Search results for "brachionus"
showing 10 items of 72 documents
Effect of a cyanobacterial diet on the competition between rotifers: a case study in Lake Albufera of Valencia, Spain
2019
espanolBrachionus havanaensis se distribuye predominantemente en las regiones Neartica y Neotropical. Ahora se encuentra incluso en las regiones Paleartica y Oriental. Durante el verano de 2015, encontramos altas densidades (> 500 ind./l) de esta especie y bajas abundancias de Brachionus angularis en la laguna de la Albufera, donde la cianobacteria (Microcystis aeruginosa) fue dominante en la comunidad de fitoplancton. Nuestra hipotesis fue que la cianobacteria era toxica para B. angularis pero no para B. havanaensis, por lo que este ultimo superaria al primero en presencia de dicha cianobacteria. Para probar la hipotesis, realizamos experimentos de competencia entre estas dos especies de r…
Using probability of extinction to evaluate the ecological significance of toxicant effects
2000
A large component of uncertainty in ecological risk assessment (ERA) arises from the disparity between the time scale of toxicity measurements and the time scale of predictions of ERA models. It is difficult to make predictions about the persistence of populations from data from short-term toxicity tests. Reproductive toxicity tests provide data about how population growth rate (r) is reduced with toxicant exposure. Although reduction in r is believed to be one of the most important effects of toxicant exposure, its ecological significance has been difficult to quantify. For rotifers, r is typically reduced by 10 to 15% at no-observed-effect concentrations (NOEC). We investigated r reductio…
Brachionus plicatilis tolerance to low oxygen concentrations
1989
Tolerance to low oxygen concentrations is expected in Brachionus plicatilis, a rotifer adapted to live in saline warm waters. The population dynamics of a clone of this species, isolated from an endorreic saline lake, was studied under controlled laboratory conditions. Although their growth and metabolism is extremely reduced, B. plicatilis populations are able to maintain relatively high-density populations (a mean of 35 ind ml−1) in oxygen concentrations below 1 mgl−1, for more than one month. Major features of population growth related to oxygen are discussed.
Allocation patterns in modes of reproduction in two facultatively sexual cryptic rotifer species
2015
Many zooplankters rely on diapausing stages to survive unsuitable conditions in time-varying habitats. In facultativesexualrotifers, reproductive effortallocatedtothe sexuallyproduced diapausingeggs isat the expenseofthe subitaneousparthenogenetic eggs, generatingatrade-offbetweencurrentand future population growth.Thetimingand the amountof sex (the sexual pattern) affect diapausing-egg production. This switch to sex is complex because the reproductivemode is separated in distinct females: asexual (female-producing), unfertilized sexual (male-producing) and fertilizedsexual (diapause-egg-producing). We studied sexual patterns and life-history variation of these females in two crypticspecies…
Predation as a factor mediating resource competition among rotifer sibling species
2004
The relevance of predation as a factor mediating the competitive interaction among ecologically very similar species is investigated by experimentally analyzing the effect of the copepod predator Diacyclops bicuspidatus odessanus on three sibling rotifer species belonging to the Brachionus plicatilis species complex. These rotifer species are similar in shape but show notable differences in body size. Predator and prey species co-occur in brackish waterbodies close to the Mediterranean coast of Spain. First, we characterized differential vulnerability of rotifers to predation. A consistent tendency of higher predation rates on smaller prey (i.e., smaller species and younger individuals) was…
Ecological genetics of a cyclical parthenogen in temporary habitats
1995
Populations of the rotifer Brachionus plicatilis inhabiting three temporary ponds in Torreblanca Marsh (Castellon, Spain) were regularly screened for allozyme variation, sexual reproduction levels and population densities during an annual cycle. Relevant ecological parameters in the ponds were also recorded. The electrophoretic survey of the three ponds (Poza Sur, Poza Norte and Canal Central) revealed a high level of overall genetic polymorphism in four marker loci, but only 13 multilocus genotypes were found. We classified clones into three clonal groups (SS, SM, L) characterized by unique arrays of alleles in the four marker loci, and significant differences in body shape and size. Clona…
Selection of low investment in sex in a cyclically parthenogenetic rotifer
2009
Cyclical parthenogens, which combine asexual and sexual reproduction, are good models for research into the ecological and population processes affecting the evolutionary maintenance of sex. Sex in cyclically parthenogenetic rotifers is necessary for diapausing egg production, which is essential to survive adverse conditions between planktonic growing seasons. However, within a planktonic season sexual reproduction prevents clonal proliferation. Hence, clones with a low propensity for sex should be selected, becoming dominant in the population as the growing season progresses. In this context, we studied the dynamics of the heritable variation in propensity for sexual reproduction among clo…
Mictic patterns of the rotifer Brachionus plicatilis Müller in small ponds
1995
Populations of the rotifer Brachionus plicatilis were monitored in three small ponds in a marsh on the Mediterranean coast. Samples were taken approximately every three weeks from July 1992 to November 1993. Salinity, temperature, conductivity, pH and oxygen concentration were measured in the field. Population density was determined from preserved quantitative samples. Individuals were classified as mictic females, amictic females, non-ovigerous females, and males, differentiating between two morphotypes (‘S’ and ‘L’). From these counts, a level of mixis was calculated. We also determined the proportion of mictic females in natural populations by culturing females isolated from fresh sample…
Environmental Variables and Planktonic Communities in Two Ponds of El Hondo Wetland (SE Spain)
2001
The annual cycle of physical and chemical variables and plankton dynamics was studied in two shallow ponds (East and West Ponds) of the El Hondo wetland, an ecosystem of international importance. Water conductivity increased up to 31-49 mS cm -1 as water level decreased due to high evaporation and minimal water inputs. Initially considered mesohaline, the waters were reclassified as polyhaline during the hot season. EP was subject to successive desiccation-flooding cycles, and flooding of the dried sediment caused the release of high concentrations of nitrogen and phosphorus compounds, which quickly depleted. The algal species composition was typical of eutrophic ecosystems, and the chlorop…
Ecología y evolución de la reproducción sexual en poblaciones de Brachionus plicatilis
2023
Esta tesis aborda la reproducción sexual, rasgo biológico crucial para entender la ecología de poblaciones y la evolución de las especies que incluyen el sexo en su ciclo de vida. Sin embargo, es paradójico que sea el tipo de reproducción más extendido entre los eucariontes, pues tiene asociados múltiples costos inmediatos entonces, teóricamente, es una estrategia desventajosa desde el punto de vista de la eficiencia biológica. Si se consideran los costos, estos deben implicar una reducción en la eficiencia, y si se consideran los beneficios, se deben buscar ventajas adaptativas que superen los costos en que se incurre. Esta tesis se basa en la investigación de los procesos ecológicos y pob…