东太平洋赤道海域茎柔鱼的营养生态位和肠道微生物组成

掌握海洋生物的营养生态位特征及其应对环境变化的响应机制,对于评估渔业和气候变化对海洋生态系统功能的影响至关重要。茎柔鱼(Dosidicus gigas)是东太平洋重要的渔业经济物种,在生态系统中具有承上启下的重要生态作用。在气候变化的大背景下,掌握茎柔鱼应对气候变化的响应过程将有利于合理把控其资源状况。本研究采用稳定同位素和高通量技术手段,分别从宏观和微观角度量化比较分析了正常时期和厄尔尼诺时期赤道海域的茎柔鱼营养生态位、肠道长度及肠道微生物组成。结果表明: 不同气候时期茎柔鱼的δ¹³C值存在显著差异,说明食物来源具有差异性;其肠道微生物主要由放线菌门、拟杆菌门、蓝细菌门、厚壁菌门、变形菌门和软壁菌门组成,不同时期微生物群落组成无显著差异,但多样性和相对丰度差异显著。在厄尔尼诺时期,茎柔鱼个体具有较小的营养生态位、较长的肠道、更高的肠道微生物群落多样性及丰富度;肠道微生物的差异主要体现在厚壁菌门、拟杆菌门、螺旋体门、WPS-2和Kiritimatiellaeota,样本距离更为集中。这表明由厄尔尼诺事件导致的栖息地环境及食物变化可能限制茎柔鱼的活动,改变其肠道微生物的结构和功能,有利于其适应环境及食性的变化。     

Dietary niche overlap in sympatric asexual and sexual livebearing fishes Poecilia spp

The present study investigated the spatiotemporal patterns in trophic resource use in a system of a gynogenetic poeciliid fish, the Amazon molly Poecilia formosa, and its sexual congeners the sailfin molly Poecilia latipinna and the Atlantic molly Poecilia mexicana using gut contents analysis. No statistically significant differences in trophic resource use were found between sexual and gynogenetic species, but gut contents varied significantly across sites and over time. In addition, variation in trophic morphology (i.e. gut length) was significant across sites but not species, and laboratory experiments indicated that gut length is phenotypically plastic. Overall, trophic differentiation between coexisting asexual and sexual Poecilia appears to be minimal, and it is unlikely that niche differentiation contributes to a stable coexistence of the two reproductive forms.     

Food composition and digestive enzymes in the gut of pond-cultured Clarias isheriensis (Sydenham 1980), (Siluriformes: Clariidae)

Food composition, diestive enzyme distribution and activity in the gut of pond-cultured Clarias isheriensis were studied It had an omnivorous diet but fed mainly on plancon (particularly Cyanophyceae) and detritus. Qualitative determinations of digestive enzymes in the gut showed that it is capable of digesting carbohydrates, proteins and lipids in its diet. Carbohydrases (amylase, cellulase, maltase, salicinase, sucrase and trehalase) were detected and their activities restricted to the stomach, duodenum and ileum. The incidence of cellulase activity could be responsible for the capacity of this fish species to digest large quantities of Cyanophyceae present in the pond. Lower activity of proteases (chymotrypsin, pepsin and trypsin) and lipases were recorded. Enzyme activity was not recorded in either oesophagus or rectum. The relative distribution and activity of the various digestive enzymes were possibly induced by the nutritional requirements of this catfish species.     

Shift between carnivory and omnivory in stream stonefly predators

Omnivory can have profound effects on the trophic dynamics of communities and ecosystems, as they may interact with multiple trophic levels simultaneously. Some species of large-bodied stoneflies may be viewed as omnivores rather than true carnivores even at later nymphal stages. We evaluated the seasonal change in the diet of stonefly predators by analyzing their stable isotope ratio, gut contents, physiological activity, and food availability. A two-source-based mixing model based on stable isotope analysis revealed that stoneflies shifted their diet between carnivory in summer and omnivory in winter—despite the higher availability of animal prey in winter. The gut content analysis showed that swift prey (mayflies) were consumed in the summer, whereas sluggish prey (Chironomidae) were consumed in the winter. The physiological activity of stoneflies also declined markedly in winter. These results suggest that, in winter, stoneflies foraged on a mixture of Chironomidae and algae. It appears that omnivory in some stream consumers is related to the seasonal change in temperature-dependent physiological activity, rather than prey availability.     

Why can't young fish eat plants? Neither digestive enzymes nor gut development preclude herbivory in the young of a stomachless marine herbivorous fish

Most young fishes lack the ability to function as herbivores, which has been attributed to two aspects of the digestive system: elevated nitrogen demand and a critical gut capacity. We compared the digestive morphology and biochemistry of two size classes of the marine herbivore Hyporhamphus regularis ardelio, pre-ontogenetic trophic shift (pre-OTS, <100mm) and post-ontogenetic trophic shift (post-OTS, >100mm), to determine what limits the onset of herbivory and how their digestive processes fit with current models of digestion. Two gut-somatic indices comparing gut length to body length (relative gut length) and body mass (Zihler's Index) demonstrated a significant decrease (RGL 0.59→0.49, P<0.01; ZI 3.24→2.44, P<0.01) in gut length relative to body size. There was little difference in enzyme activity between the two classes, with juveniles showing similar levels of carbohydrase and lipase and less protease compared with adults, indicating that juveniles did not preferentially target nitrogen and were as capable of digesting an herbivorous diet. These findings suggest that herbivory in this fish is not limited by the function of the post-oesophageal digestive tract, but rather the ability of the pharyngeal mill to mechanically process plants. Our findings offer partial support for the current model of stomachless digestion, indicating that further refinement may be necessary.     

The feeding behaviour of some common lotic insect species in two streams of differing detrital content

The trophic relationships of the benthic invertebrates at two places of differing detrital content in an oligotrophic stream system were examined during a 12 month period.
The sites are described and their detrital contents and other abiotic features compared.
The faunal list at each site is fairly similar but certain species are more common at or restricted to one or other site. The reasons for this are briefly discussed.
The predators and omnivores are in two groups: the first feed only on certain prey and are thus limited by the distribution of their prey. The others consume a wide range of prey and have wider distributions.
The predator species are non-selective in their choice of prey which are devoured in an intensity which cannot however be related to their density in the benthos.
In poorer trophic conditions predators adapt by consuming a greater quantity of algae and detritus; cannibalism and interpredator-predation occur. The prey species are more intensely consumed under poor trophic conditions.
The ecology of two species of predatory Plecoptera is examined and the results indicate that competition probably occurs between them.     

Temporal relationship between the daily profiles of gut melatonin,oxidative status and major digestive enzymes in carp Catla catla

The present study demonstrated a temporal relationship between the concentrations of melatonin, oxidative status and digestive physiology in the gut of a tropical carp Catla catla. We measured the levels of gut melatonin, malondialdehyde (MDA) – a faithful marker of intracellular stress, different antioxidants and major digestive enzymes in the carp gut at four different clock hours in a daily cycle under natural photo-thermal conditions. A correlation between the gut variables was sought to point their possible functional relationship. Gut melatonin titers displayed significant diurnal variations with a peak at midday. An identical temporal pattern with the highest value at midday and nadir at midnight was noted in the activities of superoxide dismutase, catalase and glutathione peroxidase. In contrast, levels of MDA and reduced glutathione (GSH) were highest at midnight and lowest at midday. The activity of all the studied digestive enzymes (α-amylase, cellulase, protease and lipase) showed significant daily variations with a peak at midday. Gut melatonin concentrations by showing a positive correlation with the activity of both enzymatic antioxidants and digestive enzymes, and a negative correlation with the levels of GSH and MDA indicated their possible physiological interplay in a daily cycle. Collectively, our study presented the first information on the daily profiles of oxidative stress, different antioxidants and digestive enzymes in the gut tissues of any fish species, and suggested their functional relationship with the concentrations of gut melatonin in carp Catla catla.     

Trophodynamics of Southern Ocean pteropods on the southern Kerguelen Plateau

Pteropods are a group of small marine gastropods that are highly sensitive to multiple stressors associated with climate change. Their trophic ecology is not well studied, with most research having focused primarily on the effects of ocean acidification on their fragile, aragonite shells. Stable isotopes analysis coupled with isotope‐based Bayesian niche metrics is useful for characterizing the trophic structure of biological assemblages. These approaches have not been implemented for pteropod assemblages. We used isotope‐based Bayesian niche metrics to investigate the trophic relationships of three co‐occurring pteropod species, with distinct feeding behaviors, sampled from the Southern Kerguelen Plateau area in the Indian Sector of the Southern Ocean—a biologically and economically important but poorly studied region. Two of these species were gymnosomes (shell‐less pteropods), which are traditionally regarded as specialist predators on other pteropods, and the third species was a thecosome (shelled pteropod), which are typically generalist omnivores. For each species, we aimed to understand (a) variability and overlap among isotopic niches; and (b) whether there was a relationship between body size and trophic position. Observed isotopic niche areas were broadest for gymnosomes, especially Clione limacina antarctica, whose observed isotopic niche area was wider than expected on both δ¹³C and δ¹⁵N value axes. We also found that trophic position significantly increased with increasing body length for Spongiobranchaea australis. We found no indication of a dietary shift toward increased trophic position with increasing body size for Clio pyramidata f. sulcata. Trophic positions ranged from 2.8 to 3.5, revealing an assemblage composed of both primary and secondary consumer behaviors. This study provides a comprehensive comparative analysis on trophodynamics in Southern Ocean pteropod species, and supports previous studies using gut content, fatty acid and stable isotope analyses. Combined, our results illustrate differences in intraspecific trophic behavior that may be attributed to differential feeding strategies at species level.     

Feeding of Perla grandis nymphs (Plecoptera: Perlidae) in an Apennine first order stream (Rio Berga,NW Italy)

Feeding habits of Perla grandis (Rambur) nymphs have been investigated in the Rio Berga, an Apenninic stream of Northwestern Italy. In this study, we analysed gut contents of 50 nymphs of this species, with the aim to investigate feeding preferences. Nymphs were collected from a single riffle, of which benthic coenosis was also determined. We detected a change in the diet during ontogenesis, with small instars feeding mainly on detritus and large instars strictly carnivorous. We also detected the existence of an evident trophic selection: diet was almost entirely dominated by Chironomidae, independently from their availability on the substratum. This finding is discussed on the basis of ecological and ethological considerations.     

Convergence of temperate and tropical stream fish assemblages

The hypothesis of convergence takes the deterministic view that community (or assemblage) structure can be predicted from the environment, and that the environment is expected to drive evolution in a predictable direction. Here we present results of a comparative study of freshwater fish assemblages from headwater streams in four continents (Europe, North America, Africa and South America), with the general objective of testing whether these assemblages display convergent structures under comparable environmental conditions (i.e. assemblage position in the stream longitudinal continuum). We tested this hypothesis by comparing species richness and trophic guilds of those stream fish assemblages represented in available data from multiple sites on each continent. Independent of phylogenetic and historical constraints, fish assemblage richness and trophic structure in the four continents converged along the stream continua to a substantial degree. For the four continents, assemblage richness increased, the proportion of invertivorous species decreased, and the proportion of omnivorous species increased from upstream to downstream, supporting theoretical predictions of the river continuum concept. However, the herbivore/detritivore and piscivore guilds were virtually absent from our small European and North American stream sites, unlike our African and South American stream sites. This divergence can be linked to differences in energy availability between temperate and tropical systems.     

A stable isotope approach to the eastern Weddell Sea trophic web: focus on benthic amphipods

Stable isotope (¹³C/¹²C and ¹⁵N/¹⁴N) analyses were performed on 90 species belonging to different benthic communities sampled in the eastern Weddell Sea. The study focused on eight amphipod species whose isotopic composition was compared to their previously described respective gut contents. Amphipod stable isotope ratios correspond fairly accurately to the trophic classification based on gut contents and attest to their wide spectrum of feeding types. Since the fundamental difference between the isotope and the gut content approaches to diet studies is the time scale each method addresses, this coincidence indicates that there would be no significant changes in feeding strategies over time. Three levels of the food web are covered by the eight species and, instead of belonging strictly to one trophic category, amphipods display a continuum of values from the suspension-feeder to scavengers.     

Digestive phenotypic flexibility in post-metamorphic amphibians: studies on a model organism

Studies of phenotypic flexibility are central to the understanding of evolutionary and comparative physiology. Research conducted on many vertebrate species has shown that the digestive system is highly responsive and sensitive to environmental cues. However, amphibians, which are a standard and classic model organism for the study of many physiological processes, have been poorly considered in the study of ecological consequences on digestive flexibility. Here we review and analyze the current information on this topic for amphibians. We identify three major bodies of empirical evidence: a) seasonal changes in gut development, b) lack of dietary modulation of gut attributes in adult individuals, c) a relationship between feeding habits and the magnitude of digestive performance regulation. Once the natural history characteristics of the species under study are taken into account, all the evidence is in full agreement with the predictions of digestive theory. We propose that evolutionary and comparative physiology could benefit greatly from the study of phenotypic flexibility in amphibians.     

Comparative Study of the Nymphal Biology of Two Coexisting Species of Mayflies (Insecta: Ephemeroptera) in a Mediterranean Stream in Southern Europe

We study the life history, nymphal feeding and secondary production of two leptophlebiid mayfly species (Habrophlebia eldae and Paraleptophlebia submarginata). They cohabit in a Mediterranean stream and present a very high niche overlap in terms of trophic resources. The life cycle was estimated using size‐frequency analysis of samples taken throughout a year. Both species have a similar but displaced period of the nymphal development. Secondary production was calculated by means of the size‐frequency method. Annual secondary production of P. submarginata is much higher than that of H. eldae (1.95 g DW m^–2 year^–1 vs. 0.17 g DW m^–2 year^–1), and presents a quite similar annual P/B ratio, but slightly higher in ^{P. submarginata} (6.97 in ^{P. submarginata} and 9.21 in ^{H. eldae}). The study of the gut contents revealed that they are mainly detritivores but, when larger they feed also on CPOM from leaves fallen in the stream. They present an almost total niche overlap in terms of food acquisition. However the previously mentioned shift in trophic resources utilization with size makes it possible that, because no similar size classes of each species are present at the same time, niche segregation exists between the two species. Though further studies are needed to confirm it, this could be the consequence of previous episodes of competition between them. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Cutting More from Cut Forests: Edge Effects on Foraging and Herbivory of Leaf-Cutting Ants in Brazil

Edge-mediated changes in species composition are known to result in modified species interactions. Because of the crucial trophic position of herbivores and their far-reaching impact on plant communities, it is important to understand how edge influences herbivory. In the present paper, we investigated whether and how leaf-cutting ant foraging is altered in the forest edge, as this habitat is characterized by an increased proportion of pioneer species. We assessed basic foraging data as well as the herbivory rate ( i.e. , the proportion of the leaf material harvested by a colony in relation to the available leaf area in the foraging area) of Atta cephalotes colonies at the edge versus interior sites of a large remnant of the Atlantic forest in Northeast Brazil. Our results indicated clear edge effects on leaf-cutting ants: equally sized A. cephalotes colonies located at the forest edge removed about twice as much leaf area from their foraging grounds than interior colonies (14.3 vs. 7.8%/col/yr). This greater colony-level impact within the forest edge zone was a consequence of markedly reduced foraging areas (0.9 vs. 2.3 ha/col/yr) and moderately lower leaf area index in this habitat, whereas harvest rates were the same. Our results suggest that forest edges induce increased leaf-cutting ant herbivory, probably via the release of resource limitation. Together with the increase of leaf-cutting ant populations along forest edges, this may amplify environmental changes induced by habitat fragmentation.     

Organic acid concentrations and digesta movement in the gastrointestinal tract of the bushbaby (Galago crassicaudatus) and Vervet monkey (Cercopithecidae pygerythrus)

Studies were conducted to compare digestive functions in two species of sub-human primate, the bushbaby (Galago crassicaudatus) and the Vervet monkey (Cercopithecidae pygerythrus). Major differences were observed in the rate at which digesta markers moved through their respective gastrointestinal tracts, and in the concentration of lactic acid present in the gut. In both species, the caecum and colon were the principle sites of microbial activity and organic acid production.     

Non-native prey species supporting fish assemblage biomass in a Neotropical reservoir

The present study aimed to investigate the role of four non-native invertebrates in supporting fish biomass as well as their influence on the carbon flow into the Volta Grande reservoir food web. The fish samples were carried out quarterly between October 2015 and July 2016 using gillnets. At the sampled sites, four non-native invertebrates (golden mussel, Asian clam, trumpet snail and Amazonian prawn), which are potential prey for fish in the Volta Grande reservoir, were collected by targeted sampling using a Petersen-type bottom dredger and semi-circular sieves. The gut contents of the fish were collected and analyzed under stereoscope, and samples of muscle tissue of these fish, as well as the four non-native invertebrate species sampled, were submitted for isotopic analysis. Results obtained by the present study, by both gut content and stable isotopic analyses, pointed to a trophic structure where non-native species represent not only a strong component of the fish community, but also their main carbon source. Based on gut contents and isotopic mixing models, we found that together, non-native prey are essential carbon sources for the fish fauna, fuelling more than 40.0% of the biomass in four dominant fish species. The consumption rate of non-native bivalves by the native omnivorous fish Leporinus friderici suggested these filter-feeding organisms potentially constitute an important trophic connection between littoral consumers and pelagic energy sources. In addition, non-native prey were also prominent carbon sources for non-native fish, fuelling more than half of the biomass in peacock bass and silver croaker, suggesting these prey have a fundamental role in maintaining non-native fish populations in this system. Our results may help to understand fundamental ecological issues bringing to light the extent to which these new combinations of species influence the energy flow and ecosystem properties of the Volta Grande reservoir.

     

Comparing fish assemblages and trophic ecology of permanent and intermittent reaches in a Mediterranean stream

Mediterranean streams are characterised by seasonal droughts, the frequency and intensity of which vary spatially and are expected to increase with global change. We studied the potential effects of drought and climate change on the fish assemblage and its trophic ecology in a Mediterranean stream by comparing an intermittent tributary with two more permanent neighbouring reaches. Although the three sites were dominated by the same two fish species, Mediterranean barbel (Barbus meridionalis) and chub (Squalius laietanus), the intermittent tributary had a lower overall fish density and fewer eel (Anguilla anguilla). The intermittent tributary had macroinvertebrates with lower density, smaller taxa and higher diversity. Fish in the intermittent tributary had significantly lower biomasses in their gut contents (adjusted for fish length) and more negative electivities than those in the permanent reaches, as well as significantly lower taxonomic diversity. These results indicate that there was reduced resource availability in the intermittent tributary, which resulted in significantly lower condition and gonadal weight (adjusted for length) of barbel and chub. The data obtained in this Mediterranean stream support the observation that reduced water flow may affect fish at both individual and assemblage levels.     

Gut microflora of two saltmarsh detritivore thalassinid prawns,Upogebia africana andCallianassa kraussi

The presence and digestive capabilities of bacteria associated with the digestive systems and habitats of two saltmarsh-burrowing detritivore thalassinid prawns (Upogebia africana andCallianassa kraussi) was examined.U. africana is a filter-feeding prawn inhabiting muddy deposits, whereasC. kraussi, a deposit feeder, inhabits coarser more sandy deposits. Scanning electron microscopy was used to examine the gut lining and associated microflora and the nature of the ingested food of both prawns. The gut contents of both prawns included plant fragments, fragmented diatoms, partially degraded protozoa, and bacteria attached to organic matter. In bothU. africana andC. kraussi the midgut walls and gut contents were extensively coated by filamentous bacteria which were absent in the hindgut. The hindgut epithelium ofU. africana was coated by mats of rodshaped bacteria, not reported in marine invertebrates previously. The digestive glands of both species contained bacteria in the lumen. Isolation of gut and habitat bacteria suggests that bothU. africana andC. kraussi maintain a gut microflora distinct from the habitat microflora. Bacteria isolated from the guts of both species of prawn differed from those isolated from their respective habitats with regards to both the genera isolated and their digestive capabilities. The dominant genera isolated from the guts of bothU. africana andC. kraussi wereVibrio andPseudomonas, with an unidentified fermenter andPseudomonas, respectively dominating in the digestive glands. Bacteria of the genusAcinetobacter dominated the isolates from the habitats of both species of prawn. Resident gut bacteria isolated from the guts of both species of prawn exhibited lipase, protease, chitinase, and lysozyme, but not cellulase activity, and may contribute to nitrogen aquisition by the prawns. Isolates from the prawns' habitat exhibited alginase, gelatinase, and lipase activity, a few (3%) fromU. africana habitat having cellulases. In this study a distinction between resident gut bacteria and transient gut bacteria was made. Results suggest that some habitat bacteria remain viable in the guts ofU. africana, but not inC. kraussi.     

Ecological and Geographical Reasons for the Variation of Digestive Tract Length in Anurans

Changes of environmental conditions can shape organs size evolution in animal kingdoms. In particular, environmental changes lead to difference in food resources between different habitats, thereby affecting individual's energy intake and allocation. The digestive theory states that animals consuming food with low contents of digestible materials should result in increasing gut length. In this study, to test the hypothesis of digestive theory, we studied ecological and geographical reasons for variation in digestive tract length among 35 species of anurans distributing in different altitude and latitude. The results showed that ecological type significantly affected digestive tract length among species, with aquatic and terrestrial species having longer digestive tract than arboreal ones. Latitude was positively correlated with digestive tract length. However, altitude, as well as monthly mean temperature and precipitation, did not correlate with digestive tract length among species. Our findings suggest that aquatic and terrestrial species might forage less digestible materials than arboreal species, thereby displaying relatively longer digestive tract than arboreal species.     

Inter-individual differences in the gene content of human gut bacterial species

BackgroundGene content differences in human gut microbes can lead to inter-individual phenotypic variations such as digestive capacity. It is unclear whether gene content variation is caused by differences in microbial species composition or by the presence of different strains of the same species; the extent of gene content variation in the latter is unknown. Unlike pan-genome studies of cultivable strains, the use of metagenomic data can provide an unbiased view of structural variation of gut bacterial strains by measuring them in their natural habitats, the gut of each individual in this case, representing native boundaries between gut bacterial populations. We analyzed publicly available metagenomic data from fecal samples to characterize inter-individual variation in gut bacterial species.ResultsA comparison of 11 abundant gut bacterial species showed that the gene content of strains from the same species differed, on average, by 13% between individuals. This number is based on gene deletions only and represents a lower limit, yet the variation is already in a similar range as observed between completely sequenced strains of cultivable species. We show that accessory genes that differ considerably between individuals can encode important functions, such as polysaccharide utilization and capsular polysaccharide synthesis loci.ConclusionMetagenomics can yield insights into gene content variation of strains in complex communities, which cannot be predicted by phylogenetic marker genes alone. The large degree of inter-individual variability in gene content implies that strain resolution must be considered in order to fully assess the functional potential of an individual''s human gut microbiome.

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