,9 (± 5,6) mmHg, total carbon dioxide concentration (Ceo, tot.) 22,6 (± 2,6) mmol l-1, l-lactate 0,68 (±0,5) mmol l-1; haemocyanin oxygen capacity (Cmax/Hcyo) 1,50 (± 0,11) mmol l-1; haemocyanin concentration 99,3 (± 21) mg ml-1and haemolymph oxygen content 4,11 ml O2 100 ml-1haemolymph. Haemolymph from resting crabs has P50 values of 4,5 (± 1,0) mmHg, while for exercised crabs it is 10,0 (±0,8) mmHg. Gel-chromato-graphed haemolymph increased the oxygen affinity of the haemocyanin to 1,30 (± 0,1) mmHg, an indication of the presence of oxygen affinity modulators in the haemolymph. A decrease in the pH of the haemolymph has a greater effect on oxygen affinity compared with the effects from either CO2 or l-lactate. Hill-plot analysis of both native and gel-chromatographed haemolymph reveal that co-operativity (n) of the oxygen-binding sites in the haemocyanin sub-units increases to a value of 4 with a corresponding decrease in oxygen affinity. This effect has the result that large amounts of O2 can be suddenly released by the haemocyanin to tissues such as muscle and ganglia for immediate mitochondrial use

Temperature sensitivity of the oxygenation reaction of stripped haemolysates from the freshwater fishes Labeo capensis and Ciarias gariepinus

The oxygen binding properties of haemoglobin solutions of the mudfish Labeo capensis and the catfish Clarias gariepinus, stripped by gel filtration chromatography and buffered at 23°C in 0,05 M Hepes (pH 7,48), were determined at 8°C, 15°C and 23°C. The P50 values obtained for L. capensis at these respective temperatures were 0,89 (pH 7,63); 1,29 (pH 7,52) and 3,02 (pH 7,49) and those for C. gariepinus haemoglobin were 2,47 (pH 7,61 ); 3,34 (pH 7,53) and 6,30 (pH 7,49). The lower oxygen affinity of C. gariepinus haemoglobin may be related to the obligatory air breathing of C. gariepinus by means of a branchial organ which is absent in the mudfish. The purified hemolysate from C. gariepinus also displayed higher haem-haem co-operativity (n) at all three experimental temperatures compared to L. capensis. The heat of oxygenation (ΔH) between 8°C (pH 7,63) and 23°C (pH 7,49) calculated for L. capensis haemoglobin (−56,3 kJ.mol1) exceeded that of C. gariepinus (−43,1 kJ.mol1)

Modifications to an optocardiographic method for measurement of heart rate in a range of invertebrate species

A non-invasive technique developed by Depledge & Andersen (1990) on a crab and a lamellibranchiate was used in this study to measure heart rate activity in a millipede, centipede, spider, two scorpion species, two crab species, three insect species and the garden snail. A novel technique to confine smaller arthropods in an aluminium foil bag provided with a 7 mm by 7 mm opening allowed heart rate measurements to be done on spiders, insects, centipedes and scorpions without direct body contact of the probe. For the crab and the garden snail a plastic device to hold the reflective optocoupler (ROC) probe was glued externally over the heart region. The amplitude of the heart rate signals in 1 mm depth water as medium was about 8% less than those in 1 mm of air. Four millimetres of water as medium reduced the amplitude signal by 90% when compared to zero thickness. With 4 mm of air as medium the amplitude signal decreased by 80%. The erroneous electronic circuit diagram published by Depledge & Andersen (1990) is corrected and redrawn

The effect of short-term Cu exposure on the oxygen consumption and Cu accumulation of mudfish (Labeo capensis) and the largemouth bass (Micropteris salmoides) in hard water

Sediment samples from 3 dams near the gold-mining area in the Mooi River catchment, South Africa, and fish tissue from the mudfish (Labeo capensis) and largemouth bass (Micropteris salmoides) were analysed for Cu to assess environmental pollution. Copper concentrations of sediment samples in 50 mm deep profiles at Klerkskraal Dam (22.2 mg Cu·kg-1), Boskop Dam (14.1 mg Cu·kg-1) and Potchefstroom Dam (21.7 mg Cu·kg-1) and profiles 100 mm and 150 mm deep were above the risk assessment values for Cu, as implemented by the US EPA. Lowest Cu concentrations were found in gonads and blood samples in fish from both species in the 3 dams, but accumulated 3 to 5 times more, to 110.1±17.8 mg Cu·kg-1 dry mass in the liver. After 120 min Cu exposure at 20ºC to 10 mg Cu·ℓ-1 (157.3 mmol Cu·ℓ-1) and a 96 h Cu exposure to 1 mg Cu·ℓ-1 (15.73 mmol Cu·ℓ-1) Cu accumulated mainly in liver tissue and gills. For the mudfish, upon exposure to 10 mg Cu·ℓ-1 (157.3 mmol Cu·ℓ-1), the opercular frequency increased significantly from 80 (± 5.7) cycles·min-1 to above 100 (± 5.8) cycles·min-1 after 90 min, but thereafter decreased to zero cycles·min-1. For largemouth bass the same increase in opercular frequency was found during 10 mg Cu·ℓ-1 exposure, but this Cu level did not stop opercular frequency. For L. capensis the oxygen consumption rate M· O2 for the two hour exposure period at 10 mg Cu·ℓ-1 decrease significantly from 5.17 (± 0.32) mmol O2·ℓ-1·kg-1· h-1 for the controls to 4.5 (± 0.37) mmol O2.ℓ-1·kg-1·h-1 and for experimental M. salmoides from 4.91(± 0.45) mmol O2·ℓ-1·kg-1·h-1 to 3.13 (±0.74) mmol O2·ℓ-1·g-1·h-1. For the exposure period of 96 h at 1 mg Cu·ℓ-1, M· O2 for both fish species, decreased to 2.9 (± 0.3) mmol O2·ℓ-1·kg-1·h-1. It is concluded that:• The imported M. salmoides from the USA is biologically more tolerant to acute Cu exposure compared to the endemic mudfish, Labeo capensis• For the 2 fish species Cu accumulates mainly in the liver, followed by the gills and kidney• [Cu] above 20 mg Cu·kg-1 dry sediment may be released in the water column if the pH value decreases below 5 and, together with the physical disturbance of the sediment layer, acute Cu pollution will be the result• Copper is about 10 times more toxic for the 2 fish species studied compared to Pb and Cd in hard water as found in previous studies.Keywords: Cu, sediment, fish, M· O2, opercular frequency, hard wate

Papers from the International Conference on Comparative Physiology and Biochemistry, Kruger National Park, South Africa, 31 August to 5 September 1997 : Introduction

No Abstrac

Oxygen uptake and haemocyanin oxygen affinity of Potamonautes warreni Calman after exercise

The MO2 values for exhaustively exercised crabs in water medium or air medium are nearly twice the values found for pre-exercised crabs. The l-lactate concentration in the haemolymph increases from 0,75 ± 0,37 mmol to 9,63 ± 2,1 mmol in P. warreni after air exercise, a value similar to those for other terrestrial and aquatic crabs. The same increase in the l-lactate concentration was found for water-exercised crabs. The pH in the haemolymph decreases from 7,51 (SD 0,07) to 7,11 (SD 0,08) after the 20 min air medium exercise and from 7,521 (SD 0,06) to 7,229 (SD 0,09) after 20 min exercise in water medium. In both respiratory media this causes a lowering in the haemocyanin oxygen affinity with a Bohr-factor of – 1,05 whilst the haemocyanin-oxygen co-operativity increases from 3,0 to 3,7. Preliminary in vitro experiments indicate that l-lactate (as an acid metabolite) is mainly responsible for the Bohr-effect

Haemolymph parameter changes in the South African Mooi River crab Potamonautes warreni during prolonged starvation

Animals in the wild are constrained by food resources. To understand the severity of starvation events on their biology, starvation in all its manifestations must be documented. Male Potamonautes warreni Calman crabs were collected live from the Mooi River, near Potchefstroom, South Africa, in April 2009. One hundred-microlitre haemolymph samples were collected serially at a specially prepared site on the carapace of each of the fed and starved crabs, and haemocyanin, D-glucose, chloride, calcium and pH were analysed. After six weeks’ starvation, D-glucose had decreased by 400% and haemocyanin by more than 55% in starved crabs. Chloride concentration decreased continuously during the six weeks from 316.0 (SE 5.9) to 282 (SE 6.7) mmol l−1 and from 301.0 (SE 7.9) to 266.0 (SE 3.6) mmol l−1 in fed and starved crabs, respectively. Calcium concentration and pH decreased in fed crabs, whereas calcium concentration increased and haemolymph pH decreased in starved crabs. Possible reasons for changes in haemolymph parameters in fed and starved crabs are discusse