Stages of embryonic development in the amphipod crustacean, Parhyale hawaiensis

Studying the relationship between development and evolution and its role in the generation of biological diversity has been reinvigorated by new techniques in genetics and molecular biology. However, exploiting these techniques to examine the evolution of development requires that a great deal of detail be known regarding the embryonic development of multiple species studied in a phylogenetic context. Crustaceans are an enormously successful group of arthropods and extant species demonstrate a wide diversity of morphologies and life histories. One of the most speciose orders within the Crustacea is the Amphipoda. The embryonic development of a new crustacean model system, the amphipod Parhyale hawaiensis, is described in a series of discrete stages easily identified by examination of living animals and the use of commonly available molecular markers on fixed specimens. Complete embryogenesis occurs in 250 h at 26 degrees C and has been divided into 30 stages. This staging data will facilitate comparative analyses of embryonic development among crustaceans in particular, as well as between different arthropod groups. In addition, several aspects of Parhyale embryonic development make this species particularly suitable for a broad range of experimental manipulations.     

Condition-dependent ecdysis and immunocompetence in the amphipod crustacean,Gammarus pulex

The exoskeleton of arthropods forms an efficient protection against pathogens, but this first line of defence is periodically weakened during ecdysis, increasing the opportunity for surrounding pathogens to invade the body cavity. Since the richness of pathogens in the environment can be spatially and temporally variable, arthropods may have a fitness advantage in moulting in a place and time of low infection risk. Consistent with this hypothesis, we found that the amphipod crustacean, Gammarus pulex, exhibits temporal adjustment of the moult cycle in response to elevated risks of infection. Interestingly, this phenomenon is variable between two populations and independent of levels of immune defences. These results suggest that plasticity of the moult cycle in response to elevated risks of infection is adaptive and may result from adaptation to local variations in the risk of infection.     

Cuticle differentiation in the embryo of the amphipod crustacean Parhyale hawaiensis

The arthropod cuticle is a multilayered extracellular matrix produced by the epidermis during embryogenesis and moulting. Molecularly and histologically, cuticle differentiation has been extensively investigated in the embryo of the insect Drosophila melanogaster. To learn about the evolution of cuticle differentiation, we have studied the histology of cuticle differentiation during embryogenesis of the amphipod crustacean Parhyale hawaiensis, which had a common ancestor with Drosophila about 510 million years ago. The establishment of the layers of the Parhyale juvenile cuticle is largely governed by mechanisms observed in Drosophila, e.g. as in Drosophila, the synthesis and arrangement of chitin in the inner procuticle are separate processes. A major difference between the cuticle of Parhyale and Drosophila concerns the restructuring of the Parhyale dorsal epicuticle after deposition. In contrast to the uniform cuticle of the Drosophila larva, the Parhyale cuticle is subdivided into two regions, the ventral and the dorsal cuticles. Remarkably, the boundary between the ventral and dorsal cuticles is sharp suggesting active extracellular regionalisation. The present analysis of Parhyale cuticle differentiation should allow the characterisation of the cuticle-producing and -organising factors of Parhyale (by comparison with the branchiopod crustacean Daphnia pulex) in order to contribute to the elucidation of fundamental questions relevant to extracellular matrix organisation and differentiation. This work was supported by the German Research Foundation (DFG, grant number MO 1714/1-1).     

Expression of otd orthologs in the amphipod crustacean, Parhyale hawaiensis

The arthropod head is a complex metameric structure. In insects, orthodenticle (otd) functions as a ‘head gap gene’ and plays a significant role in patterning and development of the anterior head ectoderm, the protocerebrum, and the ventral midline. In this study, we characterize the structure and developmental deployment of two otd paralogs in the amphipod crustacean, Parhyale hawaiensis. Photd1 is initially expressed at gastrulation through germband stages in a bilaterally symmetric, restricted region of the anterior head ectoderm and also in a single column of cells along the ventral midline. Late in embryogenesis, Photd1 is expressed within the developing anterior brain and the expression along the embryonic midline has become restricted to a stereotypic group of segmentally reiterated cells. The second ortholog Photd2, however, has a unique temporal–spatial expression pattern and is not detected until after the head lobes have been organized in the developing ectoderm of the germband during late germband stages. Anteriorly, Photd2 is coincident with the Photd1 head expression domain; however, Photd2 is not detected along the ventral midline during formation of the germband and only appears in the ventral midline late in embryonic development in a restricted group of cells distinct from those expressing Photd1. The early expression of Photd1 in the anterior head ectoderm is consistent with a role as a head gap gene. The more posterior expression of Photd1 is suggestive of a role in patterning the embryonic ventral midline. Photd2 expression appears too late to play a role in early head patterning but may contribute to latter patterning in restricted regions of both the head and the ventral midline. The comparative analysis of otd reveals the divergence of gene expression and gene function associated with duplication of this important developmental gene.Electronic Supplementary Material Supplementary material is available in the online version of this article at     

Cell lineage analysis of the amphipod crustacean Parhyale hawaiensis reveals an early restriction of cell fates

In the amphipod crustacean, Parhyale hawaiensis, the first few embryonic cleavages are total and generate a stereotypical arrangement of cells. In particular, at the eight-cell stage there are four macromeres and four micromeres, and each of these cells is uniquely identifiable. We describe our studies of the cell fate pattern of these eight blastomeres, and find that the eight clones resulting from these cells set up distinct cell lineages that differ in terms of proliferation, migration and cell fate. Remarkably, the cell fate of each blastomere is restricted to a single germ layer. The ectoderm originates from three of the macromeres, while the remaining macromere generates the visceral mesoderm. Two of the micromeres generate the somatic mesoderm, a third micromere generates the endoderm and the fourth micromere generates the germline. These findings demonstrate for the first time a total cleavage pattern in an arthropod which results in an invariant cell fate of the blastomeres, but notably, the cell lineage pattern of Parhyale reported shows no clear resemblance to those found in spiralians, nematodes or deuterostomes. Finally, the techniques we have developed for the analysis of Parhyale development suggest that this arthropod may be particularly useful for future functional analyses of crustacean development.     

The tropical caprellid amphipod Paracaprella pusilla: a new alien crustacean in the Mediterranean Sea

Paracaprella pusilla Mayer (Fauna und Flora des Golfes von Neapel 17:1–55, 1890), originally described from Brazil, is one of the most abundant caprellid amphipod species in tropical and subtropical seas around the world. During a survey of caprellid amphipods from marinas along the Balearic Island (Western Mediterranean Sea) carried out between November 2011 and August 2012, we found two established populations of P. pusilla in Mallorca and Ibiza, respectively. So far, its occurrence in European waters was reported only from southwestern Spain in 2010. This record represents a northward range expansion of the species’ distribution, which is found for the first time in the Mediterranean. This is also the first record of the genus Paracaprella in the Mediterranean Sea. The most probable introduction vector was ship fouling. We also found the invasive caprellid Caprella scaura Templeton (Trans Entomol Soc Lond 1:185–198, 1836) in Mallorca and Menorca, which is recorded for the first time in the Balearic Islands, confirming its rapid expansion along the Mediterranean. When comparing reproductive traits between both alien species, we found that P. pusilla has a higher fecundity than C. scaura for the same female size. Taking into account this evidence, the species may be expected to appear in other Mediterranean and adjacent areas.     

Warming chambers stimulate early season growth of an arctic sedge: results of a minirhizotron field study

We examined the effects of passive open-top warming chambers on Eriophorum vaginatum production near Toolik Lake, Alaska, USA. During the 2002 growing season, chamber warming was consistent with the magnitude and seasonality observed in recent decades throughout northwestern North America. Leaf-growth rates were higher in late May and early June; maximum growth rates in each leaf cohort occurred earlier and peak biomass was observed 20 days earlier within the chambers. Consequently, plants within the chambers maintained more live leaf biomass during the period of highest photosynthetically active radiation. Annual leaf production within the chambers (21±2 mg tiller) was not significantly different than under ambient conditions (17±2 mg tiller) (P=0.2256) despite higher early-season growth rates. Root growth began earlier; growth rates were higher in late May and early June, and maximum growth rates occurred earlier within the chambers. Therefore, plants within the chambers maintained greater root biomass during what earlier studies have identified as a period of relatively high nutrient availability. Annual root production within the chambers (191±42 g m^–2) was not significantly different than under ambient conditions (119±48 g m^–2) (P=0.1979), although there was a trend toward higher production within the chambers. The tendency toward higher root production within the chambers is consistent with previous laboratory experiments and with the predictions of biomass allocation theory.     

Host-plant adaptation in an herbivorous marine amphipod: genetic potential not realized in field populations

Evolutionary responses of herbivores to their host plants depend not only on selection from plants, but also on the genetic basis of traits relating to host use. The genetic basis of such traits has been investigated extensively among terrestrial insect herbivores, but has received almost no attention among marine herbivores. We tested whether performance traits in the herbivorous marine amphipod Peramphithoe parmerong display heritable variation and, for the first time for a marine herbivore, whether selection has resulted in local adaptation to host plants on two spatial scales. Peramphithoe parmerong displayed heritable genetic variation for survival on two host macroalgae, the high-quality Sargassum linearifolium and the poor-quality Padina crassa, and for growth on S. linearifolium. Differences in performance on different hosts thus have the potential to select for differential use of hosts by this amphipod. Despite this potential, there was no evidence among field populations of local adaptation to host algae on either scale tested: between hosts within a site or among sites differing in algal species composition. Within a site, amphipods were not more likely to prefer or perform better on the host on which they were collected. Similarly, amphipods collected from sites in which P. crassa was present were not more likely to perform well on this host than amphipods collected from sites where this alga was not found. Ecological factors that may explain the persistence of P. parmerong on P. crassa and the possibility of phylogenetic constraints on host use by P. parmerong are discussed.     

Chemoreception in the salmon louse Lepeophtheirus salmonis: an electrophysiology approach

The search for effective and long-term solutions to the problems caused by salmon lice Lepeophtheirus salmonis (Kr?yer, 1837) has increasingly included biological/ecological mechanisms to combat infestation. One aspect of this work focuses on the host-associated stimuli that parasites use to locate and discriminate a compatible host. In this study we used electrophysiological recordings made directly from the antennule of adult lice to investigate the chemosensitivity of L. salmonis to putative chemical attractants from fish flesh, prepared by soaking whole fish tissue in seawater. There was a clear physiological response to whole fish extract (WFX) with threshold sensitivity at a dilution of 10 . When WFX was size fractionated, L. salmonis showed the greatest responses to the water-soluble fractions containing compounds between 1 and 10 kDa. The results suggest that the low molecular weight, water-soluble compounds found in salmon flesh may be important in salmon lice host choice.     

Decapod crustacean chelipeds: an overview

The structure, growth, differentiation and function of crustacean chelipeds are reviewed. In many decapod crustaceans growth of chelae is isometric with allometry level reaching unity till the puberty moult. Afterwards the same trend continues in females, while in males there is a marked spurt in the level of allometry accompanied by a sudden increase in the relative size of chelae. Subsequently they are differentiated morphologically into crusher and cutter making them heterochelous and sexually dimorphic. Of the two, the major chela is used during agonistic encounters while the minor is used for prey capture and grooming. Various biotic and abiotic factors exert a negative effect on cheliped growth. The dimorphic growth pattern of chelae can be adversely affected by factors such as parasitic infection and substrate conditions. Display patterns of chelipeds have an important role in agonistic and aggressive interactions. Of the five pairs of pereiopods, the chelae are versatile organs of offence and defence which also make them the most vulnerable for autotomy. Regeneration of the autotomized chelipeds imposes an additional energy demand called “regeneration load” on the incumbent, altering energy allocation for somatic and/or reproductive processes. Partial withdrawal of chelae leading to incomplete exuviation is reported for the first time in the laboratory and field inMacrobrachiumspecies.     

全球北极底栖生物研究文献计量分析

以Thomson Reuters的Web of Science信息平台提供的SCI-E数据库为数据源,检索到从1991年至2012年期间全球北极底栖生物研究论文2127篇,利用Note Express软件,分析22年间论文发表的年度、国家、机构、作者、期刊和学科等方面的分布特征,结果表明:1)全球北极底栖生物研究论文数量、篇均作者数和篇均参考文献数都在逐年增加;2)研究论文涉及58个国家或地区,位于前7位的国家依次是美国、德国、加拿大、挪威、俄罗斯、英国和丹麦;美国、加拿大、挪威和丹麦是该领域国际合作研究最主要的国家;3)论文涉及1364个机构,前20名的研究机构中,美国有6家,德国、加拿大和挪威各有3家,俄罗斯和丹麦各有2家,波兰有1家。俄罗斯、丹麦、波兰、德国和挪威超过60%的研究力量集中在位列前20位的相关机构中。俄罗斯科学院论文总量排列首位,德国阿尔弗雷德魏格纳极地与海洋研究中心和基尔大学论文的h指数最高为32;4)论文涉及最多的4个学科是海洋与淡水生物学、生态学、海洋学和多学科地球科学。Polar Biology和Marine Ecology Progress Series是发表该领域最核心的期刊。还对中国在该领域的研究现状进行了简要的分析。从文献计量学角度揭示了全球北极底栖生物研究现状,为提升我国该领域研究的国际竞争力提供科学参考。     

Glycerol metabolism in a freeze-tolerant arctic insect: an in vivo13C NMR study

Summary Freeze-tolerance in larvae ofGynaephora groenlandica is enhanced by the accumulation of glycerol in the winter. Since summer larvae remain freeze-tolerant despite the lack of glycerol, we investigated glycerol metabolism as a function of acclimation and body temperature using non-invasive¹³C NMR spectroscopy. Major constituents of hemolymph isolated from cold- and warm-acclimated larvae were identified with the aid of standard NMR spectra and confirmed by TLC and GLC. Spectra obtained on live, warm-acclimated larvae showed the presence of lipids, glycogen, glucose, trehalose and amino acids. Similar spectra of cold-acclimated or previously frozen larvae showed the additional presence of glycerol. In vitro time-lapse¹³C spectra ofd-[1-¹³C]glucose added separately to hemolymph or extracted fat body tissue showed that glycerol is synthesized from glucose in the fat body tissue and distributed to the peripheral tissue via hemolymph. In vivo time-lapse¹³C spectra of cold- and warm-acclimated larvae were obtained after injection withd-[1-¹³C]glucose to monitor the production of labeled metabolic intermediates and end-products. [¹³C]Glycerol was produced between –30°C and 30°C but accumulated only below 5°C. Above 5°C glycerol was degraded and the¹³C label incorporated mainly into glycogen. The mechanism underlying temperature control of glycerol biosynthesis and degradation may provide a clue to the role of glycerol in enhancing freeze-tolerance in these insects.     

A silicon budget for an Alaskan arctic lake

The cycling of dissolved reactive silicate (DRS) and sedimentary biogenic SiO₂ has been examined in ultraoligotrophic Toolik Lake, Alaska. Watershed output of DRS (∼ 7 mmol m ^{− 2} yr ⁻¹) is similar to other arctic study sites, but a short water residence time results in the poor retention of DRS (∼17%) within the lake. Biogenic SiO₂ concentrations in surficial sediments average 123 mg g⁻¹ with the highest concentrations arising from the production of benthic diatoms in the littoral zone. Lake water DRS concentrations are highest prior to spring flow and photic zone concentrations exceed 23 μmol 1⁻¹ at the time of greatest primary production. Wintertime increases in watercolumn DRS concentrations and spring and summer pore water DRS flux estimates indicate that internal cycling within the lake may supply an amount of DRS equivalent to that which biologically utilized.     

Chemoreception of an oviposition deterrent associated with eggs in pieris brassicae

Electro-antennograms (EAG) in Pieris brassicae butterflies showed graded responses to the odour of intact conspecific eggs, and also to leaf and flower volatiles. Contributing to this summated potential are at least two types of sensilla on each segment of the antenna, although the terminal 6–8 segments do not respond proportionately. Analysis of the activity profiles of single olfactory cells to these compounds shows a typical generalist spectrum, with 0–3 cells per sensillum responding to the stimulus by an increase or decrease in spike frequency. The pheromone associated with eggs and deterring other females from ovipositing is not present in ovaries, but is produced in the accessory glands. It is water-soluble, has a low volatility and causes an increase in spike frequency in tarsal contact chemoreceptors.Behavioural evidence for the presence of a three-tier discrimination (visual detection of eggs or larvae: olfactory detection of aversion pheromone during fluttering over the leaves: contact discrimination by tarsae after landing (Rothschild & Schoonhoven, 1977)) is supported by electrophysiological results, which indicate the involvement of olfactory and contact chemoreceptors in recognising the presence of eggs.

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Zusammenfassung Elektroantennogramme (EAG) von Pieris brassicae Faltern zeigten abgestufte Reaktionen auf den Geruch konspezifischer Eier und auch auf flüchtige Stoffe von Blättern und Blumen. Zu diesem summierten Potential tragen mindestens zwei Typen von Sensillen auf jedem Segment der Fühler bei, wobei allerdings die 6–8 Endglieder nicht proportional reagieren. Die Aktivitätsprofile einzelner Geruchszellen entsprechen einem typischen Spektrum eines generalist. 0–3 Zellen pro Sensille reagieren auf die Reizung mit erhöhter oder erniedrigter Impulsfrequenz. Die Markierung der Eier, welche andere Weibchen von der Eiablage abhält, ist in den Ovarien nicht vorhanden, wird jedoch in den akzessorischen Drüsen erzeugt. Sie ist wasserlöslich, hat eine geringe Flüchtigkeit und verursacht eine erhöhte Impulsfrequenz bei Kontaktrezeptoren der Tarsen.

     

Delaying copulation in the amphipod crustacean Gammarus palustris: Effects on female fecundity and consequences for the frequency of amplexus

Both physiological and environmental constraints can be important selective factors on behaviors. The results of the present study showed that fecundity is significantly reduced if copulation is delayed for as short a time as 6 ± 6h in the amphipod crustacean Gammarus palustris (Bousfield, 1969). This led to the prediction that selection would favor behaviors which minimize the likelihood of delays. In amphipods of this genus, amplexus occurs before the female molts and copulation occurs within minutes afterwards. The results of field observations support the prediction; it is estimated that 99% of the females are in amplexus when they molt. However, while the physiological constraints that were demonstrated show the advantages of pairing before copulation, it is speculated that amplexus as the specific pairing behavior evolved in response to the selective pressures of the free‐roaming habits of G. palustris.     

Embryo aberrations in the amphipod Monoporeia affinis as indicators of toxic pollutants in sediments: A field evaluation

Reproduction in the amphipod Monoporeia affinis is sensitive to contaminant exposure, and embryo aberrations are used in the Swedish National Monitoring Program to indicate biological effects of contaminants. However, empirical support for a causal relationship between contaminant load and frequency of aberrations is largely based on experimental studies. A field evaluation of aberration frequency in relation to contaminant exposure is required, if we are to use reproductive disorders as indicators of contaminant effects in risk assessment. In this study, we evaluated occurrence of females carrying malformed embryos and frequency of specific embryo aberrations in broods of M. affinis in relation to concentrations of various pollutants in sediments. Gravid M. affinis and surface sediment were sampled at ten sites in the Gulf of Bothnia located at varying proximity to historical and current polluting point sources. At each site, concentrations of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and trace and heavy metals in surface sediments were determined. Amphipod fecundity and embryo development status were assayed with regard to morphologically recognizable aberrations (malformed embryos, membrane-damaged embryos, embryos with arrested development and females with dead brood). Our key finding is that different types of embryo aberrations were significantly associated with specific contaminant groups in the sediment. In particular, occurrence of females with embryo malformations was strongly related to elevated concentrations of Cd and PCBs, while females with membrane-damaged embryos occurred at high PAH concentrations. Also, frequency of embryos with arrested development was linked to elevated concentrations of PAHs and metals. Finally, frequency of females carrying dead broods, which was earlier considered to be a hypoxia-induced pathology, was significantly positively related to PAH concentrations. Thus, these reproductive aberrations in M. affinis can serve as contaminant-specific indicators of PCB, PAH and heavy metal exposure in biological effect monitoring.     

Independent migration of cell populations in the early gastrulation of the amphipod crustacean Parhyale hawaiensis

Cells are the principal component of tissues and can drive morphogenesis through dynamic changes in structure and interaction. During gastrulation, the primary morphogenetic event of early development, cells change shape, exchange neighbors, and migrate long distances to establish cell layers that will form the tissues of the adult animal. Outside of Drosophila, little is known about how changes in cell behavior might drive gastrulation among arthropods. Here, we focus on three cell populations that form two aggregations during early gastrulation in the crustacean Parhyale hawaiensis. Using cytoskeletal markers and lineage tracing we observe bottle cells in anterior and visceral mesoderm precursors as gastrulation commences, and find that both Cytochalasin D, an inhibitor of actin polymerization, and ROCKOUT, an inhibitor of Rho-kinase activity, prevent gastrulation. Furthermore, by ablating specific cells, we show that each of the three populations acts independently during gastrulation, confirming previous hypotheses that cell behavior during Parhyale gastrulation relies on intrinsic signals instead of an inductive mechanism.