Desiccation survival of the eggs of the rotifer Adleta vaga (Davis, 1873)

Age at the time of drying affects the desiccation survival of the embryos of the bdelloid rotifer Adineta vaga. Although the embryos younger than 24 hours do not survive desiccation, up to 71% and 6% of the embryos at least 45 hours old survive desiccation for 2 and 10 days, respectively.     

Contribution to the study of african rotifers: rotifers from Mali

In samples collected from different parts of the Republic of Mali (W-Africa), ninety-two taxa of rotifers were identified. Some were present in different forms; 56% were cosmopolitan, 19% thermophilous with a wide distribution, 20% tropicopolitan and 5% cold-stenothermous. These latter species seem to be relicts of palaeoclimatic conditions in Africa.     

Contributions to the knowledge of African Rotifers I. Rotifers from Senegal

24 plankton samples, collected in different parts of the Republic of Senegal (W. Africa) were examined for their rotifer content. Seventy taxa were identified to species level, some of which were present in different forms. Thirty three taxa and forms are new to Senegal, three species are new to Africa. Attention is paid to a cruciform population of Asplanchnella sieboldi and to a Brachionus quadridentatus population of very small dimensions. Two new taxa are described: Brachionus cf. angularis and Brachionus bidentatus senegalensis Koste & De Ridder.     

Morphological response of a bdelloid rotifer to desiccation

We desiccated bdelloid rotifers (Macrotrachela quadricornifera), submitting the animals to four desiccation procedures (protocols A, B, C, D) that differed in the rate of water evaporation, in the time of desiccation, and in the substrates provided. We observed external morphological changes of the rotifer bodies during drying with scanning electron microscopy and, in parallel, assessed rates of recovery after a 7-day period of dormancy. Two protocols produced disorganized morphologies of the anhydrobiotic animals, with no (A) or very poor (B) recovery. Protocols C and D gave rather high rates of recovery and dry rotifers appeared unaltered and well organized. The different protocols affected rotifer morphology during the 7-day anhydrobiosis and rates of recovery after the 7-day anhydrobiosis; high recovery rates corresponded to well-organized morphologies of anhydrobiotic bdelloids, suggesting that a proper contraction of the body into a tun shape and probably a rigorous packing of internal structures are necessary for survival after anhydrobiosis. These features are affected by the time between water shortage and full desiccation, but also by the surrounding relative humidity and by the nature of the substrate. Possible adaptations of anhydrobiotic rotifers are discussed.     

蛭态轮虫及研究动态

蛭态轮虫是国际无脊椎动物学研究领域关注的热点话题之一。通过对国内外文献的调研,本文重点介绍了蛭态轮虫的形态结构和生物学特征;归纳阐述了蛭态轮虫在形态学、生物多样性与动物地理学、孤雌生殖和低湿休眠发生机理、横向基因转移等领域的最新研究进展。已有的蛭态轮虫研究成果不仅对经典遗传学、生物化学和生理学等的传统理论提出了新的挑战,同时在"转基因"生物安全、新药研究和基因治疗方面也具一定的参考意义;国际上对蛭态轮虫新种的报道和区系的研究成果对丰富全球无脊椎动物多样性以及完善动物地理分布模式都有重要的参考价值。基于该类轮虫研究的现状及其在生物学上意义,建议国内应加强蛭态轮虫的研究。     

Problems in taxonomy of rotifers,exemplified by the Filinia longiseta - terminalis complex

The validity of taxonomical categories in parthenogenic groups is discussed. Special problems of rotifer taxonomy are caused by: facultative or obligatory parthenogenic reproduction, high morphological and genetic variability and paucity of morphological characteristics.Examples of these problems are provided by the Filinia terminalis-longiseta group. The different ecological properties of various populations belonging to this group are emphasized. Suggestions concerning the creation of new taxa are made; in particular, the importance of using ecological data is stressed.Biological Station of the Austrian Academy of Science     

Historical Ecology, Responses to Current Ecological Changes and Conservation of Australian Spiders

In response to geohistorical events from the Mesozoic through the Tertiary with contraction of mesic forest to southwestern and eastern montane and coastal regions, and expansion of woodlands and xeric shrublands, nobreak Australian spiders today comprise relict families and genera (confined to Gondwanan habitats and refuges) along with later evolved representatives which have adapted to changing environments. Tropical relicts also persist in refugia in the arid interior while some spiders (both mygalomorphs and araneomorphs) have adapted to arid conditions, mainly through specialized behaviours. Although fire has become increasingly a phenomenon of the Australian environment it is doubtful whether any spiders are adapted to fire per se. European settlement has impacted differentially on relictual and later evolved representatives; a few species, including the funnelweb (Atrax robustus) and redback spider (Latrodectus hasselti) have benefited through enhanced habitat opportunities and some species of Badumna and other genera have become synanthropic. It is suggested that conservation strategies need to consider the ecoevolutionary history of particular spiders and their natural vulnerability or resilience to environmental factors.     

Chironomids from Southern Alpine Running Waters: Ecology, Biogeography*

The chironomid fauna living in running waters in the Southern Alps was investigated from an ecological and biogeographical point of view: 202 species were identified (not including terrestrial species). It must be emphasised that species identification is tentative within some genera, especially those awaiting revision (e.g., Boreoheptagyia, Chaetocladius). Although much taxonomic work was done in the past on the chironomid Alpine fauna, there are still many unsolved problems. Most of the species found are widespread in the Palearctic Region, with no evidence of bio-geographical barriers separating different Alpine sectors. Really a relatively high number of species reported from the northern and western side (France, Switzerland, Austria) of the Alps was not captured on the southern side (Italy), whereas most species found on the southern side are also present on the northern one. Very few species are reported from southern side only. Lack of sampling, imperfect taxonomic knowledge and different environmental conditions between the northern and southern sides may be responsible of this result. A comparison of the fauna of the southern Alps with the fauna of the Apennines suggests that the differences are probably more related to ecological conditions (lack of glaciers in the Apennines) than to biogeographical barriers. Different chironomid assemblages colonise manifold habitat types: strict cold-stenothermal species tolerating high current velocity (e.g., Diamesa latitarsis – steinboecki group) are almost the sole inhabitants of kryal biotopes, while other cold-stenothermal species are restricted to cold springs (Diamesa dampfi, D. incallida, Tokunagaia rectangularis, T. tonollii), there are also species characteristic of hygropetric habitats (Syndiamesa edwardsi, S. nigra) or restricted to lacustrine habitats (Corynoneura lacustris, Paratanytarsus austriacus). It must be emphasised that different responses to environmental factors can be observed between species belonging to the same genus (e.g., Diamesa, Eukiefferiella, Orthocladius , Paratrichocladius), so species identification is really needed for a good ecological work. Water temperature, current velocity, substrate type are the most critical factors, sometime chironomid species appear to be rather opportunistic and their presence or absence cannot be clearly related to a well defined range of values of environmental variables: be it a lack of knowledge or a real datum will be the task of future studies. The waters of the Alps are still relatively unpolluted, but hydraulic stress due to river damming and canalization is a serious problem for macrofauna conservation, and as the glaciers retreat, the species confined to the glacial snouts are at risk of extinction, some of them possibly even before their existence be discovered. *The complete database with detailed taxonomical, ecological and biogeographical information can be obtained by the senior author to request (e-mail: bruno.rossaro@unimi.it). A table with species response to environmental variables is also available at the web site: http://users.unimi.it/~roma1999/rossaro.html, downloading file CHIRDB.)     

Why is sex so rare in Lecane inermis (Rotifera: Monogononta) in wastewater treatment plants?

The monogonont rotifer Lecane inermis is commonly known as a facultative parthenogen. Unexpectedly, among numerous lineages we isolated from wastewater treatment plants (WWTP), only one was capable of sexual reproduction. We investigated why sex was so rare among L. inermis in WWTP. The reproductive modes of lineages derived from the sexual lineage were examined. Among all lineages, the fraction of those reproducing only asexually for 14 d was 0.39. In the subsequent round, the fraction of asexual lineages reached 0.61. The population growth rate of the parthenogenetic lineages was significantly higher than that of the sexual lineages. We simulated the fate of rotifer populations in WWTP by removing 10% of the experimental cultures each day. After 10 d of these conditions, the mean number of females was greater in parthenogenetic than in sexual lineages. After 20 d, only solitary dormant eggs remained in the sexual lineages. It therefore appears that the loss of sex may be attributed to the specific conditions of the WWTP. When there is no risk of desiccation and no need for dormancy, the fast‐growing parthenogens outcompete lineages investing in costly sex. Furthermore, even if some resting eggs were deposited, they would be washed out from the system with the excess sludge.     

Stress during dormancy: effect on recovery rates and life-history traits of anhydrobiotic animals

To test the influence of storage conditions on recovery and life-history traits of dormant animals we subjected cohorts of a bdelloid rotifer (Macrotrachela quadricornifera) and a nematode (Panagrolaimus rigidus) to three different conditions during a 26-d anhydrobiosis period. These conditions were (1) standard conditions in our laboratory (AC), (2) a flight to the U.S.A. and storage there (KSC), and (3) a flight to the U.S.A. followed by a flight on a Shuttle-to-Mir mission (Shuttle). Another cohort (HC) was maintained under hydrated conditions and served as reference for life-history traits of the desiccated samples. The recovery after dormancy and the residual life-history traits of the different cohorts were compared. Results indicate that (a) during dormancy the animals were indifferent to the test conditions, as evidenced from both recovery capacity and life history performances, (b) the anhydrobiotic period affected the experimental species differently. At recovery both animals resumed their life cycle, but while the rotifer appeared indifferent to the time spent in desiccation, the nematode modified its life history according to the duration of anhydrobiosis. Third, (c) induction of anhydrobiosis can act as a switching mechanism for animals capable of desiccation. Anhydrobiosis probably represents a suitable method to preserve organisms during stressful conditions allowing them to return to a normal life when convenient.     

The approach to equilibrium of multilocus genotype diversity under clonal selection and cyclical parthenogenesis

Sexual generations in cyclical parthenogens are typically separated by multiple generations of clonal reproduction. In contrast to sexual reproduction, during parthenogenesis the genome of the parent is passed on to the offspring as a unit. The absence of recombination during parthenogenesis leads to differences in the action of natural selection in the two reproductive phases. In addition, since recombination is a sampling process, random genetic drift is potentially more important in sexual reproduction than in parthenogenesis. A recent development in the study of rotifer population genetics is the use of microsatellites to characterize natural populations. Microsatellites are selectively neutral, show patterns of Mendelian inheritance and tend to be much more variable than allozymes. An advantage over allozymes is that microsatellite DNA can be cloned with PCR and thus multiple loci can be assayed from a single individual. We use a new computer model in this paper to investigate the response of selectively active and selectively neutral genes to evolutionary forces during cyclical parthenogenesis. Selectively active alleles may respond differently to selection in the parthenogenetic and sexual phases of cyclical parthenogenesis. Even when strong clonal selection is acting on loci associated with adaptation, the view that emerges with microsatellites may be one of Hardy-Weinberg and linkage equilibrium. Thus studies using selectively neutral loci may fail to detect clonal selection even when it is an important feature of the rotifer population's adaptive structure.     

Complexity and Verisimilitude: Realism for Ecology

When data are limited, simple models of complex ecological systems tend to wind up closer to the truth than more complex models of the same systems. This greater proximity to the truth, or verisimilitude, leads to greater predictive success. When more data are available, the advantage of simplicity decreases, and more complex models may gain the upper hand. In ecology, holistic models are usually simpler than reductionistic models. Thus, when data are limited, holistic models have an advantage over reductionistic models, with respect to verisimilitude and predictive success. I illustrate these points with models designed to explain and predict the numbers of species on islands.     

Relation to habitat in rotifers

Rotifera should be especially suited for an analysis of habitat relations because this group contains such a high number of species, inhabiting diverse environments. Furthermore, rotifers are to a large extent cosmopolitan, implying that ecological barriers, rather than geographical, are decisive of their distribution. In this review a short characterization of the rotifer fauna in different habitats is given, whereby macroenvironments and microenvironments are reported separately. The macroenvironments are classified as follows: harmonious lakes and ponds, arctic and antarctic waters, hot springs, hypertrophic-saprobic environments, mires, strongly acidic waters, saline waters, temporary water bodies, subterranean waters, running waters, oceans, terrestrial environments. The following microenvironments are distinguished: macrophytes (housing periphytic rotifers), open water (with planktic forms), minerogenous sediments (with psammon and hyporheos), organogenous sediments, other organisms (i.e. parasites and epizoans).Many rotifers are more or less euryecious, while relatively few are strongly restricted in their choice of habitat. In extreme environments a low number of species is found, but often a high number of individuals within these species. These rotifers are usually primary consumers, and for natural reasons extreme environments are characterized by a low number of trophic levels.In environments with a high species number the separate species differ very much in their morphology, making it difficult to find common traits which may be interpreted as adaptations to the respective habitats. The most apparent adaptations ought to be found among the planktic rotifers, and these adaptations seem to constitute largely a protection against predators. Rotifers in extreme environments are usually not very apart in a morphological or taxonomical respect, with their most close relatives living in normal habitats and sometimes euryecious (an apparent exception from this rule is formed by the class Seisonidea). Adaptations to deviating chemical and physical environments may develop relatively rapidly (seen from a geological perspective), while the more fundamental changes (occurring during a longer period of time) seem to be a response to biotic factors (e.g., the development of different types of trophi for facilitating food collection).     

空间分子生态学——分子生态学与空间生态学相结合的新领域

分子标记、基因流、种群空间动态是当前生命科学研究中的热点领域。RFLPs、RAPDs、微卫星等新的分子标记的不断涌现,促进了这些领域的飞速发展。对种群空间动态研究中的等级岛屿模型、距离隔离模型、脚踏石模型、集合种群模型等方面许多令人瞩目的进展做了介绍。同时还介绍了遗传距离、基因流及其测度、基因突变模型、3S技术、空间精确性种群模型和基因频率的空间自相关等热点领域。最后,就空间分子生态学存在的问题与前景进行了讨论,指出了空间分子生态学可能的发展方向。     

Winter and spring macroinvertebrate drift in an outpocketing of the lower Mississippi River,Louisiana (USA)

145 rotifer species were previously known from Sudan, mostly from the Nile valley and the NE of the country. In the present paper planktonic, periphytic and benthic samples from the Western provinces of Darfur and Kordofan are examined. They contained 77 species, in one or different forms, of which 67% were cosmopolitan, 15% thermophilic, 14% tropicopolitan, and 4% temperate-boreal. No new taxa were found, but 23 species and one subspecies are new to Sudan, while one is new to Africa.     

Anhydrobiosis of <Emphasis Type="Italic">Adineta ricciae:</Emphasis> Costs and Benefits

To study the effect of anhydrobiosis on the rotifer life cycle, we dried a bdelloid species, Adineta ricciae, and determined the life-history traits of 1) the rehydrated animals and 2) the offspring produced after a period of dormancy. In the first experiment, a cohort was dried when 8-days-old, kept dry for 7 days and then rehydrated. Recovery was about 75%. The recovered rotifers had similar longevity and significantly higher fecundity than the hydrated controls. The time spent dry was completely disregarded by the anhydrobiotic rotifers, as predicted by the ‘Sleeping Beauty’ model. In the second experiment, we recorded the life-history traits of the orthoclones produced by recovered mothers aged 11 days, and 18 days. These orthoclones were coupled to controls that had been established from hydrated mothers aged 11 days and 18 days. The orthoclones produced after dormancy had significantly higher fecundity and longevity than the controls of same maternal age. Maternal age had a marked effect on the life-history traits of the orthoclones of both lines, causing the same loss of fitness in both.     

Comparison of five strains of a parthenogenetic species,Macrotrachela quadricornifera (Rotifera,Bdelloidea)

Five clonal populations belonging to the parthenogenetic species Macrotrachela quadricornifera were analyzed electrophoretically. The populations stemmed from samples collected from different environments paired geographically: water bodies (C, P, F) and terrestrial mosses (Ml, M2). The six enzymes considered were: leucine amino peptidase (LAP), arginine phosphokinase (APK), glucose phosphate isomerase (PGI), and esterases (EST) and malic enzyme (ME). The results are interpreted under the assumption that bdelloid rotifers have a diploid chromosome set. A genetic interpretation of the banding patterns was attempted. A relatively high degree of enzymatic polymorphism among the strains was found. Only 27% of alleles are shared by all strains. The relationship among the strains was examined by single-link cluster analysis: we can distinguish moss and water populations, regardless of their geographic origins, and in accord with the results of a life-history traits study on the same strains. The differences in life-history parameters among the five strains may be due not only to phenotypic plasticity induced by the environment, but to real genetic divergence.     

A review of the rotifer fauna of the Sudan

A collection of rotifers contained in samples from the Blue, White and joint Niles in the Sudan, the Red Sea Hills, and Jebel Marra mountains is studied, and the previous literature on the rotifera of Sudan is reviewed. A total of 145 rotifer taxa are now known from this country. Ecological and distributional notes on selected species are added. Besides cosmopolitan, pantropical, and tropical species, a small but significant fraction of the fauna is of northern origin, possibly reflecting climatic conditions of the late-Pleistocene.     

生态是什么—对生态的实质及其表现形式的初步思索

目前,好多生态学术语在社会各界广泛使用,足见生态学知识的普及,但是,却存在许多概念混淆不清而乱用的现象。在我国生态学家马世骏先生建议下,发表周小平同志这篇文章,目的是为了引起对一些生态学术语概念的讨论,澄清一些概念而便于生态学知识更深入地普及。