Electron Microscopic Localization of ATPase Activity in the Cytopharyngeal Basket of the Ciliate Pseudomicrothorax dubius

The cytopharyngeal basket of Pseudomicrothorax dubius is used to ingest filamentous blue-green algae. The basket has three main components: a sheath of microfilaments, bundles of microtubules (the nemadesmata), and ribbons of microtubules. The ribbons of microtubules (nemadesmal lamellae) are adpressed to the food vacuole during ingestion. Cytochemical techniques show that both the lamellae and the microfilamentous sheath possess ATPase activity, but the reaction product appears under different conditions in the two cases. The presence of ATPase activity within the microtubular lattices of the feeding organelle suggests the capacity for active motility. Consequently the basket seems to have two motile systems, one may be used to constrict and dilate the cytopharynx while the other is used in the inward propulsion of the forming food vacuole.     

Interaction of pheromones during food exploitation by the termite Schedorhinotermes lamanianus

Abstract. Chemical signals from secretions of different exocrine glands modulate a variety of behavioural patterns in termite societies. These signals have multiple functions and may be interactive. During food exploitation workers of the African termite Schedorhinotermes lamanianus (Isoptera: Rhinotermitidae) employ, on foraging trails, the secretion from the sternal gland both for orientation and recruitment to a food source. The secretion from the labial gland, released onto the food by gnawing termites, stimulates additional workers to gnaw at the same site, thereby forming aggregations of gnawing termites. An interaction between these two pheromones during food exploitation is demonstrated for the first time. The volatile signal from the sternal gland inhibits in a dose-dependent manner the non-volatile, highly persistent, signal from the labial gland. The development of gnawing aggregations is inhibited and established ones are dissolved. Behavioural evidence for the perception of both the volatile signal from the sternal gland by olfactory neurones and of the non-volatile signal from the labial gland by gustatory neurones on the antennae is given. The interaction of the two pheromones as a basis for the development of distinct commuting and gnawing zones on the food source, and as a means for a dynamic regulation of food exploitation, is discussed.     

Soft‐bottom tube worms: from irregular to programmed shell growth

Like other secondary soft‐bottom dwellers, serpulid and sabellid tube worms used particular strategies in order to cope with their earlier loss of mobility. This is expressed by the transition from irregular to genomically programmed morphologies of their calcareous shells that guarantee a stable horizontal resting position. In contrast to permanent recliners, however, this attitude was probably only the starting position for active resurrection after the muddy tail of storm sediments had settled on top of the displaced animal.     

Unraveling the drivers of intensifying forest disturbance regimes in Europe

Natural disturbances like wildfire, windthrow and insect outbreaks are critical drivers of composition, structure and functioning of forest ecosystems. They are strongly climate‐sensitive, and are thus likely to be distinctly affected by climatic changes. Observations across Europe show that in recent decades, forest disturbance regimes have intensified markedly, resulting in a strong increase in damage from wind, bark beetles and wildfires. Climate change is frequently hypothesized as the main driving force behind this intensification, but changes in forest structure and composition associated with management activities such as promoting conifers and increasing standing timber volume (i.e. ‘forest change’) also strongly influence susceptibility to disturbances. Here, we show that from 1958 to 2001, forest change contributed in the same order of magnitude as climate change to the increase in disturbance damage in Europe's forests. Climate change was the main driver of the increase in area burnt, while changes in forest extent, structure and composition particularly affected the variation in wind and bark beetle damage. For all three disturbance agents, damage was most severe when conducive weather conditions and increased forest susceptibility coincided. We conclude that a continuing trend towards more disturbance‐prone conditions is likely for large parts of Europe's forests, and can have strong detrimental effects on forest carbon storage and other ecosystem services. Understanding the interacting drivers of natural disturbance regimes is thus a prerequisite for climate change mitigation and adaptation in forest ecosystem management.     

Morphological and Ecophysiological Adaptations of the Marine Oligochaete Tubificoides benedii to Sulfidic Sediments

SYNOPSIS. The marine oligochaete worm Tubificoides benedii inhabitscoastal tidal sediments in which sulfide can reach toxic concentrations.The role of external ironsulfide deposition in sulfide detoxificationis discussed together with a review of morphological and ecophysiologicaladaptations of T. benedii to sulfide. The body wall of T. benediiturns black in the presence of sulfide. Histochemical studiesand micro-X-rayanalyses provide evidence for the reaction ofiron in the mucus layer above the cuticle of the worm with environmentalsulfide to produce ironsulfide. The deposited ironsulfides areeither reoxidized or shed off through moulting, a process otherwiseunknown in oligochaetes. However, calculations on the diffusionrate of sulfide into T. benedii show that the deposition ofironsulfides do not play an important role in sulfide detoxification.The first and last few segments of T. benedii are not blackenedby sulfide and do not appear to precipitate sulfide. The diffusionrate of sulfide through these segments is so rapid that internalsulfide concentrations reach levels inhibitory to cytochromec oxidase, the key enzyme of aerobic respiration, within minutes.When internal sulfide concentrations increase to toxic levels,reliance on an anaerobic metabolism represents a successfulmechanism of sulfide tolerance in T. benedii. Metabolic adaptationsto hypoxia and sulfide include the maintenance of aerobic pathwaysdespite low oxygen or high sulfide concentrations and the abilityto gain energy through anaerobic pathways when oxygen and/orsulfide concentrations become limiting     

Membrane Characteristics of Bursting Pacemaker Neurones in Aplysia

The group of endogenously active molluscan neurones, classified as bursting or oscillatory pacemakers, regularly fire bursts of three to fifteen impulses separated by periods of silence associated with membrane hyperpolarizations (Fig. 1a). The abdominal ganglion of the marine mollusc Aplysia californica contains six bursting pacemakers, L2-L6 (L-group) and R15¹; these cells maintain their membrane potential oscillations in the absence of synaptic input^2,3 and spike generation⁴. They also have K⁺-dependent inhibitory postsynaptic potentials (IPSPs) which last for some seconds after single or multiple discharges in the presynaptic neurones^5–8. In the L-group these IPSPs are mixed with short-lasting Cl^?-dependent IPSPs. Although there is a different transmitter responsible for the generation of these IPSPs in R15 as opposed to those in the L-group, somewhat similar difficulties were encountered in attempts to determine the mechanism(s) underlying their generation, activation of an electrogenic Na⁺ pump having been initially implicated in both cases^5,8. Just why their duration is prolonged remains uncertain, but the voltage clamp studies of Wachtel and Wilson⁹ on the L-group have again implicated a regenerative current source.     

Formation of Catechol Compounds from Phenylalanine and Tyrosine with Isolated Nerve Endings

THERE is much evidence that catecholamines may act as synaptic transmitters in the mammalian brain¹. Enzymatic activities necessary for the synthesis of catecholamines have been located in central neurones¹ and it is generally believed that tyrosine hydroxylase² is the rate limiting enzyme in brain as well as peripheral tissues containing catecholamines³. While it is clear that tyrosine can serve as a precursor of catecholamine synthesis in the brain^{1, 3, 4}, the significance of phenylalanine is problematic. It was believed that the mammalian brain is devoid of enzymatic activity necessary to convert phenylalanine to tyrosine^{6, 7}, while liver is known to be rich in the enzyme phenylalanine hydroxylase⁸. The earlier attempts to demonstrate hydroxylation of phenylalanine in brain tissue may have been unsuccessful due to methodological problems⁹. Recent evidence suggests that tyrosine hydroxylase prepared from peripheral sympathetically innervated tissues or from brain can hydroxylate either phenylalanine or tyrosine⁹. Initially, the rate of hydroxylation of phenylalanine by tyrosine hydroxylase was thought to be as little as 5% that of tyrosine⁹. It has been found recently, however, that structural variations in the pteridine cofactor present in the incubation mixture lead to striking changes in the ability of partially purified tyrosine hydroxylase from bovine adrenal medulla to hydroxylate phenylalanine¹⁰. Thus, tetrahydrobiopterin allowed the hydroxylation of phenylalanine to proceed at least as rapidly as that of tyrosine or faster¹⁰. As the structure of the endogenous pteridine cofactor of tyrosine hydroxylase is not known, it is possible that synthesis of catecholamines from phenylalanine as well as tyrosine could occur in intact neuronal tissues. Evidence has been presented that after the injection of large quantities of ¹⁴C-phenylalanine into the lateral ventricle of the rat brain, small amounts of labelled tyrosine and traces of newly synthesized catecholamines were detected in brain tissues, giving qualitative evidence that catecholamines may be synthesized in brain from phenylalanine in vivo¹¹.     

Effects of temperature, age and body size on moulting and growth in the freshwater amphipods Gammarus fossarum and G. roeseli

1. The total body length, cephalic length, wet weight and dry weight was measured in juveniles, males and females of Gammarus fossarum and G. roeseli kept in the laboratory. Numbers of flagellar segments on the first and second pairs of antennae of G. fossarum and G. roeseli were quantitatively related to body size and in stars. The addition of segments cannot be used to identify particular instars of individuals or to determine their ages in natural populations. 2. At experimental temperatures ranging from 3.8 to 20.2°C, the number of moults, duration of intermoults, maturation times and specific growth rates were studied from birth in isolated specimens. Sexual maturity was reached after 9 or 10 moults, at a mean wet weight of c. 5mg for females and c. 7mg for males of G. fossarum, and at c. 10 mg for females and c. 13 mg for males of G. roeseli. At 3.8°C neither species reached sexual maturity within 550 days. 3. The mean interval between moults was observed from birth to sexual maturity and was linearly related to moult number and exponentially related to age. The relationship between each intermoult interval, or the maturation time, and the experimental water temperature was described by a power function. Maturation times increased from 96 days at 20.2°C to 355 days at 7.9°C in G. fossarum, and 85 days to 403 days in G. roeseli. 4. Over the range 3.8–20.2°C there was a log—log relationship between temperature and specific growth rates. Growth was maximal at 20.2°C in newborn animals as well as in small sexually mature animals; interspecific differences were highly significant. 5. Increase in body wet weight of G. fossarum and G. roeseli fed ad libitum on a constant mixture of autumn-shed, naturally decaying, tree leaves and aquatic macrophytes was followed to senescence and death. The instantaneous or specific growth rate was maximal near birth, at c. 7.98% wet weight day^?1 in G. fossarum and 9.03% in G. roeseli. At ≥12°C, growth conformed to a logistic curve; maximum absolute increments in weight occurred about half-way through a life span of 280–300 days at 20°C, 380–420 days at 16°C and 550–600 days at 12°C. Some individuals lived longer than 850 days at ≤12°C. The wet weight at birth was 0.112mg for G. fossarum and 0.123mg for G. roeseli. Asymptotic mean body weights of males and females were, respectively, 61 and 41 mg for G. fossarum and 87 and 58 mg for G. roeseli. However, G. roeseli reached the inflection point of the logistic curve significantly faster than G. fossarum. In the latter species, growth and maturation were relatively faster at temperatures below 12°C, whereas they were faster in G. roeseli at 16–20°C. Thus G. fossarum is adapted to summer-cool streams and G. roeseli is adapted to summer-warm streams.     

Reproductive potential and lifetime potential fecundity of the freshwater amphipods Gammarus fossarunt and G. roeseli in Austrian streams and rivers

• 1 Fecundity of Gammarus fossarum populations at six stream sites (S1-S6) and G. roeseli populations at two sites (S5 and S6) was studied monthly during 1985–1988, distinguishing seven morphological stages of embryonic development. Mean survival of G. fossarum eggs was 65% (60–70%) in nature and 60% (57–63%) in the laboratory; egg survival of G. roeseli was 52% (46–58%) in nature and 41% (35–47%) in the laboratory. Regressions of egg numbers per clutch against body wet weight (WWT) decreased significantly for egg developmental stages 2 to 7 (hatching).
• 2 In stream populations, ovigerous females of G. fossarum were absent in October (six sites) and November (five sites); ovigerous G. roeseli were usually absent from October until March.
• 3 Overall mean egg volume (EV) increased significantly from 0,08 ± 0.001 mm³ and 0.075 ± 0.001 mm³ for stage 2 eggs, to 0.174 ± 0.012mm³ and 0.160 ± 0.013 mm³ for stage 6 eggs of G. fossarum and G. roeseli, respectively. The dry weights of stage 2 eggs, stage 6 eggs and neonates (stage 7) were not significantly different, within and between species; mean dry weight was 36 ± 3 μg.
• 4 Egg volumes and fecundity indices (FI, weight-specific number of eggs per clutch) were not significantly different between the same months of four successive years, so the data were pooled to give a single representative ‘year’. At most sites there were marked seasonal fluctuations in these variables. In both species, mean EV was largest for ‘winter’ eggs in December/January and smallest for ‘summer’ eggs in May, EV decreased during some months of the year when FI increased, and vice versa. Mean reproductive effort (RE = EV × FI) declined from high ‘winter’ values to low ‘summer’ values, and this difference was most marked at sites where the major foodstuff available was seasonally limited (autumn-shed tree leaves). Overall (‘annual’) mean RE was also lowest at these sites (S3 and S4) but was some 13% greater at sites where nutrients and food were present in the greatest quantifies (S5 and S6). Specific maximum potential body sizes and hence maximum potential fecundities (fifty-nine eggs for G. fossarum and eighty-seven eggs for G. roeseli) were attained only at S5 and 56. Mean RE was nearly identical for G. fossarum and G. roeseli from the same sites.
• 5 At experimental temperatures (T) in the range 3.8–20.2°C, females of the same body weight carried significantly different egg numbers per clutch. The relationship between FI and T was described by a second-order polynomial. The calculated optimum T was 12.1°C for G. fossarum and 16.3°C for G. roeseli. Interspecific differences were highly significant.
• 6 Theoretical lifetime potential fecundity was approximately 194 eggs for G. fossarum

     

Connection between the Synthesis of Differentiation Specific Proteins and the Capacity of Cells to Respond to Cytokinin in the Moss Funaria

The differentiation stage of the caulonema in Funaria hygrometrica protonema is distinguished from the chloronema stage by three additional protein bands (CSP) in the soluble protein fraction. During the change of caulonema to chloronema, which is induced by isolation of single filaments (regeneration), the CSP disappear. This is not the consequence of an accelerated degradation or turnover but of a gradual termination in the de novo synthesis of CSP during regeneration as demonstrated by pulse-chase experiments with l -[4,5–³H] leucine. Cytokinin inhibits the termination of the synthesis of CSP. The decrease in synthesis parallels the decrease in ability of the isolated caulonema cells to respond to cytokinin via bud formation. It is therefore concluded that the CSP are involved in the competence of caulonema cells to respond to cytokinins.