Negative Phototactic Response Research Articles

Effects of Oxygen Depletion and of Carbon Dioxide Buildup on the Photic Behavior of the Walleye (Stizostedion vitreum vitreum)

In laboratory experiments under overhead white light, walleyes (Stizostedion vitreum vitreum (Mitchill)) displayed a negative phototactic response consistent with field observations and histological features of the walleye eye. The strength of this innate response proved to be largely dependent on the given respiratory situation: during oxygen depletion and during buildup of free carbon dioxide, this response diminished to the point of obliteration, which occurred at levels leaving mobility and equilibrium of the test specimens still intact. Whereas during the course of oxygen depletion a wide indifference zone (little or no change of light behavior) could be observed from saturation (= acclimation) level down to about 4–2 mg/liter, the fish reacted rather sensitively to increase of free carbon dioxide. Starting from acclimation levels of 1.0–2.0 mm Hg CO2, the light avoidance response declined gradually while approaching tensions of 5 mm Hg or more, being completely abandoned at levels above 15 mm Hg. This effect could not be attributed to pH shifts.

Mechanism and computer simulation of the phototactic accumulation of Euglena in a beam of light.

Abstract— A mechanistic model is proposed which describes the phototactic behavior of Euglena during accumulation in an illuminated region. Measurements of the lag time occurring between illumination of the culture and net accumulation in the lighted zone as a function of culture density indicate that the relative strengths of the negative phototactic response inside and of the positive phototactic response outside this region are the prime factors controlling the lag phenomenon. Further evidence for this is provided by studies of the temperature dependence of the phototactic responses to polarized actinic light. It is shown that negative phototaxis as measured in the 7lsquo;phototaxigraph’ is not directed, but rather a shock‐mediated response. A ‘FOCAL’ computer program for simulation of experiments in the phototaxigraph has been written on the basis of our model. It correctly predicts the observed results under a variety of simulated experimental conditions. Measurements of the lag time and of the rate of accumulation in different parts of the actinic zone allow the calculation of motilities of the organisms with illumination and in the dark, the latter value being 0.08 mm/sec. For a 2–3‐weekold culture, the rate of negative phototaxis remained constant at light intensities above 40 ergs/cm2sec at 500 nm. At this wavelength, the threshold for the positive photophobic response was 100 ergs/cm2 sec.

Behavioural aspects of the ecology of the sand martin flea Ceratophyllus styx jordani Smit (Siphonaptera).

The behaviour of the sand martin fleaCeratophyllus styx jordaniSmit was studied in relation to its ecology.The cocooned resting imago in the host's old nest is the main over-wintering stage. Mechanical disturbance of the cocoons by the exploratory habits of the newly returned sand martins elicits emergence of the imagines in spring. The seasonal rise in temperature is not, by itself, important in causing emergence, as it does not become effective until many weeks after the martins have returned, by which time undisturbed fleas are likely to have died inside their cocoons.When the imagines break out of their cocoons they are negatively photo-tactic, but become positively phototactic within 24 h. This response takes them outwards along the martin's disused burrow until the increasing intensity of light reduces their activity so that they aggregate on the lower lip of the entrance. Positive phototaxis prevents them dispersing downwards from the entrance.Periodically the fleas bury themselves in sand; this response may function for water conservation. The proportion buried is greatest at night.The sand martin's habit of hovering close to a succession of entrances renders it accessible to the fleas, whose main host-finding response is an outward jump from the burrow entrance. This jump is released by a sudden decrease in light intensity and is directed towards dark objects. Vibration and air currents do not release jumping.Dispersal from aggregations in disused burrows may occur by transport on the host, or by spontaneous horizontal emigration along the cliff face, or by falling after an unsuccessful host-finding jump. Fleas which have fallen become negatively geotactic and positively anemotactic. Fleas wandering on the cliff face visually detect burrow entrances up to 30 cm away, and turn towards them. Preference for moister sand and, possibly, a negative phototactic response, may induce the fleas to remain in newly found burrows.Small aggregations of fleas also occur at the entrances of burrows currently in use by martins. Fleas circulate between the entrance and nest chamber of these burrows, until the martin begins to incubate its eggs. The entrance aggregation then disappears and fleas accumulate in the nest chamber. There is some interchange of fleas between infested burrows in the martin's pre-incubation period.The general pattern of behaviour resembles that ofC. gallinae. Behavioural differences between the two species are related to the ecology of their hosts.C. styxis adapted to dispersal and host finding in its host's breeding site, whereasC. gallinaeis adapted to reach foraging birds. This difference partly accounts for the narrow host specificity ofC. styxand the wide host range ofC. gallinae.My grateful thanks are due to Chris. Mead and Giles Pepler for information on sand martins' behaviour and migratory arrival. I would also like to thank Brian Little, who introduced me to several colonies in the Tyne Valley. The valuable advice of the Hon. Miriam Rothschild and Dr E. T. Burtt is especially acknowledged.

Laser Effects on Two Insects

AbstractDermestid larvae, Trogoderma versicolor (Creutzer), and adult American cockroaches, Periplaneta americana (Linné), were affected by ruby laser pulses of two intensities, 0.06 ± 0.04 per 10−7 second duration and 0.57 ± 0.06 joules per 0.2 milliseconds. Laser impact areas were 1.5 mm. in diameter. The first intensity, directed at cephalic regions of dermestid larvae, caused mortality in 3–48 hours. The same intensity directed at larval mid-abdominal areas caused visible outer integument and body-hair scorching, cessation of feeding, growth rate, and movement, and loss of negative phototactic responses. Directed at posterior abdominal regions of larvae, it caused damage to the epidermal layer noticeable in four succeeding moults. It caused temporary (10-15 min.) immobility and loss of negative phototaxis when directed at pro-thoracic regions of cockroach adults. P. americana adults were more severely affected by the second laser treatment, exhibiting immobility, loss of negative phototaxis, and cessation of eating. Total mortality in the five treated specimens occurred in 8-14 days as compared with 45-68 days in controls.