Mechanics of running of the ostrich (Struthio camelus)

Ostriches have been filmed running fast in their natural habitat. A female ostrich has been dissected and the principal bones, muscles and tendons in a leg have been measured. It is calculated that stresses up to 240 kN m⁻² and 40 MN m⁻², respectively, act in the digital flexor muscles and their tendons during running. Tensile and compressive stresses up to about 70MNm⁻² and 110 MNm⁻² act in the tibiotarsus. A large proportion of the energy which would otherwise be required for running is probably saved by elastic storage in tendons. Comparisons are made with the legs of flying birds and of antelopes.     

A relationship between irradiation, carbohydrates and rooting in cuttings of Pisum sativum

Rooting ability was studied for cuttings derived from pea plants ( Pisum sativum , L. cv. Alaska) grown in controlled environment rooms. When the cuttings were rooted at 70 μmol m⁻² s⁻, ¹ (photosynthetic photon flux density) or more, a stock plant irradiance at 100 μmol m⁻² s⁻¹ decreased rooting ability in cuttings compared to 5 μmol m⁻², s⁻¹, However, cuttings rooted at 160 μmol m⁻² s⁻¹ formed more roots compared to 5 (μmol m⁻² s⁻¹. Although a high irradiance increased the number of roots formed, it could not overcome a decreased potential for root formation in stock plants grown at high irradiance. Light compensation point and dark respiration of cuttings decreased by 70% during the rooting period, and the final levels were strongly influenced by the irradiance to the cuttings. Respiratory O₂ uptake decreased in the apex and the base of the cutting from day 2 onwards, whereas a constant level was found in the leaves. Only the content of extractable fructose, glucose, sucrose and starch varied during the early part of the rooting period. We conclude that the observed changes in the cuttings are initiated by excision of the root system, and are not involved in the initiation of adventitious roots.     

Sublittoral abundance and food consumption of Baltic gobies

Two small demersal fishes, the sand goby Pomatoschistus minutus and the common goby Pomatoschistus microps , were quantified on soft bottoms at 20–40 m depth in the Baltic Sea, using a camera placed above the bottom. The largest numbers of gobies were seen following the settlement of young in late summer and autumn. Most recorded fishes were sand gobies. An annual average of 4·7 individuals m⁻²(0·24 g dry mass m⁻²) was recorded in 1983–1985 and 2·5 individuals m⁻²(0·13 g m⁻²) in 1997–1998. Using these densities, the annual goby food consumption was estimated to 100 kJ m⁻² in 1983–1985 and 50 kJ m⁻² in 1997–1998, corresponding to most of the annual macrobenthos production available to the gobies. The resulting goby production, assumed equal to 25% of the food consumed, must have been an important food source for the larger fishes occasionally recorded in the photographs.     

Very high secondary production at a lake outlet

SUMMARY. 1. Larvae and pupae of Simulium noelleri Fried, coated the concrete of parts of an artificial lake outlet in southern England.
2. In the first two (of three) summer generations, development was synchronous and this allowed the calculation of their secondary production by the instantaneous growth method. The production of the two summer generations was, respectively, 229.1 g C m⁻² (7.4 g C m⁻²day⁻¹) and 185.5 g C m⁻² (8.8 g C m⁻² day⁻¹) The contribution of the third summer generation, and the overwintering generation, to annual production would be less than that of the first two summer generations. Nevertheless, annual production will have exceeded 500 g C m⁻² at this site.
3. Larvae are suspension feeders and they captured the rich supply of particulate and dissolved organic material which passed over them after export from the lake. As food is brought to the larvae they only require space for attachment and can thus build up very high population densities (which exceeded 1 × 10⁶ m⁻² on some occasions during the summer). The high population densities result in a high biomass and hence in the high levels of production.     

Leverage and muscle type in crab chelae (Crustacea: Brachyura)

The chelae of Cancer pagurus and Macropipus depurator were examined with respect to mechanical advantage. The closer muscles were investigated with respect to sarcomere length in the constituent fibres and to the force developed by the whole muscle during isometric contraction. Cancer chelae have a relatively high mechanical advantage, 0.329 ± 001. Cancer closer muscles contain a high proportion of fibres with long sarcomeres, mean lengths mostly falling between 12 and 15 μm, and develop a maximum stress of about 496 kN.m⁻² during contraction. These figures are typical for "slow" crustacean muscle. The chelae of M. depurator are dimorphic. In one, the strong chela, the mechanical advantage is 0.248 ± 0.066 while in the other, the fast chela, the mechanical advantage is 0.177 ± 0.006. M. depurator closer muscles contain fibres with mean sarcomere lengths mostly falling between 6 and 10 μm. The muscle develops a maximum stress of about 145 kN.m⁻² during contraction. These figures are typical of "intermediate" crustacean muscles. "Fast" muscle fibres with short sarcomeres (about 30 um) were found in the chelae of both Cancer and M. depurator but were much commoner in the latter. Thus in Cancer a high mechanical advantage is correlated with slow muscle while in M. depurator lower mechanical advantages are broadly correlated with faster muscle. Consistent correlation between mechanical advantage and muscle type in the dimorphic chelae of M. depurator , however, is lacking. No consistent regionation of fibres with similar properties was found in the muscles.     

Effect of ultraviolet radiation on accumulation and leakage of 86Rb+ in guard cells of Vicia faba

The effects of UV-C (254 nm), UV-A (365 nm) and broad-band UV (280–380 nm) on guard cells of Vicia faba L. cv. Long Pod were investigated in the presence of white light (450 μmol m⁻² s⁻¹). UV-C (7 μmol m⁻² s⁻¹) was found to cause leakage of ⁸⁶Rb⁺ from guard cells, while UV-A (0.3 μmol m⁻² s⁻¹) stimulated increased uptake in these cells. A relatively small stimulatory effect was observed by broad-band UV (3 μmol m⁻² s⁻¹) during the first 30 min of irradiation with an apparent equilibration of influx and efflux thereafter. Leakage of ⁸⁶Rb⁺ from guard cells continued despite the removal of UV-C and an increase in the amount of white light from 450 to 1500 μmol m⁻² s⁻¹, suggesting that membranes were irreversibly damaged. Irradiation of guard cells with UV-C for 30, 45 and 90 min indicated that these cells began to be affected already by 30 min UV-C irradiation.     

Development of leaf thickness for Plectranthus parviflorus – Influence of photosynthetically active radiation

Photosynthetically active radiation (PhAR) is apparently the environmental factor having the greatest influence on leaf thickness for Plectranthus parviflorus Henckel (Labiatae). A four-fold increase in leaf thickness from 280 to 1170 μm occurred as the PhAR was raised from 1.3 to 32.5 mol m⁻² day⁻¹. Compared to a constant PhAR of 2.5 mol m⁻² day⁻¹, a PhAR of 32.5 mol m⁻² day⁻¹ for one week during the first week (with return to 2.5 mol m⁻² day⁻¹ during the second and third weeks) led to an increase in final leaf thickness by 323 μm (to 802 μm). When increased PhAR was applied during the second week the increase in final thickness over the control was 217 μm, and when increased PhAR was applied during the third week it was 99 μm. However, leaf thickness was not simply responding to total daily PhAR, since a leaf 450 μm thick could occur at a low instantaneous PhAR for a long daytime (total daily PhAR of 1.5 mol m⁻² day⁻¹) and at a high PhAR for a short daytime (4.5 mol m⁻² day⁻¹). Total daily CO₂ uptake (net photosynthesis) was approximately the same in the two cases, suggesting that this is an important factor underlying the differences in leaf thickness. Leaf thickness is physiologically important, since thicker leaves tend to have greater mesophyll surface area per unit leaf area ( A ^mes/ A ) and hence higher photosynthetic rates.     

Changes in sodium and potassium in Nitellopsis cells treated with transient salt stress

Abstract. Nitellopsis cells grown in fresh water have a relatively low cytoplasmic Na⁺ (11 mol m⁻³) and high cytoplasmic K⁺ (90 mol m⁻³) content. A 30-min treatment with 100 mol m⁻³ external NaCl resulted in a high [Na⁺]_c (90 mol m⁻³) and a low [K⁺]_c (33 mol m⁻³), Subsequent addition of external Ca²⁺ (10 mol m⁻³) prevented Na⁺ influx and then [Na⁺]_c decreased slowly. Changes in [K⁺]_c were opposite to [Na⁺]_c. During the recovery time vacuolar Na⁺ increased, while vacuolar K⁺ decreased. Since all these processes proceeded also under ice-cold conditions, the restoration of original cytoplasmic ion compositions is suggested to be a passive nature. The notion that the passive movement of ions across the tonoplast can act as an effective and economic mechanism of salt tolerance under transient or under mild salt stress conditions is discussed.     

Ammonium and phosphate regenerationby the zooplankton of an Amazon floodplain lake

SUMMARY. 1. Regeneration of ammonium and phosphate by macro-zooplankton (Cladocera. adult copepods. and copepodites) was measured in Lake Calado. an Amazon floodplain lake, Macrozooplanktonabundances ranged between 1×10⁴ and 3×10⁵ individuals m⁻².
2. Phosphate regeneration ranged from 0.2 to 1.3 μ mol PO₄ m⁻² b⁻¹at station 1. located 2 km from the Solimoes River, and from 1.6 to8.3 μ mol PO₄ m⁻² h ⁻¹ at station 3, located 7 km from the SolimoesRiver. Ammonium regeneration at stations 1 and 3 ranged from 1.7 to11.9 and from 13.4 to 77.2 μ mol NH₄ m⁻² h⁻¹. respectively.
3. Zooplankton regenerated ammonium and phosphate at similarrates during rising and falling waier. Regeneration by macrozooplankton was low compared to other tropical lakes and compared to microbesand microzooplankton in Lake Calado.     

Productivity of a herbivorous pupfish population (Cyprinodon nevadensis) in a warm desert stream

Production and food intake by an herbivorous pupfish population ( Cyprinodon nevadensis amargosae ) living in the outflow of a thermal artesian well (Tecopa Bore) near Death Valley, California is described. Water issues from the ground at 47.5° C and cools 8.12° C before leaving the study area 300 m from the source. High stream temperatures restricted the pupfish population to some 41 % of the study area, with a resulting mean density of 89 individuals m⁻² (range = 13 to 196m⁻²). Biomass estimates ranged from 7 kcal m⁻² to 42 kcal m⁻². The mean annual standing crop of pupfishes (24 kcal m⁻²) turned over about five times annually. Growth rates were highest in juveniles (♂= 9.5% day⁻¹) and slowest in large adults (♀= 08% day⁻¹). Monthly production ranged from 22 kcal m⁻² in September to 3 kcal m⁻² in July and August. Pupfish in Tecopa Bore fed on algae and detritus, ingesting 1941 kcal m⁻² yr⁻¹ or 17.5% of the annual net primary production. 119 kcal m⁻² yr⁻¹ was deposited in growth. This latter value is approximately ten times greater than values previously reported for large carnivorous fishes but is comparable lo values reported for herbivorous fishes under pond culture.     

A light intensity threshold for schooling in the Atlantic mackerel, Scomber scombrus

The schooling behaviour of Atlantic mackerel was studied in a large tank at different light intensities in the range 12.6–1.8 × 10⁻¹⁰μEs⁻¹ m⁻². Variable light intensity was produced by accurately controlling the current to a green light-emitting diode (LED) 3 m above the experimental tank. Under high light levels (1.8 × 10⁻⁶μEs⁻¹ m⁻²) mackerel always formed a single school, whereas at lower levels (1.8 × 10⁻⁸μEs⁻¹ m⁻²) they swam as individuals. At light levels down to 1.0 × 10⁻⁶μEs⁻¹ m⁻² the mean nearest neighbour distance in a school remained relatively constant (0.3–0.9 body lengths), and individual mackerel swam along a path which deviated from the position of their nearest neighbours by less than 14°. As light dropped below 1.8 × 10⁻⁷μEs⁻¹ m⁻², both nearest neighbour distance and heading angle between nearest neighbours increased, with mean values of 1–1.8 body lengths and 23–92°, respectively, at 1.8 × 10⁻⁹μEs⁻¹ m⁻². The results are discussed in terms of ambient light conditions in the sea.     

Structure and function of the chelae and chela closer muscles of the shore crab Carcinus maenas (Crustacea: Brachyura)

Major and minor chelae of Carcinus maenas were investigated with respect to mechanical advantage, angles of pennation and sarcomere lengths of the closer muscle fibres, maximum pinching forces induced by nervous stimulation and maximum stress in the closer muscles. Major chelae differed from minor chelae in all these factors. Mean mechanical advantages of major and minor chelae were 0·36 and 0·26, respectively. Angles of pennation were greater at the distal ends of closer muscles and declined proximally: in half open major and minor chelae distal to proximal angles were about 35–26° and 29–19°, respectively. Mean sarcomere lengths in closer muscles of fully closed major and minor chelae were significantly different at 7·6 and 6·0 fim, respectively; there was great variation within chelae and between crabs. Major chelae pinched more strongly than minor chelae due to higher mechanical advantages, larger closer apodemes and greater stress in the muscle. Mean maximum stresses in major and minor chelae were 677 and 474 kN/m², respectively. The biggest stress recorded–1057 kN rrr²–was in a major chela. Pinching forces induced by injecting a high K⁺ and caffeine ringer were about 20% weaker than nervously stimulated pinches.     

The acquisition and accumulation of inorganic carbon by the unicellular green alga Chlorella ellipsoidea

Abstract. The uptake and accumulation of inorganic carbon has been investigated in Chlorella ellipsoidea cells grown at acid or alkaline pH. Carbonic anhydrase (CA) was detected in ceil extracts but not in intact cells and CA activity in acid-grown cells was considerably less than that in alkali-grown cells. Both cell types demonstrates low K_1/2 (CO₂) values in the range pH 7.0–8.0 and these were unaffected by O₂ concentration. The CO₂ compensation concentrations of acid- and alkali-grown cells suspended in aqueous media were not significantly different in the range of pH 6.0–8.0, but at pH 5.0, the CO₂ compensation concentrations of acid-grown cells (57.4cm³ m⁻³) were lower than those of alkali-grown cells (79.2cm³ m⁻³). The rate of photo-synthetic O₂ evolution in the range pH 7.5–8.0 exceeded the calculated rate of CO₂ supply two- to three-fold, in both acid- and alkali-grown cells, indicating that HCO₃⁻ was taken up by the cells. Accumulation of inorganic carbon was measured at pH 7.5 by silicone-oil centri-fugation, and the concentration of unfixed inorganic carbon was found to be 5.1 mol m⁻³ in acid-grown and 6.4mol m⁻³ in alkali-grown cells. These concentrations were 4.6- and 5.9-fold greater than in the external medium. These results indicate that photorespiration is suppressed in both acid- and alkali-grown cells by an intracellular accumulation of inorganic carbon due, in part, to an active uptake of bicarbonate.     

Influence of UV-B radiation on developmental changes, ethylene, CO2 flux and polyamines in cv. Doyenne d'Hiver pear shoots grown in vitro

In vitro shoots of cv. Doyenne ďHiver pear ( Pyrus communis L.) were irradiated under controlled environments for 6 h per day at 5 different levels of biologically effective UV-B radiation (UV-B_BE). UV-B exposure caused a progressive increase in apical necrosis above background levels and stimulated leaf abscission. Shoots grown for 2 weeks at 7. 8 mol m⁻² day ⁻¹ of photosynthetic photon flux (PPF) and treated with 8. 4 or 12. 0 kJ m⁻² day ⁻¹ UV-B_BE produced up to 4 times more ethylene than those given 2. 2 or 5. 1 kJ m⁻² day⁻¹ UV-B_BE or untreated controls. Exposure of shoots to 12 kJ m⁻² day ⁻¹ of UV-B_BE caused an increase in free putreseine content after 4 to 14 days of irradiation. Shoots showed a decrease in CO₂ uptake after 3 days of UV-B: thereafter, they appeared to recover their photosynthetic capacity. Under typical PPF conditions used in micropropagation (90 μmol m⁻² S⁻¹). 8. 4 kJ m⁻² day ⁻¹ of UV-B radiation was injurious to realatively tender tissues of in vitro pear shoots: increasing the level of UV-B_BE to 12 kJ m⁻² day⁻¹ produced even more adverse effects.     

Early effects of excess cadmium uptake in Phaseolus vulgaris

Abstract. Seedlings of Phaseolus vulgaris were exposed to solutions containing Cd²⁺ in the range 0 to 1 molm⁻³. Ethylene formation started following 3 h of exposure to 10⁻², 10⁻¹ and 1 mol m⁻³ Cd²⁺, peaked at 18 h and returned to a relatively low rate after 24 h. Cadmium-induced ethylene formation depended on the formation of 1-aminocyclopropane-1-carboxylic acid (ACC). Aminoethoxyvinylglycine (AVG, 0.1 mol m⁻³) inhibited ACC accumulation and ethylene production during exposure to 0.2 mol m⁻³ Cd²⁺.
Activity of soluble and ionically-bound peroxidase increased after 18 h of exposure to Cd²⁺ concentrations above 10⁻³ mol m⁻³ due to an increase in activity of cathodic isoperoxidases. Stimulation of soluble and ionically-bound peroxidase by 0.2 mol m⁻³ Cd²⁺ was reduced in the presence of 0.1 mol m⁻³ AVG.
Accumulation of soluble and insoluble ('ligninlike') phenolics was found in plants exposed to Cd²⁺ (10⁻² mol m⁻³ or above) in the presence or absence of AVG. Deposition of insoluble (autofluorescing) material occurred in cell walls around vessels and was associated with reduced expansion and water content of leaves.     

Photoinhibition of photosynthesis in Lemna gibba as induced by the interaction between light and temperature. I. Photosynthesis in vivo

The floating angiosperm Lemna gibba L. was exposed for 2 h to various combinations of photosynthetic photon flux densities and temperature. The extent of photoinhibition of photosynthesis was assayed by measuring the net CO₂ uptake before and after a photoinhibitory treatment, and the time course for photoinhibition was studied. It was found that the maximum quantum yield and the light-saturated rate of CO₂ uptake were affected by the interaction between light and temperature during the photoinhibitory treatment. At a constant photon flux density of 650 μmol m⁻² s⁻¹ the extent of photoinhibition increased with decreasing temperature showing that even a chilling-resistant plant like L. gibba is much more susceptible to photoinhibition at chilling temperatures. About 60% photoinhibition of the quantum yield for CO₂ uptake could be obtained either by a high photon flux density of 1 750 μmol m⁻² s⁻¹ and 25°C or by a moderate photon flux density of 650 μmol m⁻² s⁻¹ and 3°C. The time courses of recovery from 60% photoinhibition produced by either of these two treatments were similar, indicating that the nature of the photoinhibition was intrinsically similar. The extent of photoinhibition was related to the amount of light absorbed in excess to what could be handled by photosynthesis at that temperature. The vital importance of photosynthesis in alleviating photoinhibition is discussed.     

Photophobic stop-response in a dinoflagellate: Modulation by preirradiation

Gyrodinium dorsum Kofoid responds photophobically to flashes of blue light. The photophobic response consists of a cessation of movement (stop-response). Without background light and after a flash fluence above 10 J m⁻², 75–85% of the cells show a stop-response, while only 50% of the cells show this response at 5 J m⁻². With a flash fluence of 5 J m⁻², background light of different wavelengths either increases (614 nm. 5.5–18.2 μmol m⁻² s⁻¹) or decreases (700 nm, 18.4–36.0 μmol m⁻² s⁻¹) the stop-response. Two hypotheses for the mechanism of the modulation by background light of the photophobic response are discussed: an effect of light on the balance of the photosynthetic system (PS I/PS II) or an effect on a phytochrome-like pigment (P_r/P_fr). This study supports the idea that a phytochrome-like pigment works in combination with a blue light-absorbing pigment. It was also found that cells of Gyrodinium dorsum cultured in red light (39.8 μmol m⁻²) had a higher absorption in the red region of the absorption spectra than those cultured in white light (92.7 μmol m⁻²).     

Life-history and production of the amphipod Gammarus pulex in a Dorset chalk stream

SUMMARY. The seasonal variation in population density of Gammarus pulex was studied in a Dorset chalk stream. The numbers increased markedly in June and July and reached a maximum of c. 10000m⁻² in September whilst the most rapid decline in density occurred in October-November and reached a minimum of 820 m⁻² in February. The animals occurred in greater densities in habitats containing Ranunculus or Callitriche than in those devoid of vegetation. The population structure was determined monthly and was split into juveniles (length <4mm), immature males, immature females, mature males and ovigerous females. The percentage of juveniles (39–76) was always the highest of any of the categories. Ovigerous females were found at all times of the year. The sex ratio varied with the time of year both for immatures and matures, although there was approximately a 1:1 ratio for the mature individuals. Seasonal variation in biomass showed a maximum of 7.l g dry wt m⁻² in September and a minimum of 1.4 g dry wt m⁻² in March. Production was calculated by two methods giving values of 12.9 g dry wt m⁻² year⁻¹ and 12.8 g dry wt m⁻² year⁻¹.     

Inhibition of the glucose and amino-acid carriers of Lemna gibba by pretreatment with HgCl2

The electrical resting potential across the plasmalemma of Lemna gibba L. (G 1) cells is −230 to −250 mV and the diffusion potential in the presence of 1 mol m⁻³ KCN + 1 mol m⁻³ salicylhydroxamic acid is about −100 mV. A concentration of 0.01 mol m⁻³ HgCl₂ depolarises the transmembrane electrical potential in a largely reversible way. When the cells after 16 min of HgCl₂-application are returned to Hg-free solution, the transmembrane electrical potential is only depolarised by 24 × 13 mV (SD, n = 13) compared with the potential prior to HgCl₂ treatment. In contrast, a 16 min pretreatment with HgCl₂ followed by a wash with mercury-free solution reduces the transient depolarisations of transmembrane potential observed after addition of 5 mol m⁻³ D-glncose or 1 mol m⁻³ L-alaoine to about 60% of controls. These transient depolarisations are due to the onset of solute uptake. Accordingly, HgCl₂-pretreatment inhibits uptake of ¹⁴C-3-O-methyl- d -glucose by more than 50% and uptake of ¹⁴C- l -alanine by more than 70%. Washing with 1 mol m⁻³ 1,4-dithiothreitol does not reverse this inhibition. It is, therefore, concluded that Hg²⁺ irreversibly binds to essential SH-groups of the H⁺-hexose and the H⁺-amino-acid cotransport carriers of Lemna gibba and inhibits these carriers without appreciably affecting the electrogenic proton-extrusion pump.     

Photosynthesis and transpiration by young Larix kaempferi trees: C3 responses to light and temperature

The effects of photon flux density and temperature on net photosynthesis and transpiration rates of mature and immature leaves of three-year-old Japanese larch Larix kaempferi (Lamb.) Sarg. trees were determined with an infrared, differential open gas analysis system. Net photosynthetic response to increasing photon flux densities was similar for different foliage positions and stage of maturity. Light compensation was between 25 and 50 μmol m⁻² s⁻¹. Rates of photosynthesis increased rapidly at photon flux densities above the compensation level and became saturated between 800 and 1000 μmol m⁻² s⁻¹. Transpiration rates at constant temperature likewise increased with increasing photon flux density, and leveled off between 800 and 1000 μmol m⁻² s⁻¹. Photosynthetic response to temperature was determined in saturating light and was similar for all foliage positions; it increased steadily from low temperatures to an optimum range betweeen 15 and 21°C and then decreased rapidly above 21°C. Transpiration rate, however, increased continuously with rising temperature up to the experimental maximum. CO₂ compensation concentrations for mature foliage varied between 58 and 59 μl l⁻¹; however, foliage borne at the apex of the terminal leader compensated at 75 μl l⁻¹. None of these data support the claim that Japanese larch possesses C₄ photosynthetic characteristics.