References of "Joaquim-Justo, Célia"
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See detailInvestigating apical adverse effects of four endocrine active substances in the freshwater gastropod Lymnaea stagnalis
Giusti, Arnaud ULg; Lagadic, Laurent; Barsi, Alpar et al

in Science of the Total Environment (2014), 493

The hermaphroditic gastropod Lymnaea stagnalis is proposed as a candidate species for the development of OECD guidelines for testing of the reprotoxicity of chemicals, including endocrine active ... [more ▼]

The hermaphroditic gastropod Lymnaea stagnalis is proposed as a candidate species for the development of OECD guidelines for testing of the reprotoxicity of chemicals, including endocrine active substances (EASs). Up to now, only a few putative EASs have been tested for their reproductive toxicity in this species. In this study, we investigate the effects of four EASs with different affinities to the vertebrate estrogen and androgen receptors (chlordecone as an estrogen; cyproterone acetate, fenitrothion and vinclozolin as anti-androgens) on the reproduction of L. stagnalis in a 21-day semi-static test. Testosterone and 17α-ethinylestradiol (EE2) were used as the reference compounds. The tested EASs had no significant effect on growth and survival at the tested concentration ranges (ng to μg/L). Classical reproduction endpoints (i.e., oviposition and fecundity) were not responsive to the tested chemicals, except for chlordecone and 17α-ethinylestradiol, which hampered reproduction from 19.6 μg/L and 17.6 μg/L, respectively. The frequency of polyembryonic eggs, used as an additional endpoint, demonstrated the effects of all compounds except EE2. The molecular pathways, which are involved in such reproduction impairments, remain unknown. Our results suggest that egg quality is a more sensitive endpoint as compared to other reproductive endpoints commonly assessed in mollusk toxicity tests. [less ▲]

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See detailProteomic Analysis of the Reproductive Organs of the Hermaphroditic Gastropod Lymnea stagnalis Exposed to Different Endocrine Disrupting Chemicals
Giusti, Arnaud ULg; Leprince, Pierre ULg; Mazzucchelli, Gabriel ULg et al

in PLoS ONE (2013), 8(11), 81086

Many studies have reported perturbations of mollusc reproduction following exposure to low concentrations (ng/L range) of endocrine disrupting chemicals (EDCs). However, the mechanisms of action of these ... [more ▼]

Many studies have reported perturbations of mollusc reproduction following exposure to low concentrations (ng/L range) of endocrine disrupting chemicals (EDCs). However, the mechanisms of action of these molecules on molluscs are still poorly understood. Investigation of the modifications of protein expression in organisms exposed to chemicals using proteomic methods can provide a broader and more comprehensive understanding of adverse impacts of pollution on organisms than conventional biochemical biomarkers (e.g., heat-shock proteins, metallothioneins, GST, EROD). In this study we have investigated the impacts of four chemicals, which exhibit different endocrine disrupting properties in vertebrates, on the proteome of the hermaphroditic freshwater pulmonate gastropod Lymnaea stagnalis after 21 days of exposure. Testosterone, tributyltin, chlordecone and cyproterone acetate were chosen as tested compounds as they can induce adverse effects on the reproduction of this snail. The 2D-DIGE method was used to identify proteins whose expression was affected by these compounds. In addition to modifying the expression of proteins involved in the structure and function of the cytoskeleton, chemicals had impacts on the expression of proteins involved in the reproduction of L. stagnalis. Exposure to 19.2 μg/L of chlordecone increased the abundance of ovipostatin, a peptide transmitted during mating through seminal fluid, which reduces oviposition in this species. The expression of yolk ferritin, the vitellogenin equivalent in L. stagnalis, was reduced after exposure to 94.2 ng Sn/L of tributyltin. The identification of yolk ferritin and the modification of its expression in snails exposed to chemicals were refined using western blot analysis. Our results showed that the tested compounds influenced the abundance of yolk ferritin in the reproductive organs. Alteration in proteins involved in reproductive pathways (e.g., ovipostatin and yolk ferritin) could constitute relevant evidence of interaction of EDCs with reproductive pathways that are under the control of the endocrine system of L. stagnalis. [less ▲]

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See detailEsterification of vertebrate like steroids in molluscs: A target of endocrine disruptors?
Giusti, Arnaud ULg; Joaquim-Justo, Célia ULg

in Comparative Biochemistry and Physiology. C : Comparative Pharmacology and Toxicology (2013), 158(4), 187-198

Alterations of the reproductive organs of gastropod molluscs exposed to pollutants have been reported in natural populations for more than 40 years. In some cases these impacts have been linked to ... [more ▼]

Alterations of the reproductive organs of gastropod molluscs exposed to pollutants have been reported in natural populations for more than 40 years. In some cases these impacts have been linked to exposure to endocrine disrupting chemicals (EDCs), which are known to induce adverse impacts on vertebrates, mainly by direct binding to steroid receptors or by altering hormone synthesis. Investigations on the mechanisms of action of endocrine disruptors in molluscs show that EDCs induce modifications of endogenous titres of androgens (e.g., testosterone, androstenedione) and oestrogens (e.g., 17ß-oestradiol). Alterations of the activity of enzymes related to steroid metabolism (i.e., cytochrome P450 aromatase, acyltransferases) are also often observed. In bivalves and gastropods, fatty acid esterification of steroids might constitute the major regulation of androgen and oestrogen homeostasis. The present review indicates that metabolism of steroid hormones to fatty acid esters might be a target of synthetic EDCs. Alterations of this process would impact the concentrations of free, potentially bioactive, form of steroids. [less ▲]

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See detailImpact of anti-androgenic substances on gametogenesis of the rotifer Brachionus calyciflorus
Cruciani, Valentina ULg; Thomé, Jean-Pierre ULg; Joaquim-Justo, Célia ULg

Poster (2013, October 01)

Several studies have shown that pollutants with anti-androgenic activity have an impact on the sexual reproduction of the rotifer Brachionus calyciflorus (Joaquim-Justo et al., submit; Preston et al ... [more ▼]

Several studies have shown that pollutants with anti-androgenic activity have an impact on the sexual reproduction of the rotifer Brachionus calyciflorus (Joaquim-Justo et al., submit; Preston et al., 2001). The effects observed are compatible with the phenomenon of endocrine disruption. Fenitrothion, a non-steroidal anti-androgen induces a decrease in fertilization rate following exposure below or equal to 0,5 mg L-1.. The steroidal anti-androgen, cyproterone acetate increases number of cysts in population exposed to concentrations below or equal to 0,5 mg L-1. Cross mating experiments showed that effects of fenitrothion are due to an impact on males exclusively, while effects of cyproterone acetate exposition are due to an impact on females exclusively. In this study, we investigated the impact of fenitrothion on spermatogenesis and observed a decrease in the spermatozoa production and mobility with concentrations down to 0,5 mg L-1. We report a detailed description of the morphology of the male reproductive apparatus in B. calyciflorus based on optic, transmission electron and scanning electron microscopy in controls and exposed individuals. [less ▲]

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See detailTestosterone levels and fecundity in the hermaphroditic aquatic snail Lymnaea stagnalis exposed to testosterone and endocrine disruptors
Giusti, Arnaud ULg; Ducrot, Virginie; Joaquim-Justo, Célia ULg et al

in Environmental Toxicology & Chemistry (2013), 32(8), 1740-1745

Endocrine disruptors are known to alter endogenous free and/or esterified levels of androgenic and estrogenic steroid hormones in aquatic molluscs. However, there is still a controversy on the origin of ... [more ▼]

Endocrine disruptors are known to alter endogenous free and/or esterified levels of androgenic and estrogenic steroid hormones in aquatic molluscs. However, there is still a controversy on the origin of steroids in these animals. In this study, free and esterified testosterone concentrations were measured in the hermaphroditic aquatic gastropod Lymnaea stagnalis exposed to molecules known for their androgenic (testosterone and tributyltin), anti-androgenic (cyproterone-acetate) and estrogenic (chlordecone) properties by reference to their mode of action in vertebrates. In parallel, snail oviposition and fecundity were followed over the 21-day exposure period. Testosterone exposure resulted in increased esterified testosterone levels whereas free testosterone concentrations remained stable. In contrast, cyproterone-acetate increased significantly the free form of testosterone with no changes in the esterified form whereas chlordecone showed a tendency to reduce, though not significantly, esterified testosterone concentrations without changes in free testosterone levels. Finally, tributyltin did not alter testosterone homeostasis. The production of egg-clutches and eggs was significantly reduced only in the snails exposed to the highest concentrations of chlordecone (19.6 µg/L) and tributyltin (94.2 ng Sn/L). Overall, this study demonstrates that uptake of testosterone from the exposure medium occurs in L. stagnalis. Moreover, it shows that cyproterone-acetate and, to a lesser extent, chlordecone can alter endogenous testosterone levels in this freshwater snail. However, relationship between hormonal changes and snail reproduction has not been established. [less ▲]

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See detailReproductive impacts of tributyltin (TBT) and triphenyltin (TPT) in the hermaphroditic freshwater gastropod Lymnaea stagnalis
Giusti, Arnaud ULg; Barsi, Alpar; Dugué, Maël et al

in Environmental Toxicology & Chemistry (2013), 32(7), 1552-1560

Tributyltin (TBT) and triphenyltin (TPT) are emblematic endocrine disruptors, which have been mostly studied in gonochoric prosobranchs. Although both compounds can simultaneously occur in the environment ... [more ▼]

Tributyltin (TBT) and triphenyltin (TPT) are emblematic endocrine disruptors, which have been mostly studied in gonochoric prosobranchs. Although both compounds can simultaneously occur in the environment, they have mainly been tested separately for their effects on snail reproduction. Because large discrepancies in experimental conditions occurred in these tests, the present study aimed at comparing the relative toxicity of TBT and TPT under similar laboratory conditions in the 0–600 ng Sn/L range. Tests were performed on the simultaneous hermaphrodite Lymnaea stagnalis, a freshwater snail in which effects of TPT were unknown. Survival, shell length and reproduction were monitored in a 21d semi-static test. Frequency of abnormal eggs was assessed as an additional endpoint. TPT hampered survival while TBT did not. Major effects on shell solidity and reproduction were observed for both compounds, reproductive outputs being more severely hampered by TBT than by TPT. Considering the frequency of abnormal eggs allowed increasing test sensitivity, since snail responses to TBT could be detected at concentrations as low as 19 ng Sn/L. However, the putative mode of action of the two compounds could not be deduced from the structure of the molecules or from the response of apical endpoints. Sensitivity of L. stagnalis to TBT and TPT was compared to the sensitivity of prosobranch molluscs with different habitats and different reproductive strategies. [less ▲]

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See detailEffects of tributyltin (TBT) and triphenyltin (TPT) on the reproduction of the freshwater snail Lymnaea stagnalis
Lagadic, Laurent; Giusti, Arnaud ULg; Barsi, Alpar et al

Conference (2012, December 10)

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See detailReproductive impact and proteomic analysis of androgenic and anti-androgenic disruptors on the hermaphroditic freshwater gastropod Lymnaea stagnalis
Giusti, Arnaud ULg; Ducrot, Virginie; Joaquim-Justo, Célia ULg et al

Poster (2011, November)

In this study, e ects of two androgens (tributyltin and testosterone), one antiandrogen (cyproterone acetate) and one estrogen (chlordecone) on growth and reproduction were investigated in the ... [more ▼]

In this study, e ects of two androgens (tributyltin and testosterone), one antiandrogen (cyproterone acetate) and one estrogen (chlordecone) on growth and reproduction were investigated in the hermaphrodite gastropod Lymnaea stagnalis. In this study, exposure to a range of concentrations (ng/l to μg/l) of each chemical was performed during 21 days. e number of clutches and the number of eggs per clutch were monitored. A decrease in clutches laid per snail was observed after exposure to tributyltin (540, 1180 and 2600 ng/l) and chlordecone (10, 22, 50 and 110 μg/l). A signi cant decrease in egg laid per snail was observed after exposure to tributyltin (540, 1180 and 2600 ng/l) and chlordecone (50 and 110 μg/l). An increase of egg abnormalities ratio in exposed snails (atrophied albumen, polyembryonicity,...) was observed in L. stagnalis following exposure to testosterone (2, 22, 50 and 110 ng/l), cyproterone acetate (4,5 and 50 μg/l), tributyltin (110 and 244 ng/l) and chlordecone (4,5 and 10 μg/l). Investigation of alteration in protein expression in exposed snails was performed using proteomic analysis such as 2D-DIGE. Mass spectrometry identi cation was performed on proteins with altered expression. We could establish correlation between reproductive endpoints and changes in proteins involved in egg formation and in egg laying were underlined. Egg yolk ferritin, the main protein of egg yolk, was shown to be reduced signi cantly in relationship with a decrease of egg yolk quality after exposure to tributyltin 540 ng/l and cyproterone acetate 4,5 μg/l. Ovipostatin, a protein proved to reduce egg masses, was signi cantly over expressed in snails exposed to 50 μg/l of chlordecone and were in relationship with a reduction of clutches laid by individuals. Further western blot analysis on those proteins involved in the reproduction are underway. ese analysis will enable us to con rm and re ne with more speci city the 2D-DIGE results for the selected proteins. e results of this study can help to establish new biomarkers of exposure of endocrine disruptors in freshwater environment and can provide new insight on mode of action of endocrine disruptors in L. stagnalis. [less ▲]

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See detailGroundwater quality assessment of one former industrial site in Belgium using a TRIAD-like approach.
Crévecoeur, Sophie; Debacker, Virginie ULg; Joaquim-Justo, Célia ULg et al

in Environmental Pollution (2011), 159(10), 2461-2466

Contaminated industrial sites are important sources of pollution and may result in ecotoxicological effects on terrestrial, aquatic and groundwater ecosystems. An effect-based approach to evaluate and ... [more ▼]

Contaminated industrial sites are important sources of pollution and may result in ecotoxicological effects on terrestrial, aquatic and groundwater ecosystems. An effect-based approach to evaluate and assess pollution-induced degradation due to contaminated groundwater was carried out in this study. The new concept, referred to as “Groundwater Quality TRIAD-like” (GwQT) approach, is adapted from classical TRIAD approaches. GwQT is based on measurements of chemical concentrations, laboratory toxicity tests and physico-chemical analyses. These components are combined in the GwQT using qualitative and quantitative (using zero to one subindices)integration approaches. The TRIAD approach is applied for the first time on groundwater from one former industrial site located in Belgium. This approach will allow the classification of sites into categories according to the degree of contaminant-induced degradation. This new concept is a starting point for groundwater characterization and is open for improvement and adjustment. [less ▲]

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See detailEffects of androgenic and anti-androgenic substances on the freshwater gastropod Lymnaea stagnalis
Giusti, Arnaud ULg; Ducrot, Virginie; Joaquim-Justo, Célia ULg et al

Poster (2010, May 25)

Knowledge on the impacts of endocrine disrupting chemicals (EDCs) on gastropods is scarce and their mechanisms of action are still poorly understood. In this study, effects of 3 androgens (tributyltin ... [more ▼]

Knowledge on the impacts of endocrine disrupting chemicals (EDCs) on gastropods is scarce and their mechanisms of action are still poorly understood. In this study, effects of 3 androgens (tributyltin, testosterone and fenitrothion), 2 anti-androgens (cyproterone acetate and vinclozolin) and 1 estrogen (chlordecone) on growth and reproduction were investigated in the hermaphrodite gastropod Lymnaea stagnalis. [less ▲]

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See detailImpact of anti-androgens on the production of spermatozoa in Brachionus calyciflorus
Joaquim-Justo, Célia ULg; Cruciani, Valentina ULg; BLASZCZYK, Marie ULg et al

Poster (2010, May 23)

Putative endocrine disruptors affect rate of fertilization of sexual females by males. Preston et al. (2000) reported a decrease in fertilization rate following exposition to, notably, flutamide at 10µg/l ... [more ▼]

Putative endocrine disruptors affect rate of fertilization of sexual females by males. Preston et al. (2000) reported a decrease in fertilization rate following exposition to, notably, flutamide at 10µg/l. We observed similar effects with fenitrothion. Cross mating experiments showed that the decrease in fertilization rate is due to an impact on males exclusively. We studied the impact of anti-androgens on spermatogenesis and observed a decrease in the spermatozoa production with concentrations down to 0,5 mg L-1.We also report a detailed description of the morphology of the male reproductive apparatus in B. calyciflorus based on optic and electronic microscopy analysis and we describe the effect of anti-androgens on males and spermatogenesis in males. [less ▲]

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See detailImpacts of androgenic and antiandrogenic substances on the freshwater pulmonate gastropod Lymnaea stagnalis
Giusti, Arnaud ULg; Lagadic, Laurent; Joaquim-Justo, Célia ULg et al

Poster (2010, May 23)

Knowledge on the impacts of endocrine disruptors on gastropods is scarce and their mechanism of action poorly understood especially the impacts of androgenic and antiandrogenic compounds. In this study ... [more ▼]

Knowledge on the impacts of endocrine disruptors on gastropods is scarce and their mechanism of action poorly understood especially the impacts of androgenic and antiandrogenic compounds. In this study effects of 5 androgenics and antiandrogenics endocrine disruptors were investigated on the reproduction and life traits of the freshwater pulmonate gastropod Lymnaea stagnalis. The chemicals tested were Tributyltin, Cyproterone acetate, Methyltestosterone, Vinclozolin and Fenitrothion. Tributyltin was used as androgenic positive control. The other compounds tested are androgenic and antiandrogenic compounds either steroids or non steroids. Adult snails were exposed to 3 concentrations of each chemical for 30 days. The size and reproductive organs development were monitored throughout exposure. The number of clutches, the number of eggs per clutch were assessed during the first 10 days. The clutches were kept individually in clear water except for the clutches of the eighth day which were divided in two. Half was kept individually in clear water and the other half was individually reared in contaminated water following the same exposure as their parents. The percentage of hatching per clutch of these clutches was measured. The development size, mortality, and development of reproductive organs of the juveniles were assessed until their first clutch was laid. [less ▲]

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See detailWorkshop on rotifers in ecotoxicology
Snell, T. W.; Joaquim-Justo, Célia ULg

in Hydrobiologia (2007), 593

The aim of the workshop on rotifers in ecotoxicology was to stimulate discussions on new developments in the field. Discussions about the use of biomolecular tools indicate that gene expression analysis ... [more ▼]

The aim of the workshop on rotifers in ecotoxicology was to stimulate discussions on new developments in the field. Discussions about the use of biomolecular tools indicate that gene expression analysis with rotifers should be available in the next few years. Such analyses will be a great asset as they enable ecotoxicologists to study molecular mechanisms of toxicity. Rotifers also appear as useful tools in the risk assessment of pharmaceuticals and their metabolites that find their way into aquatic ecosystems because their sensitivity to some of these substances is higher than that of cladocerans and algae. The nature and extent of the impact of potential endocrine disruptors on aquatic invertebrates is another poorly resolved issue for which rotifers are a promising tool. Indeed, rotifers seem to be particularly sensitive to androgenic and anti-antiandrogenic substances, whereas copepods and cladocerans are typically more affected by estrogens and juvenile hormone-like compounds. Besides their usefulness in these emerging fields of aquatic ecotoxicology, it was emphasized that research with rotifers on basic issues like, e.g., toxicant interference with predation, competition, or interspecific and interclonal variation in ecotoxicological tests is still needed. [less ▲]

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See detailEFFECT OF ANTI-ANDROGENIC SUBSTANCES ON THE SEXUAL REPRODUCTION OF ROTIFERS : IMPACTS ON BRACHIONUS CALYCIFLORUS MALE FERTILITY
Joaquim-Justo, Célia ULg; Maule, P; Luy, N et al

Conference (2007, August 12)

Many substances released in aquatic ecosystems have been reported to disrupt endocrine systems in vertebrates and invertebrates. In the rotifer Brachionus calyciflorus, studies show that chemicals ... [more ▼]

Many substances released in aquatic ecosystems have been reported to disrupt endocrine systems in vertebrates and invertebrates. In the rotifer Brachionus calyciflorus, studies show that chemicals characterized by a high affinity to the vertebrate androgen receptor depress sexual reproduction at concentrations one to two orders of magnitude below those that affect asexual reproduction. We studied the effect of cyproterone acetate, an anti-androgen of steroid like structure, and of the pesticide fenitrothion, a non steroidal molecular which has a high affinity to the vertebrate androgen receptor, on the sexual reproduction of rotifers. In mating experiments we crossed control females with exposed males and vice versa to determine whether anti-androgens affected males, females or both. Fertilization rate and number of resting eggs produced were affected by both substances tested. With fenitrothion, depression of these endpoints was observed exclusively when males were treated. Cyproterone acetate enhanced production of resting eggs whereas fertilization rate was not significantly affected. Increased production of resting eggs was observed both with treated females and males. Parameters of male fertility were compared in control and in exposed males. We report impacts on spermatozoa numbers, morphology and fertilizing potential, and on male morphology, longevity and mating behaviour for the two substances tested. [less ▲]

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See detailTrophic links in the lowland River Meuse (Belgium): assessing the role of bacteria and protozoans in planktonic food webs
Joaquim-Justo, Célia ULg; Pirlot, S.; Viroux, L. et al

in Journal of Plankton Research (2006), 28(9), 857-870

Trophic interactions within the plankton of the lowland River Meuse (Belgium) were measured in spring and summer 2001. Consumption of bacteria by protozoa was measured by monitoring the disappearance of H ... [more ▼]

Trophic interactions within the plankton of the lowland River Meuse (Belgium) were measured in spring and summer 2001. Consumption of bacteria by protozoa was measured by monitoring the disappearance of H-3-thymidine-labelled bacteria. Metazooplankton bacterivory was assessed using 0.5-mu m fluorescent microparticles (FMPs), and predation of metazooplankton on ciliates was measured using natural ciliate assemblages labelled with FMPs as tracer food. Grazing of metazooplanklon on flagellates was determined through in situ incubations with manipulated metazooplankton densities. Protozooplankton bacterivory varied between 6.08 and 53.90 mg C m(-3) day(-1) (i.e. from 0.12 to 0.86 g C-1 bacteria g C-1 protozoa day(-1)). Metazooplankton, essentially rotfiers, grazing on bacteria was negligible compared with grazing by protozoa (similar to 1000 times lower). Predation of rotfiers on heterotrophic flagellates (HFs) was generally low (on average 1.77 mg C m(-3) day(-1), i.e. 0.084 g C-1 flagellates g C-1 rotfiers day(-1)), the higher contribution of HF in the diet of rotfiers being observed when Keratella cochlearis was the dominant metazooplankter. Predation of rotfiers on ciliates was low in spring samples (0.56 mg C m(-3) day(-1), i.e. 0.014 g C-1 ciliates g C-1 rotfiers day(-1)) in contrast to measurements performed in July (8.72 mg C m(-3) day(-1), i.e. 0.242 g C-1 ciliates g C-1 rotfiers day(-1)). The proportion of protozoa in the diet of rotfiers was low compared with that of phytoplankton (< 30% of total carbon ingestion) except when phytoplankton biomass decreased below the incipient limiting level (ILL) of the main metazooplantonic species. In such conditions, protozoa (mainly ciliates) constituted similar to 50% of total rotfier diet These results give evidence that microbial organisms play a significant role within the planktonic food web of a eutrophic lowland river, ciliates providing an alternative food for metazooplankton when phytoplankton becomes scarce. [less ▲]

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See detailEffect of anti-androgenic substances on the sexual reproduction of the rotifer Brachionus calyciflorus.
Joaquim-Justo, Célia ULg; Snell, T.W

Conference (2006, March 11)

Many substances released in the aquatic environment have been reported to have disruptive effects on endocrine systems of vertebrates and invertebrates. In rotifers, some of these chemicals have been ... [more ▼]

Many substances released in the aquatic environment have been reported to have disruptive effects on endocrine systems of vertebrates and invertebrates. In rotifers, some of these chemicals have been shown to depress sexual reproduction at concentrations one to two orders of magnitude below those that affect asexual reproduction. The anti-androgen flutamide impacts sexual reproduction of rotifers at particularly low concentrations. We studied the effect of different types of putative endocrine disruptors on sexual reproduction of Brachionus calyciflorus. Contaminants tested were cyproterone acetate, an anti-androgen with a steroid-like structure, the pesticides fenitrothion and linuron which both have high affinity to the androgen receptor in vertebrates, although they are nonsteroidal molecules, and lindane a widely used pesticide that binds weakly to the androgen receptor in vertebrates. A series of endpoints relative to different steps of sexual reproduction were monitored to define critical functions affected and to get information on mechanisms of action. Fenitrothion, had the strongest impact on the sexual reproduction of rotifers. We observed a decrease in the proportion of mictic females among the ovigerous individuals and in the production of fertilized eggs per female that was proportional to the dose. The most sensitive parameter was the number of males produced per mictic female which was considerably higher in treated animals even at concentrations 10 times lower than the NOEC of asexual reproduction. [less ▲]

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See detailFEEDING SELECTIVITY OF THE ROTIFER BRACHIONUS CALYCIFLORUS: EVIDENCE OF THE ROLE OF CHEMICAL CUES.
Joaquim-Justo, Célia ULg; Ayala-Andrés, N; Thomé, Jean-Pierre ULg

Poster (2005, June 19)

The rotifer Brachionus calyciflorus is a ubiquitous species that often dominates river zooplankton. It has been described as a species that selects its food mainly on the basis of the size of food ... [more ▼]

The rotifer Brachionus calyciflorus is a ubiquitous species that often dominates river zooplankton. It has been described as a species that selects its food mainly on the basis of the size of food particles and not on the basis of their taste. Nevertheless, experiments carried out with a green algae, 3,5 microns in diameter, showed that the ingestion rate of rotifers on DTAF (5-(4,6-dichlorotriazin-2-yl)aminofluorescein) stained algae is much lower than on untreated algae. The impact of all steps of the staining procedure was tested to determine the factor that elicits a negative selection against stained algae. Moreover, impact of algal abundance and light on selection was tested. Results clearly show the selection is triggered by chemical cues, DTAF itself inducing the strongest avoidance. Algal abundance influenced the degree of selectivity of rotifers; analysis of ingestion rate of treated and untreated algae throughout all treatments provide information on selection mechanisms and support the hypothesis that B. calyciflorus can detect chemical cues in the buccal funnel, even when feeding on small preys, and select its food accordingly. [less ▲]

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See detailFeeding of planktonic rotifers on ciliates: a method using natural ciliate assemblages labelled with fluorescent microparticles
Joaquim-Justo, Célia ULg; Detry, Cédric ULg; Caufman, F. et al

in Journal of Plankton Research (2004), 26(11), 1289-1299

A method was developed to allow direct measurements of predation exerted by metazooplankton on ciliates. The method relied on the use of ciliates labelled with fluorescent microparticles (FMP). Optimal ... [more ▼]

A method was developed to allow direct measurements of predation exerted by metazooplankton on ciliates. The method relied on the use of ciliates labelled with fluorescent microparticles (FMP). Optimal labelling conditions were determined with ciliates from cultures (Tetrahymena pyriformis) and with natural ciliate assemblages sampled in a river. Labelled T. pyriformis were used as tracer food to determine gut passage time (GPT) and ingestion rates of the rotifer Brachionus calyciflorus in the laboratory. Predation of metazooplankton from the lowland river Meuse (Belgium) was determined by labelling natural assemblages of ciliates and using them as tracer food for metazooplankters sampled in the river. Optimal labels of ciliates, i.e. sharp distribution of FMP in cells, were obtained with short incubations (10 min) and low FMP concentrations (1 x 10(5) mL(-1)). GPT varied between 30 and 45 min for B. calyciflorus and from 25 up to >35 min for rotifers from the river. The ingestion rate of B. calyciflorus fed with T. pyriformis was 3.3 +/- 0.6 ciliate rot(-1) h(-1), i.e. 1.4 +/- 0.3 ngC rot(-1) h(-1). Metazooplankton species for which the ingestion of ciliates could be measured were the rotifers Keratella cochlearis, Euchlanis dilatata and Synchaeta spp. Ingestion rates measured ranged from 0.4 to 12.5 ngC rot(-1) h(-1). The method proposed proved to be useful in estimating the predation of microplankton on ciliates in semi- in situ conditions; in further developments, labelled natural assemblages of ciliates could be used for in situ incubations with the Haney chamber. [less ▲]

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