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.     

Ultraviolet and temperature effects on planktonic rotifers and crustaceans in northern temperate lakes

1. Anthropogenic stressors such as climate change, ozone depletion and acidification may act in concert to alter ultraviolet (UV) light and temperature regimes in freshwater ecosystems. These physical and chemical changes will inevitably affect zooplankton community dynamics, but little is known about their relative effects on different species in natural communities. During spring, species that migrate to surface waters to take advantage of warmer temperatures may be especially vulnerable as UV levels can be high. 2. The objective of this study was to investigate the in situ effects of UV and temperature on a natural assemblage of planktonic rotifers and crustaceans during the spring. We performed in situ exposure experiments in two lakes with different surface temperatures. 3. Exposure to UV had a significant effect on the abundance and/or reproduction of four rotifers: Gastropus spp., Kellicottia bostonensis, Kellicottia longispina, Keratella spp.; two cladocerans: Holopedium gibberum, Daphnia catawba, and one copepod: Leptodiaptomus minutus. Incubation under cooler temperatures had a negative effect on K. longispina and H. gibberum. Temperature and UV had a significant interactive effect on abundance and/or reproduction of L. minutus and Ploesoma truncatum. Our results indicate that changes in underwater UV and temperature can significantly influence the composition of the zooplankton community and ultimately food web dynamics.     

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.     

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).     

A relationship between plant responses to cytokinins and cyanide-resistant respiration

Cytokinin bioassay material from six sources ( Amaranthus caudatus L.; Avena sativa L.; Cucumis sativus L.; Funaria hygrometrica Hedw.; Pisum sativum L., cv. Alaska and cv. Progress No. 9; Xanthium pensylvanicum Wallr.) was analyzed for cyanide-resistant oxygen consumption (alternative respiration) during the course of a response to benzyladenine (40 μ M ). In five of the six bioassay systems, the alternative pathway was found to be present but disengaged (ϱ=0) in the cytokinin-treated material while untreated controls continued to fully utilize the pathway (ϱ=1). The moss, Funaria hygrometrica , was the exception to this pattern, with the alternative pathway fully engaged in both treated and untreated protonemata throughout the period of cytokinin-induced bud formation. Respiration via the alternative pathway was not inhibited by benzyladenine in this latter tissue, although titrations with benzyladenine in carrot ( Daucus carota L.) cell suspensions mimicked those obtained using salicylhydroxamic acid, an inhibitor of the alternative pathway. The dwarf pea, Progress No. 9, showed no response to cytokinin application in terms of increased ethylene production, and was also found to lack any capacity for the alternative pathway. Taken together, these results point to a role for the alternative pathway in responses of at least some plant tissues to cytokinins.     

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.     

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.     

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.     

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 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 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.     

Movements in rotifers: correlations of ultrastructure and behavior

In this review, original observations on rotifer cilia and muscles are used to explain the mechanism of their movements. The following topics are discussed: (1) cilia and infraciliature of the cingulum, (2) muscle insertions into the infraciliature, (3) innervation of the muscles and non-innervation of the ciliated cells, (4) recent data on the location of gap junctions which link some muscles, (5) cilia and infraciliature of the cirri of the pseudotrochus of Brachionus calyciflorus, and the insertion of muscles onto their infraciliature, (6) the relation between muscles and integument in the foot of Philodina roseola, (7) the relation between muscles and integument in the joint present at the base of the tail of Trichocerca rattus, and (8) hypotheses on the first articulated (muscle-integument) movements which exist alongside ciliary motion in certain rotifers.Neuro-ethological summaries, based on data of the effectors and on observations on behavior and the sensitivity of rotifer sensory receptors (reviewed in Clément et al., 1983), are attempted. A more complete analysis is provided in the following instances: (1) swimming and the mechanism of turning, (2) retraction of the rotatory apparatus, (3) feeding behavior in Trichocerca rattus involving the succession swimming, crawling and nutrient intake.Other behavioral sequences, for which the ethological and ultrastructural data are incomplete, are presented and briefly discussed.Lastly, the argument is put forward that rotifers constitute an exceptional model for comparative, neuroethological studies which may enable us to better understand the mechanisms of evolution. Carrying out detailed observations, aimed at understanding how certain movements occur, should enable us to gain insights into the question of why they exist.     

Direct and acclimatory responses of dark respiration and translocation to temperature

BACKGROUND AND AIMS: Accounting for the acclimation of respiration of plants to temperature remains a major problem in analysis of carbon balances of plants and ecosystems. Translocation of carbohydrates out of leaves in the dark requires energy from respiration. In this study relationships between the responses of leaf respiration and translocation to temperature are examined. METHODS: Direct and acclimatory responses to temperature of respiration and translocation in the dark were investigated in mature leaves of soybean and amaranth. In some cases translocation from leaves was prevented by heat-girdling the phloem in the leaf petiole, or photosynthesis during the previous day was altered. KEY RESULTS: In both species short-term increases in temperature early in the dark period led to exponential increases in rates of respiration. However, respiration rates decreased toward the end of the dark period at higher temperatures. Stopping translocation largely prevented this decrease in respiration, suggesting that the decrease in respiration was due to low availability of substrates. In soybean, translocation also increased with temperature, and both respiration and translocation fully acclimated to temperature. In amaranth, translocation in the dark was independent of temperature, and respiration did not acclimate to temperature. Respiration and translocation rates both decreased with lower photosynthesis during the previous day in the two species. CONCLUSIONS: Substrate supply limited total night-time respiration in both species at high temperatures and following days with low photosynthesis. This resulted in an apparent acclimation of respiration to high temperatures within one night in both species. However, after long-term exposure to different temperatures there was no evidence that lack of substrates limited respiration in either species. In amaranth, respiration did not limit translocation rates over the temperature range of 20-35 degrees C.     

Zooplankton composition and abundance in two impoundments in Zimbabwe

The composition and abundance of the main zooplankton groups in Cleveland dam (less eutrophic) and Lake Chivero (more eutrophic) were studied. Samples were taken at two-month intervals. Rotifers were the most diverse zooplankton group in both reservoirs. Together with the copepods they formed the bulk of the zooplankton during summer. Cladocerans were particularly present in winter although still at relatively low densities.     

Fish and nutrient enrichment effects on rotifers in a Mediterranean shallow lake: a mesocosm experiment

A mesocosm experiment was conducted “in situ” in a Chara dominated shallow lake near Valencia (Spain) to study top–down and bottom–up effects on rotifers by means of nutrient and fish additions. Both processes were important in determining rotifer abundance, biomass and diversity. A total of 36 mesocoms were established with triplicate treatment combinations of three fish levels (from no fish to 45 individuals of Gambusia holbrooki males) and four nutrient enrichment levels (from no additions to 10 mg l⁻¹ nitrate-N and 1 mg l⁻¹ phosphate-P). The main effect was a notable increase of planktonic and plant associated rotifers densities with fish. Rotifers benefited from mosquitofish predation on microcrustaceans and chironomids. The results showed a marked negative relationship between rotifer and cyclopoid abundances, indicating the importance of the predatory pressure of cyclopoids on rotifers. Effects on rotifer diversity were also evident, in general rotifer diversity decreased with nutrients and increased with fish. The effects of nutrients analysed at species level showed two contrasting density responses: an increase or a decrease with nutrients, which levelled off at high nutrient concentrations. High-level nutrient additions (from 5 mg l⁻¹ nitrate-N and 0.5 mg l⁻¹ phosphate-P) induced a switch to a turbid state with macrophyte disappearance. Most planktonic rotifer species, as well as plant associated ones, diminished when the turbid state was well established, especially in the mesocosms without fish. In the turbid mesocosms, relative abundance of plant-associated rotifers (as a whole) was higher than that of planktonic rotifers. The changes in rotifer species composition after the switch from a clear to a turbid water state are also described. Species of the genus Anuraeopsis, Trichocerca and Hexarthra, dominant in the clear water state, practically disappeared in the turbid water state, in which Proalides tentaculatus and Lecane nana were the main species. Guest editors: S. S. S. Sarma, R. D. Gulati, R. L. Wallace, S. Nandini, H. J. Dumont & R. Rico-Martínez Advances in Rotifer Research     

Differential responses of auto‐ and heterotrophic soil respiration to water and nitrogen addition in a semiarid temperate steppe

Evaluating how autotrophic (SR_A), heterotrophic (SR_H) and total soil respiration (SR_TOT) respond differently to changes of environmental factors is critical to get an understanding of ecosystem carbon (C) cycling and its feedback processes to climate change. A field experiment was conducted to examine the responses of SR_A and SR_H to water and nitrogen (N) addition in a temperate steppe in northern China during two hydrologically contrasting growing seasons. Water addition stimulated SR_A and SR_H in both years, and their increases were significantly greater in a dry year (2007) than in a wet year (2006). N addition increased SR_A in 2006 but not in 2007, while it decreased SR_H in both years, leading to a positive response of SR_TOT in 2006 but a negative one in 2007. The different responses of SR_A and SR_H indicate that it will be uncertain to predict soil C storage if SR_TOT is used instead of SR_H to estimate variations in soil C storage. Overall, N addition is likely to enhance soil C storage, while the impacts of water addition are determined by its relative effects on carbon input (plant growth) and SR_H. Antecedent water conditions played an important role in controlling responses of SR_A, SR_H and the consequent SR_TOT to water and N addition. Our findings highlight the predominance of hydrological conditions in regulating the responses of C cycling to global change in the semiarid temperate steppe of northern China.     

Responses of rotifers and cladocerans to Microcystis aeruginosa (Cyanophyceae): A demographic study

The response of selected rotifers and cladocerans to Microcystis aeruginosa, offered as colonies and single cells, was compared to that on a diet of Chlorella vulgaris using the life table demography approach. The test zooplankton species were Simocephalus vetulus, Daphnia carinata, Moina macrocopa, Scapholeberis kingi, Ceriodaphnia cornuta, Brachionus calyciflorus and Hexarthra mira. To detect the development of resistance to toxins from Microcystis in zooplankton, in addition to the laboratory cultured strain of Ceriodaphnia cornuta, another strain of the same species was also used (designated as C. cornuta 2, this was collected from a pond containing Microcystis and cultured in the laboratory on Chlorella for a few weeks prior to experimentation). Experiments were conducted at 20°C and 30°C. Survivorship was high on Chlorella in most species but low on diets of Microcystis. Except for C. cornuta 2, S. kingi and S. vetulus, all other test species were adversely affected by Microcystis. The ability to utilise Microcystis improved at 30°C in M. macrocopa, D. carinata and H. mira. The longest mean lifespan was recorded for C. cornuta 2 (25.3 ± 4.86 d) and the lowest for B. calyciflorus (0.58 ± 0.05 d). The highest net reproductive rate was observed for C. cornuta 1 (44.9 ± 4.88) and the longest generation time of 26.6 ± 2.13 d for S. vetulus. Among the cladocerans that showed positive values of population growth rate (r), M. macrocopa had the highest of 0.96 ± 0.04 per day.     

Excretion and respiration rates of Neomysis integer (Mysidaceae): effects of temperature,sex and starvation

The combined effects of temperature, sex and length of pre-experimental starvation period on respiration, ammonia and inorganic phosphate excretion of the mysid shrimp Neomysis integer were studied in laboratory experiments. Of these variables, temperature had the strongest effect. A rise in experimental temperature from 6 to 16 °C increased the metabolic rates by a factor of 2 to 3.Weight-specific respiration rates of females were slightly lower than those of males. However, these differences could be attributed to differences in size. Sex did not significantly affect ammonia and inorganic phosphate excretion.A prolongation of the pre-experimental starvation period from 6 to 30 h reduced ammonia excretion of Neomys integer, but had no impact on oxygen consumption rates. Accordingly, the atomic O : N ratio increased in starved specimens. There were no discernables effects of the variables studied on atomic O : P and N : P ratios.