Formation of Chaotic Patterns of the Gastrovascular System in the Ontogenesis of the Medusa Aurelia aurita

Only the first branching of the perradial and interradial channels of the gastrovascular system of Aurelia aurita (L.) (Scyphozoa: Ulmaridae) in the metaephyra stage is always uniform. Further branch formation is variable and random. New branches originate most often at the annular channel, but some of them grow from the radial channels. The early formation of irregular and chaotic patterns of the radial channel branching is caused by the asynchrony and topographic variability of the generation of new branches of different channels. During further morphogenesis, the spatial and temporal variability of branching increases, which leads to an increased state of chaos in the morphology of the branching channels of each individual. Lack of rigid determinancy of the gastrovascular system channel branching and plasticity of this system in the course of the entire ontogenesis provide possible evidence of its adaptive responses, for example, to the disruption of tetraradial symmetry or rearrangements after damage.     

A Component of Wheat Flour Globulin Polymerized at Alkaline Sides and Depolymerized by Reduction Reversibly

1. The SDS-disc electrophoretical analysis of wheat flour globulin revealed that upon incubation with “Kansui,” a mixture of alkali carbonates, one (No. 9) of the components disappeared and another component (No. 11) increased significantly whose molecular weight was estimated to be more than one million. Incubation of flour globulin with “Kansui” resulted in decrease of SH groups of the globulin.

2. However, a mild reduction of the globulin incubated with “Kansui” caused reappearance of component No. 9 and a decrease of component No. 11.

3. Previous treatment of flour globulin with PCMB or AN completely inhibited such effects of “Kansui” as described above.

4. A fraction containing component No. 9 of flour globulin which was the main component responsible to polymerization by “Kansui,” was isolated from “Kansui”-treated globulin by chromatography on columns of Sephadex G200 and Sepharose 4B.

5. The component protein thus isolated showed a typical phenomenon of reversibility in depolymerization to the original component corresponding to No. 9 component by chemical reduction and polymerization to a component corresponding to No. 9 at alkaline sides.

     

Microhabitat use by the rainbowfish <Emphasis Type="Italic">Melanotaenia duboulayi</Emphasis> in a subtropical Australian stream

Microhabitat use and feeding behavior of the rainbowfish Melanotaenia duboulayi (Castelnau) were investigated in a slow-flowing stream adjacent to riparian forest in south-eastern Queensland, Australia. Fish were more abundant in vegetated areas, but did not enter dense Vallisneria beds, where predators were observed. In sunny conditions shoals of juveniles occurred near the water surface feeding floating material on the surface, but larger fish tended to occur at the bottom near submerged vegetation, often utilizing the overhanging aquatic plant community as a refuge and food source. In the middle of the day, juveniles and small fish seemed to show behavioral thermoregulation at the surface in the warmest site. Under cloudy conditions, however, fish of all sizes preferred deeper water. The present study suggests that in still and sunny pools thermal change caused by sunlight influences the microhabitat choice of small fish. A field experiment using a kingfisher model implies that fish swimming at the surface could escape from aerial predators in sunlit conditions by responding to moving shadows, but could not do so under cloudy conditions. Electronic Publication     

Do respiratory metabolic rates of the scyphomedusa Aurelia aurita scale isometrically throughout ontogeny in a sexual generation?

We measured the respiration rate of Aurelia aurita payingspecial attention to the relationship between its metabolic ratesand body mass throughout ontogeny of the jellyfish in a sexualgeneration. Two different regression lines between respirationrates and body dry weight were obtained in ephyra to young medusa(bell diameter 4.2–19 mm, 0.07–14 mg dry weight) and medusa(BD17-120 mm, 12-2100 mg DW), at respective temperatures of 10 and15 °C. The cut off point of the metabolic rates was foundat the developmental stage just being metamorphosed into medusashape (BD 12–20 mm). The slope value of medusa respiration ratewas close to isometric scaling (0.9), whereas that of ephyra toyoung medusa was lower (0.6). Ecological implications of allometricscaling in the early developmental stages of ephyrae and metephyraeare discussed.     

On natural metamorphosis inducers of the cnidarians Hydractinia echinata (Hydrozoa) and Aurelia aurita (Scyphozoa)

 Hydractinia echinata and Aurelia aurita produce motile larvae which undergo metamorphosis to sessile polyps when induced by external cues. The polyps are found at restricted sites, A. aurita predominantly on rocks close to the shore, H. echinata on shells inhabited by hermit crabs. It has been argued that the differential distribution of the polyps in their natural environment largely reflects the distribution of the natural metamorphosis-inducing cues. In the case of H. echinata, bacteria of the genus Alteromonas were argued to meet these conditions. We found that almost all substrates collected in the littoral to induce metamorphosis in H. echinata, and several bacterial strains isolated from the sea, including the common E. coli, induce metamorphosis efficiently. In A. aurita metamorphosis may be induced by the water–air interface, whereby metamorphosis precedes (final) settlement. Received: 7 December 1998 / Accepted: 8 July 1999     

Diet of intraguild predators affects antipredator behavior in intraguild prey

In two-predator, one-prey systems with intraguild predationand patchily distributed prey, the intraguild prey may facea choice between prey patches with and without intraguild predators.To minimize falling victim to intraguild predation, intraguildprey are expected to perceive cues specifically associated withthe presence of intraguild predators. We investigate whetherintraguild prey avoided intraguild predators and which cuestriggered this behavior in a system composed of plant-inhabitingarthropods. We found that intraguild prey recognized intraguildpredators from a distance, based on their diet: they avoidedodors of intraguild predators that had consumed shared preybut did not avoid odors of intraguild predators that had fedon other diets, including a diet of conspecifics. When intraguildprey were foraging on a patch, detection of intraguild predatorsled to longer periods of immobility and to fewer captures ofthe shared prey. However, intraguild predators that were eitherstarved or had previously consumed intraguild prey posed a higherrisk to intraguild prey than did intraguild predators that hadconsumed the shared prey. We conclude that the cues used byintraguild prey to avoid intraguild predators are associatedwith the circumstances under which they encounter intraguildpredators in the field and not to different degrees of danger.