Ecdysone and retinoid-X receptors of the blue crab, Callinectes sapidus: Cloning and their expression patterns in eyestalks and Y-organs during the molt cycle

Crustacean molting is known to be regulated largely by ecdysteroids and crustacean hyperglycemic hormone (CHH) neuropeptide family including molt-inhibiting hormone (MIH) and CHH. The surge of 20-OH ecdysone and/or ponasterone A initiates the molting process through binding to its conserved heterodimeric nuclear receptor: Ecdysone Receptor (EcR) and Ultraspiracle (USP)/Retinoid-X Receptor (RXR). To better understand the role of ecdysteroids in the molt regulation, the full-length cDNAs of the blue crab, Callinectes sapidus EcR1 and RXR1 were isolated from the Y-organs and their expression levels were determined in both Y-organs and eyestalks at various molt stages. Y-organs show the expression of four putative isoforms of CasEcRs and CasRXRs which differ in the length of the open reading frame but share the same domain structures as in typical nuclear receptors: AF1, DBD, HR, LBD, and AF2. The putative CasEcR isoforms are derived from a 27-aa insert in the HR and a 49-aa residue substitution in the LBD. In contrast, an insertion of a 5-aa and/or a 45-aa in the DBD and LBD gives rise to CasRXR isoforms. The eyestalks and Y-organs show the co-expression of CasEcRs and CasRXRs but at the different levels. In the eyestalks, the expression levels of CasRXRs are 3–5 times higher than those of CasEcRs, while in Y-organs, CasRXRs are 2.5–4 times higher than CasEcRs. A tissue-specific response to the changes in the levels of hemolymphatic ecdysteroids indicates that these tissues may have differences in the sensitivity or responsiveness to ecdysteroids. The presence of upstream open reading frame and internal ribosome entry site in 5′ UTR sequences of C. sapidus and other arthropod EcR/RXR/USP analyzed by in silico indicates a plausible, strong control(s) of the translation of these receptors.     

Do the neurohormones VIH (vitellogenesis inhibiting hormone) and CHH (crustacean hyperglycemic hormone) of crustaceans have a common precursor? Immunolocalization of VIH and CHH in the X-organ sinus gland complex of the lobster,Homarus americanus

Summary

The present study deals with the location of the vitellogenesis inhibiting hormone (VIH)-producing cells in the eyestalk of the lobster Homarus americanus. In the present study, the neurosecretory pathways of VIH in Homarus, have been described immunocytochemically by use of a mouse serum against Homarus VIH. The location of the VIH cells was compared with the location of the crustacean hyperglycemic hormone (CHH) cells visualized by a rabbit serum raised against CHH of the crayfish Astacus leptodactylus. Immunocytochemical detection procedures, both at the light and electron microscopic level, revealed frequent but not complete co-localization of VIH and CHH in a variable number of the same group of perikarya. In the sinus gland, both neuropeptides were mostly demonstrated in distinct axonal endings characterized by different granule types. Postulations on the biosynthesis of these factors and suggestions concerning the processing of both neurohormones have been made.     

Effect of storage on the fatty acid content of foods for post-larvae of the crustacean decapod Hippolyte inermis

Decapods are important in aquaculture practice and as models for marine biology research, due to peculiar endocrine and physiologic adaptations to various environments. For these reasons, decapods are cultivated. To promote their correct development and sexual maturation, the preparation of balanced diets is crucial. Several diets, both experimental and for aquaculture purposes, have been established, but the set of essential fatty acids is still unknown for most species. Furthermore, fatty acids contained in formulated feeds are differentially sensitive to decay over the storage time. Here we compare growth, maturation and mortality of post-larvae fed on a formulated diet containing Artemia sp., Spirulina sp. and a fatty acid integrator, as administered immediately after its production and after 12 months of storage. The same foods were analysed for their fatty acid contents using gas chromatography. The sets of fatty acids present in differently aged foods corresponded to differences in the growth rates and survival of the model organism Hippolyte inermis cultured in the laboratory. The differences were mainly due to seven fatty acids, whose abundance decreased during the storage, the most important of which were arachidonic and linolenic acid, that are known to be essential for other species of decapods.     

Visual perception of light organ patterns in deep‐sea shrimps and implications for conspecific recognition

Darkness and low biomass make it challenging for animals to find and identify one another in the deep sea. While spatiotemporal variation in bioluminescence is thought to underlie mate recognition for some species, its role in conspecific recognition remains unclear. The deep‐sea shrimp genus, Sergestes sensu lato (s.l.), is one group that is characterized by species‐specific variation in light organ arrangement, providing us the opportunity to test whether organ variation permits recognition to the species level. To test this, we analyzed the visual capabilities of three species of Sergestes s.l. in order to (a) test for sexual dimorphism in eye‐to‐body size scaling relationships, (b) model the visual ranges (i.e., sighting distances) over which these shrimps can detect intraspecific bioluminescence, and (c) assess the maximum possible spatial resolution of the eyes of these shrimps to estimate their capacity to distinguish the light organs of each species. Our results showed that relative eye size scaled negatively with body length across species and without sexual dimorphism. Though the three species appear capable of detecting one another's bioluminescence over distances ranging from < 1 to ~6 m, their limited spatial resolution suggests they cannot resolve light organ variation for the purpose of conspecific recognition. Our findings point to factors other than conspecific recognition (e.g., neutral drift, phenotypic constraint) that have led to the extensive diversification of light organs in Sergestes s.l and impart caution about interpreting ecological significance of visual characters based on the resolution of human vision. This work provides new insight into deep‐sea animal interaction, supporting the idea that—at least for these mesopelagic shrimps—nonvisual signals may be required for conspecific recognition.     

Chronic radiation exposure at Chernobyl shows no effect on genetic diversity in the freshwater crustacean,Asellus aquaticus thirty years on

Analysis of genetic diversity represents a fundamental component of ecological risk assessments in contaminated environments. Many studies have assessed the genetic implications of chronic radiation exposure at Chernobyl, generally recording an elevated genetic diversity and mutation rate in rodents, plants, and birds inhabiting contaminated areas. Only limited studies have considered genetic diversity in aquatic biota at Chernobyl, despite the large number of freshwater systems where elevated dose rates will persist for many years. Consequently, the present study aimed to assess the effects of chronic radiation exposure on genetic diversity in the freshwater crustacean, Asellus aquaticus, using a genome‐wide SNP approach (Genotyping‐by‐sequencing). It was hypothesized that genetic diversity in A. aquaticus would be positively correlated with dose rate. A. aquaticus was collected from six lakes in Belarus and the Ukraine ranging in dose rate from 0.064 to 27.1 µGy/hr. Genotyping‐by‐sequencing analysis was performed on 74 individuals. A significant relationship between geographical distance and genetic differentiation confirmed the Isolation‐by‐Distance model. Conversely, no significant relationship between dose rate and genetic differentiation suggested no effect of the contamination gradient on genetic differentiation between populations. No significant relationship between five measures of genetic diversity and dose rate was recorded, suggesting that radiation exposure has not significantly influenced genetic diversity in A. aquaticus at Chernobyl. This is the first study to adopt a genome‐wide SNP approach to assess the impacts of environmental radiation exposure on biota. These findings are fundamental to understanding the long‐term success of aquatic populations in contaminated environments at Chernobyl and Fukushima.     

A newly recognized Mesozoic–Recent interspecific association: calcifying bacteria on decapod crustaceans

Using microscopy and spectroscopy tools, we succeeded in identifying undescribed diminutive epibionts (as epibiotic bacterial colonies) both on exceptionally well‐preserved fossil shrimps and on extant taxa (N. Robin, S. Bernard, J. Miot, M.‐M. Blanc‐Valleron, S. Charbonnier & G. Petit, submitted). This study outlines the ecological parameters of this totally newly recognized interspecific association. To this aim, the systematics and environmental setting of fossil and modern decapod hosts are described; count of bacterial colonies is made to assess prevalence and intensity; scanning electron microscopy is used to illustrate colonial growth patterns; and histological sections of the extant colonies nested in cuticle are stained to determine their incidence on the carapace of their decapod hosts. Thus, the prevalent and intense association is found on decapods of the superfamily Penaeoidea Rafinesque‐Schmaltz 1815 occupying up to 2 cm² of the entire carapace. The association is here observed in deep environments such as that of the Jurassic La Voulte‐sur‐Rhône Lagerstätte. A non‐random distribution of colonial growth patterns is determined; it illustrates a favourite access site along the ventral margin of the shrimp carapace. SEM images and stained sections reveal strong colony embedment within the cuticle, but also damage such as erasing of the cuticular layers. This bioeroding effect, possibly linked to a feeding benefit to the bacteria, brings this interspecific association that has existed, for at least 160 myr, near to parasitism. In addition to illustrating a rare case of interaction in Recent forms that could be described due to previous recognition in fossils, it constitutes a textbook example of the preservation of intimate interactions through geological time.     

长江口浮游甲壳动物空间分布特征

2010年研究了长江口南、北支浮游甲壳动物的空间分布特征。共采集到浮游甲壳动物50种,其中桡足类39种,枝角类11种。种类数南支高于北支;平均密度北支高于南支,南、北支分别为1.7 ind./L和61.8 ind./L。基于群落相似性矩阵的CLUSTER聚类和MDS分析显示,在群落相似性为40%时,长江口区域浮游甲壳动物群落可分为北支组、南支组1和南支组2共3组。3组的优势种有差异。浮游甲壳动物的平均密度变化趋势为北支组（61.8±22.11 ind./L）〉南支组1（3.07±2.06 ind./L）〉南支组2（0.72±0.45 ind./L）。盐度、潮汐和径流量是影响长江口南北支浮游甲壳动物种类组成、密度和空间分布差异的重要环境因素。     

The Swimmeret System of Crayfish: A Practical Guide for the Dissection of the Nerve Cord and Extracellular Recordings of the Motor Pattern

Here we demonstrate the dissection of the crayfish abdominal nerve cord. The preparation comprises the last two thoracic ganglia (T4, T5) and the chain of abdominal ganglia (A1 to A6). This chain of ganglia includes the part of the central nervous system (CNS) that drives coordinated locomotion of the pleopods (swimmerets): the swimmeret system. It is known for over five decades that in crayfish each swimmeret is driven by its own independent pattern generating kernel that generates rhythmic alternating activity ^1-3. The motor neurons innervating the musculature of each swimmeret comprise two anatomically and functionally distinct populations ⁴. One is responsible for the retraction (power stroke, PS) of the swimmeret. The other drives the protraction (return stroke, RS) of the swimmeret. Motor neurons of the swimmeret system are able to produce spontaneously a fictive motor pattern, which is identical to the pattern recorded in vivo ¹.The aim of this report is to introduce an interesting and convenient model system for studying rhythm generating networks and coordination of independent microcircuits for students’ practical laboratory courses. The protocol provided includes step-by-step instructions for the dissection of the crayfish’s abdominal nerve cord, pinning of the isolated chain of ganglia, desheathing the ganglia and recording the swimmerets fictive motor pattern extracellularly from the isolated nervous system.Additionally, we can monitor the activity of swimmeret neurons recorded intracellularly from dendrites. Here we also describe briefly these techniques and provide some examples. Furthermore, the morphology of swimmeret neurons can be assessed using various staining techniques. Here we provide examples of intracellular (by iontophoresis) dye filled neurons and backfills of pools of swimmeret motor neurons. In our lab we use this preparation to study basic functions of fictive locomotion, the effect of sensory feedback on the activity of the CNS, and coordination between microcircuits on a cellular level.     

Effect of Different Levels of Selenium Supplementation on Growth Rate,Nutrient Utilization,Blood Metabolic Profile,and Immune Response in Lambs

The nutritional role of silver for the freshwater crustacean, Daphnia magna, was examined through four generations of deprivation. Silver inclusion in animal media was set at a nominal zero (employing chemicals of the highest available purity). Both reproduction (−60%) and life span (−40%) were negatively affected when compared to animals reared in the presence of 0.4 ng g⁻¹ Ag. These results strongly suggest a nutritional requirement of silver for daphnids at nanomolar concentrations.