Storage and depletion of lipid components in the pyloric caeca and ovaries of the seastarAsterias rubens during its annual reproductive cycle

Detailed information is presented on the changes in lipid-class profiles (polar lipids, total neutral lipids, free sterols, steryl esters, triacylglycerols, neutral ether lipids and free fatty acids), which are manifest during the annual reproductive cycle of the seastarAsterias rubens for both the storage organs (pyloric caeca) and utilizing organs (ovaries). The ovaries appear to accumulate all individual lipid components proportional to progression of vitellogenesis. Pyloric caeca, in contrast, show variable lipid-class levels, probably due to more complex processes in these organs, operating simultaneously: digestion of food, accumulation of storage lipids, mobilization of stored lipids and their release. The results are discussed in terms of current knowledge on the role of lipids in echinoderm reproduction.     

Observations on the function of the glands of the foot of the pediveliger of Ostrea edulis during settlement

The use during settlement of secretions of the 9 different types of gland in the foot of the pediveliger of Ostrea edulis L. was examined experimentally. During settlement, there is a progressive decrease in the crawling speed of the larva and a strengthening of its bond with the substratum. Both changes are related to (a) a change from ciliary to muscular pedal locomotion; (b) the increasing acidity and viscosity of the mucoid secretions used; (c) the secretion of a byssus thread by the glands of the byssus duet; (d) changes in the form and composition of this byssus. At the termination of settlement, the entire contents of 2 types of gland are discharged. Their secretions give rise to the cement which permanently fixes the larva to the substratum. The 9 types of gland are utilised sequentially in a manner closely related to the 6 phases recognised in settlement behaviour.     

Effects of temperature on fertilization and early cleavage of some tropical echinoderms,with emphasis on Echinometra mathaei

Select temperatures, above normal, are shown to reduce success of fertilization and normal early cleavage in the laboratory for the echinoderms Acanthaster planci (L.), Culcita novaeguineae Muller and Troschel, Linckia laevigata (L.), Echinometra mathaei (de Blainville), and Diadema savignyi Michelin. The data indicate that cleavage is more sensitive to increased temperature than is fertilization. Upper tolerance limits for early cleavage in most of the species examined is near 34.0°C. The early developmental stages of A. planci were the most sensitive to elevated temperature, and those of E. mathaei, the least sensitive. Further experiments with E. mathaei showed that unfertilized ova were still viable, dividing normally when fertilized after 2 h exposure at 36.0°C. The ova were significantly less viable after 3 h. Early cleavage stages of E. mathaei were resistant to 36.0°C for exposure times of up to 40 min, but were inhibited beyond this period. It is suggested that the ability of E. mathaei to develop normally at 34.0°C (6C° above ambient temperature) and to withstand limited exposure to 36.0°C may account for the wide distribution of this species in habitats which are often subjected to broad temperature fluctuations, such as reef flats.Contribution No. 46 from the University of Guam Marine Laboratory.     

Distribution of the cladoceran Podon polyphemoides in the Chesapeake Bay

The distribution of the cladoceran Podon polyphemoides (Leuckart) in the Chesapeake Bay (USA) estuarine system was determined by a quantitative pump sampling method, and the patterns of abundance were correlated with temperature and salinity distributions. The species was seasonally recurrent, with distinct population maxima in the central portion of the bay. Population densities in excess of 60,000 podonids/m³ have been recorded. The podonids first appeared in the spring in the shallow tributaries, when water temperatures near the bottom reached 6°C. The vernal populations disappeared when summer temperatures exceeded 27°C, but reappeared in the fall as the water cooled. The species was euryhaline and eurythermal in its distribution, but the greatest concentrations were attained within relatively narrow zones of temperatures between 11^o and 26°C, and salinities between 8 and 18. The production of males, sexual females and sexual eggs occurred both in the spring and the fall between the thermal limits of 11^o and 17°C.     

Cytological sexing of cetacea

A biopsy dart, that can be shot from a gun or crossbow, was developed to obtain skin of whales at sea. Determination of sex was found possible by staining and locating sex chromatin bodies in the nuclei of female skin cells. This procedure will be useful in many types of field studies on whales.     

Growth rates of Corallina officinalis (Rhodophyta) at different temperatures

Specimens of Corallina officinalis L. were grown in the laboratory for 6 and 8 weeks at temperatures of 6°, 12°, 18°, and 25°C. After 6 weeks, the mean growth rates of main axes were 2.8 mm at 18°C, 2.9 mm at 12°C, and 0.2 mm at 5°C; no growth occurred at 25°C. At 6°C, growth increased with lower light intensities. The mean total increase in length of branchlets present when the plants were collected did not vary significantly at 12° and 18°C. At 12°C, axial intergenicula formed in culture produced more new branchlets than did field-grown intergenicula. Also, the production of these branchlets on cultured intergenicula was higher at 12°C than at 18°C.Based on a dissertation completed at Clark University in partial fulfillment of the requirements for a Master of Arts degree by B. J. Colthart.     

Das kommensalische verhältnis zwischen Periclimenes imperator (Decapoda: Palaemonidae) und Hexabranchus sanguineus (Nudibranchia: Doridacea)

The Red Sea nudibranch Hexabranchus sanguineus, rare in this region, was found in the Gulf of Aqaba together with a pair of commensal shrimp, Periclimenes imperator. The behaviour of the shrimp, especially as regards their adaptation to the host, was studied in the field and in an aquarium. The shrimp live on the sea slug, feeding on particles adhering to its mucous surface; they move on it even when it is swimming. The shrimp's colour is well adapted to that of the host. The observed specimens never left a healthy host willingly; when, in aquarium experiments, various red substrates or mucous sea cucumbers were offered beside H. sanguineus, the shrimp always chose the nudibranch. However, dead or injured and motionless slugs were abandoned. Two days after the death of a nudibranch, its commensal shrimp accepted the brown synaptid Euapta godeffroyi as host; on a previous occasion, a shrimp was found living on this latier species in the reef. The adaptation of P. imperator to living on the temporarily free-swimming H. sanguineus apparently represents a special evolutionary stage compared with that of other members of this family, which are mostly commensal with sessile hosts. Only palaemonid cleaner-shrimps feed briefly from free-swimming substrates.

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Mit Unterstützung der Deutschen Forschungsgemeinschaft     

Diurnal vertical migration of an estuarine cladoceran,Podon polyphemoides,in the Chesapeake Bay

Populations of the marine cladoceran Podon polyphemoides (Leuckart) in the Chesapeake Bay (USA) zooplankton typically occur in large patches, extending the length of the estuary. These patches are characterized by well defined maxima, which do not move seaward during a given season. During the day, the bulk of the population is situated in the upper part of the two-layered estuarine circulation, where it is subjected to transport by net non-tidal seaward current. One mechanism for maintaining the population within the estuary is provided by the diurnal behavior of the podonids, which migrate to deeper water during the night. The landward advection of the deeper currents, thus, helps to counterbalance seaward population loss during the day. The extent of the vertical movement of the population can be modified by various environmental factors, but a suggestive correlation with light was found. It is thought that the downward component of the migration is due to passive sinking.     

Zur sexuellen Differenzierung von Ophryotrocha puerilis (Polychaeta: Eunicidae)

Intact young males of Ophryotrocha puerilis Clap. Mecz. which are about to reach the female phase are capable of producing oocytes even under conditions of fasting. Intact isolated females may change sex under fasting conditions; their oocytes are not shed but resorbed. Decerebrated males which are about to reach the female phase at the moment of decerebration are unable to develop oocytes. Decerebrated females begin earlier with the production of spermatozoa than females under fasting conditions. The oocytes of decapitated females are either resorbed (young females with oocytes ranging in diameter up to 60 μm), or shed in egg masses capable of development after fertilization (older females with oocytes of 90 μm diameter or more). The effect of decerebration on females is compensated completely by implantation of isolated prostomia from female donors. Decerebrated males with implanted isolated prostomia from female donors immediately start oocyte production; these oocytes are not shed. In the majority of cases, decerebrated females change to the male phase after implantation of prostomia isolated from male donors. The mutual influence of a pair depends on direct contact of the partners. In isolated females, anterior fragments, consisting of prostomia and some segments, may induce change of sex and shedding of oocytes. On the other hand, intact females may induce sex reversal in anterior fragments. Even isolated prostomia from female donors may induce change of sex in intact females. A possible influence of intact females upon isolated prostomia was not found. Intact females and decerebrated females with implanted prostomia from female donors exhibit no mutual influence when placed together.     

An equilibrium theory of queen production in honeybee colonies preparing to swarm

Summary An equilibrium model is developed which seeks to explain the regulation of queen rearing in honeybee colonies preparing to swarm. The model postulates that there is a balance between nurse bees becoming inhibited from queen rearing and nurses losing their inhibition, and that whether a colony does or does not rear queens reflects the equilibrium percentage of inhibited nurses. This model leads to a quantitative prediction about the size of a conoly's nurse population at which queen rearing should start. Comparing the model's predictions with empirical observations pinpoints data needed for a more complete explanation of control of queen rearing. In particular, the model suggests a central regulatory role for density-dependent changes in the behaviors involved in queen substance dispersal.