The influence of environmental factors on apparent photosynthesis and respiration of the submersed macrophyte Elodea canadensis

Abstract Oxygen effects on apparent photosynthetic and dark respiratory O₂ exchange rates of detached leaves of Elodea canadensis Michx. (Hydrocharitaceae) were determined over a range of conditions which the submersed plant is likely to experience in shallow water. Apparent photosynthesis is inhibited by O₂ under all the experimental regimes of light, temperature, CO₂ concentration and pH. This inhibition is not caused solely by an accelerated rate of dark respiration, and the observed variations in O₂ inhibition are comparable to O₂ effects on photosynthesis and photorespiration of terrestrial C₃ plants. Percentage inhibition of apparent photosynthesis is enhanced by high O₂ and also by low CO₂. These results indicate that high O₂, high pH and low CO₂ conditions could cause major losses in photosynthetic activity under field conditions. This may account for some of the losses in biomass that are observed under still water conditions.     

Reticulospinal Control of Rapid Escape Turning Maneuvers in Fishes

SYNOPSIS. In teleost fishes, the C-start is a rapid avoidancemaneuver that steers the animal away from the strike trajectoryof a predator. We review how the axial motor pattern underlyingthis movement is organized by the reticulospinal system. Thissystem includes the prominent Mauthner cells and other identifiableneurons. Typical of reticulospinal cells, the Mauthner neuronhas inputs from auditory, vestibular, and visual areas and hasoutputs to the trunk motoneurons by means of mono- and disynapticcontacts. Because reticulospinal organization and function isconserved among the vertebrates, the Mauthner network is advantageousas a model for understanding control of movement.We developthree major points. First, despite its seeming anatomical simplicity,the escape network is not a simple hierarchial system with onecell that directs the entire movement. We present evidence thatthe escape response is mediated by an array of neurons whichinclude the Mauthner cells. Second, though the firing of thiscell is adequate to result in a major component of the movement,the Mauthner cell is not indispensible for its execution. Thenetwork producing this movement is capable of regulating itsoutput so that the animal produces the normal range of responsesdespite the absence of one of its major contributors. Thesefindings can be accounted for by one of two models, though themost likely one involves lateral interactions, or corollarydischarges, within the array. Third, our recent work also showsthat the movement pattern is generated by a ballistic commandwhich does not rely on movement-induced sensory feedback. Thesesystem properties allow the animal to produce a highly reliableand orchestrated motor command in only 15 msec from sensorystimulus to EMG.     

Role of moth ocelli in timing flight initiation at dusk

ABSTRACT. The role of ocelli in timing flight initiation of cabbage looper moths, Trichoplusia ni (Hübner) (Noctuidae), at dusk was studied under simulated sunset conditions using a multichannel actograph. The mean time of flight initiation was determined for control, sham (sham/occluded, sham ablated, unilateral ablated) and experimental (ocellus occluded, ocellus ablated moths). Ocellus occlusion delayed flight initiation on the first day following treatment but was less effective on the subsequent days. Ocellus ablation also delayed flight initiation on the first day, and also produced pronounced delays on subsequent days. In studies where the sunset was advanced 1 h, control sham ocellus occluded and unilaterally ocellus ablated moths responded to the advance, but bilaterally ocellus ablated moths did not. These results indicate that moths make use of input from the ocelli in determining the threshold light intensity for flight and in making adjustments to small light-phase changes.