. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 36 A. J. SWEATT AND R. B. FORWARD, JR. !> tfi 0) CO o> — B O) rr OO?- 400 440 480 520 560 Wavelength (nm) 600 640 FIGURE 2. Action spectrum for positive phototaxis by 5. hispida. For each wavelength the reciprocal of the quanta! flux required to elicit 30% phototaxis was calculated. Each value was then divided by the value obtained at 500 nm, where sensitivity was maximal. This quotient is shown as the relative sensitivity. Error bars were calculated similarl
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 36 A. J. SWEATT AND R. B. FORWARD, JR. !> tfi 0) CO o> — B O) rr OO?- 400 440 480 520 560 Wavelength (nm) 600 640 FIGURE 2. Action spectrum for positive phototaxis by 5. hispida. For each wavelength the reciprocal of the quanta! flux required to elicit 30% phototaxis was calculated. Each value was then divided by the value obtained at 500 nm, where sensitivity was maximal. This quotient is shown as the relative sensitivity. Error bars were calculated similarly, based on the standard error of the 30% phototactic response at each wavelength. Dashed line shows an absorbance spectrum calculated from a nomogram for a visual pigment having maximum absorbance at 500 nm. the construction of an action spectrum for phototaxis (Fig. 2). The action spectrum shows that S. hispida is most sensitive to blue-green light, with maximum sensitivity at 500 nm. In Figure 2, the shape of the action spectrum corresponds roughly with the absorbance spectrum of a rhodopsin-based visual pigment with maximum ab- sorbance at 500 nm (Ebrey and Honig, 1977). This may be interpreted as evidence that S. hispida possesses a visual pigment which has an absorbance maximum near 500 nm. The small shoulder in the action spectrum at 600-620 nm could indicate the presence of another visual pigment, with an absorbance maximum near 600 nm. Experimental evidence suggests that chaetognaths are not visual predators (Reeve, 1964; Feigenbaum and Reeve, 1977). It is probable that chaetognath photoreception is mainly concerned with light dependent orientation behaviors, which could include vertical migration. Among zooplankton, light intensity is considered the most im- portant environmental cue involved in vertical migration (Forward, 1976). If chae- tognath photoreceptors are primarily used during vertical migration, then it could be expected that their spectral sensitivity s
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
