Dynamics of Gastrovascular Circulation in the Hydrozoan Podocoryne carnea: the One-Polyp Case.

Time-lapse video microscopy and image analysis algorithms were used to generate high-resolution time series of the length and volume of a single hydrozoan polyp before and after feeding. A polyp of Podocoryne carnea prior to feeding is effectively static in length and volume. At 20{deg}C, feeding elicits 8-millihertz (mHz) oscillations in polyp length and volume. A polyp connected to a colony by a single stolon displayed an abrupt transition from low-amplitude, 8-mHz oscillations to large-amplitude, 6-mHz oscillations at 1.5-2 h after feeding. The transition was preceded by a substantial decrease in polyp volume and increase in length which coincided with the export of food items from the digestive cavity of the polyp into the colonial gastrovascular system. In contrast, 8-mHz oscillations of a polyp isolated from a colony continued for 12.7 h after feeding, at which time particulates from the digestive cavity were exported into the hydrorhiza and a 4-mHz subharmonic became briefly dominant. Regular oscillatory behavior was terminated by regurgitation at comparable intervals post-feeding in coupled and isolated polyps. These observations are compatible with the hypothesis that the presence of nutrients in the digestive cavity induces polyp oscillations and that release of nutrients into the gastrovascular system similarly induces unfed polyps to oscillate, thereby distributing the contents of the fed polyp throughout the colony.

Theoretical and experimental analysis of the phage lambda genetic switch implies missing levels of co-operativity.

The behavior of the cro-repressor switch in phage lambda, a temperate phage of Escherichia coli, is described at the organismal level within a dynamical system framework. The molecular biology of the switch has been well characterized up to the level of the regulation of transcription initiation. In this paper we construct a description of a lysogen whose prophage is mutated in certain genes, so that the switch is functionally isolated from the rest of the phage genome. Such a lysogen has two stable epigenetic states, and comparison of the theory with measurements of intracellular cro concentration corresponding to one of these states suggest that additional levels of regulation, not included in the current description of the switch, should exist for this system. In addition, we suggest a new method for the measurement of intracellular concentrations.

An alternative method of estimating the cranial capacity of Olduvai Hominid 7.

The cranial capacity of Olduvai Hominid 7 is estimated to be 690 cc, with a standard uncertainty range of 538 to 868 cc. The estimate is derived from a systematic consideration of the relationships between Bregma-Asterion chords and cranial capacities obtained from a large sample of Homo sapiens and Pan troglodytes and from available fossil hominids. The estimation technique is applicable to other characters and specimens.

Slow growth rate of a deep-sea clam determined by 228Ra chronology.

The age of a deep-sea clam, Tindaria callistiformis, from 3803 m depth has been determined by 228Ra (6.7 year half-life) chronology of separated size fractions of a captured population. A length of 8.4 mm is attained in about 100 years. Shells of this size fraction show about 100 regularly spaced bands, indicating that the growth feature may be an annual one.