La forme m\ue2le atypique du Cop\ue9pode ascidicole Notodelphyidae Pachypygus gibber (Thorell, 1859) : description et synonymie avec Agnathaner minutus Ganu, 1891

Volume: 2Start Page: 455End Page: 47

Amalgam is a ligand for the transmembrane receptor neurotactin and is required for neurotactin-mediated cell adhesion and axon fasciculation in Drosophila

Neurotactin (NRT), a member of the cholinesterase-homologous protein family, is a heterophilic cell adhesion molecule that is required for proper axon guidance during Drosophila development. In this study, we identify amalgam (AMA), a member of the immunoglobulin superfamily, as a ligand for the NRT receptor. Using transfected Schneider 2 cells and embryonic primary cultures, we demonstrate that AMA is a secreted protein. Furthermore, AMA is necessary for NRT-expressing cells both to aggregate with themselves and to associate with embryonic primary culture cells. Aggregation assays performed with truncated NRT molecules reveal that the integrity of the cholinesterase-like extracellular domain was not required either for AMA binding or for adhesion, with only amino acids 347–482 of the extracellular domain being necessary for both activities. Moreover, the NRT cytoplasmic domain is required for NRT-mediated adhesion, although not for AMA binding. Using an ama-deficient stock, we find that ama function is not essential for viability. Pupae deficient for ama do exhibit defasciculation defects of the ocellar nerves similar to those found in nrt mutants

Roles of resource and partner availability in sex determination in a parasitic copepod

Because sexuality plays an essential role in gene transmission and consequently in the evolution of species, investment into male or female function constitutes a key factor in the reproductive success of individuals. Environmental sex determination permits adaptive sex choice under unpredictable environmental conditions, where the environment affects sex-specific fitness, and where offspring can predict their likely adult status by monitoring an appropriate environmental cue. The parasitic copepod Pachypygus gibber displays three sexual phenotypes (i.e. one female and two kinds of male) which are environmentally determined (i.e. after conception and in response to environmental cues). Here, we report an experimental analysis on the combined action, during larval development, of availability of food resources and sexual partners in the sex determination of this species

The ontogeny and phylogeny of copepod antennules

Comparative analysis of the development of antennulary segmentation and setation patterns across six orders of copepods revealed numerous common features. These features are combined to produce a hypothetical general model for antennulary development in the Copepoda as a whole. In this model most compound segments result from the failure of expression of articulations separating ancestral segments. In adult males, however, compound segments either side of the neocopepodan geniculation are typically formed by secondary fusion at the last moult from CoV (stage 5). The array of segments distal to the articulation separating segments XX and XXI is highly conserved both in ontogeny and phylogeny: typically the distal segmentation of the adult female is already present in the CoI. A maximum of three setae is added to the distal array during the entire copepodid phase. This morphological conservatism is interpreted as evidence of the functional continuity of the distal setal array as a mechanosensory system providing early warning of approaching predators. Sexual dimorphism typically appears late in development; the male undergoing modifications especially at the final moult to sexual maturity. These modifications include the formation of the neocopepodan geniculation at the XX to XXI articulation and, in some orders, the formation of a proximal geniculation at the XV to XVI articulation. A proximal geniculation is reported here from the Calanoida for the first time. The geniculations allow the male to grasp the female during any mate guarding and during spermatophore transfer. Particular setae on segments either side of the neocopepodan geniculation are modified as basally fused spines in at least some representatives of the Calanoida, Misophrioida, Cyclopoida, Harpacticoida and Siphonostomatoida. The antennulary chemosensory system, comprising primarily the aesthetascs, is enhanced at the final moult in many male copepods. In planktonic copepods this enhancement may take the form of a doubling of the aesthetascs on almost every antennulary segment, as in the eucalanid calanoids, or of an increase in size of existing aesthetascs, as in the siphonostomatoid Pontoeciella, or of the transformation of possibly originally bimodal, seta-like elements into distally thin-walled, more aesthetasc-like elements, as in some calanoids, harpacticoids and poecilostomatoids. Enhancement of the chemosensory capacity of adult males appears to be linked with their mate-locating role. Copepods inhabiting the open-pelagic water column are more likely to exhibit enhancement of the chemosensory system than neritic or benthic forms. Enhancement may confer a greater sensitivity to chemosensory signals, such as pheromones produced by receptive females, which may retain their directional information at lower concentrations and, therefore, for longer periods, in oceanic waters than in more turbulent neritic waters. Aesthetascs appear to be more evolutionarily labile than other setation elements, apparently being lost and regained within well-defined lineages. Caution is urged in the use of aesthetasc patterns in phylogenetic analysis. The ontogenetic analyses suggest that the timing of expression of intersegmental articulations during development may in future provide the most informative characters for phylogenetic study, rather than either segment numbers or the patterns of fused or undivided segments

Structure des genes actine muscle strie chez les prochordes

SIGLECNRS AR 11830 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Eco-ethological aspects of the symbiosis between the shrimp Athanas indicus

Four facets of the symbiosis between the shrimp Athanas indicus (Coutiere 1903) and the sea urchin Echinometra mathaei (de Blainville 1825) in the Red Sea are analyzed, i.e. (1) the constancy of the association, (2) the presence of the different postlarval stages on the host, (3) the presence of breeding adults on the host, and (4) the advantages of such a partnership. (1) Urchin-shrimp association frequently occurs in the Elat reef lagoon (about 20% of E. mathaei were occupied by one shrimp, seldom two), and appears to be strictly species-specific. The behavioural mechanism underlying this specificity was of little effect when isolated specimens were looking for a shelter (shrimps reacted visually towards any dark, round solid object of unspecific outline and not necessarily a spiny one). However, once the shrimp was on its host, a number of stimuli increased selectivity: chemical (the odour of E. mathaei), mechanical information (shrimps were repelled by Diadema setosum Leske 1778 spine movements), and ..