Ecdysteroids in the shrimp Palaemon serratus: relations with molt cycle

Impact of cadmium on the ecdysteroids production in Gammarus fossarum

Gammarus fossarum is an important test organism which is currently used as a bio-indicator as well as in ecotoxicological tests. Nevertheless, data on ecdysteroids in endocrine toxicity test are not yet available for these species, despite its crucial role in molting and reproduction. In the present paper, ecdysteroids concentrations were studied during the molt cycle (in females) and embryonic development in G. fossarum (Crustacea, Amphipoda) in order to propose an ecdysteroids toxicity test. Ecdysteroids levels in G. fossarum showed a single peak during premolt at stage Dl-D2. In embryos, ecdysteroids levels progressively increased over stages 3 and 4, with peak levels at stage 4. A Cadmium toxicity test was proposed to examine if the molting and embryogenesis disturbances previously observed after cadmium exposure (Geffard et al. 2010) could be attributed to changes in ecdysteroids titers. Exposure to the different cadmium concentrations (3; 9; 300; 900 µg/l) increased ecdysteroids secretion by Y-organs in vitro, but it had no significant effect on exposed embryos (in vivo). Based on previous findings, we are led to conclude that the molting impairments in cadmium-exposed females of G. fossarum is connected to the changes in ecdysteroids concentrations.

Gammarus spp. in aquatic ecotoxicology and water quality assessment: toward integrated multilevel tests

The amphipod genus Gammarus is widespread and is structurally and functionally important in epigean freshwaters of the Northern Hemisphere. Its presence is crucial, because macroinvertebrate feeding is a major rate-limiting step in the processing of stream detrius. In addition, Gammarus interacts with multiple trophic levels bu functioning as prey, predator, herbivore, detritivore, and shredder. Such a broad span of ecosystem participation underlines the importance of Gammarus to pollutants and other disturbances may render it a valuable indicator for ecosystem health. This review summarizes the vast number of studies conducted with Gammarus spp. for evaluating aquatic ecotoxicology endpoints and examines the suitability of this native invertabrate species for the assessment of stream ecosystem health in the Northern Hemisphere. Numerous papers have been published on how pollutants affect gammarind behavior (i.e., mating, predator avoidance), reproduction, development, feeding activity, population structure, as well as the consequences of pollution on host-parasite, predator-prey, or native-invasive species interactions. Some biochemical and molecular biomarkers have already been established, such as the measurement of vitellogenin-like proteins, metallothioneins, alkali-labile phosphates (in proteins), and lipogenic enzyme activities for assessing endocrine distribution and detoxification mechanisms.

Altered exoskeleton composition and vitellogenesis in the crustacean Gammarus sp. collected at polluted sites in the Saguenay Fjord, Quebec, Canada

Gammarus sp. individuals were collected at four intertidal sites subjected to direct sources of pollution (marinas, ferry traffic, and harbors) and at one site with no direct source of pollution. Levels of vitellogenin-like proteins (Vtg), metallothioneins (MT), alkali-labile phosphates (ALPs) in proteins, and lipogenic enzyme activities (i.e., glucose-6-dehydrogenase, isocitrate dehydrogenase, and malate enzyme) were measured in whole soft tissues. In exoskeletons, levels of pH-dependent extractable protein and chitin were determined to assess the possible impacts of pollution on exoskeleton integrity and the molting process. Results show that males were consistently heavier than females regardless of site quality but that the whole-body weight of both sexes was significantly lower at polluted sites. Females displayed either induced or decreased Vtg-like proteins at polluted sites, indicating significant changes in gametogenesis activity. MT levels were not sex dependent and tended to be induced at all impacted sites. ALP levels in acetone-fractionated proteins indicate altered phosphate mobilization at some impacted sites, where females tended to display higher ALP levels. Lipogenic enzyme activities did not vary by sex but were readily increased at impacted sites, suggesting a delay in gonad maturation rates. Exoskeleton protein characteristics revealed that the proportion of chitin in exoskeletons was a lower at most impacted site, suggesting disruption of chitin and pH-dependent protein mobilization. Principal component analysis revealed that gammarids collected at affected sites displayed substantial changes in the proportion of chitin, arthropodin, sclerotin, MTs, and intermediary glucose metabolism (glucose-6-phosphate dehydrogenase, and isocitrate dehydrogenase in soft tissues) and thus suffered from disturbed gametogenesis and exoskeleton integrity.

Shell protein characteristics and vitellogenin-like proteins in brine shrimp Artemia franciscana exposed to municipal effluent and 20-hydroxyecdysone

We developed biomarkers to monitor the endocrine-disrupting potential of contaminants and municipal effluents in aquatic arthropods. Artemia fransciscana shrimp were cultured and exposed to increasing concentrations of 20-hydroxyecdysone (20HE) and solid phase (C-8) municipal effluent extract (MEE) for 48 h at 20 degrees C. The levels of vitellogenin (Vtg)-like proteins, alkali-labile phosphates in total proteins and acetylcholinesterase (AChE) activity were determined in soft tissues. The levels of acid-soluble, alkali-soluble (sclerotin), neutral-soluble (arthropodin) proteins and chitin were determined to characterize the maturation state of shells. Both 20HE and the municipal effluent extract readily increased the total activity of acetylcholinesterase, alkali-labile phosphates in proteins and vitellogenin-like proteins in brine shrimp. In shells, 20HE and the effluent extract increased the proportion of chitin in shells and acid-soluble proteins but were not statistically significant for the latter. The proportion of sclerotin was increased by 20HE but was not changed by the effluent extract. The proportion of arthropodin was decreased by both 20HE and the effluent extract. Correlation analysis revealed that, as expected, the proportion of acid-soluble protein for biomineralisation and chitin levels were positively correlated and the proportion of arthropodin and sclerotin were negatively correlated in shells exposed to 20HE. Principal component analysis revealed that the proportion of chitin, arthropodin, sclerotin and acid-soluble proteins explained 63% of the responses. Shell protein and carbohydrate contents, controlled by the molting hormone 20HE, could be used as efficient markers for ecdysial properties of various contaminants. The municipal effluent appears to contain ecdysial-like chemicals that are capable of producing changes in shell protein composition that are similar to 20HE.

Ecdysteroid concentrations through various life-stages of the meiobenthic harpacticoid copepod, Amphiascus tenuiremis and the benthic estuarine amphipod, Leptocheirus plumulosus

Endocrine function in arthropods has principally been characterized in insects and malacostracan crustaceans. However, meiofauna represent the most abundant metazoan marine taxa, with harpacticoid copepods comprising the second most abundant taxon. In addition, their diminutive biomass has made characterization of endocrine components difficult, so little is known about endocrine control of reproduction, molting, and growth in meiofauna. In this study, a sensitive fluorometric enzyme immunoassay (EIA) was utilized to quantify and compare the arthropod molting hormone, 20-hydroxyecdysone (20E), in various life-cycle and developmental stages of a laboratory reared meiobenthic copepod, Amphiascus tenuiremis, and in an amphipod, Leptocheirus plumulosus. In copepods, gravid females carrying late stage pre-hatch embryos contained significantly more 20E (390+/-252 fmol/female) than gravids carrying early (Stage-I) embryos (172+/-83 fmol/female). In contrast, ecdysteroid levels in Stage-I L. plumulosus gravid females (277+/-83 fmol/female) was greater than pre-hatch gravid females (146+/-42). Stage-I embryos of both copepods (19+/-10) and amphipods (11+/-5 fmol/embryo) possessed lower ecdysteroid content than copepod (35+/-15) and amphipod (43+/-33 fmol/embryo) pre-hatch embryos. Ecdysteroid levels were also assessed in naupliar, juvenile, adult male and non-gravid female copepod life-stages. In addition, ecdysteroids measured in field collected copepod species indicated gravid females possessed ecdysteroid levels similar to gravid A. tenuiremis. However, upon normalization of egg sac 20E content by brood size, embryos from larger broods contained lower levels of ecdysteroids when compared to embryos from smaller clutch sizes-indicating an inverse embryo/ecdysteroid relationship may exist across species.

Dynamic interactions of behavior and amine neurochemistry in acquisition and maintenance of social rank in crayfish

This review summarizes a set of experimental approaches with which we explore fighting behavior in crayfish and the importance of aminergic systems in its control. Our results illustrate that agonistic behavior in crustaceans can be characterized within a quantitative framework, that different types of behavioral plasticity in aggressive behavior are in need of physiological explanation, and that pharmacological intervention involving serotonergic systems produces characteristic changes in fighting. Moreover, we attempt to identify changes in neurochemistry during the acquisition of social status. Many of the studies presented here summarize ongoing work. Nonetheless, results to date complement and extend previous detailed physiological, morphological and biochemical studies exploring the roles of amines in aggression.

Role of the midgut gland in metabolism and excretion of ecdysteroids by lobsters, Homarus americanus

The chromatographic profile of ecdysteroids (Ecds) from the midgut gland (MG) of juvenile female lobsters, Homarus americanus, was examined using high-performance liquid chromatography (HPLC) and radioimmunoassay (RIA) over four stages of the molt cycle. Upon initial examination, highly polar Ecd conjugates appeared to be the principal metabolites found in all molt stages. HPLC fractions containing apolar Ecds initially exhibited low RIA activity. Upon hydrolysis with a Helix pomatia enzyme preparation and reanalysis, significant amounts of other Ecds were released. Amounts of apolar Ecd conjugates were estimated, at their highest levels, to be at least 50% of the total Ecds in MGs of molt stage D3 lobsters. Only the MG formed significant amounts of apolar Ecds upon in vitro culture with [3H]ecdysone ([3H]E). Epidermis and antennal gland significantly increased their rates of [3H]E metabolism in vitro between molt stages C4 and D1. This result further supports the idea that regulation of ecdysteroid metabolism, at least in selected tissues, may be important in the molt cycle regulation of hormone titers. Using gel filtration column chromatography and sucrose density gradient centrifugation analyses, evidence was found for association of apolar Ecds with a protein(s) from MG cytosol. The protein was estimated to have a molecular weight of 180,000-200,000 and specifically bound apolar Ecds.

Ecdysteroids in relation to the molt cycle of the American lobster, Homarus americanus. I. Hemolymph titers and metabolites

Hemolymph ecdysteroid (Ecd) titers were measured using radioimmunoassay (RIA) during the molt cycle of the American lobster, Homarus americanus. Individual animals showed small, transitory rises of Ecds which increased in magnitude with the onset of premolt and culminated in a large premolt peak at morphological stages D2(2)-D3(1). Male lobsters had significant postmolt peaks and late premolt titers that remained high until ecdysis. In females, postmolt peaks were absent and late premolt titers reached basal levels before ecdysis. At least seven different Ecd metabolites were identified by high-performance liquid chromatography-RIA analyses. High polarity products (HP) were the most abundant metabolites in virtually every molt stage. Titers of HP were significantly higher in males during late postmolt-early intermolt and in late premolt. Levels of 20-hydroxyecdysone (20E) were equivalent in both sexes and correlated with the morphological changes associated with premolt. Evidence was also obtained for the presence of ecdysone, ponasterone A, and other as yet unidentified metabolites. The pattern of Ecd metabolites in the hemolymph supports other data indicative of 20E as the major molting hormone. Metabolism of 20E is primarily toward more polar compounds, including conjugates.

Ecdysteroid levels during embryogenesis in the shrimp, Palaemon serratus (Crustacea Decapoda): quantitative and qualitative changes

During the embryogenesis of Palaemon serratus profound changes in ecdysteroid concentrations were found. Ecdysteroid concentrations increase at the appearance of the Y-organ and a slight decrease is observed just before hatching. Two peaks of ecdysteroid concentration occur between these two events if Palaemon is reared at 19 degrees, but only one broad maximum is observed after rearing at 11-12 degrees. The pattern of ecdysteroids changes during embryogenesis; the ecdysone level decreases, while the 20-OH-ecdysone concentration and the amount of high polarity products increase. During the embryonic stage C the ratio of 20-OH-ecdysone to ecdysone was shown by HPLC analysis to steadily increase. After enzymatic hydrolysis of high-polarity products the main RIA-positive material elutes from reversed-phase HPLC columns as 20-OH-ecdysone.

Ecdysteroid titers during the molt cycle of Orchestia cavimana (Crustacea, Amphipoda)

Ecdysteroids were analyzed during a molt cycle in adult males of the crustacean Orchestia cavimana; levels were determined in the hemolymph and in whole bodies, using radioimmunoassay. Results show a single and sharp peak at the end of D1 stage, reaching 810 pg eq/microliter in the hemolymph (a 230-fold increase compared to the middle of intermolt). From B stage to the beginning of D1, levels are very low but increase regularly and significantly. The amplitude and the temporal position of the peak are discussed in detail, in relation to the precision of the staging (17 different stages can be easily made in Orchestia) and to the cuticle cycle (the hormonal peak occurs ca. 10 hr before the beginning of cuticle synthesis at D2). Preliminary experiments, using monoclonal antibodies during the period of low ecdysteroid titers or high-performance liquid chromatography followed by polyclonal RIA during the peak period, suggest that the immunoreactive hormone in O. cavimana behaves like 20-hydroxyecdysone. However, other minor compounds have been detected (some unknown, others migrating like ecdysone and ponasterone A in HPLC).