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Africa Gómez - One of the best experts on this subject based on the ideXlab platform.
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Fifteen species in one: deciphering the Brachionus plicatilis species complex (Rotifera, Monogononta) through DNA taxonomy
Hydrobiologia, 2017Co-Authors: Scott Mills, Atsushi Hagiwara, Africa Gómez, J. Arturo Alcántara-rodríguez, Jorge Ciros-pérez, Kayla Hinson Galindo, Christian D. Jersabek, Reza Malekzadeh-viayeh, Francesca Leasi, Jae-seong LeeAbstract:Understanding patterns and processes in biological diversity is a critical task given current and rapid environmental change. Such knowledge is even more essential when the taxa under consideration are important ecological and evolutionary models. One of these cases is the monogonont rotifer cryptic species complex Brachionus plicatilis , which is by far the most extensively studied group of rotifers, is widely used in aquaculture, and is known to host a large amount of unresolved diversity. Here we collate a dataset of previously available and newly generated sequences of COI and ITS1 for 1273 isolates of the B. plicatilis complex and apply three approaches in DNA taxonomy (i.e. ABGD, PTP, and GMYC) to identify and provide support for the existence of 15 species within the complex. We used these results to explore phylogenetic signal in morphometric and ecological traits, and to understand correlation among the traits using phylogenetic comparative models. Our results support niche conservatism for some traits (e.g. body length) and phylogenetic plasticity for others (e.g. genome size).
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Diapausing egg banks, lake size, and genetic diversity in the rotifer Brachionus plicatilis Müller (Rotifera, Monogononta).
Hydrobiologia, 2016Co-Authors: Javier Montero-pau, Manuel Serra, Africa GómezAbstract:Diapausing egg banks are reservoirs of ecological and genetic diversity in continental zooplankton. However, although habitat size has often been used as a proxy for population size, the relationship between diapausing egg bank size and genetic diversity has not been explicitly tested in zooplankton. We estimated the density and size of diapausing egg banks, habitat size and genetic diversity (for mitochondrial and nuclear markers) of 14 populations of the rotifer Brachionus plicatilis in an endorheic basin in the SE Iberian Peninsula. The size of B. plicatilis diapausing egg banks ranged across eight orders of magnitude (from 257 to 4.9 × 1010 eggs). Despite the small geographical scale, populations were strongly structured genetically, but with no evidence of isolation by distance. Habitat size (lake area) was a better predictor of genetic diversity than total diapausing egg bank size, but only for mtDNA haplotype diversity. However, as these results were driven by the strong effect of the largest lake in the database, they should be taken with caution. Our results suggest that large lakes could have a disproportionate effect on genetic diversity and that more work is needed to support the use of habitat size as a proxy of population size in rotifers
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Development of genomic resources for the phylogenetic analysis of the Brachionus plicatilis species complex (Rotifera: Monogononta)
Hydrobiologia, 2011Co-Authors: Javier Montero-pau, Africa GómezAbstract:There has been a substantial leap forward in the quantity and quality of genomic resources available for research on rotifers in recent years. We used available genomic and bioinformatics resources to identify variable regions of the genome to design PCR and sequencing primers for the Brachionus plicatilis complex. We then tested their suitability for the study of systematics of this group. Eight amplified successfully for members of the B. plicatilis complex. We sequenced the amplified products, constructed a concatenated alignment (5,511 bp) and carried out phylogenetic analyses. The resulting tree, based on mitochondrial and nuclear genes for 11 clones of six species, was well supported even at relatively deep nodes, contrasting with results of previous studies using only mitochondrial genes, which provide little phylogenetic information for the deepest nodes. The same procedure could be used to design primers for more conserved regions to be used in a wider range of rotifer groups.
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speciation in ancient cryptic species complexes evidence from the molecular phylogeny of Brachionus plicatilis rotifera
Evolution, 2002Co-Authors: Africa Gómez, Manuel Serra, Gary R Carvalho, David H LuntAbstract:Continental lake-dwelling zooplanktonic organisms have long been considered cosmopolitan species with little geographic variation in spite of the isolation of their habitats. Evidence of morphological cohesiveness and high dispersal capabilities support this interpretation. However, this view has been challenged recently as many such species have been shown either to comprise cryptic species complexes or to exhibit marked population genetic differentiation and strong phylogeographic structuring at a regional scale. Here we investigate the molecular phylogeny of the cosmopolitan passively dispersing rotifer Brachionus plicatilis (Rotifera: Monogononta) species complex using nucleotide sequence variation from both nuclear (ribosomal internal transcribed spacer 1, ITS1) and mitochondrial (cytochrome c oxidase subunit I, COI) genes. Analysis of rotifer resting eggs from 27 salt lakes in the Iberian Peninsula plus lakes from four continents revealed nine genetically divergent lineages. The high level of sequence divergence, absence of hybridization, and extensive sympatry observed support the specific status of these lineages. Sequence divergence estimates indicate that the B. plicatilis complex began diversifying many millions of years ago, yet has showed relatively high levels of morphological stasis. We discuss these results in relation to the ecology and genetics of aquatic invertebrates possessing dispersive resting propagules and address the apparent contradiction between zooplanktonic population structure and their morphological stasis.
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on the taxonomy of three sympatric sibling species of the Brachionus plicatilis rotifera complex from spain with the description of b ibericus n sp
Journal of Plankton Research, 2001Co-Authors: Jorge Cirosperez, Africa Gómez, Manuel SerraAbstract:The accumulation of evidence during the last decade led to the splitting of the Brachionus plicatilis complex (Rotifera) into two morphologically recognizable species: B. plicatilis Muller and B. rotundiformis Tschugunoff, previously referred to as L- and S-type B. plicatilis (s.l.), respectively. However, recent population genetics and molecular studies have revealed that each of these taxa concern cryptic species complexes. In particular, in Torreblanca Marsh, a wetland on the Mediterranean coast of Spain, three genetically distinct groups in this rotifer complex have been shown to co-occur. Differences in genetic markers, ecological preferences, mixis responses, mating behaviour and no evidence of gene flow between them have led to the conclusion that they must be considered as three different biological species. In this study we present a detailed comparative analysis using light and scanning electron microscopy of laboratory strains enabling a morphological characterization of the three species. Fine morphology and morphometry revealed taxonomic characters constant enough to recognize three well-defined morphologies, which always correspond with the respective biological species identified. Since no type material of both B. plicatilis and B. rotundiformis is available, we designed our Spanish clones as neotypes, which would allow further comparative work. Furthermore, B. ibericus n. sp. is described. This study sets the first step for a complete characterization of the biological diversity contained within this economically important species complex.
Atsushi Hagiwara - One of the best experts on this subject based on the ideXlab platform.
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The use of non-Brachionus plicatilis species complex rotifer in larviculture
Hydrobiologia, 2019Co-Authors: Atsushi Hagiwara, Helen S. MarcialAbstract:Due to the expanding world aquaculture production, the demand for high quality and quantity of fish larvae has also increased. Up to date, the bottleneck in larviculture is the stable and ample production of appropriate live food such as rotifers and copepods. Among rotifers, Brachionus plicatilis species complex, which encompasses 15 species with varied sizes ranging from 100 to 400 µm, is commonly used in most hatcheries. The use of B. plicatilis species complex ( B. plicatilis , B. koreanus , and B. rotundiformis ) in larviculture is reported in several review papers. In this review, we first described rotifer species not classified under B. plicatilis species complex, some of which are already used in larviculture, while some have high potential for use based on their characteristics, life history, and distribution. Rotifers, Brachionus angularis , Brachionus calyciflorus, and Proales similis , are described in detail in comparison with B. plicatilis species complex. Furthermore, we discussed some characteristics of rotifers which can affect their predation.
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Fifteen species in one: deciphering the Brachionus plicatilis species complex (Rotifera, Monogononta) through DNA taxonomy
Hydrobiologia, 2017Co-Authors: Scott Mills, Atsushi Hagiwara, Africa Gómez, J. Arturo Alcántara-rodríguez, Jorge Ciros-pérez, Kayla Hinson Galindo, Christian D. Jersabek, Reza Malekzadeh-viayeh, Francesca Leasi, Jae-seong LeeAbstract:Understanding patterns and processes in biological diversity is a critical task given current and rapid environmental change. Such knowledge is even more essential when the taxa under consideration are important ecological and evolutionary models. One of these cases is the monogonont rotifer cryptic species complex Brachionus plicatilis , which is by far the most extensively studied group of rotifers, is widely used in aquaculture, and is known to host a large amount of unresolved diversity. Here we collate a dataset of previously available and newly generated sequences of COI and ITS1 for 1273 isolates of the B. plicatilis complex and apply three approaches in DNA taxonomy (i.e. ABGD, PTP, and GMYC) to identify and provide support for the existence of 15 species within the complex. We used these results to explore phylogenetic signal in morphometric and ecological traits, and to understand correlation among the traits using phylogenetic comparative models. Our results support niche conservatism for some traits (e.g. body length) and phylogenetic plasticity for others (e.g. genome size).
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nutritional effects on the visual system of the rotifer Brachionus plicatilis sensu stricto rotifera monogononta
Journal of Experimental Marine Biology and Ecology, 2014Co-Authors: Hee Jin Kim, Koushirou Suga, Jae-seong Lee, Chihona Sawada, Jaesung Rhee, Atsushi HagiwaraAbstract:Abstract Rotifers have a light sensor called “eyespot” which is expected to be composed of rhodopsin. Based on the molecular feature of rhodopsin as regenerated with 11-cis-retinal, we hypothesized that phototactic behavior should be affected by the nutritional level of food; especially vitamin A availability. This study intended to address the following questions on the nutritional effects of using baker's yeast (Saccharomyces cerevisiae) and Nannochloropsis oculata: how does diet affect the pigmented area and absorbance of the eyespot, and how do these changes characterize phototactic behavior and population growth in the monogonont rotifer Brachionus plicatilis sensu stricto. The pigmented area of the eyespot decreased to 14.7 μm2 with baker's yeast while it was maintained at the initial size of 82.9 μm2 with N. oculata. Maximum absorbance of the eyespot was observed at a range of 470 to 525 nm in the initial rotifers and it was not significantly changed with diet type and culture day. The value of the maximum absorbance was maintained with N. oculata, while it rapidly decreased on day 10 with baker's yeast. Stronger positive phototaxis with N. oculata was observed under lower light intensity (0.1 and 0.5 W m− 2) at 470 nm. On the other hand, phototaxis with baker's yeast became weak and no phototactic reactions were observed under the same lighting condition. From the genomic DNA database of rotifers, 12 putative opsin-relevant genes were identified. These results corroborate the hypothesis that rhodopsin is the visual pigment in the rotifer eyespot. Lack of vitamin A with baker's yeast should induce reduction of the pigmented area and the sensitivity of the rotifer eyespot resulting in weak phototaxis. The population growth of rotifers showed different patterns related to the food type and light intensity. The lowest population growth (0.33–0.37 day− 1) was shown with baker's yeast diet at 0.5 W m− 2. This phenomenon may be significantly related to malnutrition on baker's yeast which is deficient not only in vitamin A but also in fatty acids, vitamin B12 and its derivatives.
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dietary effect of selenium fortified chlorella vulgaris on reproduction of Brachionus plicatilis species complex rotifera monogononta
International Review of Hydrobiology, 2014Co-Authors: Hee Jin Kim, Koh Nakamura, Atsushi HagiwaraAbstract:We investigated the effects of fortifying a diet of Chlorella vulgaris with Selenium (Se) on sexual and asexual reproduction of rotifers in the Brachionus plicatilis species complex: i.e. two strains of B. plicatilis sensu stricto and one of Brachionus rotundiformis. These rotifers were cultured for 8–10 days on one of three different diets that were adjusted to provide the same dry weight of food: non-fortified Chlorella, Se-fortified Chlorella, and Nannochloropsis oculata. B. plicatilis (Makishima strain), which is obligatorily asexual, showed no difference in population growth rate among the three different diets (r = 0.55–0.61). On the other hand, B. plicatilis (NH17L strain), which reproduces by cyclical parthenogenesis, showed higher population growth (r = 0.25) and also higher rates of fertilization (35.9%) and absolute resting egg production (2803.9 eggs/g food) with the Se-fortified Chlorella diet than with other foods. Although B. rotundiformis (Kochi strain), which also exhibits cyclical parthenogenesis, showed no differences in population growth among the three different diets (r = 0.42–0.48), sexual reproduction parameters were different depending on the feeding regime. The highest mixis (26.2%), fertilization (72.6%), and resting egg production (3489.9 eggs/g food) were observed with the Se-fortified Chlorella diet. We posit that the effect of Se-fortified diet was greater on the resting egg production by enhancing male fertility than on population growth.
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axenic culture of Brachionus plicatilis using antibiotics
Hydrobiologia, 2011Co-Authors: Koushirou Suga, Yukari Tanaka, Yoshitaka Sakakura, Atsushi HagiwaraAbstract:The rotifer Brachionus plicatilis culture is composed of complex microcosms including bacteria, protozoans, algae, and fungi. Previous studies reported methods to establish axenic rotifer cultures, but further refinement of these techniques is needed, for molecular biological research which requires pure culture to isolate nucleic acids from rotifers only. In order to render rotifer culture axenic, we tested five antibiotics: ampicillin (Amp), chloramphenicol (Cp), kanamycin (Km), nalidixic acid (Na), and streptomycin (Sm) at 30–100 μg/ml. Except for Cp, which reduces rotifer reproduction, all other antibiotics at the tested concentrations did not affect rotifer reproduction or show any toxic effects. A rotifer disinfection method was finally established by treating the resting eggs with 0.25% (w/v) sodium hypochlorite (NaOCl) for 3 min, washing with sterilized sea water, and then exposing the neonates to an Amp, Km, Na, and Sm mixture. Using four nutrient media, we confirmed that this protocol renders the rotifer culture bacterial and fungus free. The axenic rotifer culture generated here is useful not only for genetic analysis of Brachionus plicatilis, but for studying the rotifer life cycle without bacterial influence.
Manuel Serra - One of the best experts on this subject based on the ideXlab platform.
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evidencing the cost of sexual reproduction in the rotifer Brachionus plicatilis
Hydrobiologia, 2019Co-Authors: Nohemi Dimasflores, Manuel Serra, Eduardo M Garciaroger, Maria Jose CarmonaAbstract:Sex poses an immediate cost for monogonont rotifers, which combine exclusively asexual reproduction with periods of co-occurrence between asexual and sexual reproduction in their life cycle. Because sex is linked to dormancy, sexual daughters do not contribute to the current growth of a clonal genotype, as they only produce males or diapausing eggs. Therefore, the expectation under the all-else equal assumption (i.e., sexual and asexual females having equivalent life-history traits) is that female genotypes investing more in sexual daughters during the planktonic growing season will have slower rates of clonal growth. Here, we tested if these genotypes compensate for this greater investment in sex with higher fecundity and/or survival. We studied 45 genotypes (clones) of Brachionus plicatilis established from diapausing eggs isolated from sediments of ten brackish ponds in Spain. Using a life-table experiment, we estimated the investment in sexual reproduction of these genotypes and several life-history traits (lifespan, lifetime reproductive success, generation time and intrinsic growth rate). Results showed that there was a lack of correlation between sex-investment and any other life-history trait. Neither fecundity nor survival compensated the investment in sexual reproduction, so we conclude that the all-else-equal assumption holds and sex is costly in B. plicatilis.
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Diapausing egg banks, lake size, and genetic diversity in the rotifer Brachionus plicatilis Müller (Rotifera, Monogononta).
Hydrobiologia, 2016Co-Authors: Javier Montero-pau, Manuel Serra, Africa GómezAbstract:Diapausing egg banks are reservoirs of ecological and genetic diversity in continental zooplankton. However, although habitat size has often been used as a proxy for population size, the relationship between diapausing egg bank size and genetic diversity has not been explicitly tested in zooplankton. We estimated the density and size of diapausing egg banks, habitat size and genetic diversity (for mitochondrial and nuclear markers) of 14 populations of the rotifer Brachionus plicatilis in an endorheic basin in the SE Iberian Peninsula. The size of B. plicatilis diapausing egg banks ranged across eight orders of magnitude (from 257 to 4.9 × 1010 eggs). Despite the small geographical scale, populations were strongly structured genetically, but with no evidence of isolation by distance. Habitat size (lake area) was a better predictor of genetic diversity than total diapausing egg bank size, but only for mtDNA haplotype diversity. However, as these results were driven by the strong effect of the largest lake in the database, they should be taken with caution. Our results suggest that large lakes could have a disproportionate effect on genetic diversity and that more work is needed to support the use of habitat size as a proxy of population size in rotifers
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speciation in ancient cryptic species complexes evidence from the molecular phylogeny of Brachionus plicatilis rotifera
Evolution, 2002Co-Authors: Africa Gómez, Manuel Serra, Gary R Carvalho, David H LuntAbstract:Continental lake-dwelling zooplanktonic organisms have long been considered cosmopolitan species with little geographic variation in spite of the isolation of their habitats. Evidence of morphological cohesiveness and high dispersal capabilities support this interpretation. However, this view has been challenged recently as many such species have been shown either to comprise cryptic species complexes or to exhibit marked population genetic differentiation and strong phylogeographic structuring at a regional scale. Here we investigate the molecular phylogeny of the cosmopolitan passively dispersing rotifer Brachionus plicatilis (Rotifera: Monogononta) species complex using nucleotide sequence variation from both nuclear (ribosomal internal transcribed spacer 1, ITS1) and mitochondrial (cytochrome c oxidase subunit I, COI) genes. Analysis of rotifer resting eggs from 27 salt lakes in the Iberian Peninsula plus lakes from four continents revealed nine genetically divergent lineages. The high level of sequence divergence, absence of hybridization, and extensive sympatry observed support the specific status of these lineages. Sequence divergence estimates indicate that the B. plicatilis complex began diversifying many millions of years ago, yet has showed relatively high levels of morphological stasis. We discuss these results in relation to the ecology and genetics of aquatic invertebrates possessing dispersive resting propagules and address the apparent contradiction between zooplanktonic population structure and their morphological stasis.
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on the taxonomy of three sympatric sibling species of the Brachionus plicatilis rotifera complex from spain with the description of b ibericus n sp
Journal of Plankton Research, 2001Co-Authors: Jorge Cirosperez, Africa Gómez, Manuel SerraAbstract:The accumulation of evidence during the last decade led to the splitting of the Brachionus plicatilis complex (Rotifera) into two morphologically recognizable species: B. plicatilis Muller and B. rotundiformis Tschugunoff, previously referred to as L- and S-type B. plicatilis (s.l.), respectively. However, recent population genetics and molecular studies have revealed that each of these taxa concern cryptic species complexes. In particular, in Torreblanca Marsh, a wetland on the Mediterranean coast of Spain, three genetically distinct groups in this rotifer complex have been shown to co-occur. Differences in genetic markers, ecological preferences, mixis responses, mating behaviour and no evidence of gene flow between them have led to the conclusion that they must be considered as three different biological species. In this study we present a detailed comparative analysis using light and scanning electron microscopy of laboratory strains enabling a morphological characterization of the three species. Fine morphology and morphometry revealed taxonomic characters constant enough to recognize three well-defined morphologies, which always correspond with the respective biological species identified. Since no type material of both B. plicatilis and B. rotundiformis is available, we designed our Spanish clones as neotypes, which would allow further comparative work. Furthermore, B. ibericus n. sp. is described. This study sets the first step for a complete characterization of the biological diversity contained within this economically important species complex.
Clauspeter Stelzer - One of the best experts on this subject based on the ideXlab platform.
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Morphological and taxonomic demarcation of Brachionus asplanchnoidis Charin within the Brachionus plicatilis cryptic species complex (Rotifera, Monogononta)
Hydrobiologia, 2017Co-Authors: Evangelia Michaloudi, Spiros Papakostas, Clauspeter Stelzer, Alexander Triantafyllidis, Ilias Kappas, Scott Mills, Kalliopi Vasileiadou, Konstantinos Proios, Theodore John AbatzopoulosAbstract:Three well-defined groups, consisting of 15 species, have recently been ascribed to organisms historically identified as the Brachionus plicatilis species complex. One of these groups, the large clade, is composed of two named species ( Brachionus plicatilis s.s. and Brachionus manjavacas ) and two species identifiers ( B. ‘Nevada’ and B. ‘Austria’). B. ‘Austria’ has been confirmed to be B. asplanchnoidis . As no type specimen exists for this species, and the original taxonomic description is lacking in detail, we give a detailed account of this species using material from Obere Halbjochlacke in Austria where B. ‘Austria’ was first identified genetically. Our analysis of B. asplanchnoidis populations was of global scope, an approach that revealed a great degree of morphological variability. However, combining aspects of both the dorsal and ventral surfaces clearly discriminated B. asplanchnoidis from the rest of the large-type members. This approach may prove useful in taxonomic studies of other cryptic species with relatively few morphological features. We also observed a geographic pattern of genetic divergence within B. asplanchnoidis . Average uncorrected COI divergences for a 554-bp fragment of the COI gene ranged from 3.9% within species to 17.5% between species of the large clade and indicate deep divisions within the cryptic species complex.
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genome size evolution at the speciation level the cryptic species complex Brachionus plicatilis rotifera
BMC Evolutionary Biology, 2011Co-Authors: Clauspeter Stelzer, Simone Riss, Peter StadlerAbstract:Background Studies on genome size variation in animals are rarely done at lower taxonomic levels, e.g., slightly above/below the species level. Yet, such variation might provide important clues on the tempo and mode of genome size evolution. In this study we used the flow-cytometry method to study the evolution of genome size in the rotifer Brachionus plicatilis, a cryptic species complex consisting of at least 14 closely related species.
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a protein signal triggers sexual reproduction in Brachionus plicatilis rotifera
Marine Biology, 2006Co-Authors: Terry W Snell, Julia Kubanek, William M Carter, Audra B Payne, Jerry Kim, Melissa K Hicks, Clauspeter StelzerAbstract:The defining feature of the life cycle in monogonont rotifers such as Brachionus plicatilis (Muller) is alternation of asexual and sexual reproduction (mixis). Why sex is maintained in such life cycles is an important unsolved evolutionary question and one especially amenable to experimental analysis. Mixis is induced by a chemical signal produced by the rotifers which accumulates to threshold levels at high population densities. The chemical features of this signal were characterized using size exclusion, enzymatic degradation, protease protection assays, selective binding to anion ion exchange and C3 reversed phase HPLC columns, and the sequence of 17 N-terminal amino acids. These studies were carried out over two years beginning in 2003 using B. plicatilis Russian strain. When rotifer-conditioned medium was treated with proteinase K, its mixis-inducing ability was reduced by 70%. Proteinase K was added to medium auto-conditioned by 1 female ml−1 where typically 17% of daughters became mictic and mixis was reduced to 1%. A cocktail of protease inhibitors added to conditioned medium significantly reduced degradation of the mixis signal by natural proteases. Conditioned medium subjected to ultrafiltration retained mixis-inducing activity in the >10 kDa fraction, but the <10 kDa fraction had no significant activity. The putative mixis signal bound to an anion exchange column, eluting off at 0.72 M NaCl. These fractions were further separated on a C3 reversed phase HPLC column and mixis-inducing activity was associated with a 39 kDa protein. Seventeen amino acids from the N-terminus have strong similarity to a steroidogenesis-inducing protein isolated from human ovarian follicular fluid. The 39 kDa protein is an excellent candidate for the rotifer mixis induction signal.
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induction of sexual reproduction in Brachionus plicatilis monogononta rotifera by a density dependent chemical cue
Limnology and Oceanography, 2003Co-Authors: Clauspeter Stelzer, Terry W SnellAbstract:Induction of mixis (sexual reproduction) in rotifers of the genus Brachionus is believed to be triggered by a chemical that is released into the water and accumulates at high population densities. However, direct and conclusive evidence for this hypothesis is thus far lacking. In this study, two mass cultures of the rotifer Brachionus plicatilis were monitored as they grew from low to high population densities. Conditioned water was prepared daily from these cultures, and females were exposed in a bioassay, which consisted of juvenile Brachionus, cultured individually in large volumes that would normally suppress mixis. Conditioned water induced mixis in the bioassay at rates comparable to those found in the mass cultures. Both in bioassay and mass cultures, mixis was essentially absent in the beginning of the experiment, when population densities were very low. The first mictic females appeared at densities of 0.1 females ml-1, and their proportion increased rapidly as the populations grew to ≫1 female ml-1. The maximum rates of mixis in the bioassay were highly significant and reached 51% of those observed in the mass cultures. These results strongly support the hypothesis that mixis in Brachionus plicatilis is induced by a density-dependent chemical cue.
Terry W Snell - One of the best experts on this subject based on the ideXlab platform.
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synergistic toxicity of macondo crude oil and dispersant corexit 9500a to the Brachionus plicatilis species complex rotifera
Environmental Pollution, 2013Co-Authors: Roberto Ricomartinez, Terry W Snell, Tonya L ShearerAbstract:Using the marine rotifer Brachionus plicatilis acute toxicity tests, we estimated the toxicity of Corexit 9500A®, propylene glycol, and Macondo oil. Ratios of 1:10, 1:50 and 1:130 for Corexit 9500A®:Macondo oil mixture represent: maximum exposure concentrations, recommended ratios for deploying Corexit (1:10–1:50), 1:130 the actual dispersant:oil ratio used in the Deep Water Horizon spill. Corexit 9500A® and oil are similar in their toxicity. However, when Corexit 9500A® and oil are mixed, toxicity to B. manjavacas increases up to 52-fold. Extrapolating these results to the oil released by the Macondo well, suggests underestimation of increased toxicity from Corexit application. We found small differences in sensitivity among species of the B. plicatilis species complex, likely reflecting phylogenetic similarity. Just 2.6% of the water-accommodated fraction of oil inhibited rotifer cyst hatching by 50%, an ecologically significant result because rotifer cyst in sediments are critical resources for the recolonization of populations each Spring.
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molecular evolution of the membrane associated progesterone receptor in the Brachionus plicatilis rotifera monogononta species complex
Hydrobiologia, 2011Co-Authors: Hilary A Smith, David Mark B Welch, Terry W SnellAbstract:Many studies have investigated physiological roles of the membrane associated progesterone receptor (MAPR), but little is known of its evolution. Marked variations in response to exogenous progesterone have been reported for four brachionid rotifer species, suggesting differences in progesterone signaling and reception. Here we report sequence variation for the MAPR gene in the Brachionus plicatilis species complex. Phylogenetic analysis of this receptor is compared with relatedness based on cytochrome c oxidase subunit 1 sequences. Nonsynonymous to synonymous site substitution rate ratios, amino acid divergence, and variations in predicted phosphorylation sites are examined to assess evolution of the MAPR among brachionid clades.
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a protein signal triggers sexual reproduction in Brachionus plicatilis rotifera
Marine Biology, 2006Co-Authors: Terry W Snell, Julia Kubanek, William M Carter, Audra B Payne, Jerry Kim, Melissa K Hicks, Clauspeter StelzerAbstract:The defining feature of the life cycle in monogonont rotifers such as Brachionus plicatilis (Muller) is alternation of asexual and sexual reproduction (mixis). Why sex is maintained in such life cycles is an important unsolved evolutionary question and one especially amenable to experimental analysis. Mixis is induced by a chemical signal produced by the rotifers which accumulates to threshold levels at high population densities. The chemical features of this signal were characterized using size exclusion, enzymatic degradation, protease protection assays, selective binding to anion ion exchange and C3 reversed phase HPLC columns, and the sequence of 17 N-terminal amino acids. These studies were carried out over two years beginning in 2003 using B. plicatilis Russian strain. When rotifer-conditioned medium was treated with proteinase K, its mixis-inducing ability was reduced by 70%. Proteinase K was added to medium auto-conditioned by 1 female ml−1 where typically 17% of daughters became mictic and mixis was reduced to 1%. A cocktail of protease inhibitors added to conditioned medium significantly reduced degradation of the mixis signal by natural proteases. Conditioned medium subjected to ultrafiltration retained mixis-inducing activity in the >10 kDa fraction, but the <10 kDa fraction had no significant activity. The putative mixis signal bound to an anion exchange column, eluting off at 0.72 M NaCl. These fractions were further separated on a C3 reversed phase HPLC column and mixis-inducing activity was associated with a 39 kDa protein. Seventeen amino acids from the N-terminus have strong similarity to a steroidogenesis-inducing protein isolated from human ovarian follicular fluid. The 39 kDa protein is an excellent candidate for the rotifer mixis induction signal.
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induction of sexual reproduction in Brachionus plicatilis monogononta rotifera by a density dependent chemical cue
Limnology and Oceanography, 2003Co-Authors: Clauspeter Stelzer, Terry W SnellAbstract:Induction of mixis (sexual reproduction) in rotifers of the genus Brachionus is believed to be triggered by a chemical that is released into the water and accumulates at high population densities. However, direct and conclusive evidence for this hypothesis is thus far lacking. In this study, two mass cultures of the rotifer Brachionus plicatilis were monitored as they grew from low to high population densities. Conditioned water was prepared daily from these cultures, and females were exposed in a bioassay, which consisted of juvenile Brachionus, cultured individually in large volumes that would normally suppress mixis. Conditioned water induced mixis in the bioassay at rates comparable to those found in the mass cultures. Both in bioassay and mass cultures, mixis was essentially absent in the beginning of the experiment, when population densities were very low. The first mictic females appeared at densities of 0.1 females ml-1, and their proportion increased rapidly as the populations grew to ≫1 female ml-1. The maximum rates of mixis in the bioassay were highly significant and reached 51% of those observed in the mass cultures. These results strongly support the hypothesis that mixis in Brachionus plicatilis is induced by a density-dependent chemical cue.
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effect of some vertebrate and invertebrate hormones on the population growth mictic female production and body size of the marine rotifer Brachionus plicatilis muller
Hydrobiologia, 1997Co-Authors: Atsushi Hagiwara, Wenresti G Gallardo, Yuichi Tomita, Kiyoshi Soyano, Terry W SnellAbstract:Eight vertebrate and invertebrate hormones were screened for their effect on population growth, mictic female production, and body size of the marine rotifer Brachionus plicatilis. Growth hormone (GH) or human chorionic gonadotropin (HCG) at 0.0025–25 I.U. ml−1 and estradiol-17s (E2), triiodothyronine (T3), 20-hydroxyecdysone (20-HE), 5-hydroxytryptamine (5-HT), gamma-aminobutyric acid (GABA) or juvenile hormone (JH) at 0.05–50 mg 1−1 were added to 5-ml of Nannochloropsis oculata suspension (7 × 106 cells m1−1). From an initial density of 1 individual m1−1, rotifers were cultured with hormones for 48 hours in 22 ppt seawater at 25 °C, in darkness. Rotifers were counted and classified into female types and transferred to a new algal food suspension without hormone every other day until day 8 when body size was measured.