Analysis of phototaxis in nemato des using directional statistics
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The direction of horizontal movement of 2 nematode species with eyespots was observed both with and without directional sources. The results comprise statistical proof of phototaxis in nematodes and demonstrate the usefulness of directional statistics in evaluating and comparing the responses.
Two directional sources were tried, one including all the visible spectrum but red (“blue source”) and one containing only red. Both species had a significant tendency to move in the direction away from the blue source (0°), whereas the directions taken under control conditions were not significantly different from random (Fig. 2, and Table 2). A tendency to move away from the red source was significant forOncholaimus vesicarius but not forEnoplus anisospiculus.
Bimodal distributions with <90° between the modes occurred in at least 2 cases (Fig. 2, Table 3) and their statistical treatment is illustrated and discussed.
The component of the mean direction along the 0° direction,rc, was significantly greater forO. vesicarius than forE. anisospiculus. However a measure of the tendency to move horizontally indicated no significant difference between species. Therefore the difference inrc is probably not due to a difference in motivation. A difference in steering strategy is suggested by a negative correlation betweenr c and the angle between modes.
The results are interpreted in terms of ocellus morphology and possible steering strategies.
KeywordsNegative Correlation Statistical Treatment Visible Spectrum Bimodal Distribution Horizontal Movement
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