SIZE, SHAPE AND SHELL MORPHOLOGY IN THE ANTARCTIC LIMPET NACELLA CONCINNA AT SIGNY ISLAND, SOUTH ORKNEY ISLANDS

Comparison of the size, shape and shell morphology in littoraland sub-littoral morphs of the Antarctic limpet Nacella concinnareveal differences in shell morphology which are enhanced bystructural anomalies within the shells of the two types. Infestationof sub-littoral shells by the conchocelis phase of an endolithicalga significantly affects shell density and total chlorophylllevels in the two shell morphs. The surface sculpture of sub-littoralshells is characterised by a series of grooves, the configurationof which closely resembles that of the radular teeth in N. concinna.Limpets utilise the available food supply within the shell matrixof other limpets by grazing the shell material. Epibiotic growthof calcareous algae prevent erosion and preserve underlyingshell layers. In severe cases, where protection is lacking,intraspecific shell grazing may remove parts of the shell exposingthe internal tissues. The Dominican Gull, Larus dominicanus, is a major shore predatorof both shell morphs. Gull middens contain both shell typesbut are dominated by the more accessible littoral shells. Comparisonof living populations and midden assemblages indicates thatsize and shape selection of prey occurs, with pear-shaped limpetsbetween 21 mm and 29 mm in length being taken preferentially. Apparent differences in shell form are induced by physical,biological and behavioural influences. Littoral animals arerobust in nature, resist avian pre-dation and are not extensivelygrazed whereas those of the sub-littoral are not subject tothe same degree of predatory attention but suffer a gradualdepletion of their shallower shell form through a combinationof algal infection and intraspecific shell grazing. (Received 21 February 1990; accepted 5 July 1990)     

TEMPORAL VARIATION IN FORAGING BEHAVIOUR OF PATELLA GRANULARIS (PATELLOGASTROPODA) AND SIPHONARIA CONCINNA (BASOMMATOPHORA) ON A SOUTH AFRICAN SHORE

Foraging activity of two mid- to low- shore species of limpet,Patella granulans (Prosobranchia) and Siphonaria concinna (Pulmonata)from an exposed shore on the Eastern Cape coast of South Africawas monitored. In both species, activity was compared duringspring and neap tides and, in P. granularis between summer andwinter. Rhythms of activity of the two species were similar,with foraging excursions being mainly associated with nocturnallow tide times, although some P. granularis foraged during daytimelow tides. It is suggested that foraging excursions in P. granularisare triggered by wave action. Both species foraged further onspring tides than on neap tides and this is suggested to bea result of the limited time limpets have to forage. P. granulariswas also found to forage further during summer when comparedto winter and the possibility that seasonal micro-algal productivityinfluences foraging distances in limpets is discussed. The foraging activity of both species could be divided into3 distinct phases, a relatively rapid outward phase, a muchslower foraging phase and a rapid homeward phase. Whether ornot these limpets graze throughout an excursion is not known.S. concinna was found to home to a fixed scar, although duringthe experiment some scar-swapping occurred. P. granularis didnot home to a fixed scar but possessed a ‘home range’(approx. 5 cm²) to which it returned after each excursion. Patella granularis was found to move randomly during foraging,whilst S. concinna foraged in a non-random direction -whichtook individuals upshore. No tidal-influence is thought to bepresent in this case and the possibility of a learning componentin the foraging behaviour of certain limpet species in relationto the return to optimal feeding patches is discussed. (Received 18 May 1996; accepted 2 September 1996)     

Duration tenacity: A method for assessing acclimatory capacity of the Antarctic limpet, Nacella concinna

The limpet, Nacella concinna, collected from the Antarctic Peninsula (67°S), was incubated at − 0.3 °C and 2.9 °C for 9 months to test if the previously reported absence of acclimation capacity in Antarctic marine ectotherms could be due to the extended time it takes for them to adjust their physiology to a new stable state. Acclimation was tested through acute measurements of upper lethal limit and a modified measure of tenacity, that tested muscle capacity by measuring the length of time that N. concinna were able to remain attached to the substratum at different temperatures. Both measures acclimated in response to incubation to the higher temperature. Lethal limits were elevated in N. concinna incubated at 2.9 °C (8.1 ± 0.3 °C) compared to those incubated at − 0.3 °C (6.9 ± 0.4 °C). 2.9 °C incubated N. concinna also had a maximum tenacity at 2.1 °C, a higher temperature than the maximum tenacity of those incubated at − 0.3 °C, which occurred at − 1.0 °C. This study is the first to show that the Antarctic limpet can acclimate its physiology, but that it requires a greater period of time for acclimation to occur than previous studies have allowed for.     

THE PHYSIOLOGY AND FEEDING BEHAVIOUR OF TWO MARINE SCAVENGING GASTROPODS IN HONG KONG: THE SUBTIDAL BABYLONIA LUTOSA (LAMARCK) AND THE INTERTIDAL NASSARIUS FESTIVUS (POWYS)

Aspects of the physiology and feeding behaviour of the scavengingsnails, Babylonia lutosa and Nassarius festivus have been studiedand compared. N. festivus has a wider physiological tolerancethan B. lutosa; upper lethal temperatures being 31.5°C and28.5°C respectively and lower lethal salinities 15.5 and11.5. N. festivus was also more resistant to desiccation. N.festivus is adapted to an intertidal environment that is morevariable than the subtidal habitat of B. lutosa. The metabolicrate of adult N. festivus was two to three times higher thanthat of adult B. lutosa, the specific oxygen consumption rateof the former being 7.91±0.49x10^–6 mol of O₂.g^–1wet wt.hr^–1. This correlates with estimates of consumptionobtained for the two animals, B. lutosa eating, on average,6.57% of its wet tissue weight per day, N. festivus 15.33%.Standardization of the data for 2 g animals of both species,however, reveals no significant difference in terms of oxygenconsumption and thus the enhanced consumption by N. festivussimply reflects its smaller size. Both species are opportunisticfeeders and can survive long periods of starvation (>100days). The feeding strategies of the two are also different,N. festivus eating faster than B. lutosa, possibly because ofthe more ephemeral nature of carrion in the intertidal. Starvationaffected the feeding behaviour of N. festivus more than B. lutosaand N. festivus was able to perceive carrion from greater relativedistances than B. lutosa. (Received 27 February 1989; accepted 24 July 1989)     

PREDATION ON THE BIVALVE CHOROMYTILUS MERIDIONALIS (KR.) BY THE GASTROPOD NATICA (TECTONATICA) TECTA ANTON

The effects of a population of the boring gastropod Natica tectaon the bivalve Choromytilus meridionalis were investigated atBailey's Cottage, False Bay, South Africa. In July 1979 theN. tecta density on the mussel bed averaged 69 m^–2 andthe population consisted mainly of reproductively mature individualsbetween 20–33 mm shell width. Laboratory experiments on N. tecta showed that prey size selectionis an increasing function of predator size. The prey size rangetaken by large N. tecta is also greater than that taken by smallindividuals. The position of the borehole on the mussel shellis a function of the way in which the shell is held by the footduring the boring process. Consumption rates measured in thelaboratory showed an increase from approximately 1 kJ per weekin 18 mm N. tecta to 4.5 kJ per week in 28 mm individuals. Populationconsumption in the field was calculated as 663 kJ m^–2month^–1. It was estimated that at this rate the standingcrop of mussels in the pool would be eliminated within 10 months.Field measurements showed significant depletion after 6 months. New spat settlement of mussels occur every 4–6 years.The growth curve shows that after one year the population meansize exceeds 30 mm shell length, which is beyond the prey selectionsize range of small N. tecta. It was concluded that at the timeof a new mussel settlement a niche is provided for the simultaneoussettlement and growth of juvenile N. tecta in high densities.However, within one year the increase in prey size, togetherwith depletion due to over-exploitation, limits population growthand density in N. tecta. (Received 14 March 1980;     

THE EFFECT OF ENVIRONMENTAL VARIABLES ON THE OXYGEN CONSUMPTION OF THE PROTOBRANCH BIVALVE NUCULA TURGIDA (LECKENBY AND MARSHALL)

The oxygen consumption of the protobranch bivalve Nucula turgidawas measured in relation to size and to variation in temperatureand ambient oxygen tension. The slope of the line relating logsize and log oxygen uptake varied from 0.539 to 0.884 over therange 5°C to 40°C in summer – conditioned (S)animals but for winter – conditioned (W) animals the slopevaried from 0.561 to 0.762 over the range 5°C to 15°Conly; from 20°C to 35°C the values for the slope fellfrom 0.298 to 0.092. There was evidence of reverse acclimation,since the absolute rate of oxygen consumption was greater inS animals than in W over the temperature range studied. Thelethal limit for both groups appeared to be between 30°Cand 35°C. At all temperatures (5°C–25°C) N. turgida wasfound to be a near complete oxyconformer with b₂ x 10³ valuesranging from +0.0754 to –0.0234. The responses to temperature differ little from those of eulamellibranchbivalves, but the lack of ability to oxyregulate does demonstratea difference which may be linked to the different gill structure. (Received 13 January 1983;     

EFFECTS OF TEMPERATURE ON CHRONIC HYPOXIA TOLERANCE IN THE NON-INDIGENOUS BROWN MUSSEL, PERNA PERNA (BIVALVIA: MYTILIDAE) FROM THE TEXAS GULF OF MEXICO

Effects of temperature (15°, 20° and 25°C), O₂ partialpressure (P_O2=0, 1, 2, 4, and 6 kPa), and individual size(12–79 mm shell length; SL) on survivorship of specimensof the non-indigenous, marine, brown mussel, Perna perna, fromTexas were investigated to assess its potential distributionin North America. Its hypoxia tolerance was temperature-dependent,survivorship being significantly extended at lower temperaturesunder all tested lethal P_O2. Incipient tolerated P_O2 was 4 and6 kPa at 15 and 20°C, respectively, with >50% mortalityoccurring at 25°C at all tested levels of hypoxia. P_O2 hadless of an effect on survival of hypoxia than temperature. At25°C, survivorship was not different over a P_O2 range of0–2 kPa and increased only at 4 and 6 kPa. Survivorshipwas size-dependent. Median survival times increased with increasingSL in anoxia and P_O2=1 kPa, but at 2, 4 and 6 kPa,smaller individuals survived longer than larger individuals.With tolerance levels similar to other estuarine bivalve species,P. perna should withstand hypoxia encountered in estuarine environments.Thus, its restriction to intertidal rocky shores may be dueto other parameters, particularly its relatively low temperaturetolerance. (Received 26 January 2004; accepted 31 March 2005)     

WATER EXCHANGE, TEMPERATURE TOLERANCE, OXYGEN CONSUMPTION AND ACTIVITY OF THE NAMIB DESERT SNAIL, TRIGONEPHRUS SP.

Water exchange, temperature tolerance and oxygen consumptionof the snail, Trigonephrus sp., from the southern Namib desertof Namibia were examined and related to activity. At 25°Cand 15% R.H. mean water loss and food and water uptake were5.95 mg. day^–1 and 630 mg.day^–1, respectively. Bodytemperature tracked sand temperature. Snails tolerated sandtemperatures as high as 45°C. Mean ± S.D. oxygenconsumption rates were 32.0 ± 2.94 µlO₂.g totalbody mass^–1.h^–1 at 15°C, when the snails wereactive, and 11.27 µlO₂.g total body mass^–1.h^–1at 25°C, when the snails were inactive. These values are2-6 times lower than those recorded for the similarly sizedmesic snail, Helix aspersa. Activity experiments indicated thatlow ambient temperatures and high humidities were favoured bythe snails. This, together with the burying behaviour of thesesnails during high temperatures, suggests that they limit stressby restricting activity to physiologically-favourable periods,even though more-extreme conditions may be tolerated. (Received 7 June 1990; accepted 20 November 1990)     

THE ULTRASTRUCTURE OF CILIATED CELLS FROM THE SIPHON OF SOLEN CAPENSIS (MOLLUSCA, BIVALVIA)

The structure of ciliated cells from the siphon of Solen capensishas been studied by both scanning and transmission electronmicroscopy. Two types of ciliated cell, based on the numberand length of cilia have been described which resemble thosedescribed in Donax. Type I is characterized by having 26–57({macron}= 43, n = 50) cilia which are 2.5 µm in length;Type II has fewer cilia (5–10; {macron}= 7) which are5 µn long. Both are primary receptors. Estimations ofabundance show that receptors are most numerous on the tipsof the siphon tentacles (8.8 x 10³/mm²). (Received 15 January 1985;     

Thermal plasticity of mitochondria: A latitudinal comparison between Southern Ocean molluscs

Mitochondrial volume density (Vv_(mt,f)), cristae surface density (Sv_(im,mt)), cristae surface area (Sv_(im,f)) and citrate synthase (CS) activity were analysed as indicators of thermal acclimation in foot muscle of the limpet, Nacella concinna, and the clam, Laternula elliptica, collected from 4 locations within the Southern Ocean, South Georgia (54°S, N. concinna only), Signy (60°S), Jubany (L. elliptica only ? 62°S) and Rothera (67°S). Animals were acclimated to 0.0 °C whilst a sub-set of N. concinna (South Georgia, Signy and Rothera) and L. elliptica (Rothera) were acclimated to 3.0 °C. At 0.0 °C N. concinna had higher Vv_(mt,f), Sv_(im,mt), Sv_(im,f) and muscle fibre specific CS activity than L. elliptica which correlated with the more active life style of N. concinna. However, mitochondrial density was very low, 1–2% in both species, suggesting that low temperature compensation of mitochondrial density is not a universal evolutionary response of Antarctic marine ectotherms. Both Sv_(im,mt) and Sv_(im,f) were reduced by warm acclimation of N. concinna. South Georgia N. concinna maintained muscle fibre specific CS activity after acclimation, in contrast to N. concinna from Rothera and Signy and L. elliptica from Rothera, indicating that they have the physiological plasticity to respond to their warmer, more variable thermal environment.     

THE RATIO OF CALCAREOUS AND ORGANIC SHELL COMPONENTS OF FRESHWATER SPHAERIID CLAMS IN RELATION TO WATER HARDNESS AND TROPHIC CONDITIONS

Shells from 14 populations of sphaeriid clams including Sphaeriumstriatinum, S. simile, Pisidium walkeri, Musculim partumeiumand M. iransversum were analyzed for organic carbon (µgCmg^–1 shell), nitrogen (µg,N mg^–1 shell) andCaCO_s (%CaCO₃ of total clam dry weight). Habitat waters wereassessed for total hardness (expressed as ppm CaCo₃), ppm Ca,ppm Mg, conductivity (µmho) and suspended organic Carbon(µgCl^–1). For all populations, shell organic C andN are positively correlated and there is an inverse relationshipbetween the amounts of shell CaCO₃ and shell organic carbon.Trophic considerations give the best correlation with shelltype at the generic level of consideration since species ofMusculium are found at the opposite end of the trophic scale(eutrophic) from all other populations studied. For S. striatinum,the most extensively studied species, the amount of shell CaCO₃is inversely related to water hardness. The selection of shellsin the Sphaeriidae is discussed in relation to structural-functionalneeds and habitat conditions ¹ Present Address: Department of Biology, Syracuse University,Syracuse, New York 13210, U.S.A. ² Present Address: Department of Zoology, Miami University,Oxford, Ohio 45056, U.S.A. (Received 5 December 1978;     

COMPARISON OF THE STRUCTURE OF THE PALLIAL TENTACLES OF SEVEN SPECIES OF SOUTH AFRICAN PATELLID LIMPET

The ultrastructure of the pallial tentacles of seven speciesof patellid limpet is described. The tip of most of the tentaclesexamined bears a crown of long cilia, whereas the shaft of thetentacles has small tufts (5–10 µm diameter) ofshorter cilia. Sections through the ciliated tufts show themto be composed of several cells, each bearing cilia. The ciliacontain 5–7 central microtubules and therefore do nothave the conventional 9 + 2 arrangement of microtubules. Nerveprocesses run from the base of each ciliated cell to a nervebundle in the centre of the tentacle, suggesting a sensory function.Estimates of densities of ciliated tufts suggest that the territoriallimpets (Patella cochlear and P. longicosta) have the greaternumber of tufts. Electron dense plate-like structures are foundin the centre of the pallial tentacles of Patella cochlear,P. longicosta, P. granularis, P. barbara and Helcion pruinosus.Each plate is about 0.2 µm wide and is surrounded by adouble membrane. It is suggested that these may play a rolein scattering or reflecting light and thus form part of thedermal light sensing ability of these animals. (Received 26 January 1987;     

LARVAL GROWTH AND THE INDUCTION OF METAMORPHOSIS OF A TROPICAL SPONGE-EATING NUDIBRANCH

The Hawaiian dorid nudibranch Hypselodoris infucata (Rppell& Leuckart, 1828) was reared to metamorphosis in the laboratory.Egg diameter averaged 88 µm and veligers hatched, afterabout 5 days at 25°C, with a coiled shell averaging 149µm in length. Larvae fed on phytoplankton grew to a maximumshell length of 306 µm in about 15 days. Larval growthwas affected by both quality and quantity of the algal diet.Some larvae were competent to metamorphose 16 days post-hatchingat 26°C, and competence could be retained for at least oneweek. Metamorphosis is complete within 24 hours of exposureto an inducer. At least three species of sponge, Halichondriacoerulea, Sig-modocia sp., and Tedania macrodactyla, in additionto the nudibranch's adult prey species, Dysidea sp., inducedmetamorphosis of competent larvae. Primary films grown on glassslides also induced metamorphosis in some larvae, as did 20µM excess potassium ions in seawater. These data suggestthat nonspecific induction of metamorphosis occurs in this specieseven though the adult nudibranchs are highly prey specific.This implies that in the field, H. infucata find Dysidea sp.after settlement and metamorphosis Present address: Dept of Genetics and Development, College ofPhysicians and Surgeons of Columbia Univeisity, 701 West 168thStreet, NewYork, 10032, USA (Received 22 June 1987; accepted 3 March 1988)     

Transport of Oxygen by the Blood of the Land Crab, Gecarcinus lateralis

Parameters relating to transport of oxygen were measured inthe pericardial blood and venous outflow from the first walkingleg of Gecarcinus lateralis. O₂-equilibrium curves of the hemocyaninof G. lateralis were found to be sigmoid and, at 27°C andpH 7.45, to have a half-saturation pressure of about 17 mm Hgoxygen. Average partial pressures of oxygen as measured by O₂-electrodewere 32 mm Hg in pericardial blood and 9 mm Hg in the venoussamples. Analysis of the O₂-content in corresponding samplesby the Van Slyke technique revealed an average of 2.17 volumes% O₂-capacity for whole blood, 1.45 volumes % for pericardialblood, and 0.61 volumes % for venous blood. Estimates basedon the Van Slyke analyses indicated an average pO₂ of 29 and14 mm Hg in pericardial and venous samples, respectively. Thesefigures agree fairly well with those obtained by means of O₂-electrodes.Of the oxygen carried to the tissues, about 94% is carried asoxyhemocyanin and about 6% is carried in physical solution.As the blood passes through the gills, the hemocyanin, on anaverage, becomes 80–85% saturated with oxygen and returnedfrom the tissues 18–45% saturated with oxygen. These resultsindicate that the blood of G. lateralis has a higher O₂-capacitythan the blood of most other decapod crustaceans for which similarinformation is available. In addition, the blood of G. lateralistransports more oxygen to the tissues per unit volume than doother crustacean bloods.     

Influence of Temperature on the Autolytic Phase of Growth of Aspergillus niger

The variation in the extent to which autolysis of Aspergillusniger van Tieghem occurs in response to alteration of temperatureand of the length of the period of autolysis has been studied.The degree of autolysis at 10, 15, 20, 25, 30 and 35 °Cwas 15–8, 23–9, 35–2, 40–8, 49–1and 56–2 per cent, respectively. Autolysis increased sharplywith the length of the period of autolysis reaching a plateautowards the second day at the lowest temperatures (0–20°C) and towards the fourth day at the higher temperatures.Theextent of the increase of autolysis plotted against temperatureindicates a linear relationship between these two parameters.The release of protein from autolysing mycelium of A. nigeris greatly affected by temperature, amounting to 1–9 percent at 10 °C, whereas at 30 °C it reached 5–1per cent. On the other hand, gradual increase of temperatureduring autolysis seems not to alter the content of mycelialcarbohydrates of A. niger.     

A QUANTITATIVE STUDY OF A CERASTODERMA -- NEPHTHYS COMMUNITY IN THE LIMFJORD, DENMARK, WITH SPECIAL REFERENCE TO PRODUCTION OF CERASTODERMA EDULE

Cerastoderma edule is the dominant member of a non-random Cerastoderma—Nephthyscommunity, occupying a physically, homogeneous, submerged sandbankin the Limfjord, Denmark. C. edule is patchily distributed withinthis community, growth rates showing a clear density-dependence.Individual production is about 35%lower in high density patchesthan outside them; at low density annual individual flesh dryweight increment is 295 mg. Seasonal variation in water, ash,lipid, protein and glycogen contents is studied, and a sizedependent(= density-dependent) relationship is shown to exist for someparameters. Population production, estimated by a new graphicalmethod, and taking into account gametic and shell protein production,attains 150 g dry flesh weight, m^–2.yr^–1 at meanpopulation density rising to 250 g dry flesh weight. m^–2.yr^–1in the high density patches. ¹Present address: Institut für Physiologische Chemie, Abt.Zellbiochemie, Universitat Hamburg, Martinistrasse 52, 2000Hamburg 20 (Received 10 March 1980;     

MORPHOLOGICAL AND GENETIC VARIATION IN THE ANTARCTIC LIMPET NACELLA CONCINNA (STREBEL, 1908)

Samples of the Antarctic limpet, Nacella concinna (Strebel,1908), were collected from four sites in the South Orkney Islandsand from Stromness in South Georgia during 1988. At three SouthOrkney sites, both littoral and sub-littoral samples of limpetswere taken. Shell dimensions were measured and littoral andsub-littoral limpets were shown to have significantly differentshell shapes. Foot and digestive gland tissues were subjectedto electrophoresis and five polymorphic loci {Es-1, lcd-1, lcd-2,Gpi, Got-1 and Pgm-1) and two monomorphic loci (Es-2 and Got-2)were scored. Genetic identities between littoral and sub-littoralforms and also between sites were calculated. At the loci scored,the littoral and sub-littoral forms were virtually identicaland this suggests that the shell shape differences between theforms are the result of environmentally induced phenotypic plasticity.However, significant genetic differences and some morphologicaldifferences were apparent between the sample of limpets fromSouth Georgia and all other sites. Genetic identity values suggestedthat the South Georgia and South Orkney N. concinna are geographicallyseparated populations of a single species rather than distinctsub-species. (Received 21 November 1990; accepted 17 April 1991)     

RNA Synthesis in Phaseolus Chloroplasts: I. RIBONUCLEIC ACID SYNTHESIS IN CHLOROPLAST PREPARATIONS FROM PHASEOLUS VULGARIS L. LEAVES AND SOLUBILIZATION OF THE RNA POLYMERASE

Chloroplast preparations from the young primary leaves of Phaseolusvulgaris L. cv. Canadian Wonder carry out the DNA-dependentincorporation of UTP into RNA at rates between 8 and 14 pmolUTP µg^–1 chlorophyll h^–1. It is estimatedthat 90% of the activity was localized in the chloroplasts.The incorporation proceeded for between 20 and 30 min at 35°C. The maximum rates of RNA synthesis were attained atpH 8.3, in the presence of 15 mM MgCl₂. Chloroplasts were alsoactive, to a lesser extent, with 1.5 mM MnCl₂. The simultaneouspresence of MnCl₂ and MgCl₂ resulted in inhibition of activity.Nuclear material prepared from young P. vulgaris leaves incorporatedUTP at a rate of about 12 pmol UTP µg^–1 DNA h^–1.On a chloroplast (Tritonsoluble) DNA basis chloroplast activitywas over 40-fold that of nuclei. Methods of solubilizing chloroplastRNA polymerase were explored. Yields of over 75% were achieved,but methods suitable for one species were not always successfulwhen applied to another. The highest yields of the P. vulgarisenzyme were obtained using EDTA and KCl. All methods resultedin solubilization of DNA. RNA synthesis by the soluble P. vulgarisenzyme proceeded for more than 40 min at 35 °C.     

UPTAKE OF ACETATE BY NEOTRICULA APERTA (GASTROPODA: POMATIOPSIDAE), THE SNAIL HOST OF SCHISTOSOMA MEKONGI IN THE LOWER MEKONG BASIN

All three races of Neotricula aperta, an epilithic, schistosometransmitting, snail of the Mekong and Mul rivers of NortheastThailand and southern Laos, were found to take up acetate froma dilute solution. After 48 h incubation the mean specific netuptake rates (µmol^–1 g^–1 h^–1), from750 µM acetate, were: 1.86, -race; 1.39, ß-raceand 3.25, y-race. Over 48 h the snails were able to achievereductions in the ambient acetate concentration of up to 60%.Incubations under bacteriostatis suggested that bacteria arenot involved in the uptake of acetate by N. aperta. The uptakecharacteristics conform to the Michaelis-Menten model. The transportconstants, J_max (µmol^–1 g^–1 h^–1) andK_t (µM) were 1.10 and 102 respectively (-race). Racialdifferences in uptake characteristics are discussed in relationto micro-habitat differences. HPLC indicated concentrations of acetate in y-N. aperta microhabitatsof around 325 µM. This suggests a pool size sufficientto satisfy only 6% of the snail's basal metabolic rate (BMR).Levels within the epilithic aufwuchs, however, are probablyhigh enough to provide for more than 50% of the BMR. The possible role of acetate in the energy metabolism of N.aperta is discussed. Short-chain carboxylic acids (such as acetate),arising from the decomposition of the aufwuchs, could representsources of fermentable organics that may be taken up by N. apertasnails and used to supplement their nutrition during times offood shortage. However, further investigations involving ¹⁴C-labellingtechniques are required. The findings of this investigationhave implications for the chemical ecology and life-cycle ofN. aperta. (Received 16 June 1994; accepted 28 July 1994)     

The Influence of Temperature on Root Hair Infection of Trifolium parviflorum and T. glomeratum by Root Nodule Bacteria: I. THE EFFECTS OF CONSTANT ROOT TEMPERATURE ON INFECTION AND RELATED ASPECTS OF PLANT DEVELOPMENT

The onset and rate of infection in root hairs of T. parviflorumand T. glomeratum inoculated with Rhizobium trifolli strain5 varied much with root temperature. At moderate root temperature(18, 24, and 30 °C) infections were initiated earlier andin larger numbers than at low (6 and 12 °C) or moderatelyhigh (36 °C) temperatures. Both species showed a broad temperatureoptimum between 18 and 30 °C. The site of thread initiation(apically or laterally in a hair) was independent of temperature,as was also the proportion of successful threads penetratingthe root cortex, which increased with seedling age. Threadsgrew more slowly at low temperatures. The size of hair nucleinear infection threads remained unaffected by temperature, butnuclei associated with laterally originating threads were largerthan those associated with apical threads. Infection was non-randomly distributed along the main root atall temperatures. More zones of infection were found at moderatetemperatures than at temperature extremes (6–12 or 36°C). Probit plots of numbers of infections for individualplants were steplike, the linear sloping parts correspondingto normal distributions of infection within zones. Between 18 and 30 °C numbers of infections increased exponentiallyin two phases, the first more rapid phase ending at about thetime nodules appeared. A model devised for the infection processand fitted to the data suggested the existence of two kindsof infections: primary ones occuring randomly at a slow rateand probably not affected by temperature and secondary infectionsthat appeared to increase with rising temperatures in the range12 to 30 °C. Nodule numbers were relatively more sensitive to high and lowtemperatures than infection. The numbers of infections and nodulesand the root lengths of T. parviflorum were twice those of T.glomeratum except at the temperature extremes. Numbers of infectionswere otherwise unrelated to root length or cotyledon or leafareas. The development of lateral organs (primordia, lateralroots, and nodules) was reduced at temperatures below 18 °Cand above 30 °C.