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Adaptive color vision in Pullosquilla litoralis (Stomatopoda, Lysiosquilloidea) associated with spectral and intensity changes in light environment

Alexander G. Cheroske^1,*, Thomas W. Cronin¹ and Roy L. Caldwell²

¹ Department of Biological Sciences, University of Maryland, Baltimore County, Baltimore, MD 21250, USA
² Department of Integrative Biology, University of California, Berkeley, CA 94720, USA

View larger version (11K): [in a new window]   Fig. 1. Irradiance spectra of experimental light treatments (N=5 animals per treatment). The white line represents full-spectrum, high-intensity `white' light, the blue line represents the narrow-spectrum `blue' light and the gray line represents the reduced-intensity full-spectrum light treatment. The gray line is calculated from the full-spectrum irradiance and the absorbance of the four layers of 50% neutral density filter material.

View larger version (29K): [in a new window]   Fig. 2. Absorbance spectra for Pullosquilla litoralis intrarhabdomal filters from each of the three light treatments. Each spectrum is normalized to its peak. (A) Row 2 distal filters, (B) Row 2 proximal filters, (C) Row 3 distal filters. In A-C, each trace represents an average for an individual animal. The color of the trace represents the light treatment that the animal inhabited: blue represents the narrow-spectrum, short-wavelength treatment; gray represents the reduced-intensity, full-spectrum treatment; and white represents the high-intensity, full-spectrum treatment. The yellow traces represent animals from the white treatment that developed a shorter wavelength class of Row 3 filter. Variance in baselines among curves is due to differences in the quality of the scans. (D) Means of the three spectral classes of Row 3 receptors from the light treatments. Each curve represents the mean of all animals within a treatment with a particular Row 3 filter class [the blue line represents blue light (N=4), the gray line represents reduced-intensity light (N=5), the white line represents long-wavelength filter class from white light (N=3), and the yellow line represents shorter-wavelength filter class from white light (N=2)]. All curves have baselines normalized to zero to facilitate comparison.

View larger version (32K): [in a new window]   Fig. 3. Calculated sensitivity spectra for the tiered photoreceptors in the four midband ommatidial rows of Pullosquilla litoralis from experimental light treatments. (A) Sensitivities for white-light-treated animals. (B) Sensitivities for blue- or gray-light-treated animals. All spectra are normalized to their peak. Rows with intrarhabdomal filters (Rows 2 and 3) are plotted as broken lines, while others (Rows 1 and 4) are plotted as solid lines. The number above each curve denotes the row; D, distal; P, proximal.

View larger version (13K): [in a new window]   Fig. 4. Comparison of the spectrum of downwelling irradiance in two depth environments of Pullosquilla litoralis with the calculated percentage photon capture rate for animals with Row 3 receptors adapted to shallow and deep light environments. Downwelling irradiance spectra were measured in waters off Moorea, French Polynesia. R3D, Row 3 distal tier; R3P, Row 3 proximal tier.

View larger version (13K): [in a new window]   Fig. 5. Ratio of photoreceptor photon capture rates in `deep-adapted' and `shallow-adapted' photoreceptors in Pullosquilla litoralis. Values are calculated from spectral sensitivity functions for photoreceptors in Rows 2 and 3 combined with measured downwelling irradiances in various depth environments (see text for details). The broken line on the y-axis at a ratio of 1.0 indicates a level at which photon capture rates between deep and shallow animals would be the same. Row 3 photoreceptor calculations are ratios of a `deep' photoreceptor with a short-wavelength shifted distal filter compared with a `shallow' photoreceptor with a long-wavelength distal filter, each capturing photons of the available light at 1 m intervals from 1 m to 22 m depth. All Row 2 comparisons are photon capture rates of each photoreceptor at 1-22 m relative to capture rates at 1 m depth. Row 2 calculations are also a ratio of photon capture rates but, as the proximal and distal filter in this row did not vary, changes in photon capture ratios show the effects of decreasing light intensity and spectral range with increasing depth only. By contrasting the photon capture rates of Row 2 receptors and Row 3 receptors, the significant increase in photoreceptor sensitivity due to the adaptable intrarhabdomal filters in Row 3 is evident. In depths of 1-7 m, the adaptable distal filters in Row 3 increase the photon capture rate of underlying photoreceptors as much as fourfold, overcoming the actual decrease in illumination with increasing depth. Thus, capture rates for `deep' photoreceptors at 6-8 m are equivalent to those of `shallow' receptors operating at a depth of 1 m.