On the cultivation of free-living marine and estuarine nematodes

Although a large body of literature exists on the systematics and ecology of free-living marine and brackish-water nematodes, key questions on the nature and magnitude of interactions between nematodes and other organisms in the benthos remain unanswered. Relatively few authors have investigated live nematodes in food web studies or in experiments dealing with the nematodes’ response to a varying environment. It is mainly for the latter purpose that attempts have been made to maintain, rear and cultivate selected species. This paper describes the methodology used for the maintenance, rearing, and eventual permanent agnotobiotic cultivation of a variety of estuarine nematodes. Spot plates, where small samples of sediment or macrophyte material are inoculated on a sloppy agar layer, have been used for the purpose of maintenance and initial cultivation. Those species that reproduce on spot plates are then selected for monospecific cultivation on agar layers with different nutrient enrichments and with micro-organisms cotransferred from the spot plates as food. Mixtures of bacto and nutrient agar prepared in artificial seawater were specifically suitable for the xenic cultivation of nine bacterivorous and, when supplied with Erdschreiber nutrients, two algivorous/bacterivorous nematode species. Up to three generations of five other nematode species have been reared under laboratory conditions, and several more were kept alive and active for variable periods of time on agar. Generation times observed on spot plates forAdoncholaimus fuscus andOncholaimus oxyuris were substantially shorter than previously published estimates and suggest a correspondingly higher predatory and scavenging potency for these and related enoplids. A procedure for the long-term storage of nematodes at −80°C with glycerol as a cryoprotectant was successfully used forDiplolaimella dievengatensis, Panagrolaimus sp. 1, andPellioditis marina, but not forDiplolaimelloides meyli. The authors have also summarized the existing literature on the cultivation of marine and brackish-water nematodes. Continuous cultivation appears to have been successful mainly for Aufwuchs and epiphytic nematodes; only few sediment-dwellers have been established in permanent culture. Of only just over 30 species that have ever been cultivated, more than half belong to one family (Monhysteridae) and three are Rhabditida, an order poorly represented in the marine environment. Four species have been grown in monoxenic and one in axenic culture, the latter though with limited success. It is concluded that our understanding of the basic nutritional requirements of marine nematodes is as yet insufficient, and that the culture techniques which have so far mainly deployed agar or liquid substrates, while being suitable for the cultivation of Aufwuchs and epiphytic nematodes, do not accurately enough mimic gradients specific of the natural habitat of many sediment-dwellers.     

Species composition and distribution of free-living marine nematodes in Vostok Bay, Sea of Japan

The qualitative and quantitative composition of free-living marine nematodes have been studied in Vostok Bay (Peter the Great Bay, Sea of Japan). It is found that the population density of nematodes in the bottom sediments of Vostok Bay shows an uneven distribution. The mean population density equaled 56800 ± 23400 specimens/m². A correlation has been revealed between the population density of nematodes and the substrate type. Altogether, 85 species of nematodes have been found; they were dominated by Sabatieria palmaris, Rhabdodemania orientalis, Araeolaimus parvibulbosus, Oncholaimium paraolium, Doryolaimopsis peculiaris, and Metachromadora itoi. Six taxocenoses of nematodes were distinguished, taking into account the species dominating in the population density and using cluster analysis of the obtained data. The dominating trophic assemblage of nematodes was “scrapers.” In general, the species composition of nematodes in Vostok Bay is characterized by the relatively great similarity with that in other areas of Peter the Great Bay (Sea of Japan).     

Dispersal and gene flow in free-living marine nematodes

Dispersal and gene flow determine connectivity among populations, and can be studied through population genetics and phylogeography. We here review the results of such a framework for free-living marine nematodes. Although field experiments have illustrated substantial dispersal in nematodes at ecological time scales, analysis of the genetic diversity illustrated the importance of priority effects, founder effects and genetic bottlenecks for population structuring between patches <1 km apart. In contrast, only little genetic structuring was observed within an estuary (<50 km), indicating that these small scale fluctuations in genetic differentiation are stabilized over deeper time scales through extensive gene flow. Interestingly, nematode species with contrasting life histories (extreme colonizers vs persisters) or with different habitat preferences (algae vs sediment) show similar, low genetic structuring. Finally, historical events have shaped the genetic pattern of marine nematodes and show that gene flow is restricted at large geographical scales. We also discuss the presence of substantial cryptic diversity in marine nematodes, and end with highlighting future important steps to further unravel nematode evolution and diversity.     

Relationships between body size and abundance in ecology

Body size is perhaps the most fundamental property of an organism and is related to many biological traits, including abundance. The relationship between abundance and body size has been extensively studied in an attempt to quantify the form of the relationship and to understand the processes that generate it. However, progress has been impeded by the under appreciated fact that there are four distinct, but interrelated, relationships between size and abundance that are often confused in the literature. Here, we review and distinguish between these four patterns, and discuss the linkages between them. We argue that a synthetic understanding of size-abundance relationships will result from more detailed analyses of individual patterns and from careful consideration of how and why the patterns are related.     

The free-living inland aquatic nematodes of Africa — a review

During the past three decades, much attention has been given to free-living nematodes and, in particular, to the species of the African continent. Despite the current absence of evidence for the existence of planktonic species, several conditions are suggested that could lead to intrusion of the planktonic habitat, e.g. turbulent shallow waters, high food densities and preadaptations such as swimming ability and negative geotaxis. A new and more practical ecological classification of the inland free-living nematodes is proposed to avoid further incoherency in this regard. All the free-living inland aquatic species described in Africa are presented here in a checklist, including notes on their ecology and distribution. Many of the cosmopolitan species, included in the checklist, are now increasingly being recognized as conglomerates of species, each species of which occupies a restricted area. Finally the distribution of free-living inland aquatic species in Africa is discussed and some preliminary notes are presented.     

Dynamic relationships between body size,species richness,abundance, and energy use in a shallow marine epibenthic faunal community

We study the temporal variation in the empirical relationships among body size (S), species richness (R), and abundance (A) in a shallow marine epibenthic faunal community in Coliumo Bay, Chile. We also extend previous analyses by calculating individual energy use (E) and test whether its bivariate and trivariate relationships with S and R are in agreement with expectations derived from the energetic equivalence rule. Carnivorous and scavenger species representing over 95% of sample abundance and biomass were studied. For each individual, body size (g) was measured and E was estimated following published allometric relationships. Data for each sample were tabulated into exponential body size bins, comparing species‐averaged values with individual‐based estimates which allow species to potentially occupy multiple size classes. For individual‐based data, both the number of individuals and species across body size classes are fit by a Weibull function rather than by a power law scaling. Species richness is also a power law of the number of individuals. Energy use shows a piecewise scaling relationship with body size, with energetic equivalence holding true only for size classes above the modal abundance class. Species‐based data showed either weak linear or no significant patterns, likely due to the decrease in the number of data points across body size classes. Hence, for individual‐based size spectra, the SRA relationship seems to be general despite seasonal forcing and strong disturbances in Coliumo Bay. The unimodal abundance distribution results in a piecewise energy scaling relationship, with small individuals showing a positive scaling and large individuals showing energetic equivalence. Hence, strict energetic equivalence should not be expected for unimodal abundance distributions. On the other hand, while species‐based data do not show unimodal SRA relationships, energy use across body size classes did not show significant trends, supporting energetic equivalence.     

Interactions between body size,abundance, seasonality,and phenology in forest beetles

Body size correlates with a large number of species traits, and these relationships have frequently been used to explain patterns in populations, communities, and ecosystems. However, diverging patterns occur, and there is a need for more data on different taxa at different scales. Using a large dataset of 155,418 individual beetles from 588 species collected over 13 years of sampling in Norway, we have explored whether body size predicts abundance, seasonality, and phenology in insects. Seasonality is estimated here by flight activity period length and phenology by peak activity. We develop several methods to estimate these traits from low‐resolution sampling data. The relationship between abundance and body size was significant and as expected; the smaller species were more abundant. However, smaller species tended to fly for longer periods of the summer and peaked in midsummer, while larger species were restricted to shorter temporal windows. Further analysis of repeated sampling from a single location suggested that smaller species had increased flight period lengths in warmer years, but larger species showed the opposite pattern. The results 1) indicate that smaller species are likely to be disproportionately valuable in ecological interactions, and 2) provide potential insights into the traits influencing the vulnerability of some larger species to disturbances and climate change.     

The relationship between body size and population abundance in animals

On average, large-bodied species live at lower densities than small-bodied ones. Early studies suggested that population densities might scale so that the energy use of a population is independent of body size. However, recent work shows that, at the scale of local communities, this is rarely true and that the pattern varies among taxonomic or ecological subsets of those communities. Energetic considerations may only be relevant to the densities of more abundant species. In fact, within natural assemblages o f organisms, the underlying relationship is very variable; in subsets of those assemblages, ecological processes such as competition may structure abundance patterns.     

Relationships between body size and biomass of aquatic insects

SUMMARY. Predictive equations were developed to estimate dry weight from body length measurements for forty-three taxa of aquatic insects. The inter-relationships between dry weight, body length and head capsule width of individuals grouped according to the eight major orders of aquatic insects were also examined. Regression analysis indicated that the relationship between biomass and body size was best expressed by a power equation, Y =_aX^b, rather than by linear or exponential equations. Changes in body length versus head capsule width were best expressed by linear equations, with three distinct relationships being observed. Body length estimated biomass better than head capsule width. Populations often species of insects collected from two different rivers generally did not differ significantly in their dry weight to body length relationships.     

海洋微型浮游动物的丰度和生物量

综合了海洋微型浮游动物研究的历史沿革,微型浮游动物在海洋生态系统中的作用、丰度和生物量,微型浮游动物的研究方法以及我国研究海洋微型浮游动物的情况。     

Relationships between geographical range size, body size, local abundance, and habitat breadth in North American suckers and sunfishes

Aim I examine the relationship between geographical range size and three variables (body size, an index of habitat breadth, and an index of local abundance) within a phylogenetic framework in North American species of suckers and sunfishes. Location North America Methods Regressions after independent contrasts of geographical range size, body size, habitat breadth, and local abundance. Results Species with large range sizes tend to be larger-bodied, be more locally abundant, and have higher habitat breadths. Character reconstructions support the prediction that variables associated with rarity (small geographical range size, low local abundance, low niche breadth, and large body size) evolve in unison, although large body size was associated with the opposite traits in these taxa. Gaston & Blackburn (1996a) suggested using visual identification of the lower boundary of the geographical range-body size relationship to identify extinction-prone species; this resulted in thirteen species that are potentially extinction-prone. Main conclusions Similar evolutionary mechanisms appear to operate on body size and other variables related to rarity, even in distantly related taxa.     

Biodiversity of marine nematodes in Australian sandy beaches from tropical and temperate regions

The universal occurrence and abundance of nematodes provides opportunities to investigate ecological factors that may influence biodiversity. Clarke and Warwick (2001) have proposed diversity indices average taxonomic distance(AvTD), variation in taxonomic distinctness (VarTD) for computing marine nematode biodiversity based on classification trees. Faith [Biological Conservation 61 (1992) 1] had previously proposed a diversity index based on phylogenetic trees, though not applied to nematodes. Clarke and Warwick (2001) also considered an index AvPD analogous to AvTD. These indices have been applied to five very large collections of free-living nematodes from three exposed sandy beaches in Australia. Two were from a beach close to Darwin in northern Australia, two from the temperate southeast coast of Australia and one from the south of the Australian mainland. The collections extend over a considerable range of latitude, from 12°26S to 38°33S and the controversial hypothesis that latitudinal gradients per se influence the biodiversity of marine nematode assemblages is examined. AvTD did not vary among collections and its value for any collection was indistinguishable from that of random samples of the same size drawn from the total species pool. VarTD showed no variation for three of the collections, but was slightly higher than expected for the mid-latitude beach, attributed to unevenness in the classification trees. AvTD and VarTD were not greatly affected by differences in sampling intensity. PD varied directly with the number of species found but observed PD did not differ from the PD of random samples of the same number of species taken from the total species pool. Thus, the observed variation in PD is wholly accounted for by variations in species richness. The number of species found increased with decreasing latitude. It appears that species richness by itself is an adequate index of biodiversity for the free-living nematodes of these sandy beaches, and more complex indices such as AvTD, VarTD and PD are unnecessary.     

污水排海对小型底栖生物丰度和生物量的影响

为了解污水排海对小型底栖生物丰度和生物量的影响,于2011年4、8、10、12月对青岛汇泉湾第一海水浴场中潮带一个排污口附近不同距离站位的小型底栖生物进行了春、夏、秋、冬4个季度的采样调查.结果表明： 研究区域小型底栖生物年平均丰度为(1859.9±705.1) ind·10 cm^-2,最高值出现在距离排污口20和40 m的站位S₂和S₃,分别为(2444.9±1220.5)和(2492.2±1839.9) ind·10 cm^-2,最低值出现在距离排污口0 m的站位S₁,为(327.9±183.2) ind·10 cm^-2.小型底栖生物的年平均生物量为(1513.4±372.7) μg·10 cm^-2.小型底栖生物在丰度和生物量上呈现明显的季节变化,最高值出现在春季,最低值出现在夏季.共鉴定出11个小型底栖生物类群,包括线虫、桡足类、多毛类、寡毛类、缓步动物、海螨、涡虫、介形类、等足类、甲壳类幼体及其他类.自由生活海洋线虫是最优势的类群,占总丰度的83.1%,其次为底栖桡足类,占12.8%.在垂直分布上,小型底栖生物在0~2 cm表层分布最多,向深层呈现递减趋势,冬季部分向下迁移.Pearson相关分析表明,小型底栖生物丰度和生物量与沉积物中值粒径和有机质含量呈极显著负相关.此外,旅游等人为扰动也是影响小型底栖生物数量及分布的因素.与历史资料中的同类研究结果进行了比较,并探讨了线虫与桡足类丰度的比值
在有机质污染监测中的适用性.     

Evolutionary influences on body size in free-living and parasitic isopods

The influence of mode of life and habitat characteristics on the evolution of body size in isopods was investigated in a comparative analysis based on data from 746 free-living and parasitic species. The phylogeny of isopods allowed 24 independent comparisons to be made between higher taxa (families or superfamilies), each corresponding to a separate branching event. The evolution of parasitism was consistently associated with reductions in body size. On the contrary, invasion of freshwater habitats was consistently coupled with increases in body size. Lineages moving to higher latitudes were significantly more likely to evolve larger body sizes than those shifting toward the equator. In addition, colonizing deeper water resulted in a weak tendency to evolve larger body size. The analysis suggests that the large size of some isopod groups parasitic on fish (e.g. Cymothoidae) may have been inherited from a free-living ancestor and is not the product of directional selection toward large size and greater fecundity.     

Connecting species richness, abundance and body size in deep-sea gastropods

Aim This paper examines species richness, abundance, and body size in deep‐sea gastropods and how they vary over depth, which is a strong correlate of nutrient input. Previous studies have documented the empirical relationships among these properties in terrestrial and coastal ecosystems, but a full understanding of how these patterns arise has yet to be obtained. Examining the relationships among macroecological variables is a logical progression in deep‐sea ecology, where patterns of body size, diversity, and abundance have been quantified separately but not linked together. Location 196–5042 m depth in the western North Atlantic. Method Individuals analysed represent all Vetigastropoda and Caenogastropoda (Class Gastropoda) with intact shells, excluding Ptenoglossa, collected by the Woods Hole Benthic Sampling Program (3424 individuals representing 80 species). Biovolume was measured for every individual separately (i.e. allowing the same species to occupy multiple size classes) and divided into log₂ body size bins. Analyses were conducted for all gastropods together and separated into orders and depth regions (representing different nutrient inputs). A kernel smoothing technique, Kolmogorov‐Smirnov test of fit, and OLS and RMA were used to characterize the patterns. Results Overall, the relationship between the number of individuals and species is right skewed. There is also a positive linear relationship between the number of individuals and the number of species, which is independent of body size. Variation among these relationships is seen among the three depth regions. At depths inferred to correspond with intermediate nutrient input levels, species are accumulated faster given the number of individuals and shift from a right‐skewed to a log‐normal distribution. Conclusion A strong link between body size, abundance, and species richness appears to be ubiquitous over a variety of taxa and environments, including the deep sea. However, the nature of these relationships is affected by the productivity regime and scale at which they are examined.     

Predator–prey interactions between Dugesia gonocephala and free-living nematodes

1. Three groups of laboratory experiments clarified the role of nematodes as a potential food resource for the triclad Dugesia gonocephala. The first group measured the functional response of adult D. gonocephala feeding on juvenile or adult Caenorhabditis elegans. The feeding rates of D. gonocephala on adult and juvenile C. elegans followed a type II functional response. The maximum number of adult nematodes and juvenile nematodes eaten by a single D. gonocephala individual within 3 h was 94 and 197 nematodes, respectively. 2. A second group of microcosm experiments investigated the effect of D. gonocephala on the density and the vertical distribution of a nematode community in fine sand. The following treatments were performed: (i) microcosms with 400 nematodes and (ii) microcosms with 400 nematodes and one D. gonocephala. After 5 days, nematodes as a group, as well as the dominant species Tobrilus pellucidus and Trischistoma monohystera, showed no significant difference in vertical patterns between the treatments with and without D. gonocephala. 3. The third group of experiments determined whether grain size of the sediment (sand, fine gravel and coarse gravel) altered the ability of D. gonocephala to consume adult C. elegans. Sand and fine gravel reduced the predation effectiveness of D. gonocephala by 100%, whereas the predator consumed nematodes in coarse gravel (19 nematodes within 3 h).     

The Aphelenchoides genomes reveal substantial horizontal gene transfers in the last common ancestor of free-living and major plant-parasitic nematodes

Aphelenchoides besseyi is a plant-parasitic nematode (PPN) in the family Aphelenchoididae capable of infecting more than 200 plant species. A. besseyi is also a species complex with strains exhibiting varying pathogenicity to plants. We present the genome and annotations of six Aphelenchoides species, four of which belonged to the A. besseyi species complex. Most Aphelenchoides genomes have a size of 44.7–47.4 Mb and are among the smallest in clade IV, with the exception of A. fujianensis, which has a size of 143.8 Mb and is one of the largest. Phylogenomic analysis successfully delimited the species complex into A. oryzae and A. pseudobesseyi and revealed a reduction of transposon elements in the last common ancestor of Aphelenchoides. Synteny analyses between reference genomes indicated that three chromosomes in A. besseyi were derived from fission and fusion events. A systematic identification of horizontal gene transfer (HGT) genes across 27 representative nematodes allowed us to identify two major episodes of acquisition corresponding to the last common ancestor of clade IV or major PPNs, respectively. These genes were mostly lost and differentially retained between clades or strains. Most HGT events were acquired from bacteria, followed by fungi, and also from plants; plant HGT was especially prevalent in Bursaphelenchus mucronatus. Our results comprehensively improve the understanding of HGT in nematodes.     

近岸海洋线虫与细菌、古菌的共现性及其对碳、氮循环的影响

【目的】初步探究海洋线虫与微生物的相互作用对碳、氮循环的影响。【方法】利用16S r RNA和18S r RNA基因高通量测序方法,对33个近岸沉积物样品中细菌、古菌和真核生物的多样性进行调查;对海洋线虫与细菌、海洋线虫与古菌的共现性进行网络分析,并采用Spearman统计学方法,识别出与海洋线虫共现性呈显著相关性的微生物种类。【结果】在夏季,红树林和潮间带泥滩样品中线虫OTU平均相对丰度基本呈随深度增加而递减趋势;冬季的红树林样品中发现相类似变化规律,只有在冬季潮间带泥滩样品中线虫OTU平均相对丰度在深层较高于表层。相对丰度最高的海洋线虫隶属于单宫目(47%)、色矛目(19%)、刺嘴目(16%)和垫刃目(9%),它们与热源体古菌、深古菌、γ-和δ-变形菌等微生物有显著正/负相关关系。【结论】在香港米埔湿地沉积物中,与相对丰度最高的5种线虫显著相关的几大类微生物均在碳、氮、硫等元素循环方面起十分重要的作用,暗示海洋线虫与微生物潜在的相互作用对元素地球化学循环具有重要影响。研究结果有助于深入了解线虫在生态系统中未被揭示的生态功能,有助于更清晰地认识海洋线虫在底栖生态系统中所扮演的角色。