On choice of substrate and habitat in bdelzoid rotifers

Information on the distributions of 77 bdelloid rotifers from diverse waters in south and central Sweden was analyzed to reveal their relationships to substrate and habitat. Only two species were reported from plankton, both in low frequency. An artificial substrate, white cotton, was utilized only by few bdelloids, mainly by species with eyes. Only one species occurred at higher frequency on the saprobic substrate Sphaerotilus. Most bdelloids prefer environments rich in oxygen, but some species may be found in soft-bottom sediments. Several species dwell preferentially in diverse habitats of bogs. Some bdelloids have an exceptionally broad ecological range, but even for these is it possible to distinguish a pattern of preference and avoidance.     

On choice of substrate and habitat in brachionid rotifers

Information on the distribution of 28 rotifers of the family Brachionidae from diverse waters in south and central Sweden was analyzed to reveal their relationships to substrate and habitat. Some brachionids are preferably planktic, others periphytic and/or benthic. Some non-planktic habitats are utilized more than others, but there is no evidence of a chemical attraction from any substrate. Instead, some substrates seem to be avoided, possibly depending on a poorer flora of periphytic algae. Besides substrate type, the following factors are found to be important for creating separate ecological niches in the brachionid family: temperature, oxygen content, trophic degree, chemical environment, food choice and sensitivity to predation. It is possible to delineate separate ecological niches for all brachionid rotifers, implying that Hutchinson's ideas about the plankton paradox are contradicted. Some species are specialists, other are generalists, the latter being characterized by a great morphological variation. The species are adapted in different ways to their preferential habitats, as regards foot, egg-carrying, protrusions and other lorical structures etc. Longer spines, for instance, are generally found in more transparent water, being a supposed protection against visual predators.     

On relation to substrate in sessile rotifers

Information on the distribution of 45 sessile rotifers from diverse freshwaters in south and central Sweden was analyzed to reveal possible relationships to their substrates. Almost all of them showed an exclusively periphytic occurrence. The highest number of species was found on Utricularia, but otherwise it was not possible to correlate rotifer presence to any special macrophyte or category of plants (e.g., fine-leaved or floating-leaved species).     

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.     

The ecology of periphytic rotifers

The ecology of rotifer assemblages in the periphyton has received little attention relative to that of pelagic rotifers. This paper reviews the ecology of periphytic rotifers, with particular emphasis on the role of macrophytes in the structuring of rotifer assemblages spatially and temporally, and compares these aspects with the dynamics of better known pelagic rotifer communities. Littoral rotifer periphyton communities are typically diverse in lakes, and have composition dissimilar to that of the open water. In rivers, diversity and composition in the pelagic and littoral appear to be similar. Rotifers show preference for macrophyte species they associate with, probably through differences in physical structure or complexity, food concentration or composition, chemical factors, macrophyte age, and differences in the degree of protection from predation provided by macrophytes. These mechanisms are in general not well investigated in rotifers. Factors affecting the seasonal dynamics of periphytic communities appear to be similar to pelagic communities, with seasonal dynamics of substrates and disturbance by flooding or drying also being important.     

Bdelloid rotifers in aerophytic mosses: influence of habitat structure and habitat age on species composition

The rotifer species composition from two different moss species growing on roofs of different ages was investigated.     

On the ecology of Lecane (Rotifera)

A material consisting of 49 taxa of Lecane (Rotifera), from diverse waters in south and Central Sweden, was analyzed to reveal their relationships to substrate and habitat. Most species did not show any pronounced preference for any substrate, occurring in several diverse substrates, and especially in periphytic environments. Only a few species seemed to specialize in bog substrates. Some taxa were found, sometimes at a high frequency, on an artificial substrate, white cotton, indicating a high degree of mobility.     

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     

Diatoms and rotifers in cytological smears

We describe several uncommon contaminants presumably derived from the tap water used in the staining procedure of cytological specimens. We would like to draw attention to the occasional presence of diatoms and fragments of rotifers in cytological specimens. Whilst most of these entities are harmless curiosities, they may cause concern as to their nature and significance.     

Physiological responses to variable environments: storage and respiration in starving rotifers

1. Zooplankton exist in environments where food availability varies greatly over time, and success depends in part on the ability to store resources when food is abundant and to conserve them when food is scarce. This paper reports on interspecific differences in the size of stored reserves, and in respiration rate during food deprivation, of four species of planktonic rotifers.
2. The size of reserves varied from 42 to 71% of initial (well-fed) body mass. Interspecific differences in reserve size explained some of the previously observed differences in starvation time.
3. The initial response of respiration rate to food deprivation was quite variable between species. Brachionus calyciflorus was the only species to conserve energy by decreasing respiration rate in response to food deprivation. In contrast, the respiration rate of starved Asplanchna priodonta increased, while that of A. silvestrii and Synchaeta pectinata did not change, during food deprivation.
4. Theory predicts that temporal variation in resource level may facilitate the coexistence of competing species. This theory depends upon trade-offs between traits that confer competitive success in different environments. Although rotifers show a trade-off between competitive ability and maximum population growth rate, we found no evidence for trade-offs between either of those two traits and the size of reserves.     

Larval metamorphosis in sessile rotifers

Postnatal development of six species of sessile rotifers in the families Flosculariidae (Floscularia decora, Lacinularia flosculosa, Limnias ceratophylli, Ptygura crystallina) and Collothecidae (Collotheca ornata, Stephanoceros fimbriatus) was investigated by observing free-swimming and newly settled larvae until they metamorphosed into adults. Three variants of metamorphosis were observed. A hypothetical explanation of changes of the coronal construction of orders Gnesiotrocha and Pseudotrocha is considered.     

Rotifers in aging research: use of rotifers to test various theories of aging

Four theories of aging are discussed to examine how effectively they might explain the aging process in rotifers. One of the early theories, the rate of living theory of aging can perhaps be discounted. Although the theory predicts that increased biological energy expenditure, in the form of increased activity or reproduction, would lead to a shorter lifespan, these predictions are not born out by experimental evidence. At the whole animal level, a case can be made for a theory of programmed aging, where the end of reproduction signals the end of the lifespan. Support for this view comes from the observation that lifespan is positively correlated with reproductive parameters, that treatments that extend lifespan usually act to extend the reproductive period, and that the end of reproduction is associated with high mortality and senescent biochemical changes. Two molecular theories of aging are also discussed; the free radical theory of aging and the calcium theory of aging. These theories point to the fact that molecular damage accumulates and that calcium influx increases in the course of aging. When free radical buildup or calcium homeostasis is reduced, lifespan is extended. A molecular explanation of aging does not necessarily exclude the idea of programmed aging. It is probable that an eventual understanding of the aging process will rest on both a physiological and molecular basis.     

Parasites in rotifers from the Volga delta

Internal parasites were recorded in more than 20 species of rotifers from water bodies of the Volga delta. The most abundant species, Asplanchna priodonta Gosse and Brachionus calyciflorus Pallas, were infested every year. The infestation was usually recorded in May and June during the spring-summer maximum in abundance. B. calyciflorus was usually infested by Microsporidium asperospora (Fritsch, 1895), while A. priodonta was more often infested by Pythium sp. and bacteria. At times, the incidence of infestation was as high as 20–40%. The main developmental stages of some parasites were examined and photographed on living material.     

Oxygen consumption rate in rotifers

The oxygen consumption rate (OCR) is a cumulative index of metabolic losses during aerobic metabolism. The generalized relationship of oxygen consumption rate (R, n1 O₂ ind^–1 h^–1) and dry body mass (M, µg) for rotifers is described by the equation: R = 9.15M^0.716. The level of rotifer metabolism is slightly lower than that of multicellular poikilothermic animals. Differences of OCR values in ontogenesis are substantial. Embryos and senile individuals are characterized by minimal OCR values. The OCR of oviparous females in the beginning of reproduction exceeds 2–3 times OCR values of juveniles. Differences in oxygen consumption intensity (OCI) are not so essential. OCR depends on food concentration. An increase of food concentration from 1.4 to 7.0 µg dry mass m1^–1 resulted in Brachionus calyciflorus in an OCR escalation of 2.5 times at 30°C, and 0.5 times at 25°C. Maximal OCR values occur at food concentration close to the saturation concentration for population growth rate. An exponential equation is adequate to describe R-t dependence for animals, long-term adapted to different constant temperatures (2 < Q₁₀ < 3). Acclimation effects observed during sharp temperature changes are determined by peculiarities of compensation reactions in species and separate populations. The formation of a zone of relative temperature independence of OCR (Q¹⁰ 1) at fluctuating temperature is observed. It is necessary to study enzymatic activities parallel to OCR and OCI measurements.     

Some rotifers from Republic of Korea

The author gives account of rotifers found at ten locations in the Republic of Korea, and elaborates some detail of specimens encountered with remarks and drawings. Thirty-seven different rotifer species were found, mostly belonging to the Order Monogononta. Twenty-two are new to the species list compiled by Yamamoto (1953). Keratella hiemalis was found for the first time in Asia. To date, one-hundred and two species of rotifers have been found in Korea.     

A perspective on aging in rotifers

Most research on aging in rotifers has been performed with populations, not with individuals. As a consequence, the dependent variable in these studies is usually either mean lifespan or rate of survivorship. After a brief consideration of the literature published since the last major review (King, 1969), the results of a series of experiments are presented. Males and females of three genetically distinct clones of Brachionus plicatilis were used for a factorial life table analysis at three different temperatures. The results of these experiments indicate several potential problems in using populations to study the aging process of individuals. These problems derive from the fact that lifespan is only one component of fitness, and its relative duration may not reflect the evolutionary success of the clone. That is, lifespan is free to vary in response to both stochastic and deterministic events without significantly reducing fitness. Under these conditions, neither mean lifespan nor pattern of survivorship will provide meaningful data on the determinants of individual senescence.We gratefully acknowledge the aid and advice of William R. Rice in conduct of the regression analysis. This work was supported by grants from the National Science Foundation and National Institutes of Health to CEK.     

Recipes for successful anhydrobiosis in bdelloid rotifers

We tested the effect of several environmental variables on the ability of three bdelloid rotifers (Macrotrachela quadricornifera, Philodina roseola and Adineta oculata) to recover from the anhydrobiotic state. The variables we examined were (1) rate of water evaporation, (2) relative humidity during anhydrobiosis, (3) temperature during anhydrobiosis, (4) duration of anhydrobiosis, and (5) rehydration rate. Our results indicate that bdelloids can regulate to some degree net water balance during onset and termination of anhydrobiosis.     

Abundance and diversity of planktonic rotifers in the Po River

Zooplankton samples from the middle reach of the Po River were collected daily from 27 July to 24 August 1988 from a station located near Viadana. Changes in the biocoenosis structure were analyzed in relation to variations in flow rate. Rotifers accounted for more than 99% of the total zooplankton (protozoans excluded) in every sample. The dominant species were Brachionus calyciflorus, Brachionus bennini, Brachionus budapestinensis and Epiphanes macrourus. Under scanty flow conditions, the taxocoenosis showed marked stability. An increase in flow rate acts as a disturbance factor leading to a significant decrease in both total density and dominance.     

Sexual communication in copepods and rotifers

The problem of locating mates and identifying them as conspecifics is similar for Copepoda, Cladocera, and Rotifera since they are all relatively small animals moving in a large volume of water. Chemoreception is a potentially effective means of identifying mates in aquatic environments. In zooplankton, mate recognition systems based on chemoreception have evolved which can distinguish conspecifics from other species and can discriminate males from females. The evidence for the role of chemical signals in copepod mating is indirect, based on observations of mating behavior. The small size and limited metabolic capability of zooplankton, and high diffusion rates at 1–10 mm spatial scales, restrict the volume through which chemical signals can be effectively transmitted. An alternative to using diffusible molecules for sexual communication is to bind signal molecules to cell surfaces, allowing energetically costly molecules like proteins to serve as signals without their loss through diffusion. Contact chemoreception has been described in copepod and rotifer mating and perhaps represents a general solution to the problem of chemical communication by small zooplankters. The types of signals used, their mechanisms of transmission and reception, and their role in maintaining reproductive isolation among species has yet to be characterized for any aquatic invertebrate. In this review, I compare the methods used by copepods and rotifers for mate seeking and recognition, describe the behavioral evidence supporting the existence of chemical cues, and examine experiments describing the biochemical characteristics of the signal molecules. In copepods, male mate seeking behavior occurs without previous female contact, suggesting the reception of a diffusible signal. The signal molecule is small and lacks species specificity in the species investigated. Male rotifers do not respond to females from a distance. Mates are located by random male swimming and contact chemoreception of a species-specific signal. Mate recognition in both copepods and rotifers is based on contact chemoreception of a species-specific signal. The pheromones responsible are not known for copepods, but surface glycoproteins with pheromonal activity have been identified in rotifers. The structure of the rotifer sex pheromone has been probed by selective enzymatic degradation and lectin binding, electrophoretic characterization, and attachment to agarose beads to assess its biological activity. Glycoproteins play a key role in the sexual communication of some algal and ciliate species and have well characterized roles in cellular recognition phenomena like sperm-egg binding. The significance of these studies lies in their contribution to our understanding of zooplankton reproductive biology, the chemical ecology of male-female communication, the molecular basis of chemoreception in the aquatic environment, and the evolution of pre-mating reproductive isolating mechanisms in zooplankton.     

生境破碎化对植物-昆虫及昆虫之间相互关系的影响

生境破碎化对生物多样性和生态系统功能影响是当前国内外生态学家研究的热点问题之一。文章针对生境破碎化的内涵、量度指标进行介绍,着重分析生境破碎化对植物-昆虫关系的影响,包括植物与植食性昆虫的关系、植物与传粉昆虫的关系、种子与种子捕食者的关系,植物及其分解者的关系,还分析生境破碎化对昆虫-昆虫关系的影响,包括昆虫及其拟寄生物的关系、捕食者与猎物的关系。通过对上述方面的阐述,旨在更好地理解生境破碎化对动植物群落相互关系产生的深刻影响,并提出今后研究中应注意的问题和研究热点。