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This research has been carried out to determine diversity and abundance of Rotifera in Kadıköy Reservoir. For this purpose, Rotifera and water samples were collected monthly from March 2010 to February 2011 at three different stations in the reservoir. A total of 33 species from Rotifera were determined in the qualitative evaluation of samples taken from the reservoir. The quantitative evaluation of the Rotifera samples revealed presence of an average of 70 472 ind m-3 in Kadıköy Reservoir. The maximum number of Rotifera were recorded at 1st station (81 819 ind m-3); in May (100 901 ind m-3) and in spring season (83 458 ind m-3). Asplanchna priodonta, Brachionus angularis, Filinia terminalis and Keratella cochlearis sampling in all months were found to be the most common species during the study. When we evaluate the species identified in the reservoir, the distribution of the individuals that make up the Rotifera fauna and physical-chemical parameters as a whole, it has been concluded that Kadıköy Reservoir is in meso-eutrophic character in terms of Rotifera. [ABSTRACT FROM AUTHOR]

While induced defense of aquatic organisms against predators has been considerably studied by both laboratory and field research, our understanding is still limited about, for example, whether induced defense is variable between microhabitats within the same lake and how multiple predators influence induced defense in the natural environment. Here, we examined whether a rotifer species, Brachionus calyciflorus showed a different development degree of induced defenses against its predator Asplanchna and cyclopoid copepods between the microhabitats of a macrophyte bed consisting of Trapa species and open water. B. calyciflorus was more abundant and had larger posterolateral spines as a defensive trait in open water than in the Trapa bed. Asplanchna was more abundant in open water than in the Trapa bed, whereas cyclopoids were more abundant in the Trapa bed. Both of the predators significantly affected the development of the defense trait. The effect of Asplanchna on the defense trait was positive, whereas the effect of cyclopoids was negative. Thus, a spatial difference in the development degree of induced defense between the microhabitats occurred as the dense Trapa bed influenced the abundance of the two predators. The results also suggest that the induced defense of B. calyciflorus was effective in reducing the predation pressure from Asplanchna while B. calyciflorus was not able to avoid predation by cyclopoids in the Trapa bed. [ABSTRACT FROM AUTHOR]

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Two morphologically distinct Brachionus calyciflorus hatched from Lake Littra sediment: a typical B. calyciflorus Pallas and B. (calyciflorus) "Darling", a reproductively isolated, globular taxon without posteromedian spines. The Darling taxon is well defended against Asplanchna by its large size (adult lorica length ≥ 310 μm) and short (~50 μm) Asplanchna-induced posterior spines that protect small, vulnerable neonates. The typical B. calyciflorus is smaller (adult lorica length 169-195 μm) and is a mixture of interbreeding clones with or without constitutive posterolateral spines. In one of the former clones, adult posterolateral spine length increased significantly with maternal age, from ~62 to 78 μm. Asplanchna induced increased lorica length and pronounced spine development in all clones and its effect on females with constitutive posterolateral spines was additive. With Asplanchna, posterolateral spine length was 159 μm for a clone without constitutive posterolateral spines and 207 μm in a clone with 74μm-long constitutive posterolateral spines. Coexistence of clones with and without constitutive posterolateral spines suggests a trade-off between the benefit of long defensive spines and some cost to spine development. It likely is maintained by fluctuating directional selection in response to changing Asplanchna abundance and by a sediment bank of diapausing eggs produced by sexual reproduction. [ABSTRACT FROM AUTHOR]

We conducted life table experiments on the freshwater rotifer Asplanchna brightwellii to analyze its demography when fed with prey items from several taxonomic groups (cladocerans, protozoans, and rotifers) and under two different temperature regimes (20 and 25°C); the aim of the study was to determine the preferred prey for A. brightwellii in terms of fitness (evaluated as reproductive success) among five cladoceran, protozoan, and rotifer preys, and to test which temperature (20 or 25°C) is better for life table parameters of Asplanchna. Our analysis identified Brachionus calyciflorus as the preferred prey for A. brightwellii based on life table statistics, ingestion rate and electivity indices. The greatest values for net reproductive rate and intrinsic growth rate were achieved when A. brightwellii was fed B. calyciflorus. Greater reproductive values ( R and r) were found at 25°C than at 20°C for A. brightwellii across the five prey species. We found significant differences in the ingestion rate and electivity index among zooplanktonic and benthic preys. The influence of temperature, the cost of predation, and how prey selection by A. brightwellii is influenced by: biomass, size, and swimming speed; they are discussed hoping to gain a better understanding of trophic transfers in zooplankton communities. [ABSTRACT FROM AUTHOR]

ABSTRACT Pronounced non-genetic polymorphisms, or polyphenisms, occur in some monogonont rotifers reproducing by diploid, female parthenogenesis. In many brachionids, there is great variation in spine length. In trimorphic species of Asplanchna, females can vary in size and shape, from a small saccate morph to giant cruciform and campanulate morphs. In species that also reproduce sexually, diploid eggs can develop into two types of females. Amictic females produce diploid eggs that develop parthenogenetically into females; mictic females produce haploid eggs that develop parthenogenetically into males or, if fertilized, into resting eggs. In a species of Synchaeta, amictic females produce diploid eggs that can be either thin-shelled and subitaneous or thicker-shelled and diapausing. In all cases, morph determination occurs during the oogenesis or embryological development of diploid eggs in the maternal body cavity. For the first time, these polymorphisms are reviewed together and compared regarding a number of features associated with transitions from default to induced morphs: ( i) type of variation (morphological, physiological, or both; continuous or discrete); ( ii) inducing signal (environmental, endogenous, or both); ( iii) universality of response to that signal (all or only some individuals); ( iv) fitness cost; ( v) reversibility; and ( vi) ecological significance. Most of the polymorphisms fall into two major categories regarding these features. Transitions suitable for predictable environments involve: universal responses to environmental signals; continuous morphological variation; low reproductive cost; rapid reversibility; and adaptations for defence, hydrodynamics or prey ingestion. Transitions suitable for unpredictable environments are bet-hedging strategies and usually involve: partial (stochastic) responses to environmental or endogenous signals; discontinuous physiological variation; initiation of diapause, and thus high reproductive cost and slow reversibility. Two cases of morphological variation also involve the simultaneous production of different morphs and likely are adaptations for an uncertain future: continuous spine-length variation due to maternal age in Brachionus calyciflorus, and production of discrete cruciform and campanulate females in Asplanchna spp. [ABSTRACT FROM AUTHOR]

We tested the hypothesis that the spatial distribution and diet composition of Asplanchna species might be affected by the presence of aquatic macrophytes in 33 wetlands in South Korea. We estimated the densities of Asplanchna and other rotifer and crustacean, together with environmental parameters, in both vegetated and open water zones, from May to June 2011. In the present study, two species of Asplanchna, A. priodonta and A. herrickii, were observed and significantly more abundant in open water zones lacking macrophytes. In particular, the density of A. priodonta was higher than that of A. herrickii, and the density of A. priodonta was strongly positively correlated with the area of open water. In addition, gut content analysis was used to determine their dietary preferences, with the finding that there was apparent differentiation in food source utilisation between the two Asplanchna species; A. priodonta consumed some protozoa, phytoplankton, and exclusively pelagic rotifer, while A. herrickii consumed primarily Euglena. In particular, Keratella and Polyarthra were most commonly consumed by A. priodonta in open water. Macrophytes represent a suitable habitat for epiphytic rotifer but not for pelagic rotifer; this characteristic drives pelagic rotifer such as Asplanchna towards open water and may be responsible for the significant negative correlation that we observed between macrophyte and Asplanchna densities.

1. Inducible defences reduce the probability of prey being killed by their predators. However, these defences are often accompanied by costs. Most studies associated with aquatic communities have focused on the effects of inducible defences on the growth and reproduction of prey species, while their effects on sex investment remain unclear. 2. Brachionus calyciflorus is a common freshwater rotifer that develops a defensive morphology in response to the kairomones released by the predatory rotifer Asplanchna. Some studies have reported that no detectable cost, such as decreased reproductive output, is associated with the spines in B. calyciflorus. Thus, we studied the sex investment (i.e. production of mictic offspring and resting eggs) of B. calyciflorus populations at three Asplanchna kairomone concentrations (0, 10, and 100 Asplanchna L-1) and two food levels (1 and 12 mg C L-1) to evaluate the sex cost of inducible defences. We also evaluated the crowding threshold required to trigger sex investment (i.e. lowest population density at which mictic female is produced) in B. calyciflorus under different kairomone and food treatments. 3. Results showed that (i) the B. calyciflorus population exposed to kairomones produced offspring with elongated posterolateral spines; (ii) the production of mictic offspring and resting eggs decreased in the B. calyciflorus population exposed to kairomones, suggesting an investment trade-off exists between inducible defence and sex investment; (iii) the decrease in sex investment was higher at the high kairomone concentration than at the low kairomone concentration; (iv) the decrease of sex investment was higher at the low food level than at the high food level; and (v) the crowding threshold of the B. calyciflorus population increased upon exposure to kairomones. 4. The results of this study suggest that the decreased sex investment in defended B. calyciflorus is a form of defence cost. Our findings add to our understanding of the effect of predation on the ecology and evolution of phenotypic plasticity in rotifers. [ABSTRACT FROM AUTHOR]

Maternal effects on the induction of defensive morphology are regarded as an adaptive strategy. For instance, a female can transmit environmental conditions related to predation risk to offspring of the same generation or succeeding generations. However, studies have presented limited information regarding such an adaptive maternal effect on monogonont rotifers. In the present study, the maternal effects on the spine development of rotifers were evaluated using Brachionus calyciflorus- Asplanchna models. Asplanchna can release soluble kairomones into the environments, thereby inducing B. calyciflorus to form defensive morphs (e.g., elongated posterolateral spines). Our empirical data supported the hypothesis that an amictic Brachionus-experienced Asplanchna kairomones could produce offspring with longer posterolateral spine in the current or succeeding generation than those of a non-experienced amictic female. On the basis of our data, we speculated that the maternal effect of B. calyciflorus may involve the transfer and dilution of inducers (e.g., hormone) within and between generations. On one hand, our results reinforced the within-generation maternal effects on induction of defensive morphology of rotifers; on the other hand, our results enhanced transgenerational inducible defense to other planktonic taxa that have been only observed in cladocera. [ABSTRACT FROM AUTHOR]

Brachionus variabilis, a facultative epibiont on cladocerans, has a pronounced morphological response to Asplanchna. Adult amictic females of the Asplanchna-induced morph, compared with those of the basic or non-induced morph, had a 13% larger lorica, 150% longer posterior spines and 30–40% longer anterior spines. Similar responses occur in many other brachionid rotifers as an effective defense against Asplanchna predation, but the response of B. variabilis is surprising. The large size and epizoic habit of B. variabilis should provide good protection against this predator. Also, a smaller epizoic congener (Brachionus rubens) readily ingested by Asplanchna has no morphological response to it. Brachionus variabilis also has a pronounced behavioral response to Asplanchna. Without Asplanchna, most individuals are actively swimming, with only a small proportion of them attached to surfaces. With Asplanchna, the proportion of attached individuals is much higher. Significant attachment responses in both young and adult individuals occurred shortly (∼5 h) after exposure to live Asplanchna (three experiments) or to its kairomone (five experiments), but not to a Daphnia kairomone. The Asplanchna-enhanced propensity for attachment to surfaces, possibly including cladoceran hosts, may be an additional defense against this predator. This is the first report of a predator kairomone inducing a behavioral shift in a rotifer. [ABSTRACT FROM PUBLISHER]

The aim of this work is to evaluate whether interference competition between predators plays an important role in a rotifer predator–prey system. Our results indicated that higher predator density leads to depression of predation rates even if sufficient prey was offered. Crowded culture volume strengthens competition. In addition, this competition might be time-dependent. Our contour plots show that the behavior of the predators changed with time spent foraging. [ABSTRACT FROM PUBLISHER]

Rotifers, in nature, are consumed by several vertebrates and invertebrates. In response to predation, they show a certain degree of plasticity in their life history traits. In this regard, there is an ample database of information on the effect of Asplanchna on brachionids; much less is known on the effect of other common freshwater predators. We studied the chemical effects of four invertebrate predators, Stenostomum leucops (Turbellaria), Asplanchna girodi (Rotifera), Eosphora najas (Rotifera) and Mesocyclops pehpeiensis (Copepoda) on the demography of Brachionus havanaensis. Population growth and life table demography experiments were conducted in 50 mL vessels with 25 mL of moderately hard water and 0.5 × 106 cells mL−1 of Chlorella vulgaris as food. Two predators of each phylum were introduced into small meshes with 50 µm mesh and fed 15 individuals of another rotifer species Plationus patulus. Each experiment was set up with two controls, with and without the prey ( P. patulus) in meshes, as in all the other treatments. We started the experiments with 15 individuals of B. havanaensis in the population growth experiments and 15 neonates (<12 h old) in the life table studies. The population growth studies were terminated after 20 days and the life table studies after the last individual of each cohort died. We also tested the feeding rates of A. girodi, S. leucops and M. pehpeiensis on B. havanaensis by observing the prey consumed at different time intervals from 15 to 90 min. The presence of P. patulus alone had an impact on the reproductive but not on the survivorship variables of Brachionus as compared to the controls. We found that among the predators, S. leucops had the least impact on the population dynamics and life history variables. The survivorship ranged from 16 to 18 days with no significant impact of infochemicals from any of the test predators. The population growth rate of B. havanaensis ranged from 0.2 to 0.34 day−1 and was highest in the presence of M. pehpeiensis and A. girodi. We also observed maximal differences in the life history strategy of B. havanaensis, as compared to the controls, in response to the most voracious predator, A. girodi. [ABSTRACT FROM AUTHOR]

We studied the demographic responses (average lifespan (ALS), gross reproductive rate (GRR), net reproductive rate (NRR), generation time (GT) and the rate of population increase per day ( r) of the predatory rotifer A. silvestrii cultured under five different durations of light conditions (L:D = 24:0, 18:6, 12:12, 6:18, and 0:24 in a 24 h cycle) and under two prey ( Plationus patulus) densities (0.5 and 5.0 ind. mL−1). Our data showed that regardless of prey density, the survivorship of A. silvestrii was affected by the duration of photoperiod; the longest ALS was under complete darkness. For any given prey density, lowest GRR was recorded at 24L:0D. The NRR was lower under continuous light (24L:0D) regime. The longest GT was recorded when Asplanchna silvestrii was fed on high prey density and under total dark regime. The r ranged from 0.15 (24L:0D photoperiod in low prey density) to 0.6 day−1 (18L:6D and high prey density) and for the rest of treatments, the values remained within this range. [ABSTRACT FROM AUTHOR]

Predator–prey interactions play major and direct roles in the structuring of zooplankton communities. Asplanchna usually predates ciliates, rotifers, cladocerans and sometimes even copepods, its predation may drive not only the ecological, but also the evolutionary dynamics of prey populations. In the present study, the life-table demography and the population growth of Asplanchna brightwelli were investigated at four temperatures (16, 20, 24 and 28°C) using Brachionus angularis as prey at four densities (10, 20, 30 and 40 ind.mL−1). The results showed that temperature affected significantly all the life-table demographic parameters (age-specific survivorship and fecundity, average lifespan, life expectancy at hatching, generation time, net reproductive rate and intrinsic rate of population increase) and the population growth rate obtained from the population growth studies, prey density affected the generation time, the net reproductive rate, the intrinsic rate of population increase and the population growth rate, and the interaction between temperature and prey density affected the generation time and the population growth rate. Both the average lifespan and the life expectancy at hatching were the longest at 16°C, the generation times were longer at lower temperatures (16 and 20°C) and higher prey densities (30 and 40 ind.mL−1), the net reproductive rates were higher at lower temperatures (16 and 20°C) and 20–40 ind.mL−1 of B. angularis, and the population growth rates were higher at 20°C under 20–40 ind.mL−1 of B. angularis. [ABSTRACT FROM PUBLISHER]

Highlights: [•] Dimethoate effects on predator rotifer A. brightwelli are reported first time. [•] Different responses of two rotifers under same stress were compared first time. [•] Our endpoints are more sensitive and ecological than the traditional methods. [ABSTRACT FROM AUTHOR]

Brachionus calyciflorus typically develops long, defensive spines only in response to a kairomone from the predatory rotifer, Asplanchna. However, in the absence of any environmental induction, females of some clones produce daughters with increasingly long spines as they age; late-born individuals can have posterolateral spines as long as those induced by Asplanchna: up to 50% or more of body length. Here, we construct a model using data from life-table and predator-prey experiments to assess how this maternal-age effect can influence the distribution of spine lengths in reproducing populations and provide defense against Asplanchna prédation. When Asplanchna is absent, the frequency of individuals with late birth orders rapidly becomes extremely low; thus, any cost associated with the production of long-spined individuals is minimal. When Asplanchna is present at densities too low for spine induction, and preys selectively on individuals with no or short posterolateral spines, the frequency of long-spined individuals rapidly increases until a stable birth-order structure is reached. As a result, mortality from Asplanchna prédation is greatly reduced. The pronounced and novel birth-order effect in this rotifer appears to be an effective bet-hedging strategy to limit prédation by Asplanchna when its kairomone induces no or less than maximal spine development. [ABSTRACT FROM AUTHOR]

In many small planktonic rotifers, predator kairomones induce the development of longer spines, which can provide effective post-contact defense against the predators. This review briefly discusses potential trade-offs associated with pronounced spine development, focuses on an evaluation and synthesis of experimental work comparing the reproductive potential of basic (non-induced) and Asplanchna-induced morphs and suggests areas for future research. To date, the only convincing evidence for an association between induced spine development and reduced reproduction is for Keratella testudo. This rotifer has a dense lorica (skeleton), so that elongated spines increase its sinking rate and thus presumably an offsetting swimming effort. In contrast, several studies with Brachionus calyciflorus and Keratella tropica, which have a thin lorica, showed that morphs with pronounced spine development reproduced at the same rate as basic morphs. In other studies with several different species, and also with B. calyciflorus, the presence of Asplanchna did inhibit reproduction. However, this inhibition generally was not clearly related to Asplanchna density or the degree of spine development, and could not be attributed to a defense cost. While predator-induced morphs of some species do not have a reduced reproductive potential in the laboratory, they may be at a disadvantage in certain interactions or conditions occurring in more complex, natural ecosystems. Such environmental costs, or plasticity costs resulting from the evolution of mechanisms for detecting and responding to predators, may explain why long spines in some rotifers are an inducible rather than a constitutive defense. [ABSTRACT FROM AUTHOR]

Trait-mediated biotic interactions within zooplankton, such as inducible defences against predation, are key determinants of community structure and dynamics in lentic ecosystems. The role of such interactions in lotic environments, however, has been rarely investigated, as abiotic constraints related to hydrology are generally thought to impair the occurrence of biotic interactions in rivers. We hypothesize that, under conditions of reduced flow during summer, trait-mediated predator-prey interactions can be significant driving forces in the main channel of a large river, despite the disruptive effect of downstream transport. To verify this assumption, we carried out a field study in the lowland stretch of the Po River (Italy). We analysed temporal patterns of morphometric variation in a population of Brachionus calyciflorus, potentially triggered by the predatory rotifer Asplanchna brightwellii. Our results indicate that the presence of Asplanchna can impact the variability of different morphological traits in B. calyciflorus even under the disturbance effect of turbulence and drift. Asplanchna feeding electivity on several taxa was also investigated, confirming the predator ability to efficiently and selectively feed under lotic conditions. We suggest that complex interactions and trade-offs might occur among life-history traits, predator-prey relationships and physical constraints imposed by flow within zooplankton communities in large rivers. [ABSTRACT FROM AUTHOR]

This study examines two aspects of predator-induced, morphological defense in rotifers: developmental time lags for acquisition and loss of the defense, and cost of the defense. When the predator and its inducing kairomone disappear from a community, the extent to which prey population growth is inhibited by the retention of the induced defense will be determined by the reversibility of the defense and the magnitude of any cost associated with the defense. In Brachionus calyciflorus, Asplanchna-induced posterior spines were lost more slowly than acquired. When females of the induced morph were removed from Asplanchna kairomone after oviposition of their first egg, they continued to produce long-spined offspring throughout their life. Even when cultured from birth to death without Asplanchna kairomone, females born with long, induced spines produced daughters with some induced spine development. In contrast, when females of the basic (non-induced) morph were exposed to Asplanchna kairomone after oviposition of their first egg, some of their second and all of their subsequently oviposited eggs developed into daughters with long spines. In B. calyciflorus and also Keratella tropica, the reproductive cost of Asplanchna-induced defense was determined by comparing population growth rates of basic and Asplanchna-induced morphs. Populations were initiated with individuals of either morph, and Asplanchna was present with the induced morph to assure that all individuals born during the culture period had long spines. In each of three separate experiments with each rotifer species, population growth rates of basic and induced morphs were statistically indistinguishable. Thus, possession of long spines in the absence of Asplanchna is unlikely to inhibit the reproduction of these rotifers through any allocation or energetic cost. [ABSTRACT FROM AUTHOR]

This study investigates two different effects of an ostracod on a rotifer. The rotifer Keratella tropica and the ostracod Cypris pubera were cultured on the alga Cryptomonas erosa. Adult ostracods (2.2 mm body length) significantly reduced the population growth rate (r day-1) of K. tropica from 0.42 to 0.13. Individuals of this size ingested live rotifers and produced fecal pellets with rotifer loricas. Smaller ostracods (both 0.59 and 1.61 mm body lengths) did not affect K. tropica 's population growth rate. Surprisingly, C. pubera significantly inhibited spine development in K. tropica. Rotifers cultured with juvenile, non-predatory ostracods had similar lorica lengths but right and left posterior spines that were 10 and 30% shorter, respectively. The spine reduction induced by the ostracod kairomone is in striking contrast to the spine elongation induced in this rotifer by kairomones from copepods, cladocerans and Asplanchna. In shallow ecosystems, large ostracods that swim in the plankton may be important predators of rotifers. In addition, the presence of ostracods in plankton communities may be one of many factors affecting rotifer spine development. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

A Patagonian strain of Keratella tropica exhibits extensive non-genetic variation in spine development and body size. This study experimentally investigates the effect of temperature (10, 15, 20, and 25°C), both alone and with Daphnia and Asplanchna kairomones, on spine and lorica length. Temperature by itself had a major effect on right and left posterior spines and the lorica; these increased in length as temperature decreased, most notably from 20 to 15°C. At these two temperatures and a high food level (1 × 10 cells Cryptomonas erosa ml), lengths were, respectively, ca. 24 and 38 μm for the right posterior spine, 19 and 32 μm for the left posterior spine, and 116 and 126 μm for the lorica. A lower food concentration (2 × 10 cells C. erosa ml) at these two temperatures had little effect; the left posterior spine and lorica were slightly but significantly smaller. The growth-promoting effects of low temperature and kairomones generally were additive. Daphnia induced a moderate increase in the length of both posterior spines and lorica; these increases were significantly greater at 15 than 20°C. Asplanchna induced a great elongation of the right posterior spine, a reduction or loss of the left posterior spine, and moderate elongation of the outer two pairs of anterior spines. The right posterior spine and anterior spines were of similar length at 15 and 20°C, but the left spine and lorica were significantly longer at 15°C. Temperature and kairomones from Asplanchna and some crustaceans control the expression of a great variety of phenotypes and probably are largely responsible for seasonal changes in the spine development of this rotifer in natural communities. [ABSTRACT FROM AUTHOR]

1. Keratella tropica has qualitatively distinct spine-development responses to kairomones released by the predatory rotifer Asplanchna and the cladoceran interference competitor Daphnia. Asplanchna induces a fourfold lengthening of the right posterior spine (to c.100 μm), a shortening or loss of the left posterior spine and a lengthening of two pairs of anterior spines. Daphnia induces a moderate elongation of both right and left posterior spines. This study tests three hypotheses regarding the sensitivity of these responses to enemy density, and the response priority when both enemies are present. 2. First, since K. tropica and Brachionus calyciflorus have similarly pronounced and effective spine-development responses to Asplanchna, with no appreciable demographic cost, they should be similarly sensitive to Asplanchna density. This was the case. Both showed an exponential response to increasing Asplanchna density, well described by an asymptotic exponential regression model, and exhibited 50% maximal spine development at statistically similar Asplanchna densities-2.5 and 1.7 μg dry weight L (1.8 and 1.2 individuals L), respectively. Strong selection for these Asplanchna-induced responses clearly has led to a coupling of exuberant and effective morphological defence with an unrivalled sensitivity to predator density. 3. Second, since K. tropica's response to Daphnia is much less pronounced and effective than its response to Asplanchna, it should be less sensitive to Daphnia density. This hypothesis was supported. Spine development increased linearly with increasing Daphnia density and was 50% maximal at 454 μg dry weight Daphnia L, a biomass density 180 times greater than that inducing a comparable response to Asplanchna. 4. Third, since K. tropica's response to Daphnia does not reduce Asplanchna predation, K. tropica should respond to Asplanchna when both enemies are present at densities sufficient to induce spine development. This was the case. The presence of Daphnia neither reduced nor increased the length of the right posterior spine; it only limited the extent to which the left spine was reduced or lost. [ABSTRACT FROM AUTHOR]

1. Recently, the potential for parasites to influence the ecology and evolution of their zooplankton hosts has been the subject of increasing study. However, most research to date has focussed on Daphnia hosts, and the potential for parasites to influence other zooplankton taxa remains largely unstudied. 2. During routine sampling of zooplankton in a eutrophic lake, we observed that the rotifer Asplanchna girodi was often infected with a parasitic oomycete. Epidemics of this parasite occurred frequently, with three separate events in a single year. Prevalence at peak infection ranged from 29 to 41% and epidemics lasted from 17 to 56 days. Our data indicate that high densities of the host population are required for epidemics to occur. 3. Our morphological and molecular analyses suggest that this parasite is in the genus Pythium. Most Pythium spp. are plant pathogens, but our study supports recent work on Daphnia, suggesting that Pythium spp. are also important parasites of zooplankton. 4. As the parasite in this study was recalcitrant to cultivation, we developed an alternative method to verify its identity. Our approach used quantitative PCR to show that the ribosomal sequences identified increased with increasing density of infected hosts and, thus, were associated with the parasite. This approach should be generally applicable to other plankton parasites that are difficult to cultivate outside their hosts. 5. Infections significantly reduced host fecundity, lifespan and population growth rate. As a result of the virulence of this parasite, it is likely to influence the population ecology and evolution of its Asplanchna host, and may be a useful model system for studies on host-parasite coevolutionary dynamics. [ABSTRACT FROM AUTHOR]

Chemical communication may inform about the location of prey, predators, co-specifics, and mate partners in zooplankton. In this study, we evaluated several life-history traits of the rotifer, Brachionus calyciflorus, exposed to conditioned media by a rotifer predator ( Asplanchna brightwelli) and a cladocera competitor ( Daphnia similis), quantifying population growth and life-table demography at two algal food levels (2.0 and 0.5 × 10 cells ml of Chlorella pyrenoidosa). At both food levels, B. calyciflorus grown in predator-conditioned media had lower population abundance and slower population growth rate than controls. Conversely, the competitor-conditioned media treatments produced both higher rotifer population abundance and faster population growth rate than controls. Life-history parameters varied significantly depending on the presence of predator and competitor-conditioned media. The Asplanchna-conditioned media significantly decreased gross reproductive rate (GRR): 8-9 offsprings per female; net reproductive rate ( R): 6-7 offsprings per female; population growth rate ( r): 0.34-0.37 day; and increased generation time ( T): 5.5-5.6 days. On the other hand, The Daphnia-conditioned media significantly increased the GRR (13-14 offsprings per female); net reproductive rate (8-9 offsprings per female); population growth rate (0.42-0.43 day); and decreased generation time (4.9-5.0 days). However, the effects of food level on the life-history characteristic were not significant in both treatments. Maximum values of the population abundance and the population growth rate are significantly influenced by the predator densities and pre-culture time. This study suggests that rotifers use variable life-history strategies (low reproduction and high survivorship versus high reproduction and low survivorship) based on the presence of predators and competitors. [ABSTRACT FROM AUTHOR]

The aim of this work is to evaluate the effect of environmental factors: temperature and photoperiod on the zooplankton predator-prey system. Rotifers, an important and cosmopolitan group of zooplankton in freshwater, were used in our study. We investigated the effect of temperature (20, 23, and 30°C) and of photoperiod (L:D = 12:0 and 0:12) on the predatory rotifer Asplanchna brightwelli consuming rotifer Brachionus calyciflorus as prey. Under A. brightwelli predation, populations of B. calyciflorus prey were consumed more slowly at 20 ± 1 and 30 ± 1°C as compared to 23 ± 1°C. Prey consumption by A. brightwelli increased from 0.63 ± 0.09 ind. predator at 20°C to a peak of 1.22 ± 0.12 ind. predator at 23°C, then decreased significantly to 0.93 ± 0.14 ind. predator at 30 ± 1°C. In addition, predation responded to temperature changing sensitively and rapidly. Statistical analysis showed that the prey consumption were significant different under altered temperature periods during 12 h. Photoperiod also significantly influenced the rate of A. brighwelli predation. B. calyciflorus suffered less predation in darkness than in light. The rate of prey consumption in light (1.06 ind. predator) was twice the average of that in darkness (0.51 ind. predator). Furthermore, predation rate varied under changing photoperiod but predators moved back into the light did not resume their original consumption rate. Our results demonstrate that whether the predation in rotifer successfully or not is strongly influenced by temperature and photoperiod. [ABSTRACT FROM AUTHOR]

1. A key aspect of the ecology and evolution of adaptive prey responses to predator risk is the timing by which the former develop a defensive trait in response to inducing signals released by the latter. This property, called reactivity, has been shown to affect population stability and persistence. 2. Theoretically, the minimal predator density required by prey to exhibit induced defences is expected to increase with the effectiveness of the defence and decrease with its cost. Likewise, the time required for the prey population to exhibit an induced defence is expected to increase together with cost. 3. The freshwater rotifers Brachionus calyciflorus and B. havanaensis and their predator Asplanchna brightwelli were used to test the hypothesis that prey species exhibiting defences that offer a larger fitness benefit and lower fitness cost are more reactive to predator signals, in terms of requiring shorter exposure time and lower signal concentration to trigger a morphological defence reaction. 4. Our results showed that both prey species exhibited costly and effective defences after induction by predator infochemicals. Faster reactions were observed at higher levels of predator cues. Nevertheless, the observed relationship between reactivity and benefit/cost of defences did not agree with our expectations. 5. To our knowledge, this is the first study in which the timing of induction of morphological defences is experimentally assessed over a gradient of risk signals. We propose new research directions to disentangle the mechanisms and project the consequences of prey decisions at the morphological level. [ABSTRACT FROM AUTHOR]

Plankton samples collected from two sampling stations of Deepor Beel (a Ramsar site in Assam, northeastern India) between November 2002 and October 2003, reveal 110 and 100 species of Rotifera, exhibit monthly richness ranging between 43-65 (56 ± 6) and 38-60 (52 ± 7) species and record 48.9-88.1 and 53.1-89.7% community similarities respectively. Rotifera (231 ± 60 and 198 ± 70 n/l) comprise between 48.7 ± 6.1 and 42.6 ± 4.1% of zooplankton abundance at station I and II respectively, and follow trimodal annual patterns with peaks during winter. Brachionidae (90 ± 43, 79 ± 39 n/l) > Lecanidae (45 ± 13, 29 ± 9 n/l) form important quantitative components of Rotifera while Asplanchnidae > Synchaetidae > Trochosphaeridae are other notable families. Lecane > Brachionus > Keratella > Asplanchna > Platyias contribute notably to temporal variations of the rotifers. Asplanchna priodonta, Keratella cochlearis, Platyias quadricornis, Lecane leontina, Polyarthra vulgaris, Keratella tropica and Brachionus falcatus are important species. Analysis of variance comparisons indicate significant temporal variations in richness and abundance of Rotifera between stations and months.The rotifer communities exhibit higher species diversity, higher evenness, lower dominance and lack of quantitative dominance of any individual species. The present results show no definite periodicity of richness and abundance of this group, families or species. Individual abiotic factors register limited influence on richness and abundance while multiple regression exhibits higher cumulative influence of ten abiotic factors on these parameters at both sampling stations. [ABSTRACT FROM AUTHOR]

1. A Patagonian strain of Keratella tropica has very different induced morphological responses to two predators – the carnivorous rotifer Asplanchna brightwelli and the interference competitor Daphnia pulex. Asplanchna induces the most exuberant morph. Compared to the basic morph, it has a fourfold longer right posterolateral spine (up to c. 115 μm), greatly elongated anterolateral and anterosubmedian spines, and no left posterolateral spine. Transitional morphs have an incompletely developed right posterolateral spine and a reduced left posterolateral spine. Daphnia induces moderate development of both posterior spines but no elongation of any anterior spines. Induction of these morphs by Asplanchna and Daphnia is mediated by kairomones. 2. The Asplanchna-induced morph is much better defended against large (0.9 mm) Asplanchna than either the basic or Daphnia-induced morph. The long right posterolateral spine usually prevents capture or ingestion. The Asplanchna- and Daphnia-induced morphs are similarly susceptible to interference from large (3 mm) D. pulex. 3. Life-table experiments with cohorts of the basic and Asplanchna-induced morphs at 5 × 103 and 2 × 104 cells of Cryptomoas erosa per millilitre indicate little or no cost of the induced defense. Lifetime fecundity (13–15 offspring per female) did not differ significantly between morphs. The mean intrinsic rate of natural increase ( rm day−1) of the induced morph was very slightly but significantly lower than that of the basic morph at the lower food concentration (0.46 versus 0.48) but no different from it at the higher food concentration (0.53 versus 0.54). However, spine development may involve undetermined allocation costs and environmental costs relating to interactions with other organisms. 4. It is not clear why K. tropica has separate induced responses to Asplanchna and Daphnia. Moderate spine development probably reduces damage or ingestion by small (<1.5 mm) daphniids, as in other species of Keratella, but further development may confer no protection against larger ones. Thus, the ratio of benefit to cost with daphniids (and other cladocerans) may be highest for intermediate spine development. In contrast, much greater spine development seems necessary for effective defense against Asplanchna. The more moderate response to Daphnia also may reflect less likely spatial and temporal overlap. [ABSTRACT FROM AUTHOR]

1. Maternal effects have long been known to influence phenotypic plasticity in rotifers. Females in Brachionus calyciflorus and several other species produce long-spined offspring when the predatory rotifer Asplanchna is present; B. calyciflorus also develops short spines when food concentrations are low. These spines protect against predation and decrease food threshold concentrations. 2. Some strains of B. calyciflorus develop long spines even in the absence of Asplanchna and other environmental stimuli. We demonstrate in this study that spine length in such cases is dependent on the age of the mother. 3. In strains from Florida and Georgia, offspring spine length increased significantly with birth order, sometimes to lengths formerly observed only in the presence of Asplanchna. Significant variation in this trait was found among and within clones of a strain. Offspring body size also increased with maternal age. This is the first time maternal age has been shown to affect rotifer morphology. 4. These birth-order effects may have important ecological implications and explain phenotypic plasticity and polymorphism in body size and spine length in populations when predators are absent and food concentrations are high. They may be a bet-hedging mechanism to assure adaptation to rapid changes in predation pressure or food conditions. [ABSTRACT FROM AUTHOR]

A number of records of rotifers from Turkey are discussed. An account is given on trophi morphology in 4 species of Asplanchna Gosse, 1850. Cephalodella segersi De Smet, 1998 is recorded for the second time after its description, and Lecane shieli Segers and Sanoamuang, 1994 is recorded from Turkey for the first time. Both these and a population of Hexarthra polyodonta polyodonta (Hauer, 1957) from the species' type locality, Lake Van, are illustrated using light and scanning electron microscopic techniques. [ABSTRACT FROM AUTHOR]

In the present study, we evaluated the effects of a graded series of different intensities of predation by predatory rotifer Asplanchna brightwellii (0, 1, 2, 5, 10 and 20 ind. per 50 ml) on the competition outcome between two herbivorous rotifers, Brachionus calyciflorus (196 ± 12 μm in length) and Brachionus patulus (145 ± 8 μm in length), at high (3 × 106 cells ml−1) and low (0.5 × 106 cells ml−1) algae food ( Chlorella pyrenoidosa) levels. Under low predation intensity (0, 1, 2, 5 predators), B. patulus was able to outcompete and coexist with B. calyciflorus at low and high food level, respectively. Further, increased predation intensity decreased competitive ability of B. patulus at each food level, and it was eliminated from the culture assemblage at high predation intensity (20 predators). However, B. calyciflorus could persist under the highest predation intensity in this experiment. Population growth rate of B. calyciflorus was affected by food level, not by predation intensity, while that of B. patulus showed a reverse result. The maximum population density of B. patulus was significantly influenced by both predation intensity and food level, but for that of B. calyciflorus, food level was the only influence factor. The results suggest that the competition outcome between herbivorous rotifer species with different body sizes are not only affected by food level but also influenced by the predation intensity. [ABSTRACT FROM AUTHOR]

We tested the hypothesis that small prey can coexist with large predators. For this we confronted two predators (smaller Asplanchna brightwellii: 900 μm and larger A. sieboldi: 1400 μm) with three prey rotifers (smaller: Anuraeopsis fissa (70 μm); larger: Brachionus calyciflorus (200 μm) and intermediate: B. patulus (120 μm)) using functional response, prey preference, population growth and life table demography. Regardless of prey type, A. sieboldi was able to consume more prey than A. brightwellii and it consumed higher number of B. patulus than of B. calyciflorus or A. fissa. Prey preference experiments showed that A. brightwellii had no preference for B. calyciflorus regardless of prey density, while A. sieboldi preferred B. calyciflorus and avoided A. fissa. Data on population growth showed that A. brightwellii was always numerically more abundant than A. sieboldi. Prey type had a significant effect on peak abundances of A. sieboldi but not of A. brightwellii. Life table demography data revealed a significantly lower lifespan in A. brightwellii fed B. calyciflorus, compared to B. patulus, but not when compared to A. fissa. A. sieboldi lifespan was not affected by prey type. Depending on prey type and predator species, generation time varied from 2 to 3 days. Both lowest (0.38 d−1) and highest (0.98 d−1) population growth rates were observed in A. sieboldi. We suggest that reduced reproductive output in Asplanchna was caused by either large ( B. calyciflorus) or small ( A. fissa) prey. At natural densities of Anuraeopsis, it is unlikely that Asplanchna reaches abundances high enough to exterminate this prey. By its extremely small size (combining low energetic profitability with low encounter rates with predators) A. fissa may coexist with Asplanchna in nature. [ABSTRACT FROM AUTHOR]

The combined effect of temperature, food level and the presence of an invertebrate predator on the body size of the rotifer Brachionus havanaensis were tested in this study. B. havanaensis was cultured at 15, 20, and 25°C under three different Chlorella vulgaris levels (0.5 × 106, 1.0 × 106 and 2.0 × 106 cells ml−1) in the presence and in the absence of Asplanchna girodi. For each treatment we maintained three replicates and constant (0.4 ind ml−1) population density of B. havanaensis. In treatments containing A. girodi, the predator was separated from the prey by a mesh (pore size 50 μm). On the last day of the experiment, a portion of the B. havanaensis population was sampled for several morphometric measurements (adult lorica length, width, posterior spine length, body volume, and the egg volume). Size measurements were done by drawing the specimens using a calibrated camera lucida. Statistically significant impact of temperature as well as the predator’s presence was observed on the lorica length, posterior spine, and egg volume of B. havanaensis. The interactions of food × temperature, or predator´s presence × food × temperature were non-significant ( P > 0.05) for lorica length, spine length, body volume, and egg volume. Regardless of the type of treatment, there was a direct positive correlation between lorica length and width. Egg volume was linearly related to the adult size. Notably long posterior spines were observed in treatments containing the presence of A. girodi. [ABSTRACT FROM AUTHOR]

Theoretical studies have predicted that inducible defenses affect food chain dynamics and persistence. Here we review and evaluate laboratory experiments that tested hypotheses developed from these theoretical studies. This review specifically focuses on the effects of inducible defenses in phytoplankton-rotifer food chain dynamics. First, we describe the occurrence of colony formation within different strains of green algae (Scenedesmaceae) in response to infochemicals released during grazing by the herbivorous rotifer Brachionus calyciflorus. Then we examined the effects of inducible defenses on the population dynamics of this planktonic system in which algal strains that differed in their defense strategies were used. Simple food chains were composed of green algae (Scenedesmaceae), herbivorous rotifers ( Brachionus calyciflorus) and carnivorous rotifers ( Asplanchna brightwellii). In this system B. calyciflorus exhibits an inducible defense against predation by developing long postero-lateral spines. Experimental studies showed that inducible defenses, as opposed to their absence, could prevent high-amplitude population fluctuations. We discuss the dual effects of induced defenses on extinction probabilities and consider the fit of a theoretical model to experimental data to understand the mechanisms that underlie the observed dynamics. [ABSTRACT FROM AUTHOR]

The zooplankton assemblages in Crater Lake exhibited consistency in species richness and general taxonomic composition, but varied in density and biomass during the period between 1988 and 2000. Collectively, the assemblages included 2 cladoceran taxa and 10 rotifer taxa (excluding rare taxa). Vertical habitat partitioning of the water column to a depth of 200 m was observed for most species with similar food habits and/or feeding mechanisms. No congeneric replacement was observed. The dominant species in the assemblages were variable, switching primarily between periods of dominance of Polyarthra-Keratella cochlearis and Daphnia. The unexpected occurrence and dominance of Asplanchna in 1991 and 1992 resulted in a major change in this typical temporal shift between Polyarthra-K. cochlearis and Daphnia. Following a collapse of the zooplankton biomass in 1993 that was probably caused by predation from Asplanchna, Kellicottia dominated the zooplankton assemblage biomass between 1994 and 1997. The decline in biomass of Kellicottia by 1998 coincided with a dramatic increase in Daphnia biomass. When Daphnia biomass declined by 2000, Keratella biomass increased again. Thus, by 1998 the assemblage returned to the typical shift between Keratella- Polyarthra and Daphnia. Although these observations provided considerable insight about the interannual variability of the zooplankton assemblages in Crater Lake, little was discovered about mechanisms behind the variability. When abundant, kokanee salmon may have played an important role in the disappearance of Daphnia in 1990 and 2000 either through predation, inducing diapause, or both. [ABSTRACT FROM AUTHOR]

We investigated the phylogenetic relationships of Family Asplanchnidae using both morphological and molecular data. The morphological database, comprising 23 characters from 19 taxa (15 Asplanchnidae and 4 outgroups), was compiled from a survey of the literature and our own observations; the molecular data (ITS and V4 region nuclear regions and mitochondrial cox1) was sequenced from specimens that we collected. Our analysis of the morphological data set (maximum parsimony) yielded 12 most-parsimonious trees with a tree length of 27 steps. From this analysis we conclude (1) Asplanchnidae is a monophyletic group as are the three genera comprising it, (2) there is no compelling support for the argument that Asplanchna should be separated into two discrete genera, and (3) there is some support for the proposal that Asplanchnidae and Synchaetidae are sister groups. Our analysis of the molecular data set supports the first two of these conclusions while the sister group of the family varied depending on the gene region analyzed and families and genera included. Current understanding of the phylogeny of Asplanchnidae is hampered by the need for additional informative morphological characters and a lack of molecular data for the genus Harringia and several other members of the Asplanchnidae. [ABSTRACT FROM AUTHOR]

We observed different morphotypes of some species in the family Brachionidae from the seasonal plankton samples of Lake Xochimilco collected during 2002–2003. We measured the body length, width, and spine lengths (posterior and anterior spines) of Brachionus havanaensis, Keratella americana, K. cochlearis and K. tropica during the periods when the predator Asplanchna brightwellii was present in great abundance but also when it was nearly absent. In general, spines of most of the selected rotifer species were longer if A. brightwellii was abundant. Relatively, small spines were observed if the predator was rare. The body lengths of brachionid rotifers widely varied in samples with more and less abundant A. brightwellii. Morphometric data are interpreted in terms of morphological adaptations of Brachionus and Keratella in response to Asplanchna predation. [ABSTRACT FROM AUTHOR]

We present the first results of immunocytochemical (ICC) observations on serotonin (5-HT) and FMRFamide (Phe–Met–Arg–Phe–NH2) immunoreactivity patterns in the rotifer nervous system investigated using a confocal laser scanning microscope (CLSM). Three species of rotifers are studied: Platyias patulus ( Plationus patulus, Segers et al., 1993; Hydrobiologia 268: 1–8), Euchlanis dilatata and Asplanchna herrickii. Independently from their systematic position, these species possess similar nerve structures. However, some differences were observed in the innervation of the corona, mastax, foot, and mostly in the pattern of the cerebral neurons. The general numbers of 5-HT-immunoreactive (IR) and FMRFamide-IR neurons are low (10–34), but constant for each species. The sizes of the neurons vary from 2, 5 to 10 μm. From 4 to 14 cerebral neurons lie at different levels and are arranged into an X- or a ring- or a curved arch shape. One or two pairs of neurons are localized along longitudinal nerve cords. Double staining of 5-HT and FMRFamide-IR elements shows no co-localization. [ABSTRACT FROM AUTHOR]

Edmondson’s egg ratio (number of amictic eggs per female) is an important life history variable, which has been in wide use to understand and predict patterns of population growth in planktonic rotifers under field conditions. It is also useful as an indicator of the health of rotifers under culture conditions. Generally, an inverse relationship exists between the egg ratio and the density of females in a population. A number of abiotic and biotic factors influence the egg ratio. For example, temperature can cause marked changes in the egg ratio by influencing the frequency of egg production and the hatching times of parthenogenetic eggs. Also, preferential feeding on ovigerous females of rotifers by invertebrate predators such as Asplanchna will lower the egg ratios of the population. The easy detachment of eggs, as may be the case in some members of the Brachionidae especially during enhanced reproduction when food levels are high, may also cause an underestimation of the egg ratio. In this review, we discuss the egg ratio of selected rotifer species in relation to the role of diel changes in egg production, the frequency or the intensity of feeding, the problems of distinguishing between different egg types and the negative effect of stressors such as toxicants and diet quality. [ABSTRACT FROM AUTHOR]

Three main groups of planktonic animals inhabit the limnetic zone of inland waters and compete for common food resources: rotifers, cladocerans and copepods. In addition to competition, their mutual relationships are strongly influenced by the variable, herbivorous and carnivorous feeding modes of the copepods. Most copepod species, at least in their later developmental stages, are efficient predators. They exhibit various hunting and feeding techniques, which enable them to prey on a wide range of planktonic animals from protozoans to small cladocerans. The rotifers are often the most preferred prey. The scope of this paper is limited to predation of freshwater copepods on rotifer prey. Both cyclopoid and calanoid copepods (genera Cyclops, Acanthocyclops, Mesocyclops, Diacyclops, Tropocyclops, Diaptomus, Eudiaptomus, Boeckella, Epischura and others) as predators and several rotifer species (genera Synchaeta, Polyarthra, Filinia, Conochilus, Conochiloides, Brachionus, Keratella, Asplanchna and others) as prey are reported in various studies on the feeding relationships in limnetic communities. Generally, soft-bodied species are more vulnerable to predation than species possessing spines or external structures or loricate species. However, not only morphological but also behavioural characteristics, e.g., movements and escape reactions, and temporal and spatial distribution of rotifer species are important in regulating the impact of copepod predation. The reported predation rates are high enough to produce top-down control and often achieve or even exceed the reproductive rates of the rotifer populations. These findings are discussed and related to the differences between the life history strategies of limnetic rotifer species, with their ability to quickly utilize seasonally changing food resources, and adjust to the more complicated life strategies of copepods. [ABSTRACT FROM AUTHOR]

We collected rotifers during one year (2002-2003) from four different sites in Lake Xochimilco and analyzed the species diversity. We found on an average 25-30 species co-existing at any one site, and rotifer species density was highest in the summer months. The common genera found throughout the year were Brachionus, Keratella, Polyarthra, Trichocerca, Filinia and Asplanchna, and we often found six to eight species of Brachionus in the same sample. Keratella cochlearis and K. tropica were often found together, as were Trichocerca similis, T. pusilla and T. cylindrica. The genus Asplanchna was represented almost exclusively by A. brightwelli. [ABSTRACT FROM AUTHOR]

Comparative studies were performed on the zooplankton composition and some physical and chemical properties of the Kurtbo&gcaron;az&í and Çamlídere reservoirs. Zooplankton abundance, conductivity, organic matter, hardness and orthophosphate concentrations were lower and Secchi depth was higher in .amlídere than in Kurtbo&gcaron;azí (P < 0.01). Rotifera species such as Polyarthra dolichoptera, Keratella quadrata, Asplanchna priodonta and Ascomorpha saltans showed peaks, particularly in spring, summer and late summer. Diaphanosoma lacustris, Bosmina longirostris and Ceriodaphnia quadrangula of Cladocera species increased in late summer whereas Bosmina longirostrisand Daphniaspp. were prominent in spring. The cyclopoid copepod Cyclops vicinus was dominant in Kurtbo&gcaron;az&í and calanoid Acanthodiaptomus denticornisin .amlídere. [ABSTRACT FROM AUTHOR]

1. We investigated the numerical response, functional response and prey preference of Asplanchna sieboldi to five different prey brachionids. We also analysed the feeding behaviour of the predator in terms of encounters, attacks, capture and prey ingested per unit time. 2. The five prey species ( Brachionus havanaensis, B. rubens, B. patulus, B. macracanthus and B. calyciflorus) differed in their body size and spine length. 3. The population growth rates of A. sieboldi ranged from 0.074 ± 0.03 to 0.431 ± 0.02 depending on prey type and density. There was a significant impact of the spine length rather than body size per se on the population growth rates of the predator. 4. The maximum number of prey consumed depended on both body size and spine length. In the functional response analyses, the plateau was reached at a prey density of 4–8 ind. mL−1. 5. There was a significant impact of prey density on the prey preference of the predator. [ABSTRACT FROM AUTHOR]

Population growth and life table demography of the predatory rotifer A. girodi using spineless Brachionus calyciflorus and spined Brachionus havanaensis as prey at densities of 1, 2, 4 and 8 ind. ml-1 at 25 °C were studied. Regardless of the prey species, the population of A. girodi increased with increasing availability of Brachionus in the medium. At any given prey density, A. girodi fed B. calyciflorus showed consistently better growth than when fed B. havanaensis. The maximum population densities of A. girodi varied from 0.28 to 1.8 ind. ml-1 depending on the prey species and the density. The rate of population increase observed in population growth studies varied from 0.17 to 0.43 day-1 when fed B. calyciflorus and 0.09 to 0.27 day-1 when fed B. havanaensis. Male population of A. girodi was closely related to female density. The lowest average lifespan was observed for A. girodi when fed B. havanaensis at 1 ind. ml-1, while the converse was the case when fed B. calyciflorus at comparable prey concentration. Net reproductive rates varied from 16 to 26 offspring female-1 lifespan-1 depending on the prey species and concentration. Generation time of A. girodi decreased with increasing food concentrations for both the prey species. The rates of population increase obtained from life table demography were lower for A. girodi when fed B. havanaensis than when fed B. calyciflorus. [ABSTRACT FROM AUTHOR]