Cellular src gene product detected in the freshwater sponge Spongilla lacustris.

Serum from Rous sarcoma virus tumor-bearing rabbits immunoprecipitated from extracts of the freshwater sponge Spongilla lacustris a tyrosine-specific protein kinase with characteristics similar to the chicken pp60c-src kinase activity. An immune competition assay confirmed the relationship between the protein from sponges and viral pp60v-src.     

Cytoskeletal organization and cell organelle transport in basal epithelial cells of the freshwater sponge Spongilla lacustris

Summary Different antibodies against actin, tubulin and cytokeratin were utilized to demonstrate the spatial organization of the cytoskeleton in basal epithelial cells of the freshwater sponge Spongilla lacustris. Accordingly, actin is localized in a cortical layer beneath the plasma membrane and in distinct fibers within the cytoplasmic matrix. Microtubules exhibit a different distributional pattern by radiating from a perinuclear sheath and terminating at, the cell periphery; in contrast, intermediate filaments are lacking. Cytoplasmic streaming activity was studied by in-vivo staining of mitochondria and endoplasmic reticulum by means of fluorescent dyes. Single-frame analysis of such specimens revealed a regular shuttle movement of mitochondria and other small particles between the cell nucleus and the plasma membrane, which can be stopped in a reversible manner with the use of colcemid or colchicine but not with cytochalasin D. The results point to the microtubular system as a candidate for cell organelle transport, whereas the actomyosin system rather serves for changes in cellular shape and motility.     

Plastic changes in tadpole trophic ecology revealed by stable isotope analysis

Amphibian larvae constitute a large fraction of the biomass of wetlands and play important roles in their energy flux and nutrient cycling. Interactions with predators and competitors affect their abundance but also their foraging behaviour, potentially leading to non-consumptive cascading effects on the whole trophic web. We experimentally tested for plastic changes in larval trophic ecology of two anuran species in response to competitors and the non-lethal presence of native and non-native predators, using stable isotope analysis. We hypothesized that tadpoles would alter their diet in the presence of competitors and native predators, and to a lesser extent or not at all in the presence of non-native predators. First, we conducted a controlled diet experiment to estimate tadpole turnover rates and discrimination factors using Pelobates cultripes and Bufo calamita. Turnover rates yielded a half-life of 15–20 days (attaining a quasi-isotopic equilibrium after 2 months), whereas discrimination factors for natural controlled diets resulted in different isotopic values essential for calibration. Second, we did an experiment with P. cultripes and Rana perezi (=Pelophylax perezi) where we manipulated the presence/absence of predators and heterospecific tadpoles using microcosms in the laboratory. We detected a significant shift in trophic status of both amphibian species in the presence of non-native crayfish: the δ¹⁵N values and macrophyte consumption of tadpoles increased, whereas their detritus consumption decreased. This suggests that tadpoles could have perceived crayfish as a predatory risk or that crayfish acted as competitors for algae and zooplankton. No dietary changes were observed in the presence of native dragonflies or when both tadpole species co-occurred. Stable isotopic analysis is an efficient way to assess variation in tadpoles’ tropic status and hence understand their role in freshwater ecosystems. Here we provide baseline isotopic information for future trophic studies and show evidence for plastic changes in tadpoles’ use of food resources under different ecological scenarios.     

Contractile vacuoles in cells of a fresh water sponge,Spongilla lacustris

Summary Forty or more independently functioning contractile vacuoles (CVs) occupy the central region of fresh water sponge pinacocytes. Each CV undergoes a cycle of enlargement by fusion, movement, shape change, rounding up, and emptying over the course of 5–30 min. Diameter at discharge varies between 1 and 13 m. CVs in all cell types are associated with submicroscopic coated vesicles. Filled CVs are bounded by an unmodified trilaminar membrane, but vacuoles with excess membrane frequently show coated evaginations. These evaginations are thought to pinch off as coated vesicles, providing an avenue for membrane recycling in the CV system.Supported by NIH grants AS-T01-GM-0723 and GM-23708-CBY     

Trophic ecology of the Lake Superior wave zone: a stable isotope approach

Stable carbon and nitrogen isotope ratio analyses were used to characterize the primary energy sources and trophic positions of 16 common Lake Superior wave zone invertebrate species. Isotope data from six tributary species that were taxonomically and ecologically matched with common wave zone species revealed broad energetic separation between these similarly structured benthic food webs. Previously published stable isotope data for Lake Superior wetland and pelagic food webs were used to assess the relative importance of inter-habitat energy flow within the Lake Superior ecosystem. The results of these comparisons indicate that the Lake Superior wave zone is energetically distinct from its tributaries, wetlands, and to a lesser extent from its vast pelagic realm. This information and approach should prove useful in future studies on the bioenergetics of inter-zonal migrants and other species that forage in multiple habitats within the lake and also in revealing energetic connections among terrestrial, riverine, littoral, and pelagic food webs in the coastal ecosystems of Lake Superior.     

On the hibernation of Spongilla lacustris (L.)

Summary The osmotic pressure of the summer-sponge is about 25–30 mM NaCl. At and after gemmulation it increases to about 110 mM (in a single case 175 mM was found), due to a liberation of small organic molecules. Osmotic pressure remains constant for a time, but in January and February (i. e. before the germination) it is again reduced to the summer values. The shell allows a high hydrostatic pressure to develop and thereby prevents osmotic rupture of the gemmula. The hibernation may be divided into three periods: The prehibernation, the posthibernation and intercalated between them the hibernation proper. In the prehibernation and in the posthibernation definite changes take place in the tissue, but in the hibernation proper no changes are observed. In Nature the hibernation lasts about six months at, say, 4°, but at 22 degrees the whole hibernation will abbreviate to about 13 days.This is due to an abbreviation of all the three periods of hibernation, but whereas the pre- and the posthibernation will only be accelerated in a manner similiar to that of other physiological processes, such as processes of growth, development and metabolism, the hibernation proper will be accelerated much more, and in fact it will be almost abolished at 22°. This strange effect of temperature on hibernation proper is discussed. Since development often occurs at very low temperatures (2–5°), we may conclude that a mechanism must be present in the gemmulae which ensures development after a certain time, here 6 months. The different phases of hibernation may serve as an indicator of this mechanism. It is suggested, that the transformations taking place during prehibernation and posthibernation, and resulting in the germination of the gemmula are inhibited during hibernation proper by a substance formed in prehibernation.     

Trophic relationships in a tropical stream food web assessed by stable isotope analysis

1. Stable isotope analysis, coupled with dietary data from the literature, was used to investigate trophic patterns of freshwater fauna in a tropical stream food web (Guadeloupe, French West Indies).
2. Primary producers (biofilm, algae and plant detritus of terrestrial origin) showed distinct δ¹³C signatures, which allowed for a powerful discrimination of carbon sources. Both autochthonous (¹³C-enriched signatures) and allochthonous (¹³C-depleted signatures) resources enter the food web. The migrating behaviour of fishes and shrimps between marine and freshwater during their life cycles can be followed by carbon isotopes. Here, shrimp δ¹³C signatures were shown to shift from −16‰ (for juveniles under marine influence) to −24.7‰ (for adults in freshwater habitats). For resident species, δ¹³C values partly reflected the species' habitat preferences along the river continuum : species living in river mouths were ¹³C-enriched in comparison with those collected upstream.
3. Nitrogen isotopic ratios were also discriminating and defined three main trophic guilds among consumers. The δ¹⁵N values of herbivores/detritivores were 5.0–8.4‰, omnivores 8.8–10.2‰ and carnivores 11–12.7‰.
4. Mixing model equations were employed to calculate the possible range of contribution made by respective food sources to the diet of each species. The results revealed the importance of omnivorous species and the dependence of riverine biota on terrestrial subsidies, such as leaf detritus and fruits. Finally, the abundance of shrimps and their feeding habits placed in relief their key role in tropical freshwater food webs. Isotopic analysis provides a useful tool for assessing animal feeding patterns.     

稳定同位素分析在鸟类生态学中的应用

稳定同位素作为一种自然标记物是研究鸟类生态学的重要工具之一,与传统研究方法相比其呈现的信息更为真实全面,是一种日趋成熟的鸟类生态学研究方法。近几年该方法在鸟类迁徙生态学、取食生态学等方面取得较大成就,展现出传统研究方法无可比拟的优越性。但目前该方法在我国鸟类生态学上的应用较少,基于此,从迁徙、取食等方面分别阐述稳定同位素在鸟类生态学上的应用,以促进我国鸟类生态学的快速发展和推动稳定同位素生态学与其它学科的交叉融合。     

稳定同位素分析在昆虫生态研究中的应用

综述了稳定同位素分析的原理与方法以及应用于昆虫生态研究的理论基础与进展,并对其发展前景进行初步探讨。该方法的应用以寄主植物同位素组成差异为前提,常用的同位素包括 D,13C,15N和18O,主要涉及确定食物来源,探寻寄主间转移规律及迁移路线、生态系统中物质与能量流动、食物网构建等方面。对长期保存标本与昆虫化石的同位素分析则扩展了研究的时间范围。同位素转化时间的确定、质量平衡方程和混合模型的应用则是验证相关生态问题的重要步骤;生态、生理和生化过程对同位素分馏的影响尚需深入研究。     

The role of intragemmular osmotic pressure in cell division and hatching of gemmules of the fresh-water sponge Spongilla lacustris (Porifera)

Summary The gemmule coat of Spongilla lacustris is histologically single-layered in the gemmules studied in this work. This single layer is comparable to the classically described internal chitinous membrane of Leveaux (1939). It has been found to contain collagen with an axial period in electron micrographs of about 120 Å and is bounded internally by a thin dense layer which is separate from the internal gemmular cells, and which may be chitinous.Gemmules of this sponge studied during March to June of 1973 respond to 230 mOsmolar solutions of small molecules by: 1. undergoing no change, in which case the substances are freely permeable to the gemmule coat and cells; 2. displaying shrinkage of the cell mass, in which case the substances are permeable to the coat but relatively impermeable to the cells; 3. displaying folding of the coat and cell mass shrinkage because the substances are relatively impermeable to both the coat and the cells; and 4. displaying complete collapse of the gemmule due to impermeability to the coat. The lipid solubility of a substance is directly related to its ability to penetrate the coat. Further, molecular size and charge are also of apparent importance.Substances which penetrate the coat and remain osmotically active (are not metabolized) inhibit hatching. Low concentrations of sodium chloride (23 mOsmolar) have been demonstrated to reversibly inhibit hatching. Higher concentrations cause irreversible damage at 20° C but have little effect at 4° C, indicating that damage is related to the metabolic level of the cells. Once hatching is stimulated by increased temperature the cells become progressively less sensitive to an increase in osmotically active substances.Inhibition of gemmule hatching can theoretically occur by: 1. an addition of solutes to the gemmular fluid, or 2. through an increase in concentration of intragemmular solutes by water withdrawal.Our results raise the question of whether the inhibition of hatching by gemmulostasine, reported by Rasmont (1965) and Rozenfeld (1970, 1971), is due to an osmotic effect rather than to a specific physiological one.Based upon the results reported here and on the work of Zeuthen (1939) and Schmidt (1970) we propose a tight coupling between the intragemmular osmotic pressure and the triggering of hatching (cell division). Any substance which increases intragemmular osmotic pressure to a large enough extent will inhibit hatching. Furthermore, it can be hypothesized that hatching is normally triggered by a decrease in osmotic pressure due to water movement into the gemmule, the movement of solutes out of the gemmule, or to a combination of these.This work was supported by a grant from the National Science Foundation (GB-37775) to T. L. S.     

Life cycle of Spongilla lacustris (Porifera,Spongillidae): a cue for environment-dependent phenotype

We studied the life cycle and growth of Spongilla lacustris in a stream with three distinct habitats. Sponge populations in the habitats exhibited different adaptive strategies. Growth forms of S. lacustris ranged from encrusting to digitate and branched. Environmental factors controlled the appearance of each growth form. In the most hospitable habitat, a variety of colonization strategies and different growth forms were present. In the less hospitable habitat growth was restricted to small and encrusting specimens. In the optimal habitat, the largest and most luxuriant specimens developed. Gemmulation and hatching were dephased among specimens in the three habitats; hence gemmules were present for long periods of time. S. lacustris was found capable of displaying two life strategies: r in the short run, K in the long run.     

Feeding ecology of granivorous carabid larvae: a stable isotope analysis

Although most carabids are primarily carnivorous, some carabid species are omnivorous, with mainly granivorous feeding habits during the larval and/or adult stages (granivorous carabids). This feeding habit has been established based on laboratory and field experiments; however, our knowledge of the feeding ecology of these beetles in the field is limited owing to the lack of an appropriate methodology. In this study, we tested the utility of stable isotope analysis in investigations of the feeding ecology of granivorous carabids in the field, using two closely related syntopic species, Amara chalcites and Amara congrua. We addressed two issues concerning the feeding ecology of granivorous carabids: food niche differentiation between related syntopic species during the larval stage and the effect on adult body size of supplementing seeds with an animal diet during the larval stage. To investigate larval feeding habits, we analysed newly emerged adults, most somatic tissues of which are considered of larval origin. In the two populations examined, both δ¹⁵N and δ¹³C were significantly higher in A. chalcites than A. congrua, suggesting that the two species differentiate food niches, with A. chalcites larvae being more carnivorous than A. congrua larvae. The two isotope ratios of A. chalcites samples from one locality were positively correlated with body size, suggesting that more carnivorous larvae become larger adults. However, this relationship was not detected in other species/locality groups. Thus, our results were inconclusive on the issue of diet supplementation. Nevertheless, overall, these results are comparable with those of previous laboratory‐rearing experiments and demonstrate the potential utility of stable isotope analysis in field studies on the feeding ecology of granivorous carabids.     

Trophic ecology of the pikeperch (Sander lucioperca) in its introduced areas: a stable isotope approach in southwestern France

During the last decades, non-native predatory fish species have been largely introduced in European lakes and rivers, calling for detailed information on the trophic ecology of co-existing native and non-native predators. The present study describes the trophic ecology of the introduced pikeperch (Sander lucioperca) in two southwestern French rivers, using stable isotope analysis. Pikeperch could be categorized as a top-predator, and had a significantly higher trophic position (TP, mean±SE=4.2±0.1) compared to other predatory fish such as the native pike (Esox lucius, TP=3.7±0.1) and the introduced European catfish (Silurus glanis, TP=3.8±0.1). Most studies of resource use in freshwaters consider predatory fish as ecologically equivalent; however, this study showed that the pikeperch occupied a higher trophic niche compared to other predatory species in the Lot and Tarn rivers (Garonne River basin). This apparent specialization may thus have consequences upon interspecific relationships within the predatory guild and upon the functional organization of biological communities. To cite this article: D. Kopp et al., C. R. Biologies 332 (2009).     

Feeding ecology and phylogenetic structure of a complex neotropical termite assemblage,revealed by nitrogen stable isotope ratios

1. In the current ecological classification of termites, four feeding groups (I–IV) are recognised, corresponding to a gradient of decomposition from sound wood to highly mineralised organic matter in the soil. 2. Nitrogen stable isotopes (hereafter δ¹⁵N) were used to place termites from French Guiana rainforests along a wood‐soil decomposition gradient, to test (i) whether feeding group assignation based on morphological characters was accurate and actually represented diet specialisation thresholds, and (ii) to what extent the dietary specialization of species is explained by phylogeny (phylogenetic autocorrelation). 3. δ¹⁵N values vary over a range of 13‰, suggesting that diet diversification contributes to the high species diversity in French Guiana. δ¹⁵N values span a similar interval in all Termitidae subfamilies. Ranges of different subfamilies broadly overlap, although each of them diversified preferentially on one side of the wood‐soil decomposition gradient. Congeneric species share similar feeding habits, whereas distant species tend to feed on distinct substrates. 4. Feeding groups did not completely match stable isotope data: there was no discontinuity between Groups III and IV, and no correlation between anatomical criteria used to distinguish these groups and δ¹⁵N values. Nor was there any consistent difference in δ¹⁵N values between wood feeders of the families Rhinotermitidae (Group I) and Termitidae (Group II). We also suggest that species feeding outside the wood‐soil gradient should be distinguished for their peculiar feeding requirements.     

Insights into fish host-parasite trophic relationships revealed by stable isotope analysis

Trophic relationships between 10 species of fish host and their associated nematode, cestode, and copepod parasites were investigated using stable isotopes of carbon and nitrogen. Nematodes and cestodes were consistently depleted in 15N with respect to their host, and such fractionation patterns are unlike those conventionally observed between consumers and their diets. Species of copepod parasite were sometimes depleted and sometimes enriched in 15N with respect to fish hosts, and this confirms earlier reports that the nature and magnitude of ectoparasite-host fractionations can vary. Significant differences in delta15N and delta13C were observed among fish tissues, and the isotopic signature of parasites did not always closely correspond to that of the tissue with which the parasite was found most closely associated, or on which the parasite was thought to be feeding. Several possible explanations are considered for such discrepancies, including selective feeding on specific amino acids or lipids, migration of the parasite among different fish tissues, changes in the metabolism of the parasite associated with life history and migration between different host animals.     

Life-cycles of lotic populations of Spongilla lacustris and Eunapius fragilis (Porifera: Spongillidae)

SUMMARY. The life-cycles of green and white morphs of the freshwater sponge Spongilla lacustris were examined in the light of past evidence that zoochlorellae may augment their sponge host's nutrition. Field collections from a lotic population of S. lacustris were supplemented by laboratory experiments on gemmule hatching and gemmule size. Both white and green S. lacustris produced sperm for a 6-week period in 1976 starting in the middle of May. Out of thirty white and thirty green sponges examined during this period, twenty white and ten green sponges contained sperm. Sperm production in both morphs was limited primarily to the basal 3.18mm of sponge tissue, and the density of sperm packets in the two morphs was the same. Out of 180 white and green sponges examined in 1976, only four eggs, no embryos, and no larvae were observed. White sponges gemmulated a week or two earlier, and produced smaller gemmules which were more uniform in size than those of green sponges. White and green gemmules hatched synchronously in the spring. In 1977 one female and numerous male specimens of S. lacustris , and numerous females but no males of another sponge, Eunapius fragilis , were found. The life-cycles are discussed in the light of other recent studies on freshwater sponges.