Environmental constraints on sound transmission by humpback whales.

Singing humpback whales in Hawaii produce a variety of sounds at high source levels (ca. 185 dB re: 1 microPa), in coastal waters 15-500 m deep. These sounds are attenuated and distorted as they propagate away from a singer, limiting the utilizable range of the sounds. In the current study, simulations based on normal-mode theory were used to investigate how the effects of shallow-water propagation constrain humpback whales' use of sound. It is shown that humpbacks can greatly affect transmission range by adjusting their positions and sounds in response to environmental factors. Source depth, in particular, is shown to be a major determinant of which frequencies propagate the farthest. A preliminary analysis of range-dependent distortion suggests that spectral cues can potentially provide listening whales with information about how far a sound has traveled.

The role of calcium accumulation and the cytoskeleton in the perception and response of Coprinus cinereus to gravity.

The role of Ca2+ in the gravitropic perception and/or response mechanism of Coprinus cinereus was examined by treating stipes with inhibitors of Ca2+ transport and calmodulin. Inhibitors had no effect on gravity perception but significantly diminished gravitropism. It is concluded that, under the conditions tested, Ca2+ is not involved in gravity perception by Coprinus stipes, but does contribute to transduction of the gravitropic impulse. The results would be consistent with regulation of the gravitropic bending process requiring accumulation of Ca2+ within a membrane-bound compartment. Treatment of stipes with an actin inhibitor caused a significantly delayed response, a result not observed with the Ca2+ inhibitors. This suggests that cytoskeletal elements may be involved directly in perception of gravity by Coprinus stipes while Ca(2+)-mediated signal transduction may be involved in directing growth differentials.

Gravitational biology of mushrooms: a flow-chart approach to characterising processes and mechanisms.

Flow charts are presented which systematise recently published work on gravitropic responses of the mushroom stipe of Coprinus cinereus. The hypothetical model represented by the charts suggests that the meiotic division is a pivotal point in the gravitational biology of the mushroom fruit body. The unilateral gravity vector seems to be required for formation of the tissues in which meiosis normally occurs, and stipes become gravitropically competent only after onset of meiosis. The gravitropism flow-chart also indicates that two signals emanate from the upper regions of the stipe, one promotes the process of gravitropic bending, and is followed by a second signal which compensates for excess bending and adjusts the stipe apex to the vertical. Formalisation of the various observations into flow-charts, even though comparatively simple at the moment, facilitates comparison with other species and concentrates attention on aspects requiring further experimental analysis.

Kinetics and mechanics of stem gravitropism in Coprinus cinereus.

Using video recordings we have completed the first kinetic analysis of mushroom stem gravitropism. The stem became gravireceptive after completion of meiosis, beginning to bend within 30 minutes of being placed horizontal. Stem bending first occurred in the apical 15% of its length, then the position of the bend moved rapidly towards the base, traversing 40% of stem length in 2.5 h. Meanwhile, the stem elongated by 25%, mostly in its upper half but also in basal regions. If the apex was pinned horizontally the stem base was elevated but overshot the vertical, often curling through more than 300 degrees. When the base was pinned to the horizontal (considered analogous to the normal situation), 90% of the initial bend was compensated as the stem brought its apex accurately upright, rarely overshooting the vertical. The apex had to be free to move for this curvature compensation to occur. Stems transferred to a clinostat after some minutes gravistimulation showed curvature which increased with the length of initial gravistimulation, indicating that continued exposure to the unilateral gravity vector was necessary for continued bending. Such gravistimulated stems which bent on the clinostat subsequently relaxed back towards their original orientation. Reaction kinetics were unaffected by submergence in water, suggesting that mechanical events do not contribute, but submerged stems bent first at the base rather than apex. In air, the gravitropic bend appeared first near the apex and then moved towards the base, suggesting basipetal movement of a signal. In water, the pattern of initial bending was changed (from apex to base) without effect on kinetics. Taken together these results suggest that bending is induced by a diffusing chemical growth factor (whose extracellular propagation is enhanced under water) which emanates from the apical zone of the stem. The apex is also responsible for regulating compensation of the bend so as to bring the tip to the vertical. The nature of this latter stimulus is unknown but it is polarized (the apex must be free to move for the compensation to occur) and it may not require reference to the unilateral gravity vector.

Rapid determination of the critical temperature in simulated annealing inversion.

Knowledge of the critical temperature, T(*), the temperature at which a phase change occurs, greatly improves the efficiency of simulated annealing when used for optimization or inversion. A numerical method of accurately determining T(*) in a relatively short computation time has been developed. This method is used to recover the seismic soundspeed profile from wavefield data, a problem in which cycle skipping causes many local minima of the energy function and the averaging of the medium by finite length waves results in many states with similar energies. Computations indicate that it is cost-effective to spend about 80 percent of the computing budget looking for T(*) instead of annealing, and that in the course of finding T(*) many states with energies near the global minimum will also be found. The a posteriori probability distribution of the solution has been constructed from trial solutions generated at T(*).