Dynamics of glucocorticoids in the ontogenesis of freshwater crawfish <Emphasis Type=Italic>Astacus leptodactylus Esch</Emphasis>

Dynamics of changes in glucocorticoid (hydrocortisone and corticosterone) levels was studied in the ontogenesis of freshwater crawfish Astacus leptodactylus Esch. It was shown that steroid concentrations increase during the embryogenesis period. Decrease in the glucocorticoid levels during postembryonic development is most probably related to the stabilization of young fish growth and the attainment of hormone levels typical for adult individuals.     

Ultrastructure and ion transport in gill epithelium of the crayfish,Astacus leptodactylus Esch

Summary Active ion transport against a high electrochemical potential gradient occurs across the epithelium of the gill processes of crayfish. The transport occurs in a thin sheet of cytoplasm underlying cuticula. This cytoplasm is supplied with irregular microvilli on the apical side. The basal plasma membrane invaginates into the cytoplasm forming a dense membrane system which is in close contact with numerous elongated mitochondria. The cytoplasm of the adhering cells is divided by a septated desmosome. It is suggested that the infolded membranes are the main place of ion transport and the close contact of mitochondria with them supplies the optimal energetic conditions for transport.Abbreviations ATP Adenosine-5-triphosphate - ADP adenosine-5-diphosphate     

Ontogeny of osmoregulation in the crayfish Astacus leptodactylus

Osmoregulation was studied during the postembryonic development of Astacus leptodactylus Eschscholtz 1823 in juvenile stages 1-8 and in adults. Juveniles hatch and later stages develop in freshwater or in moderately saline waters. The time of acclimation from freshwater to a saline medium increased from early juveniles to adults. At all stages, it was longer than in comparable stages of marine crustaceans, reflecting the high impermeability of the teguments to water and ions. All stages were able to hyperisoosmoregulate. In freshwater, the ability to hyperosmoregulate was established at hatching and increased during development. The hemolymph osmolality increased from 286 mosm kg-1 in stage 1 juveniles to 419 mosm kg-1 in adults. All stages also hyperregulated at low salinities (7 per thousand and 13 per thousand salinity) and were osmoconformers at higher salinities up to 21 per thousand salinity. The lowest isosmotic salinity tended to increase with the developmental stages. The ability to osmoregulate at hatch and throughout postembryonic development is probably a key physiological adaptation in this and other freshwater crayfish.     

Crayfish freshwater adaptation starts in eggs: ontogeny of osmoregulation in embryos of Astacus leptodactylus

Osmoregulation was studied throughout the embryonic development of Astacus leptodactylus. Egg-carrying females were held in freshwater (FW) and in three dilute seawater media (200, 400, 600 mosm kg(-1), 6.8, 13.6, 20.4 per thousand salinity). In FW, changes in peri-embryonic fluid (PEF) and (when available) embryonic hemolymph osmolality were followed from newly-laid eggs to hatching (for an embryonic eye index, EI, of 430-450 microm) and in first-stage juveniles. The PEF and/or hemolymph osmolality remained stable at about 360-380 mosm kg(-1) from early to late (EI 410 microm) embryos; it decreased prior to hatching (EI 420 microm) and in newly-hatched juveniles, down to 290 mosm kg(-1). Artificial opening and removal of the egg membranes, followed by direct exposure to FW, demonstrated that the ability to hyper-osmoregulate, and consequently to survive, in FW appears in embryos with EI > or = 410 microm, i.e., only a few hours or days before hatching. Following a transfer to the dilute seawater media, the PEF/hemolymph osmolality increased slowly over 18-20 days and became isosmotic with the external media at 13.6 and 20.4 per thousand. The embryos died at EI 380-395 microm in these media, and only at 6.8 per thousand was the development completed until successful hatch. These results demonstrate that (1) the embryos become able to osmoregulate in FW shortly before hatching, (2) the embryos are osmo-protected in the eggs during their development, (3) embryonic development and hatching are possible up to a salinity of 7 per thousand. These results are discussed in relation to freshwater adaptation of crayfish.     

The reaction of nitrite with the haemocyanin of Astacus leptodactylus.

The reaction of nitrite at pH 5.7 with deoxyhaemocyanin of Astacus leptodactylus yielded methaemocyanin in two one-electron steps, as nitrite was reduced to NO. This methaemocyanin could be almost fully regenerated by an anaerobic treatment with HONH2, in contrast with the methaemocyanin prepared with H2O2. A destruction of active sites on treating oxyhaemocyanin with HONH2 explains the partial regeneration of methaemocyanin under air, as traces of H2O2 are formed in the autoxidation of HONH2. The reaction rate of nitrite with deoxyhaemocyanin is almost 15 times that with oxyhaemocyanin. The slope of -1.0 for the logarithm of the pseudo-first-order rate constants plotted against pH indicates that HNO2 is the reacting species. Methaemocyanin was e.p.r.-undetectable, but a binuclear signal was observed at g = 2 on binding nitrite to methaemocyanin. This signal disappeared with a pKa of 6.50, suggesting that a mu-aquo bridging ligand, which can be replaced by nitrite, is deprotonated to a mu-hydroxo bridging ligand, which resists substitution by nitrite. The intensity of this triplet e.p.r. signal allowed the determination of the association constant of nitrite to the active site of Astacus methaemocyanin and yielded a value of 237 M-1 at pH 5.7. The interpretation by some authors of nitrosylhaemocyanin as a nitrite derivative of semimethaemocyanin is contradicted by this rapid reaction of nitrite with copper(I) in deoxyhaemocyanin and in semi-methaemocyanin and by the low binding constant of nitrite to the active site of methaemocyanin.     

Temperature adaptation influences the aggregation state of hemocyanin from Astacus leptodactylus

When Astacus leptodactylus were kept at various temperatures for several weeks, different ratios between di-hexameric and hexameric hemocyanins were observed in their hemolymph. The higher the temperature the more hexamers were present. This long-term adaptation to different temperatures or/and to temperature-induced pH-shifts as observed in the hemolymph has different effects on the expression of subunit types building up hexamers and those which covalently link two hexamers within the di-hexamers. The oxygen binding behaviour of di-hexameric hemocyanins from cold and warm adapted animals do not show differences with respect to affinity, Bohr effect and cooperativity.     

The abdominal muscle receptor organ in Astacus leptodactylus (Crustacea)

The structure of both the slow- and the fast-adapting abdominal muscle receptor organ of Astacus leptodactylus is described with particular reference to differences between the two systems. The receptors are composed of a thin muscle that extends from the front edge of one segment to the front edge of the following and a sensory cell connected with this muscle. In the zone where the sensory cells enter their respective muscle, muscle fibers are reduced (zone of relative muscle exclusion = ZRME) and partly replaced by connective tissue. The occurrence of dendritic processes of both the slow and the fast neurons is confined to this zone. The following differences between the two receptor types are established: (1) The fast receptor muscle reveals a smaller sarcomere length than the slow receptor muscle and a higher myosin/actin filament ratio. (2) Muscle fibers that pass the ZRME are always found at its periphery in the fast system, separated from dendritic processes by layers of connective tissue, while in the slow system muscle fibers frequently are intermingled with the sensory elements. (3) The ZRME of the slow receptor is 20-30% longer than that of the fast receptor. (4) The dendritic varicosities of the slow neuron, on an average, contain many more mitochondria than those of the fast neuron. (5) Dendritic processes (fine twigs as well as varicosities) are juxtaposed to the sarcolemma of the muscle fibers only in the slow system; in the fast system dendrites and muscle are spatially separated by connective tissue. It is assumed that these differences between the two receptor types are at least in part responsible for the different thresholds observed in physiological experiments.     

The ultrastructure of the sinus gland of the crayfish Astacus leptodactylus (Nordmann)

Summary An ultrastructural study of the sinus gland of the crayfish Astacus leptodactylus demonstrates that this gland is mainly composed of glial cells, axons and axon terminals. On the basis of the size, shape and electron density of the neurosecretory granules, we could distinguish five different types of axon terminals.     

Glio-neuronal and glio-glial syncytial cytoplasmic connections in peripheral nerve trunks of the crayfish Astacus leptodactylus

The paper considers various aspects of glial sheaths of neuritis in the crayfish peripheral nerve trunks and roots. There are revealed dotted glio-neurite tight junctions and a varicose deformation of the intercellular glio-neurite cleft. Rupture of membranes in the area of contact leads to formation of the glio-neurite pore (less than 10 nm) that is enlarged and forms wide (up to 240 nm) syncytial perforations. At the edge of perforation, either remnants of tight junctions are present or damaged membranes that fuse and are rounding. The lumen of perforations always contains residual membranous bodies in the form of vesicles. Their deviation from the median line can indicate a mutual translocation of substances of the glio- and neuroplasm. In the adjacent layers of the multilayer glial sheath there is noted a similar phenomenon of formation of the glio-glial syncytial connection terminating by fusion of neighbor glial layers, which is terminated by fusion of neighbor glial layers into the single lamina. The process begins from the varicose deformation of interglial clefts, which appears as a result of massive formation of dotted and expanded tight membranous contacts. As a result of transformation of ellipsoid varicose deformations into the spherical ones, syncytial pores (less than 10 nm) between them are formed, which are enlarged and break the paired gliolemmas into fragments. As a result, the adjacent glial layers are united. Since this process in intact animals occurs on the background of undamaged nerve structures, a suggestion is put forward about its reversibility and the functional nature.     

Population structure and genetic analysis of narrow-clawed crayfish (Astacus leptodactylus) populations in Turkey

The genetic differentiation among Turkish populations of the narrow-clawed crayfish was investigated using a partial sequence of cytochrome oxidase subunit I gene (585 bp) of 183 specimens from 17 different crayfish populations. Median joining network and all phylogenetic analyses disclosed a strong haplotype structure with three prominent clades diverged by a range between 20 and 50 mutations and substantial inter-group pairwise sequence divergence (5.19–6.95 %), suggesting the presence of three distinct clades within the Anatolian populations of Astacus leptodactylus. The divergence times among the three clades of Turkish A. leptodactylus are estimated to be 4.96–3.70 Mya using a molecular clock of 1.4 % sequence divergence per million years, pointing to a lower Pliocene separation. The high level of genetic variability (H _d  = 95.8 %, π = 4.17 %) and numerous private haplotypes suggest the presence of refugial populations in Anatolia unaffected by Pleistocene habitat restrictions. The pattern of genetic variation among Turkish A. leptodactylus populations, therefore, suggests that the unrevealed intraspecific genetic structure is independent of geographic tendency and congruent with the previously reported geographic distribution and number of subspecies (A. l. leptodactylus and A. l. salinus) of A. leptodactylus.