Analysis of Ca(2+) uptake into the smooth endoplasmic reticulum of permeabilised sternal epithelial cells during the moulting cycle of the terrestrial isopod Porcellio scaber.
In terrestrial isopods, large amounts of Ca(2+) are transported across anterior sternal epithelial cells during moult-related deposition and resorption of CaCO(3) deposits. Because of its toxicity and function as a second messenger, resting cytosolic Ca(2+) levels must be maintained below critical concentrations during epithelial Ca(2+) transport, raising the possibility that organelles play a role during Ca(2+) transit. We therefore studied the uptake of Ca(2+) into Ca(2+)-sequestering organelles by monitoring the formation of birefringent calcium oxalate crystals in permeabilised anterior and posterior sternal epithelium cells of Porcellio scaber during Ca(2+)-transporting and non-transporting stages of the moulting cycle using polarised-light microscopy. The results indicate ATP-dependent uptake of Ca(2+) into organelles. Half-maximal crystal growth at a Ca(2+) activity, a(Ca), of 0.4 micromol l(-1) and blockade by cyclopiazonic acid suggest Ca(2+) uptake into the smooth endoplasmic reticulum by the smooth endoplasmic reticulum Ca(2+)-ATPase. Analytical electron microscopical techniques support this interpretation by revealing the accumulation of Ca(2+)-containing crystals in smooth membranous intracellular compartments. A comparison of different moulting stages demonstrated a virtual lack of crystal formation in the early premoult stage and a significant fivefold increase between mid premoult and the Ca(2+)-transporting stages of late premoult and intramoult. These results suggest a contribution of the smooth endoplasmic reticulum as a transient Ca(2+) store during intracellular Ca(2+) transit. (+info)
Postembryonic eye growth in the seashore isopod Ligia exotica (Crustacea, Isopoda).
The eye of Ligia exotica is of the apposition type and has open rhabdoms. The facets are hexagonal, and the dioptric apparatus consists of a flat cornea and a spherical crystalline cone placed in the center of two large cone cells. Each ommatidium has seven regular retinula cells and one eccentric cell; a basement membrane forms the proximal boundary of the retina. With increases in body size from 0.6 to almost 4.0 cm, facet numbers and ommatidial diameters increased from 800 to 1500 and 35 microm to 100 microm, respectively; eye length and width grew from 1.2 to 3.2 and 0.9 to 2.5 mm, respectively; and length of dioptric apparatus and width of retinal layer changed from 70 microm to 180 microm and about 70 microm to 120 microm. Visual angles and interommatidial angles of centrally located ommatidia remained constant at about 30 and 6.9 degrees, respectively. An almost perfect linear relationship was found when eye length was plotted against the product between the square root of the total number of ommatidia and the ommatidial diameter. No difference between males and females was observed in any of the relationships, but the results suggest that, compared with smaller specimens, larger ones possess increased absolute sensitivity in single ommatidia, increased sensitivity to point sources, and overall larger angular visual fields for the eye in its totality. This means that larger individuals of L. exotica (which are also faster) have an advantage over smaller individuals at night, but that smaller individuals may cope better with bright lights. Vision in L. exotica seems useful not only in detecting potential danger, but also in locating and approaching cliffs from a distance of 2-4 m when swimming in seawater. (+info)
Long-term fasting and realimentation in hypogean and epigean isopods: a proposed adaptive strategy for groundwater organisms.
The effects of long-term fasting and subsequent refeeding on digestive physiology and energy metabolism were investigated in a subterranean aquatic crustacean, Stenasellus virei, and in a morphologically similar surface-dwelling species, Asellus aquaticus. Metabolic response to food deprivation was monophasic in A. aquaticus, with an immediate, large decrease in all energy reserves. In contrast, S. virei displayed three successive periods of phosphageno-glucidic, lipidic and, finally, proteo-lipidic-dominant catabolism over the course of the nutritional stress. To represent the responses of subterranean crustaceans to food stress and renutrition, a sequential energy strategy was hypothesized, suggesting that four successive phases (called stress, transition, adaptation and recovery) can be distinguished. Based on these results, a general adaptive strategy for groundwater organisms was proposed. Their remarkable resistance to long-term fasting may be partly explained by (1) a depressed metabolism, during which they mainly subsist on lipid stores, (2) a prolonged state of glycogen- and protein-sparing, (3) low energetic requirements and (4) large body stores. In addition, these groundwater species displayed high recovery abilities during refeeding, showing an optimal utilization of available food and a rapid restoration of their body reserves. These adaptive responses might be considered for numerous subterranean organisms as an efficient energy-saving strategy in a harsh and unpredictable environment where fasting (and/or hypoxic) periods of variable duration alternate with sporadic feeding events (and/or normoxic periods). Therefore, food-limited and/or hypoxia-tolerant groundwater species appear to be good examples of animals representing a low-energy system. (+info)
Tension sensitivity of the heart pacemaker neurons in the isopod crustacean Ligia pallasii.
In the crustacean neurogenic heart, the cardiac ganglion (CG) acts as a peripherally located central pattern generator (CPG) by producing rhythmic motor output that initiates the heartbeat. In the isopod Ligia, the CG consists of six electrically coupled neurons that all function both as endogenous oscillators and as glutamatergic motoneurons innervating heart muscle. In the present study, we present several lines of evidence to suggest that the CG neurons are sensitive to passive stretch and active tension of the heart muscle. Stretching the heart wall caused a sustained decrease in the burst frequency of the CG neuron. Releasing from the stretch caused a rebound increase in burst frequency above the control rate. A brief stretch (200-300 ms duration) caused either phase advance or phase delay of the following CG bursts, depending on the timing at which the stretch was applied. Repeated brief stretches could entrain the CG bursts to either higher or lower frequencies than the free-run burst frequency. Intracellular recording from one of the CG neurons revealed that it exhibited hyperpolarization during the stretch. The stretch-induced hyperpolarization was followed by a burst discharge upon release from the stretch. With increased stretch amplitude, the amplitude of hyperpolarizing response increased and the timing of the following burst was advanced. When the myogenic activity of the heart muscle was pharmacologically isolated from the ganglionic drive by applying a glutamatergic antagonist, Joro spider toxin (JSTX), the spontaneous muscle contraction caused a hyperpolarizing deflection in the CG neuron. Under specific conditions made by JSTX and tetrodotoxin, the CG burst became entrained to the myogenic rhythm. These results suggest that the Ligia CG neurons have tension sensitivity in addition to their pacemaker and motoneuronal functions. Such multifunctional neurons may form a single neuron reflex arc inside the heart. (+info)
Repellents in the Japanese cedar, Cryptomeria japonica, against the pill-bug, Armadillidium vulgare.
Sandaracopimarinol and (1S,6R)-2,7(14),10-bisabolatrien-1-ol-4-one were isolated and identified from Cryptomeria japonica as repellents against Armadillidium vulgare which is well known as an unpleasant pest in the house and as vegetable pest in Japan. These compounds strongly repelled A. vulgare when they were combined, although each compound alone did not show any activity. (+info)
Disparity in population differentiation of sex-linked and autosomal variation in sibling species of the Jaera albifrons (Isopoda) complex.
The genetic variation at four enzyme loci is described for 22 populations of three Jaera species--J. albifrons, J. ischiosetosa, and J. praehirsuta--in the J. albifrons complex (Crustacea, Isopoda) in Denmark. The variation at three of the loci is similar, with the allele frequency spectra close to each other in all three species. An evolutionary tree based on the variation at these three loci revealed that the populations from the different species are completely intermixed in the tree. This was supported by hierarchical F-statistics where the between-species component was zero. At a fourth locus, Gpi (glucose phosphate isomerase), the species differ substantially. This locus is sex linked in J. ischiosetosa, but in the two other species, J. albifrons and J. praehirsuta, it is either found on autosomes or is sex linked with a high recombination rate between the locus and the centromere. An evolutionary tree for this locus partitions the populations into separate groups and a hierarchical F-statistic has a between-species component of about 50%. The results are attributed to introgression with a higher rate for autosomes than for sex chromosomes. (+info)
Molecular characterisation of the smooth endoplasmic reticulum Ca(2+)-ATPase of Porcellio scaber and its expression in sternal epithelia during the moult cycle.
The anterior sternal epithelial cells of the terrestrial isopod Porcellio scaber transport large amounts of calcium during the formation and resorption of intermittent calcium carbonate deposits. Recent investigations on epithelia involved in mineralisation processes suggest a role of the smooth endoplasmic reticulum Ca(2+)-ATPase (SERCA) in transcellular calcium transport. We present the first molecular characterisation of a SERCA within a crustacean mineralising epithelium. We cloned the SERCA from a cDNA library of the anterior sternal epithelium and used in situ hybridisation to compare the expression of the SERCA mRNA between three different moulting stages. The full-length SERCA cDNA has an open reading frame of 3006 nucleotides. The deduced 1002 amino-acid polypeptide has a predicted molecular mass of 109.7 kDa and 87% identity to the SERCA of Procambarus clarkii axial muscle isoform. In situ hybridisation confirmed expression within the anterior sternal epithelium and revealed an increase in SERCA mRNA abundance from the non-transporting, early premoult stage to the calcium transporting, late premoult and intramoult stage. The results support previous indications of a contribution by the smooth endoplasmic reticulum to transcellular calcium transport and suggest a transcriptional regulation of SERCA activity. (+info)
Host-parasite relationships: occurrence and effect of the parasitic isopod Mothocya epimerica on sand smelt Atherina boyeri in the Mesolongi and Etolikon Lagoons (W. Greece).
The parasite-host relationship between Mothocya epimerica, Costa 1851 (Isopoda: Flabellifera: Cymothoidae) and sand smelt Atherina boyeri (Osteichthyes: Atherinidae) fish populations were studied in the Mesolongi and Etolikon Lagoons (W. Greece). Prevalence varied during the year from 12.5% in November to 52.5% in September; overall mean prevalence was 41.9%. Parasite size increased with host size. Infections did not have a significant effect on the host's body condition, such as length-weight relationship, gonadosomatic index, hepatosomatic index and relative condition factor. Histological damage to the host was observed on the gills (especially in the second and third and arches upon which the female parasite rests her abdomen). The physiological cost resulting from this infection seems to be little and probably does not constitute a serious threat for individual host survival. (+info)