Search results for "Rotifer"
showing 10 items of 82 documents
Life-history variation, environmental fluctuations and competition in ecologically similar species: modeling the case of rotifers
2015
Competition for resources can lead to species exclusion. However, this exclusion may be avoided if species show differential adaptation to physical environment. Empirical studies on competition are difficult when species are phylogenetically close and have complex life cycles. This is the case of B. plicatilis and B. manjavacas, two cryptic rotifer species differing in their salinity niches and in life-history traits related to sex and diapause. These differences have been suggested to promote the stable co-occurrence observed in natural populations of these species. However, in a previous empirical study, the outcome of competition between both species was always exclusion. Here, we theore…
Cryptic diversity, niche displacement and our poor understanding of taxonomy and ecology of aquatic microorganisms
2022
AbstractThe analysis of ecological niche is an important task to correctly identify the role exerted by species within ecosystems, to assess their vulnerability, to plan effective measures addressed at fulfilling the postulates of biological conservation, and ultimately to prevent biodiversity loss. However, for the majority of organisms our knowledge about the actual extent of their ecological niche is quite limited. This is especially true for microscopic organisms. Evidence exists that in different geographical areas allegedly conspecific populations can show different, if not antithetical, ecological requirements and not-overlapping ecological niches. This opinion paper discusses whethe…
Rotifer vertical distribution in a strongly stratified lake: a multivariate analysis
1998
The main source of variation of rotifer species distributions in lake Arcas-2, a small karstic lake near Cuenca (Spain), was explored by means of principal components factor (PCA) and canonical correlation (CCA) analyses. PCA was performed using rotifer densities and CCA using rotifer densities plus physical and chemical parameters. Factor 1 of PCA separated summer species from winter-spring species and Factor 2 accounted for the variation in the vertical profile. Three summer species with different food habits (Polyarthra dolichoptera, Hexarthra mira and Asplanchna girodi) were grouped together at the positive end of Factor 1, while Factor 2 separated the two hypolimnetic species (Filinia …
Starvation tolerance of rotifers produced from parthenogenetic eggs and from diapausing eggs: a life table approach
2006
Monogonont rotifers have to cope with environmental variation by producing diapausing stages.Cyclically, parthenogenetic rotifers produce females by (i) parthenogenetic eggs and (ii) sexuallyproduced eggs. Parthenogenetic eggs hatch shortly after ovoposition, frequently while they are carriedby their mothers. Sexual eggs go into dormancy and hatch in the sediment, in response to specificenvironmental cues. Therefore, it is expected that post-diapause and parthenogenetic offspring wouldface different environments. Moreover, resource allocation is higher in diapausing eggs than inparthenogenetic eggs. In this study, the response to starvation of females obtained from partheno-genetic eggs and …
Hatching and viability of rotifer diapausing eggs collected from pond sediments
2006
SUMMARY 1. Planktonic rotifers inhabiting variable environments produce diapausing eggs that accumulate in the sediment of lakes and ponds, forming egg banks that may withstand adverse periods. A common assumption in zooplankton diapausing egg bank studies is to count as viable all eggs in the sediment that look healthy. This assumption should be challenged by asking how effectively ‘healthy-looking’ eggs represent viable eggs. 2. In this study, viability of more than 1100 ‘healthy-looking’ diapausing eggs belonging to the Brachionus plicatilis species complex was assessed in a laboratory hatching experiment. Eggs were collected at different depths from sediment cores obtained from 15 ponds…
Effect of pentachlorophenol on predator-prey interaction of two rotifers
1997
Abstract The effect of pentachlorophenol (PCP) on the predator-prey relationship of two rotifers (Asplanchna girodi and Brachionus calyciflorus) was studied using Asplanchna predatory behavior as an endpoint. The experimental design included three treatments: prey and predator exposure, only prey exposure, and only predator exposure. This enabled us to distinguish toxic effects on the predator from those on the prey and to detect interactions. The main toxic effects observed were on the predator and involved the number of predator-prey encounters. Encounters decreased in a dose-dependent manner, with a no observed effect threshold at 0.11 mg PCP l−1. Decrease in encounter rate reduced the n…
Ecotoxicological studies with the freshwater rotifer Brachionus calyciflorus. Resource competition between rotifers and daphnids under toxic stress
1993
Abstract This study examined the ability of the freshwater rotifer Brachionus calyciflorus to coexist with the large cladoceran Daphnia magna, and the effect of sublethal concentrations of copper on the competition between both species. Preliminary laboratory experiments showed that large Daphnia (> 1.2 mm) can kill and rapidly exclude the rotifer B. calyciflorus in mixed-species cultures. Brachionus populations were suppressed by Daphnia both through exploitative competition for shared, limited food resources and through mechanical interference. At a food concentration of 1 X 105 cells/ml of Nannochloris oculata, competition caused high mortality rates and decreased fertility in the rotife…
Effect of the insecticide methylparathion on filtration and ingestion rates of Brachionus calyciflorus and Daphnia magna
1993
The freshwater rotifer Brachionus calyciflorus and the cladocera Daphnia magna were exposed to sublethal levels of methylparathion to determine the effect on filtration and ingestion rates. The experiments were performed using the unicellular algae, Nannochloris oculata in a density of 5 × 105 cell/ml. Prior to feeding experiments, preliminary acute toxicity tests were carried out to determine 24-h LC50 values for both species, these values indicated that Daphnia magna was more sensitive to methylparathion acute exposure than Brachionus calyciflorus was. Rates of filtration and ingestion declined with increasing methylparathion concentrations after an exposure of 5 h to this toxicant. The e…
Allozyme electrophoresis: its application to rotifers
1998
Allozyme electrophoresis is a well established technique for revealing genetic variation that has given useful results in a wide range of organisms. However, in rotifers it has been applied scarcely and only in a few species. In this paper the methods of acetate allozyme electrophoresis are introduced, including laboratory setup, equipment and staining recipes that have been successfully applied to brachionid rotifers. In addition, the literature published on allozyme electrophoresis in rotifers is reviewed and the main results and future prospects of the technique are discussed. We conclude that, despite the onset of DNA techniques, allozyme electrophoresis is promising and can yield impor…
Effects of population outcrossing on rotifer fitness
2010
Abstract Background Outcrossing between populations can exert either positive or negative effects on offspring fitness. Cyclically parthenogenetic rotifers, like other continental zooplankters, show high genetic differentiation despite their high potential for passive dispersal. Within this context, the effects of outcrossing may be relevant in modulating gene flow between populations through selection for or against interpopulation hybrids. Nevertheless, these effects remain practically unexplored in rotifers. Here, the consequences of outcrossing on the rotifer Brachionus plicatilis were investigated. Cross-mating experiments were performed between a reference population and three alterna…