Genetic diversity in populations of a freshwater ciliate

RAPD fingerprinting with nine different primers revealed that all of 18 E. aediculatus isolates from nine ponds and streams in western Germany, France and the U.S.A. were genetically different. The extent of genetic similarity between genotypes from different waters did not show a significant relationship with the geographical distance among habitats, although genotypes isolated from the same habitat showed a higher genetic similarity than genotypes isolated from different habitats. Phylogenetic analyses of RAPD patterns indicate a separation of E. aediculatus strains into subgroups within one species, but all strains were genetically more similar to one another than to strains from two other Euplotes species. Crossings of the different E. aediculatus strains revealed they belonged to seven mating types of one gene pool. The high genetic diversity observed is explained by a frequent occurrence of conjugation in the studied populations.     

Effects of sampling and sub-sampling variation using the STAR-AQEM sampling protocol on the precision of macroinvertebrate metrics

As part of the extensive field sampling programme within the European Union STAR project, replicate macroinvertebrate samples were taken using the STAR-AQEM sampling method at each of 2–13 sites of varying ecological quality within each of 15 stream types spread over 12 countries throughout Europe. The STAR-AQEM method requires the sub-sampling and taxonomic identification of at least one-sixth of the sample and at least 700 individuals. Replicate sub-samples were also taken at most of these sites. Sub-sampling effects caused more than 50% of the overall variance between replicate samples values for 12 of the 27 macroinvertebrate metrics analysed and was generally greatest for metrics that depend on the number of taxa present. The sampling precision of each metric was estimated by the overall replicate sampling variance as a percentage P_samp of the total variance in metric values within a stream type. Average over all stream types, the three Saprobic indices had the lowest percentage sampling variances with median values of only 3–6%. Most of the metrics had typical replicate sampling variances of 8–18% of the total variability within a stream type; this gives rise to estimated rates of mis-classifying sites to ecological status class of between 22 and 55% with an average of about 40%. This suggests that the precision of such metrics based on the STAR-AQEM method is only sufficient to indicate gross changes in the ecological status of sites, but there will be considerable uncertainty in the assignment of sites to adjacent status classes. These estimates can be used to provide information on the effects of STAR-AQEM sampling variation on the expected uncertainty in multi-metric assessments of the ecological status of sites in the same or similar stream types, where only one sample has been taken at a point in time and thus there is no replication.     

应用流式细胞术测定绢毛苣属4种8居群基因组大小

以绢毛苣属（Soroseris）植物肉菊（S.umbrella（Franch.）Lipsch）、绢毛苣（S.glomerata（Decne.）Stebbins）、羽裂绢毛苣（S.hirsuta（Anth.）Shih）和金沙绢毛菊（S.gillii（S.Moore）Stebbins）4个种的8个居群为材料,采用WPB和Galbraith's buffer两种裂解液分别处理样品,运用流式细胞术测定DNA含量,并使用常规染色体压片法确定其细胞倍性。结果显示：两种裂解液中,最适于绢毛苣属植物DNA含量测定的裂解液为WPB;4个物种中,羽裂绢毛苣的基因组最小;细胞倍性水平对1Cx-值的影响较小。此外,本研究发现可采用种子萌发形成的幼苗代替难以获取的植物幼嫩叶片作为实验材料。     

Variance effective population size is affected by census size in sub-structured populations

Measurement of allele frequency shifts between temporally spaced samples has long been used for assessment of effective population size (N_e), and this ‘temporal method’ provides estimates of N_e referred to as variance effective size (N_eV). We show that N_eV of a local population that belongs to a sub-structured population (a metapopulation) is determined not only by genetic drift and migration rate (m), but also by the census size (N_c). The realized N_eV of a local population can either increase or decrease with increasing m, depending on the relationship between N_e and N_c in isolation. This is shown by explicit mathematical expressions for the factors affecting N_eV derived for an island model of migration. We verify analytical results using high-resolution computer simulations, and show that the phenomenon is not restricted to the island model migration pattern. The effect of N_c on the realized N_eV of a local subpopulation is most pronounced at high migration rates. We show that N_c only affects local N_eV, whereas N_eV for the metapopulation as a whole, inbreeding (N_eI), and linkage disequilibrium (N_eLD) effective size are all independent of N_c. Our results provide a possible explanation to the large variation of N_e/N_c ratios reported in the literature, where N_e is frequently estimated by N_eV. They are also important for the interpretation of empirical N_e estimates in genetic management where local N_eV is often used as a substitute for inbreeding effective size, and we suggest an increased focus on metapopulation N_eV as a proxy for N_eI.     

Localization of centrins in the hypotrich ciliate Paraurostyla weissei

Centrins are ubiquitous cytoskeletal proteins that are generally associated with the centrosome and form large cytoskeletal networks in protists. To obtain more data on the respective role of different centrin proteins, we studied their distribution and behavior in one ciliate species, Paraurostyla weissei, using specific antibodies. In this species, only two major proteins of 21 and 24 kDa corresponding to centrins, were identified by 1D and 2D electrophoresis. Immunofluorescence analysis showed that these two proteins displayed non-overlapping localization in the interphase cell and during morphogenesis. Both centrin proteins localize on the fibrous network linking the oral basal bodies in the interphase cell and in the form of marginal dots, which correspond to the proximal ends of the striated rootlets; the 21 kDa centrin was also detected within the basal bodies, whereas the 24 kDa centrin allowed identifying new structures, the frontal dashes. During morphogenesis, the 21 kDa centrin locates at the basal bodies, while the 24 kDa centrin is detected along the striated rootlets and in close association with the basal bodies pairs. These data are discussed in terms of the potential roles of the two centrins in different cellular functions.     

Studies on the in vitro cultivation of ciliate protozoa from the kangaroo forestomach

The methods used for culturing rumen protozoa were found to be unsatisfactory for growth of ciliate protozoa from the kangaroo forestomach. Based on published measurements of physical parameters in the marsupial forestomach, several modifications were incorporated into the procedure, i.e., an increase in % hydrogen in the gas phase, adjustment of initial pH of the medium to 6.9–7.0 range, feed only forage as a substrate and incubate at a lower temperature (33–36 °C). Only incubation at the lower temperature increased survival time of the kangaroo protozoa. Two species of Bitricha were still viable after 28 d in culture. Cultures had to be terminated at that time. One of the species differed considerably in size and shape from previously described species and based on 18S rRNA data, may represent a new species of Bitricha. The second species, present in low numbers was identified as Bitricha oblata. In a separate trial, Macropodinium yalanbense survived for 11 d, at which time these cultures also had to be terminated.     

Evaluating shell variation across different populations of a freshwater snail

The freshwater snail Potamopyrgus antipodarum has become a model system for studying invasion ecology, host–parasite coevolution, the maintenance of sexual reproduction and ecotoxicology. One understudied aspect of this snail is the variation in morphology within and among populations, which could provide insights into ecological differences across its native range. In this study of 17 New Zealand lake populations of P. antipodarum we used linear measurements and geometric morphometrics to compare several aspects of shell size and shape. We found that, except for those from Lake Te Anau, most lake populations of P. antipodarum differ slightly in shape, but differ significantly in size and in the presence of spines, where larger and spinier snails are found in deeper regions. These striking distinctions in size and shell armature, but not in shape, suggest that the various components of form are under different selective regimes. Snails from Lake Te Anau are different in both shape and size, implying that this population is diverging from the rest of the species in multiple ways, making it an interesting study population for further research.     

Volatility in the effective size of a freshwater gastropod population

Despite the utility of gastropod models for the study of evolutionary processes of great generality and importance, their effective population size has rarely been estimated in the field. Here, we report allele frequency variance at three allozyme‐encoding loci monitored over 7 years in a population of the invasive freshwater pulmonate snail Physa acuta (Draparnaud 1805), estimating effective population size with both single‐sample and two‐sample approaches. Estimated N_e declined from effectively infinite in 2009 to approximately 40–50 in 2012 and then rose back to infinity in 2015, corresponding to a striking fluctuation in the apparent census size of the population. Such volatility in N_e may reflect cryptic population subdivision.     

The effect of predator and prey density on the induced defence of a ciliate

1. The level of antipredator defence should be proportional to the actual attack probability to minimize the cost of defence and maximize the net benefit.
2. The hypothesis that the induced antipredator morphology of Euplotes octocarinatus is a graded response to the actual risk of predation by Stylonychia mytilus was tested by manipulating the density of both prey and predator populations.
3. The magnitude of the response was graded according to both predator and prey density. A dense prey population may be protective since a prey is more exposed to a predator's attack as a solitary individual.
4. The results suggest that Euplotes is able to 'estimate' the real risk of predation and respond appropriately, without mobilizing more resources than needed.
5. Separation of the prey and predator with a nylon net revealed that the response was not induced by a water-transmitted factor but that direct cell-to-cell contacts were important. This finding departs from those of other studies.     

Reduced fecundity in small populations of the rare plant Gentianopsis ciliate (Gentianaceae)

Habitat destruction is the main cause for the biodiversity crisis. Surviving populations are often fragmented, i.e., small and isolated from each other. Reproduction of plants in small populations is often reduced, and this has been attributed to inbreeding depression, reduced attractiveness for pollinators, and reduced habitat quality in small populations. Here we present data on the effects of fragmentation on the rare, self-compatible perennial herb Gentianopsis ciliata (Gentianaceae), a species with very small and presumably well-dispersed seeds. We studied the relationship between population size, plant size, and the number of flowers produced in 63 populations from 1996-1998. In one of the years, leaf and flower size and the number of seeds produced per fruit was studied in a subset of 25 populations. Plant size, flower size, and the number of seeds per fruit and per plant increased with population size, whereas leaf length and the number of flowers per plant did not. The effects of population size on reproduction and on flower size remained significant if the effects were adjusted for differences in plant size, indicating that they could not be explained by differences in habitat quality. The strongly reduced reproduction in small populations may be due to pollination limitation, while the reduced flower size could indicate genetic effects.     

Non-specific activation of mouse peritoneal macrophages by a freshwater ciliate, Tetrahymena pyriformis

Toxoplasma-killing activities of mouse peritoneal macrophages activated by the extracts of Tetrahymena pyriformis (Korean and Chinese strains) were evaluated, and the active protein fractions from both strains were partially characterized by a method including chromatographies and SDS-PAGE. The first peak in Korean strain and the second peak in Chinese strain of T. pyriformis obtained by DEAE-Sephadex A-50 chromatography were most effective in the activation of macrophages to kill Toxoplasma gondii tachyzoites in vitro. Subsequent fractionations of obtained peak fractions were performed on a Sephadex G-200 gel. The first peaks fractionated from both strains of T. pyriformis had the highest toxoplasmacidal activities, and when subjected to the SDS-PAGE, one prominent band was visualized for each of the strains showing the same molecular weight of ca. 52.6 kDa. This active protein is suggested to be related to non-specific activation of mouse peritoneal macrophages.     

Estimation of the size of the vCJD epidemic

Estimates of the final size of the variant Creuzfeldt-Jakob Disease epidemic have been made by fitting theoretical curves of the incubation period distribution to the histogram of observed annual deaths to 2002, using various assumptions of the mean and standard deviation of this distribution, and also of the efficacy of the Specified Bovine Offals ban of 1989. Unless the mean incubation time is greater than 15 to 20 years the estimates lie in the low hundreds to about a thousand, and the most likely situation, of a mean between 11 and 15 years, gives estimates of about 150 to 500 deaths. Numbers above a few thousands would only occur if the mean incubation period is of the order of 25 to 30 years and reasons are adduced to indicate this is very unlikely. These numbers are not greatly increased if the ban was poorly observed. This method of analysis may be applicable to other situations where a cause that is limited in space and time is expected to have late effects.     

Multimodality in the individual size distributions of bird communities

Aim Body size often plays a significant role in community assembly through its impacts on the life history and ecological attributes of species. Insight into the importance of size in structuring communities can be gained by examining the distribution of sizes of individuals [i.e. the individual size distribution (ISD) or size spectrum] in a community. ISDs have been studied extensively in aquatic and tree communities, but have received little attention in terrestrial animal communities. Here, we conduct the first macroecological analysis of ISDs in terrestrial animal communities to determine whether they show broad‐scale consistency in shape. Location North America, north of Mexico. Methods Using likelihood‐based methods and Gaussian mixture modelling, coupled with data from the Breeding Bird Survey and Christmas Bird Count, we determine whether the ISDs for thousands of breeding and wintering North American bird communities are: (1) monotonically decreasing, (2) unimodal or (3) multimodal. Results We find that avian ISDs are consistently multimodal, with most characterized by more than five modes in both breeding and wintering communities from local to continental scales. In addition, the positions of these modes along the size axis are remarkably consistent. Main conclusions The striking consistency in the ISD within bird communities, as with tree and aquatic communities, indicates that the ISD is an important and informative characterization of resource utilization within an ecological assemblage. The differences in shape of the ISD among these groups also suggest that differences in body size‐related constraints affect interactions within a group and with the environment. Our results confirm that avian assemblages do exhibit structure along the body size axis, and therefore it will be fruitful to explore this pattern in greater detail.     

Grazing rates of the freshwater ciliate Balanion planctonicum determined by flow cytometry

Feeding of Balanion planctonicum on the cryptomonad Rhodomonassp. was recorded in vivo at 2–3 min intervals by flowcytometry. Ingestion rates were 1.6–1.7 algal cells ciliate^–1h^–1. On average, 20–30 min elapsed between ingestionand egestion.     

食物浓度对角突臂尾轮虫种群增长、个体大小和卵大小的影响

以蛋白核小球藻为食物 ,应用群体累积培养法研究了食物浓度对角突臂尾轮虫种群增长、个体大小和卵大小等的影响 .结果表明 ,食物浓度对角突臂尾轮虫种群增长率、个体大小和卵大小均有极显著影响 .其中 ,轮虫种群增长率与食物浓度间呈曲线相关 ;当食物浓度为 8.2 4 5 3× 10 6cells·ml-1时 ,种群增长率达最大值 0 .6 0 85d-1;在所研究的食物浓度范围内 ,轮虫个体具有随食物浓度的增大而增大的趋势 ,轮虫卵体积在中等食物浓度范围 (6 .0× 10 6～ 9.0× 10 6cells·ml-1)时较大     

Seasonal variation of behavior and brain size in a freshwater fish

1. Teleost fishes occupy a range of ecosystem, and habitat types subject to large seasonal fluctuations. Temperate fishes, in particular, survive large seasonal shifts in temperature, light availability, and access to certain habitats. Mobile species such as lake trout (Salvelinus namaycush) can behaviorally respond to seasonal variation by shifting their habitat deeper and further offshore in response to warmer surface water temperatures during the summer. During cooler seasons, the use of more structurally complex nearshore zones by lake trout could increase cognitive demands and potentially result in a larger relative brain size during those periods. Yet, there is limited understanding of how such behavioral responses to a seasonally shifting environment might shape, or be shaped by, the nervous system.
2. Here, we quantified variation in relative brain size and the size of five externally visible brain regions in lake trout, across six consecutive seasons in two different lakes. Acoustic telemetry data from one of our study lakes were collected during the study period from a different subset of individuals and used to infer relationships between brain size and seasonal behaviors (habitat use and movement rate).
3. Our results indicated that lake trout relative brain size was larger in the fall and winter compared with the spring and summer in both lakes. Larger brains coincided with increased use of nearshore habitats and increased horizontal movement rates in the fall and winter based on acoustic telemetry. The telencephalon followed the same pattern as whole brain size, while the other brain regions (cerebellum, optic tectum, olfactory bulbs, and hypothalamus) were only smaller in the spring.
4. These findings provide evidence that flexibility in brain size could underpin shifts in behavior, which could potentially subserve functions associated with differential habitat use during cold and warm seasons and allow fish to succeed in seasonally variable environments.

     

Live sieving of freshwater zooplankton: a technique for monitoring community size structure

A simple method is described for a quick determination of thesize structure of zooplankton communities. This is based onsieving of a live sample, using one or two sieves of known meshsize, and determining the dry weight of the size fractions.Size separation by live sieving is validated statistically onDaphnia galeata, a common planktonic cladoceran, by comparingsize-sieved fractions against direct microscopic measurementsof individuals. A non-linear model was used for assessment ofsieving statistics. The sieving technique facilitates the gatheringof size-structured biomass data for zooplankton for routinemonitoring or long-term studies.     

Warming alters the size spectrum and shifts the distribution of biomass in freshwater ecosystems

Organism size is one of the key determinants of community structure, and its relationship with abundance can describe how biomass is partitioned among the biota within an ecosystem. An outdoor freshwater mesocosm experiment was used to determine how warming of～4 °C would affect the size, biomass and taxonomic structure of planktonic communities. Warming increased the steepness of the community size spectrum by increasing the prevalence of small organisms, primarily within the phytoplankton assemblage and it also reduced the mean and maximum size of phytoplankton by approximately one order of magnitude. The observed shifts in phytoplankton size structure were reflected in changes in phytoplankton community composition, though zooplankton taxonomic composition was unaffected by warming. Furthermore, warming reduced community biomass and total phytoplankton biomass, although zooplankton biomass was unaffected. This resulted in an increase in the zooplankton to phytoplankton biomass ratio in the warmed mesocosms, which could be explained by faster turnover within the phytoplankton assemblages. Overall, warming shifted the distribution of phytoplankton size towards smaller individuals with rapid turnover and low standing biomass, resulting in a reorganization of the biomass structure of the food webs. These results indicate future environmental warming may have profound effects on the structure and functioning of aquatic communities and ecosystems.     

Individual size variation reduces spatial variation in abundance of tree community assemblage,not of tree populations

Research on individual trait variation has gained much attention because of its implication for ecosystem functions and community ecology. The effect of individual variation on population and community abundance (number of individuals) variation remains scarcely tested. Using two established ecological scaling laws (Taylor's law and abundance–size relationship), we derived a new scaling relationship between the individual size variation and spatial variation of abundance. Tested against multi‐plot tree data from Diaoluo Mountain tropical forest in Hainan, China, the new scaling relationship showed that individual size variation reduced the spatial variation of community assemblage abundance, but not of taxon‐specific population abundance. The different responses of community and population to individual variation were reflected by the validity of the abundance–size relationship. We tested and confirmed this scaling framework using two measures of individual tree size: aboveground biomass and diameter at breast height. Using delta method and height‐diameter allometry, we derived the analytic relation of scaling exponents estimated under different individual size measures. In addition, we used multiple regression models to analyze the effect of taxon richness on the relationship between individual size variation and spatial variation of population or community abundance, for taxon‐specific and taxon‐mixed data, respectively. This work offers empirical evidence and a scaling framework for the negative effect of individual trait variation on spatial variation of plant community. It has implications for forest ecosystem and management where the role of individual variation in regulating population or community spatial variation is important but understudied.