Phototaxic Response Research Articles

Environmentally relevant concentrations of herbicides impact non-target species at multiple sublethal endpoints

There is concern over herbicide exposure effects on aquatic primary production and zooplankton as herbicides are found in aquatic ecosystems at concentrations potentially toxic to phytoplankton. We first aimed to determine the effect concentrations (growth inhibition) and mixture interactions of the herbicides diuron (0.5 to 50μg/L) and hexazinone (0.5 to 40μg/L) on the green algae Pseudokirchneriella subcapitata. Secondly, we evaluated chronic effects on Daphnia magna that were periodically fed on P. subcapitata that had been exposed to low, medium, and high concentrations. We hypothesized that based on the mode of action of the herbicides we would observe additive growth inhibition in algae, and sublethal effects on D. magna. Growth inhibition in P. subcapitata following mixture exposure was most consistent with the concentration addition (CA) concept; while the independent action (IA) model underestimated the combined effect. The lowest observed effect concentrations (LOEC) were 1.50μg/L hexazinone, 1.18μg/L diuron, and 0.125 TU (0.30μg/L diuron×0.12μg/L hexazinone) in the single and binary mixture exposures, respectively. High hexazinone exposure decreased D. magna survival (80% vs. 55.6%). Neonate number was reduced by 13.9% in high mixture and 23.5% in high hexazinone treatments. Gravid body length was reduced by 9.5% following exposure to the high mixture. Herbicide exposure decreased neonate size, especially in later broods. Herbicides decreased the phototaxic responses of neonates in most treatments. Herbicide exposure effects were detected at environmentally relevant concentrations, levels considered to be safe according to current USEPA aquatic life benchmarks, suggesting that these benchmarks need to be updated to improve ecological risk assessment. As herbicides are some of the most applied pesticides worldwide, sublethal endpoints can serve as sensitive early warning tools to indicate their presence and can support regulatory assessments and monitoring to protect aquatic life.

Dscam2 affects visual perception in Drosophila melanogaster.

Dscam2, a cell surface protein that mediates cellular repulsion, plays a crucial role in the development of the Drosophila melanogaster visual system. Dscam2 generates boundaries between neighboring modules in the fly optic lobe; in Dscam2 mutants this visual system modularity is compromised. Although developmental wiring defects have been well described in the Dscam2 mutant, behavioral consequences have not been investigated. To address this, we examined the visual behavior of Dscam2 mutant flies. Using a phototaxis assay, we ascertained that these flies are not blind, but have a reduced phototaxic response. Through population-based and single fly optomotor assays, we found that Dscam2 mutant flies can track motion but that their response is opposite to control flies under defined experimental conditions. In a fixation paradigm, which allows tethered flies to control the angular position of a visual stimulus, mutant flies' responses were diametrically opposed to those seen in control flies. These data suggest that modest changes in the modularity of the fly visual system in the Dscam2 mutant can dramatically change the perception of specific visual cues and modify behavior.

Potential effects of artificial light associated with anthropogenic infrastructure on the abundance and foraging behaviour of estuary‐associated fishes

As a consequence of a positive phototaxic response, the findings of this study suggest that artificial light often associated with man‐made structures has the potential to alter fish communities within urban estuarine ecosystems by creating optimal conditions for predators. Future coastal developments should consider the ecological implications of lighting on aquatic communities. We recommend that lighting be minimized around coastal infrastructure and the use of red lights, which have limited penetration though water, be considered.

Effect of Turbidity Duration on Culture of Walleye Larvae

AbstractAlthough turbid water is an essential environmental requirement for intensive larviculture of walleyes Sander vitreus on formulated feed, research has not determined the duration of turbidity required to achieve optimal benefits for survival and growth while reducing cannibalism. We conducted a replicated, single‐factor analysis to determine the effect duration of turbidity on these performance indicators at 28 d posthatch (dph). Four treatments, each with three replicate 150‐L tanks, involved culture of larvae in turbid water (84–125 nephelometric turbidity units [NTU]) from 3 dph to 7, 14, 21, or 28 dph. After culture under turbid conditions for the specified period, the fish were then cultured in clear water until 28 dph (i.e., fish in the 28‐dph treatment received no clear‐water culture). At 28 dph, substantial differences were observed in survival and growth among treatments. Fish survival for the 7‐ and 14‐dph treatments (1% and 2%, respectively) was significantly less than that for the 21‐ and 28‐dph treatments (11% and 14%, respectively). There was a significant difference in total length at 28 dph among the 7‐, 14‐, and 21‐dph treatments but not between the 21‐ and 28‐dph treatments. Fish in the 28‐dph treatment were 177% heavier than those in the 14‐dph treatment. A shift in phototaxic response at about 20 dph further reduced the need for turbid‐water culture to prevent clinging behavior in walleye larvae. Cannibalism (2–5%) was observed in all treatments between 7 and 13 dph but not thereafter. The study substantiates benefits of turbid‐water culture for larval walleyes and demonstrates that duration of turbidity should extend through 28 dph to maximize survival and growth but that it is less important for preventing cannibalism after 13 dph and clinging behavior after 20 dph.

Effects of parasitism on diel vertical migration, phototaxis/geotaxis, and swimming speed of the bloom-forming dinoflagellate Akashiwo sanguinea

Eukaryotic parasites are believed to play important roles in bloom dynamics of red-tide dinoflagellates; however, little is known about their impact on host behavior. To address this issue, we examined the influence of the parasitic dinoflagellate Amoebophrya sp. on diel vertical migration (DVM), phototaxis/geotaxis, and swimming speed of the bloom-forming dinoflagellate Akashiwo sanguinea. Uninfected A. sanguinea exhibited strong DVM, yielding subsurface aggregations during the day and evenly dispersed populations at night. DVM of parasitized A. sanguinea was compara- ble to that of uninfected host for much of the infection cycle; however, subsurface accumulations of host cells were dramatically reduced or eliminated as parasites matured. The absence of DVM in the latter part of the infection cycle appeared to be associated with changes in phototaxic response and swimming speed of parasitized cells. While uninfected A. sanguinea exhibited strong positive photo- taxis, hosts with late-stage infections exhibited strong negative phototaxis. By contrast, infected and uninfected A. sanguinea did not differ in geotaxis or sinking. Swimming speed of infected A. san- guinea decreased with parasite age, differing significantly from that of uninfected hosts 24 h after ini- tiation of infections. A. sanguinea with late-stage infections exhibited a 37.3% lower swimming speed than uninfected hosts. Results indicate that parasitism by Amoebophrya sp. disrupts 'internal' factors that control DVM in dinoflagellates. Data also suggest that modification of host behavior by para- sitism may contribute to vertical variations in phytoplankton species-composition and -abundance, particularly during epidemics when late-stage infections are prevalent.

Understanding avian vision: the key to using light in bird management

Author(s): Blackwell, Bradley F. | Abstract: Vision is a primary and highly developed sensory pathway in birds. Light, both diffuse and wavelength-specific (e.g., as produced by lasers) has recently been demonstrated as a potential means of effecting changes in timing and consistency of flock response to an approaching vehicle (simulating an aircraft) and as an avian dispersal method. However, in experiments to date, the effectiveness of light in eliciting an avoidance or dispersal response in birds has varied by species and context. To effectively use light in managing avian conflicts with humans, a better understanding of the complexities of avian retinal physiology relative to phototaxic responses to the environment is necessary. My objectives are to provide an overview of research pertaining to 1) anatomical features of the avian eye and 2) the ecological implications of retinal wavelength sensitivity, and 3) discuss the application of light for resolving avian conflicts with humans. I also suggest that future evaluations of light-based management methods for birds should include integration of aposematic colors and color pattern treatments for seeds and in combination with chemical repellents, as well as quantification of the effects of light wavelength, pulse frequency, and beam configurations of lasers, and aircraft-mounted light in eliciting avian dispersal and avoidance behavior.

Measures of phototaxis and movement detection in the larval salamander

In this investigation, we describe two precise tests of visual function that integrate quasinatural situations with time-lapse video recording and infrared computerized monitoring of activity to assess movement detection and phototaxic tendencies, respectively. Four groups of larvae from A. punctatum, A. tigrinum, A. mexicanum, and a mutant albino axolotl were tested in an alley containing light and dark halves and lined with infrared sensors to monitor their phototaxic response. A. punctatum showed no phototaxic tendency, while the other three groups displayed a strong negative phototaxic response. Enucleation of the eyes in mutant albinos eliminated the negative phototaxis. Visual detection of motion was tested by videorecording the behavior of A. punctatum, A. mexicanum, and the mutant albino axolotl larvae while they explored a large bowl with 6 small vials on the perimeter, one of which contained white worms. A. punctatum rapidly approached the worm vial and engaged in intense predatory behavior. A. mexicanum responded to the presence of worms very slowly and rapidly lost interest. Albino axolotls displayed no visual recognition of the worms. The results indicate that visual function can be precisely determined in larval salamanders utilizing behavioral measures consistent with the animal's natural tendencies.

A simplified method for detection of visual abnormality in rats on reproduction study: the critical intensity of illumination and the effect of dark-adaptation

A newly designed Y-shaped box was previously reported by authors to be useful for a screening test of visual abnormality in rats because of easy numerization and statistical analysis of the results. In the present paper, the relationship between the intensity of illumination and the negative phototaxic response were examined. The total selection rate for the dark area (total time of selecting dark area/total trials) of non-treated rats under 30 lux illumination was 98% and identical wit the result of those under 1600 lux. The selecting rates of non-treated rats under the illumination of 15, 10, 7.5, 5 and 1.25 lux were 95, 93, 89, 82 and 67%, respectively. On the other hand those of dark-adapted rats one hour under 15, 7.5 and 5 lux showed 98, 95 and 92%, respectively. From these results, the critical intensities of illumination-unaffected selection rate for darkness in non-treated and dark-adapted rats were estimated at 30 and 15 lux, respectively. There was an obvious effect of dark-adaptation on the visual ability of rats. The selection rate of eyelid-sutured rats under 30 lux was 52%, an approximate theoretical value of true blindness, but it was 85% under 1600 lux. It is suggested that a more exact detection of visual abnormality would be possible under the critical intensity of illumination-unaffected selection rate for darkness.

Colour and Brightness Preferences in the Lizard Anolis Carolinensis

Lizards of the species Anolis carolinensis were tested for colour and brightness preferences by using the phototaxic response. A choice was given between two alleys leading to frosted Perspex panels back-projected with light varying in hue and brightness, the variation being controlled by Munsell colour and neutral-density filters. Five colours were combined with several levels of brightness in a series of tests from which estimates could be made of relative preferences. The assumptions that the effects of hue and brightness combine additively to determine preference, and that relative preferences are independent of pairing, were tested by attempting to fit an appropriate linear model to the data. Choice proportions for any comparison were plotted on a normal probability scale against filter density, and it was found, to a reasonably close fit, that the preference for any particular colour increased linearly with filter density on the comparison colour. The rate of increase was approximately the same for all comparisons, and it was possible to use the y intercepts of the regression lines of preference against filter density as a measure of the scale values of the preferences for each colour. Scale values remained invariant over comparisons, with one exception: the preference for red over yellow was greater than predicted from the comparisons of these two colours with others. This may be a contrast effect.

A Supplemental Sampling Method for Estuarine Ichthyoplankton with Emphasis on the Atherinidae

A three-stage sampler, filtering water from the 0–5 cm, 5–25 cm, and 25–45 cm microhorizons was tested during conventional ichthyoplankton studies. The sampler was as much as 240X more efficient than 0.5 m nets in the collection of larval atherinids. The atherinids were found most abundantly in the 0–5 cm microhorizon, probably due to a positive phototaxic response.

Summer zooplankton distribution in a Georgia Estuary

Zooplankton were collected with Van Dorn bottles at two estuarine stations near Savannah, Georgia, USA, during summer, 1974, from the surface, 2 m, 4 m, and at the bottom of the water column at 2-h intervals for 11 days. Acartia tonsa occurred at the surface at night and during high and rising tides in higher concentrations than at the same depth during daylight and other tide stages. The highest bottom concentrations of this calanoid copepod occurred at high tide. A negative phototaxic response was also apparent in this species. While not quantitatively sampled by Van Dorn bottles, harpacticoid copepods and Pseudodiaptomus coronatus Were distributed in a manner similar to that of A. tonsa. Copepod nauplii, on the other hand, were always more abundant at the surface than at the bottom, with the highest concentration occurring during low tide. The distribution pattern of nauplii appears to be a function of dilution and concentration by tidally induced changes in water volume, whereas more advanced copepod stages follow a complexly controlled distribution pattern linked with tidal mixing dynamics as outlined in a previous study by Jacobs (1968).

A Rapid Separation of Larvae of the Indian Meal Moth1 from Rearing Medium

Laudani (1948) described a variation of the Berlese technique for separation of the larvae of the carpet beetle, Anthrenus scrophulariae (L.), from diet medium based on the negative phototaxis of the larvae. Because our biochemical and physiological investigations of the Indian meal moth, Plodia interpunctella (Hübner), often require many larvae, we attempted to modify Laudani's technique by utilizing the negative thermotaxic and phototaxic responses of Indian meal moth larvae. Larval development, adult emergence, egg production, and egg viability of insects removed by this method were not adversely affected.

Automatic Collection of Mass-Reared Codling Moths by Phototaxic Response and a Chilled Environment1

Automatic Collection of Mass-Reared Codling Moths by Phototaxic Response and a Chilled Environment1

Color vision of the female stable fly, Stomoxys calcitrans.

The stable fly, Stomoxys calcitrans (L.), is well known as a farm pest, and the sporadic appearance of this bloodsucking insect along recreational beaches is of increasing importance. My study considers the phototaxic response of S. calcitrans to specific wavelengths of light and the possible role of color vision in the occurrence of this fly along the southern shores of Lake Superior.

Euglena: An Experimental Organism for Biochemical and Biophysical Studies

This excellent monograph summarizes the present knowledge concerning this most interesting organism, Euglena gracilis . In recent years, Euglena has been found to be an excellent tool for investigations of fundamental biology and even as an aid in clinical diagnosis since they are used to measure vitamin B 12 by bioassay. These simple, unicellular organisms make it possible to study such complex biological processes as photosynthesis, photoreception, phototaxic responses, and the relationship of molecular structure to the biological function of subcellular particles from a fundamental point of view. In addition, Euglena has proved to be a most satisfactory organism for nutritional studies. Dr. Wolken has written a very thorough review of all the aspects of this phytoflagellate, including a detailed resume of his own contributions to the store of biological knowledge which he has gained at the hands of Euglena .