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PubMed2003

Population structure and recruitment of the ectoparasite Argulus coregoni Thorell (Crustacea: Branchiura) on a fish farm.

The population structure and recruitment of Argulus coregoni was monitored at a Finnish fish farm during the open water periods of 1999 and 2001 by weekly sampling of attached argulids. In 2001 the numbers of rainbow trout examined increased in the autumn when the A. coregoni population was declining. When the water temperature exceeded 10 degrees C, at the end of May, A. coregoni egg hatching commenced. A mean number of 98 (S.D. +/- 5.4) juvenile A. coregoni was recorded on each fish, before the start of female egg laying in July 1999. The abundance of lice was lower in 2001. The main recruitment of A. coregoni juveniles occurred in early summer, but the hatching of eggs continued until September. However, no pulses of hatching were recorded later in the summer and the numbers of lice on fish substantially decreased after mid-July in both years. On average, only 0.6 (S.D. +/- 0.72) parasites/fish were found between August and late October 2001 and none in November. We suggest that there is 1 main A. coregoni generation annually in Central Finland. Environmental conditions, especially temperature, affects the population cycle of A. coregoni: we found a more synchronous and intense population cycle during the summer 1999, when the early summer was warmer than in 2001. The overall sex ratio (female:male) of A. coregoni was nearly 1:1 in June 1999, but was male biased (1:1.4) in June 2001. It was also shown that from July onwards, many females detached from the fish host in order to lay their eggs on the bottom of the pond. Large males were often bigger than the largest females between mid-July and early September 2001, when as many as 3.7 (s.r. +/- 1.48) times more males than females were present in the lice samples.

Animals↗
PubMed2004

Seasonal dynamics of egg laying and egg-laying strategy of the ectoparasite Argulus coregoni (Crustacea: Branchiura).

Substrate preferences, spatial aggregation patterns and seasonal dynamics in the egg laying of ectoparasitic Argulus coregoni were studied at a commercial fish farm in Finland. Pilot experiments showed that A. coregoni females selected specific types of substrates for egg laying. Significantly more A. coregoni eggs were laid on dark substrates than on light ones suggesting the use of visual cues. Therefore, egg-laying plates of dark colour were constructed for further experiments. Most A. coregoni eggs were deposited in locations in shadow and in the deepest water in a 2 m deep farming canal. Relatively more eggs were laid on bottom stones situated near each egg-laying trap than on artificial egg-laying plates indicating a preference for irregular stones in the deeper locations in the canal. The plates were located 20 cm above the bottom. However, a total of 5,863 A. coregoni egg clutches, corresponding approximately to 1.5 million unhatched metanauplii, were successfully destroyed with the plates indicating that egg-laying traps can be used as an ecological control method against argulids in certain situations. For traps to be effective, ponds should not contain stones or any other hard substrata attracting female lice. The egg laying of A. coregoni in this study started on 5 July in 2001 and extended over 3.5 months up to mid-October. The egg-laying pattern of A. coregoni population was unimodal, supporting the view that only a single A. coregoni generation occurred annually in Central Finland.

Animals↗
PubMed2005

Aggregation of Argulus coregoni (Crustacea: Branchiura) on rainbow trout (Oncorhynchus mykiss): a consequence of host susceptibility or exposure?

By sampling individual rainbow trout, Oncorhynchus mykiss, at a fish farm we showed that Argulus coregoni were aggregated within their host population. The relative significance of susceptibility and exposure generating the observed pattern was tested using experimental infections. We examined, whether rainbow trout developed protective resistance mechanisms against the louse following a challenge infection and if there was variation between individual trout in their susceptibility to A. coregoni metanauplii. Fish were exposed to 20 A. coregoni for 5, 25, 50, 85 or 120 min and the numbers attaching recorded. Three weeks later, developing argulids were removed and the experiment repeated with a standardized exposure of 20 metanauplii. Prior exposure of fish with A. coregoni did not reduce the total infection intensity compared to naive fish, but fish gained infection more rapidly. We suggest that there is no protective acquired resistance of pre-exposed rainbow trout to subsequent Argulus exposure. The possibility that an immunosuppressive mechanism by argulids was acting enabling the higher attachment rate could be refuted since control individuals, not previously exposed to lice, gained the infection at a similar rate as the fish challenged twice. Our results do not indicate clear differences in susceptibility among individual fish but the transmission of metanauplii on fish seemed to be opportunistic and non-selective. Our results support the view that variation in exposure time, rather than differences in susceptibility of individual hosts, might be the key factor in generating the aggregated distribution of Argulus on their hosts.

Animals↗
PubMed2004

The notodelphyid genus Doroixys Kerschner, 1879 (Crustacea: Copepoda: Cyclopoida), with the description of a new species from the Russian far east.

Doroixys simplex n. sp. is described from material collected from a tunicate of the genus Ciona, collected on the North Pacific coast of Russia. This is the fourth species of the genus and the first for which the male has been found. The new species differs from congeners most noticeably in the absence of posterolateral processes from the rear margin of the dorsal cephalic shield. A key to species is provided.

Animals↗
PubMed2005

Mitochondrial COI-NC-COII sequences in talitrid amphipods (Crustacea).

Mitochondrial (mt) sequences from cytochrome oxidase subunit I to the subunit II gene (COI, COII) were analysed in crustacean talitrid amphipods. Species of the genera Orchestia, Talitrus and Talorchestia from the Mediterranean-East Atlantic area were examined. The expected tRNALeu-UUR gene was not revealed between COI and COII. Instead, a short (35-48 bp) noncoding (NC) AT-rich (ca. 90%) region with putative stem loops was found. Here, we discuss briefly the NC region and explore its potential involvement in generating this novel rearrangement. The COI-NC-COII organization, as well as preliminary phylogenetic results, based on both COI-COII nucleotide and amino-acid sequence indicate monophyly of these talitrid taxa.

Amphipoda↗
PubMed1992

Purification and characterization of a proteolytic active fragment of DNA topoisomerase I from the brine shrimp Artemia franciscana (Crustacea Anostraca).

The ATP-independent type I topoisomerase from the crustacean Artemia franciscana was purified to near-homogeneity. Its activity was measured by an assay that uses the formation of an enzyme-cleaved DNA complex in the presence of the specific inhibitor camptothecin. The purification procedure is reported. Purified topoisomerase is a single-subunit enzyme with a molecular mass of 63 kDa. Immunoblot performed on the different steps of purification shows that the purified 63 kDa peptide is a proteolytic fragment of a protein with a molecular mass of 110 kDa. Similarly to the other purified eukaryotic topoisomerases, the crustacean enzyme does not require a bivalent cation for activity, but is stimulated in the presence of 10 mM-MgCl2; moreover, it can relax both negative and positive superhelical turns. The enzyme activity is strongly inhibited by the antitumour drug camptothecin. The enzyme inhibition is related to the stabilization of the cleavable complex between topoisomerase I and DNA.

Animals↗
PubMed2000

Sex, linkage disequilibrium and patterns of parasitism in three species of cyclically parthenogenetic Daphnia (Cladocera: Crustacea).

To gain insight into genetic variation for resistance to parasites, this study assayed clonal variation in cyclically parthenogenetic Daphnia magna with respect to parasitic infection. Samples were collected from natural populations, and the allozyme phenotypes of infected hosts were compared to those of uninfected hosts. Differences between the clonal composition of the infected and uninfected class were evident in only two of 16 populations examined. This result stands in contrast to a study of species in the D. pulex and D. longispina species complexes, where clonal variation for infection was found in 12 of 25 populations (Little & Ebert, 1999). Considering all populations from both studies, associations between host genotype and infection were typically evident only in populations that showed low genotypic diversity and evidence of genetic disequilibria, with D. magna showing the least amount of disequilibria. This pattern is compatible with at least two possibly overlapping hypotheses. First, it may be that those populations lacking clonal variation for infection experienced weaker parasite-mediated selection. We can not rule out variation in selection pressure as an explanation, but found no evidence that the prevalence or intensity of parasitism differed either among species, or between those populations which showed clonal variation for infection and those that did not. Second, it could be that some populations, especially those of D. magna, have more frequent sexual recruitment than others. Sexual recombination breaks up gene combinations which are in linkage disequilibrium, and our method to detect clonal variation for resistance relies on linkage between genetic markers (allozymes) and resistance loci. Past work on Daphnia has shown that the level of sexual recruitment (which is in turn mediated by habitat permanency) is indeed commonly linked to the occurrence of genetic disequilibria. Our results may thus underestimate the prevalence of clonal variation for infection (especially for D. magna), because most of the populations analysed appeared to have high levels of sexual recruitment and therefore lacked the linkage disequilibrium that underlies associations between allozymes and susceptibility.

Animals↗
PubMed2002

Genetic, ecological, and behavioural divergence between two sibling snapping shrimp species (Crustacea: Decapoda: Alpheus).

Examination of genetic and ecological relationships within sibling species complexes can provide insights into species diversity and speciation processes. Alpheus angulatus and A. armillatus, two snapping shrimp species with overlapping ranges in the north-western Atlantic, are similar in morphology, exploit similar ecological niches and appear to represent recently diverged sibling species. We examined phylogenetic and ecological relationships between these two species with: (i) sequence data from two mitochondrial genes (16S rRNA and COI); (ii) data on potential differences in microhabitat distribution for A. armillatus and A. angulatus; and (iii) data from laboratory experiments on the level of reproductive isolation between the two species. DNA sequence data suggest A. armillatus and A. angulatus are sister species that diverged subsequent to the close of the Isthmus of Panama, and that haplotype diversity is lower in A. armillatus than in A. angulatus. Both species are distantly related to A. heterochaelis and A. estuariensis, two species with which A. angulatus shares some similarities in coloration. Ecological data on the distribution of A. angulatus and A. armillatus from two locations revealed differences in distribution of the two species between habitat patches, with each patch dominated by one or the other species. However, there was no apparent difference in distribution of the two species within habitat patches with respect to microhabitat location. Ecological data also revealed that heterospecific individuals often occur in close proximity (i.e. within metres or centimetres) where sympatric. Behavioural data indicated that these species are reproductively isolated, which is consistent with speciation in transient allopatry followed by post-divergence secondary contact. Our data further resolve taxonomic confusion between the sibling species, A. armillatus and A. angulatus, and suggest that sympatry in areas of range overlap and exploitation of similar ecological niches by these two recently diverged species have selected for high levels of behavioural incompatibility.

Animals↗
PubMed2003

Molecular approach to aquatic environmental bioreporting: differential response to environmental inducers of cytochrome P450 monooxygenase genes in the detritivorous subalpine planktonic Crustacea, Daphnia pulex.

In order to examine the usefulness of detoxifying genes as molecular markers in different chemical environments, isolation of cytochrome P450 genes (CYPs) belonging to the CYP4 family was performed in different samples from two subalpine populations of Daphnia pulex. The use of degenerate primers allowed us to isolate seven cDNAs. Four of them were assigned to the CYP4C subfamily, and were closely related to previously isolated crustacean CYP4s while the others were assigned to new CYP4AN and CYP4AP subfamilies. Expression studies, using semiquantitative polymerase chain reaction (PCR) followed by Southern blot hybridization with specific probes revealed differences in CYP4C32 and CYP4AP1 expressions between the two populations, which differ in the polyphenol richness of the vegetation surrounding their aquatic habitat. Further exposure to toxic dietary polyphenols showed different CYP induction patterns. Taken together, these preliminary results suggest a possible involvement of CYP4s in the ecological differentiation of subalpine D. pulex populations related to the polyphenol richness of the environmental vegetation. CYP4s may thus be considered as possible molecular markers in aquatic environmental bioreporting.

Amino Acid Sequence↗
PubMedDate not supplied

Embryonic expression patterns of the Hox genes of the crayfish Procambarus clarkii (Crustacea, Decapoda).

Higher crustaceans (class Malacostraca) represent the most species-rich and morphologically diverse group of non-insect arthropods. The superorders Eucarida and Peracarida, two large groups that separated over 350 million years ago, encompass most malacostracan diversity. Recently, the Hox genes of the peracarid woodlouse Porcellio scaber(Isopoda) were shown to be expressed in domains that coincide with morphological boundaries of body tagmata, which differ from those in insects (Abzhanov and Kaufman 1999a,b). Moreover, observed changes in Hox expression domains during ontogeny correlate with morphological remodeling, such as a transformation of the first thoracic leg into mouthpart maxillipeds, which occurs in the trunk of the embryo. Decapods have a different modification of the malacostracan bodyplan, with up to three pairs of maxillipeds and extensive fusion and cephalization of the thorax. Here we describe expression patterns of the trunk Hox genes Scr, Antp, Ubx, abd-A and cad in the eucarid crayfish Procambarus clarkii (Decapoda). We find that the crayfish expression patterns, for the most part, resemble those of the woodlouse Porcellio scaber(Isopoda), but are more modulated and complex. Nevertheless, as in Porcellio the boundaries of the Hox expression domains do correlate with morphological features and their modulations to transformations in the embryo. Thus we propose that the trunk Hox genes were likely important in the evolution of and currently play an essential role in the development of the complex decapod bodyplan.

Amino Acid Sequence↗
PubMed2001

Sites of lanthanum occlusion in the testis of the crayfish Procambarus paeninsulanus (Crustacea: Cambaridae).

The presence of stage-dependent occlusive junctions between adjacent Sertoli cells in the seminiferous epithelium of the crayfish testis was demonstrated by a lanthanum tracer study. The germinal epithelium did not appear to be compartmentalized, as evidenced by access of lanthanum to spermatogonia, spermatocytes, and spermatids. During late spermiogenesis, when encapsulated stage VI spermatids were concentrated in the center of an acinus, lanthanum was excluded apically, coincident with lumen formation. This is the first study examining occluding junctions using a barrier penetration method in the testis of a crustacean.

Animals↗
PubMed2006

Suitability of Crangonyx pseudogracilis (Crustacea: Amphipoda) as an early warning indicator in the multispecies freshwater biomonitor.

BACKGROUND: Biological monitors are increasingly important in 'Biological Early Warning Systems' (BEWS) for monitoring water quality. This study examines the freshwater amphipod Crangonyx pseudogracilis as a potential new indicator species when used in the Multispecies Freshwater Biomonitor (MFB). The MFB is an online continuous biomonitor which uses impedance conversion to record behavioural responses of vertebrates and invertebrates. METHODS: Four experiments were undertaken to establish: (1) if the electrical field generated by the MFB affected the organisms' behaviour, (2) if defined behaviours and their response to a gradient of ammonium chloride could be detected by the MFB, (3) if there was variation in the behaviour of C. pseudogracilis over a diel cycle, and (4) if behaviour changed significantly in response to a pulse of ammonium chloride. RESULTS AND DISCUSSION: Results showed no significant effect of the MFB's current on behaviour of C. pseudogracilis. Four behaviours; swimming, walking, grooming and inactivity, were observed and identified in the MFB. In the MFB, each behaviour changed significantly in response to an increasing gradient of ammonium chloride exposure. The MFB also detected increases in nocturnal activity by C. pseudogracilis. The MFB also detected a significant increase in activity after a pulse of ammonium chloride. CONCLUSION: The range of behaviours exhibited by Crangonyx pseudogracilis, together with its ease of culture, suggest future potential of this species as an indicator species for the Multispecies Freshwater Biomonitor. RECOMMENDATIONS AND OUTLOOK: Further testing is required over a range of toxicants and concentration gradients to establish threshold responses and the full compliment of behaviours that could be useful in online biomonitoring.

Ammonium Chloride↗