Contraction of protoplasm. IV. Cinematographic analysis of the contraction of some peritrichs

The contraction and relaxation of Vorticella difficilis, V. campanula and Carchesium sp. were studied by high speed cinematography. In Vorticella it was shown that coiling of the stalk usually started near the zooid and spread downwards; the point of initiation bore no relation to the position of the stimulating electrodes. Contraction took about 5 msec to complete, and the fully contracted animals were 29 ± 3.9% of their original lengths. The zooids were 66 ± 5.0% and the stalks 14 ± 6.0% of their original lengths (V. difficilis). The shortening of the stalk was mostly in the form of coiling. Measurement of the myoneme length demonstrated that its real shortening was less than 10%. Thus the contraction is virtually isometric, producing a helical deformation of the stalk. As the stalk contracts it takes the form of a steeply pitched helix. This change in shape should produce rotational forces on the zooid (torque). Physical models of similar proportions produced about 1.5 revolutions of torque for similar changes in pitch. However during contraction no turning of the zooid was detected, though rotation did occur after the completion of contraction. In Carchesium the contraction is not so isometric, the myoneme apparently shortening by 20%. While the coiled shape of the contracted Vorticella stalk can be explained by its acentric structures, the stalk of Carchesium is much more symmetrical in cross-section, demonstrating that a high acentricity is not necessary for helical coiling. In all three species there seems to be some separation of the control of zooid and stalk contraction.     

Regulation of splenic contraction persists as a vestigial trait in white-blooded Antarctic fishes

In fishes, the spleen can function as an important reservoir for red blood cells (RBCs), which, following splenic contraction, may be released into the circulation to increase haematocrit during energy-demanding activities. This trait is particularly pronounced in red-blooded Antarctic fishes in which the spleen can sequester a large proportion of RBCs during rest, thereby reducing blood viscosity, which may serve as an adaptation to life in cold environments. In one species, Pagothenia borchgrevinki, it has previously been shown that splenic contraction primarily depends on cholinergic stimulation. The aim of the present study was to investigate the regulation of splenic contraction in five other Antarctic fish species, three red-blooded notothenioids (Dissostichus mawsoni Norman, 1937, Gobionotothen gibberifrons Lönnberg, 1905, Notothenia coriiceps Richardson 1844) and two white-blooded “icefish” (Chaenocephalus aceratus Lönnberg, 1906 and Champsocephalus gunnari Lönnberg, 1905), which lack haemoglobin and RBCs, but nevertheless possess a large spleen. In all species, splenic strips constricted in response to both cholinergic (carbachol) and adrenergic (adrenaline) agonists. Surprisingly, in the two species of icefish, the spleen responded with similar sensitivity to red-blooded species, despite contraction being of little obvious benefit for releasing RBCs into the circulation. Although the icefish lineage lost functional haemoglobin before diversifying over the past 7.8–4.8 millions of years, they retain the capacity to contract the spleen, likely as a vestige inherited from their red-blooded ancestors.     

Contraction of protoplasm. III. Cinematographic analysis of the contraction of some heterotrichs

The contraction of Stentor and Blepharisma, in response to mechanical and electrical stimulation and of Spirostomum in response to mechanical stimulation is described. All three species respond to electrical stimulation by contraction of the cytoplasm, beginning at the anodal end regardless of orientation of the animal. The differences in contractile ability and shapes during contraction are discussed in relation to body form and microanatomy. Stentor and Spirostomum also respond to mechanical stimulation. Dropping a weight on the slide causes contraction of the whole body of Spirostomum, but not of Stentor. Stimulation of the oral region of Stentor by means of a vibrating needle causes a contraction of the entire body, but this sensitivity is limited to the oral region. Blepharisma does not respond to mechanical stimulation. Spirostomum and Stentor undergo rapid spontaneous contractions, but Blepharisma does not contract spontaneously.     

Distribution and status of the declining garden dormouse Eliomys quercinus

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Trajectories to extinction: spatial dynamics of the contraction of geographical ranges

Aim We examined the range contraction of 309 declining species of animals and plants to determine if the contraction dynamics better matched predictions based on the demographic characteristics of historical populations (demographic hypothesis) or based on the contagion‐like spread of extinction forces (contagion hypothesis). Location Species included in the analysis came from all biogeographic regions. Methods We obtained range maps for 309 species from literature or through personal correspondence with authorities. Hypotheses were contrasted by examining the sequence of changes in the proportion (C) of the remnant range that fell within the central region of the historical range. Monte Carlo simulations and polynomial regressions were employed to examine changes in C during the process of range contraction. Results The results of the Monte Carlo simulations indicated that more species had observed range contractions consistent with the contagion hypothesis than expected by chance (z‐score = 2.922, P = 0.002). The Monte Carlo analysis also indicated that the number of species whose observed range contractions were consistent with the demographic hypothesis was no greater than expected by chance (z‐score = 0.337, P = 0.367). The results of the polynomial regression analysis for the two most common taxonomic groups (mammals and birds) and for all geographical regions (Australia, Africa, Eurasia, and North America) we examined also supported the contagion hypothesis. Main conclusions Most of the examined range contractions are consistent with the contagion hypothesis and that the most likely contagion is human related disturbance. These results have important implications for the conservation of endangered species.     

Climate hindcasts: exploring the disjunct distribution of Diopatra biscayensis

The ecosystem engineer onuphid polychaete Diopatra biscayensis has a continuous population in the Bay of Biscay from the Cantabria coast in Spain to southern Brittany in France. A group of disjunct populations also are found in the English Channel, separated from the Biscay population by more than 400 coastal kilometers. It remains unclear whether D. biscayensis is native to the Bay of Biscay; it is also debated whether the disjunct populations in the English Channel are relics of a formerly continuous population, or the product of recent introductions through aquaculture. Here, we use climate hindcasts to explore hypotheses about the D. biscayensis historical distribution in Europe. If D. biscayensis is native, its range would have been restricted to southern Iberia and the Mediterranean during the Last Glacial Maximum (21,000 BP). However, the species is completely absent from both regions today, further supporting its interpretation as a non‐native species. If it was historically present in Europe, the climate hindcasts are congruent with range contraction in the Last Glacial Maximum (21,000 BP), expansion in the Mid‐Holocene Warm Period (6000 BP), and contraction again in the past 1000 years (850–1850), prior to the first reports of D. biscayensis on the Spanish and French Atlantic coasts. However, the simulations do not support there being climatic refugia along the English Channel coast that would account for the existence of relic populations. Taken together, the evidence suggests that D. biscayensis has been introduced to the Bay of Biscay, and that disjunct populations in the English Channel are the result of recent transport through human activities, perhaps aquaculture.     

Does irrigation affect leaf phenology in deciduous and evergreen trees of the savannas of northern Australia?

Abstract Soil moisture was augmented experimentally during two successive dry seasons and the intervening wet season in a humid tropical savanna in Darwin, northern Australia. Leaf phenology was monitored in four common tree species Termmalia ferdinandiana and Planchonia careya (both deciduous species), and Eucalyptus miniata and Eucalyptus tetrodonta (both evergreen species). Irrigation produced consistently significant effects in only T. ferdinandiana. In this species leaf-flush was significantly earlier, canopy decline and leaf-fall were significantly later and the attainment of full canopy was earlier in irrigated compared with non-irrigated trees. Litterfall, and the seasonal patterns of contraction and expansion of stems (a measure of stem water status or storage) were not significantly affected by irrigation in any species. Leaf longevity in the deciduous species was 6–8 months; some eucalypt leaves lived for approximately 1 year, but none lived longer than 18 months. Irrigation had relatively little effect on leaf longevity. While variation in soil moisture is a potentially important cue to both leaf-fall and leaf-flush, stem water status and climatic factors such as vapour pressure deficit may also be important climatic cues to phenological behaviour.     

Defensive Behavior in Primary- and Secondary-Host Generations of the Soldier-Producing Aphid, Pemphigus bursarius (Hemiptera: Aphididae)

The genus Pemphigus comprises several species that produce soldiers (defensive morphs) in galls on the primary host. At the moment, it is unclear if host-alternating species also produce defenders on their secondary host. We therefore examined how P. bursarius morphs of the secondary host generations respond to predators to test whether they show defensive behavior. We further examined how this response compares with the antipredator behavior of soldiers in P. bursarius and P. spyrothecae occurring on the primary host. We performed two manipulative experiments using two predatory species to quantify the behavior of the different morphs in response to predators. In both experiments, secondary host morphs of P. bursarius showed no attacking behavior and antipredator behavior in these morphs was limited to escaping natural enemies by walking away. In contrast, the first instars of the primary host generations in both Pemphigus species showed attacking behavior and were capable of killing the predators.     

Within-lake dispersal of the prosobranch snails,Viviparus ater and Potamopyrgus jenkinsi

Summary The gastropod species Viviparus ater and Potamopyrgus jenkinsi have both colonized Lake Zürich relatively recently. If it is assumed that they have dispersed in the Lake starting from one location, a model of random diffusion is insufficient to explain their present distribution in Lake Zürich. It is suggested that both species were dispersed by humans. In P. jenkinsi, passive dispersal by birds, fish or on floating algae may also have occurred. To estimate the rate of within-lake dispersal, life tables were constructed and the diffusivity estimated for the two species. Per capita population growth rates were calculated to be 0.00337/d for V. ater and 0.0159/d for P. jenkinsi. Diffusivity was close to 1 m²/d in both species.     

Functional morphology and neuronal innervation of the prothoracic defence gland in Timema

Timema is the most basal genus of Phasmatodea and the sister group to the remaining stick and leaf-insects (Euphasmatodea). An autapomorphy of all phasmids is the paired prothoracic exocrine defence glands. In this study, the anatomy and innervation of the defence glands in Timema petita and Timema chumash are described and compared with the data on Euphasmatodea. In all phasmids, the glands consist of a cuticular epithelium, a secretory epithelium and muscular fibres that compress the lumen. In Timematodea, the muscular part of the gland is less developed than in Euphasmatodea and the ejection of the defence secretion depends on the dorsal longitudinal neck muscles. On the neuroanatomical level, Timema petita and Timema chumash lack neurons that are involved in the independent contraction of the gland in euphasmids. In both studied species of Timema, neck muscles play an active role in the gland function which is not observed in any other phasmid. Considering the basal position of this genus, this supports the hypothesis that in euphasmids, the muscular part of the gland evolved from the dorsal longitudinal neck muscles. Additionally, the same nerves that innervate the dorsal longitudinal neck muscles in all Polyneoptera also innervate the defence glands in phasmids.     

The Effects of Climate Change on the Long-Term Conservation of Fagus grandifolia var. mexicana, an Important Species of the Cloud Forest in Eastern Mexico

We examined the effects of climate change on the future conservation and distribution patterns of the cloud forests in eastern Mexico, by using as a species model to Fagus grandifolia Ehr. var. mexicana (Martínez) Little which is mainly located in this vegetation type, at the Sierra Madre Oriental. This species was selected because it is restricted to the cloud forest, where it is a dominant element and has not been considered for protection in any national or international law. It is probably threatened due to the fact that it plays an important social role as a source of food and furnishing. We used a floristic database and a bioclimatic modeling approach including 19 climatic parameters, in order to obtain the current potential distribution pattern of the species. Currently, its potential distribution pattern shows that it is distributed in six different Mexican Priority Regions for Conservation. In addition, we also selected a future climate scenario, on the basis of some climate changes predictions already proposed. The scenario proposed is characterized by +2 °C and −20% rainfall in the region. Under this predicted climatic condition, we found a drastic distribution contraction of the species, in which most of the remaining populations will inhabit restricted areas located outside the boundaries of the surrounding reserves. Consequently, our results highlight the importance of considering the effects of possible future climate changes on the selection of conservation areas and the urgency to conserve some remaining patches of existing cloud forests. Accordingly, we believe that our bioclimatic modeling approach represents a useful tool to undertake decisions concerning the definition of protected areas, once the current potential distribution pattern of some selected species is known.     

The Role of White Clover in the Loss of Diversity in Grassland Habitat Restoration

A field experiment was designed to recreate a species‐rich mesotrophic grassland community of conservation worth. Trifolium repens (white clover) was observed to increase significantly in both frequency and abundance in sown plots grazed by cattle, but not in plots cut in June and subsequently grazed by cattle. In both these treatments permanent quadrats containing clover patches were found to be lower in species richness than were quadrats without clover. In both treatments botanical diversity was seen to decline over time. In the grazed‐only treatment the loss of diversity may be linked to the increase in clover. In the cut and grazed plots, T. repens did not become so abundant but diversity was still seen to decline, possibly due to the loss of low growing species from the taller sward. A pot experiment which varied the sowing density of a mix of seven wild flower species in full factorial combination with cutting frequency was established on soils from an arable field also sown with a single density of clover. T. repens was seen to decline from initial high cover estimates in infrequently cut and uncut treatments. In the pot experiment where a grass component to the vegetation was absent, clover was seen to have less impact on the other forbs than it did in the field. It is suggested that, being a nitrogen fixer, T. repens may have a competitive edge in ex‐arable soils low in available nitrogen. The observed reduction in botanical diversity may be a result of this increase in available nitrogen, facilitating the spread of the sown grasses and preventing the recovery of the sown forbs that were excluded by the invasion of T. repens. It is suggested that reducing the proportion of grass in the seed mixtures during grassland habitat creation on these soils may help reduce or delay this effect.     

Influence of native and alien Prunus species and light conditions on performance of the leaf beetle Gonioctena quinquepunctata

The polyphagous beetle Gonioctena quinquepunctata Fabricius (Coleoptera: Chrysomelidae) is a serious leaf pest of the native European bird cherry, Prunus padus L., and the invasive alien black cherry, Prunus serotina Ehrh. (Rosaceae). In the shade, leaf damage is extensive in both species, whereas in full light, it is extensive in P. padus, but very low in P. serotina. We determined the influence of Prunus species and light conditions on differences in performance of both sexes of this folivore. In a laboratory experiment in which larvae were fed with leaves of a single species grown under particular light conditions, we measured larval, pupal, and adult mass, efficiency of conversion of ingested food (ECI), duration of development, total food eaten, and relative growth rate. In the field, we observed differences in beetle mass on shrubs of the two species growing under various light conditions. From the field observations, we hypothesised that leaves of the invasive P. serotina are not an equally good food source as leaves of P. padus for G. quinquepunctata, and the preference of these beetles for shaded shrubs is most favourable for their growth and development. Under laboratory conditions, we found that the beetle growth rate was not affected significantly by Prunus species or light conditions, despite the significant effect of light condition on the structure and chemical composition of Prunus seedlings. The lower ECI value for larvae feeding on sunlit leaves was compensated for by their higher level of consumption. In the field, adult insect mass was higher on P. padus than on P. serotina, and higher on sunlit shrubs of both species than on shaded ones. Under natural conditions, the mass of adult insects is probably also affected by other factors, such as predators and competition among folivores.     

Estimating Z‐ring radius and contraction in dividing Escherichia coli

We present a fluorescence recovery after photobleaching‐based method for monitoring the progression of septal Z‐ring contraction in dividing Escherichia coli cells. In a large number of cells undergoing division, we irreversibly bleached cytosolically expressed Enhanced Green Fluorescent Protein on one side of the septal invagination and followed the fluorescence relaxation on both sides of the septum. Since the relaxation time depends on the cross‐sectional area of the septum, it can be used to determine the septal radius r. Assuming that the fraction of the observed cells with r‐values in a given interval reflects the duration of that interval in the division process we could derive an approximate time‐course for the contraction event, as a population average. By applying the method repeatedly on individual cells, the contraction process was also followed in real time. On a population average level, our data are best described by a linear contraction process in time. However, on the single cell level the contraction processes display a complex behaviour, with varying levels of activity. The proposed approach provides a simple yet versatile method for studying Z‐ring contraction in vivo, and will help to elucidate its underlying mechanisms.     

The role of adrenaline as a modulator of cardiac performance in two Antarctic fishes

The present work was performed to test the hypothesis that Antarctic teleosts rely mostly on cholinergic inhibition for autonomic modulation of the heart. The effects of adrenaline on the inotropic properties on paced, isometrically contracting muscle strips were examined in two distinct Antarctic teleosts, the haemoglobinless icefish Chaenocephalus aceratus and the red-blooded Notothenia coriiceps. All tissues examined revealed a negative force-frequency relationship. Under baseline conditions C. aceratus contracted with a force twice as great as that of N. coriiceps. While the degree to which ventricular tissues responded to adrenaline varied between species, adrenergic stimulation significantly increases myocyte contraction force in this group of fishes. Contraction and relaxation times were not significantly affected by adrenaline concentration while absolute rates of contraction were. Adrenergic stimulation does not enable tissues to achieve higher contraction frequencies, but is shown to be a potent modulator of contraction force.     

THE USE OF BENZOCAINE HYDROCHLORIDE AS FISH TRANQUILLIZER AND ANAESTHETIC IN SALINE WATERS

SUMMARY

The anaesthetic effects of various concentrations of benzocaine hydrochloride were tested on Liza macrolepis and Sarotherodor mossambicus in sea water and diluted sea water, respectively. Induction time for anaesthesia was negatively correlated with increasing anaesthetic concentrations in L. macrolepis.

In S. mossambicus, however, operculum clamping appeared to be responsible-f or induction times increasing with increased anaesthetic concentration.

The tranquillizing effects of low concentrations of benzocaine hydrochloride on L. macrolepis was also studied.     

Isoenzyme and Total Protein Analysis by Agarose Isoelectric Focusing, and Taxonomy of the Genus Acanthamoeba

Thirty axenically grown reference strains belonging to 15 different Acanthamoeba spp. were investigated for isoenzyme patterns by agarose isoelectric focusing in the pH range 3–10. Zymograms of acid phosphatase, leucine amino peptidase, malate dehydrogenase, propionyl esterase, glucose phosphate isomerase, phosphoglucomutase, and alcohol dehydrogenase were compared. The same strains were also analyzed for protein patterns separated by agarose isoelectric focusing in a pH gradient of 5–8. The results suggested changes in taxonomy within morphology group II of Pussard & Pons. Acanthamoeba paradivionensis becomes a synonym of A. divionensis. Although this species seems to be related to A. rhysodes, it could not be concluded that the species names are synonyms since the type strain of A. rhysodes was not available for comparison. In the subgroup A. polyphaga–A. quina–A. lugdunensis, A. lugdunensis becomes the species name for pathogenic strains of this subroup, A. quina for the nonpathogenic strains, while A. polyphaga is the species name for an atypical strain. Two strains of A. castellanii showed different zymograms from strain Neff of this species, but related protein patterns. In group III, A. pustulosa is found to be a synonym of A. palestinensis, while one strain of A. lenticulata is also found to belong to the A. palestinensis species. All other species names in both morphology groups could be retained as valuable, on the basis of the techniques used. Group I was not investigated, as axenic cultures could not be obtained.     

Calcium efflux during the cold-induced contraction of mammalian striated muscle fibres

The efflux of ⁴⁵Ca from mammalian slow twitch muscle fibres has been studied to provide a measure of the concentration of free Ca²⁺ in the sarcoplasm. The kinetically complex early phases of washout of the isotope are succeeded by a prolonged slower phase which exhibits first-order kinetics. This later phase is accelerated by caffeine, by preventing oxidative phosphorylation and also during an isometric contraction, whether this contraction is produced by lowering the temperature or by electrical stimulation. The local anaesthetic tetracaine abolishes the contraction caused by cold and in this case the rate constant for efflux is progressively lowered as the temperature is reduced (Q₁₀ value of 2.3). The removal of external Na⁺ and Ca²⁺ reduces the efflux rate constant. Caffeine, sodium removal and the inhibition of oxidative phosphorylation, all potentiate the cold contraction and the associated extra ⁴⁵Ca efflux. Ca removal causes the cold contraction to become phasic. It appears that caffeine, sodium removal, the inhibition of oxidative phosphorylation and a decrease in temperature to below 10°C are all treatments which, like electrical stimulation, increase the sarcoplasmic free calcium concentration to varying degrees.     

Gene rearrangements in Chlamydomonas chloroplast DNAs are accounted for by inversions and by the expansion/contraction of the inverted repeat

To gain insight into the mutational events responsible for the extensive variation of chloroplast DNA (cpDNA) within the green algal genus Chlamydomonas, we have investigated the chloroplast gene organization of Chlamydomonas pitschmannii, a close relative of the interfertile species C. eugametos and C. moewusii whose cpDNAs have been well characterized. At 187 kb, the circular cpDNA of C. pitschmannii is the smallest Chlamydomonas cpDNA yet reported; it is 56 and 105 kb smaller than those of its C. eugametos and C. moewusii counterparts, respectively. Despite this substantial size difference, the arrangement of 77 genes on the C. pitschmannii cpDNA displays only three noticeable differences from the organization of the corresponding genes on the collinear C. eugametos and C. moewusii cpDNAs. These changes in gene order are accounted for by the expansion/contraction of the inverted repeat and one or two inversions in a single-copy region. In land plant cpDNAs, these kinds of events are also responsible for gene rearrangements. The large size difference between the C. pitschmannii and C. eugametos/C. moewusii cpDNAs is mainly attributed to multiple events of deletions/additions as opposed to the usually observed expansion/contraction of the inverted repeat in land plant cpDNAs. We also found that the mitochondrial genome of C. pitschmannii is a circular DNA molecule of 16.5 kb which is 5.5 and 7.5 kb smaller than its C. moewusii and C. eugametos counterparts, respectively.     

Allozyme analysis of cryptic species in the Asplenium niduscomplex from West Java,Indonesia

In various fern species, a large amount of rbcL sequence variation has been reported, and it is possible that these species contain several reproductively isolated cryptic species. In our previous study on Asplenium nidus L., it was suggested that the plants growing in Mt. Halimun National Park, West Java, Indonesia, consist of several cryptic species based on the results of crossing experiments among rbcL sequence types. In this study, we examined allozyme polymorphisms of five rbcL sequence types found in West Java in order to test the hypothesis that the assemblages of A. nidus delimited based on the rbcL sequences are separate Mendelian populations and gene flow is disrupted by reproductive isolation from one another. The calculated fixation indices suggested that the individuals in each rbcL type are randomly crossing at least in the investigated localities. Nevertheless, these rbcL-based assemblages were genetically differentiated in allozymes that are encoded in their nuclear genomes, and it is also suggested that gene flow is disrupted even between sympatrically distributed pairs of rbcL sequence types. Therefore, our findings support the view that the five rbcL sequence types in West Java are potential cryptic species. Electronic Publication