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First published online June 7, 2004
Journal of Experimental Biology 207, 2471-2485 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01047

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Interspecific and intraspecific views of color signals in the strawberry poison frog Dendrobates pumilio

Afsheen Siddiqi¹, Thomas W. Cronin^1,*, Ellis R. Loew², Misha Vorobyev³ and Kyle Summers⁴

¹ Department of Biological Sciences, University of Maryland Baltimore County, Baltimore, MD 21250, USA
² Department of Biomedical Sciences, Cornell University, Ithaca, NY 14853, USA
³ Vision Touch and Hearing Research Centre, University of Queensland, Brisbane, Queensland 4072, Australia
⁴ Department of Biology, East Carolina University, Greenville, NC 27858, USA

View larger version (103K): [in a new window]   Fig. 1. Images of 14 of the 15 color morphs of Dendrobates pumilio included in the current study, all from the Bocas del Toro region of Panama. The name designating each type indicates the location at which the particular color morph is collected. The one color morph not illustrated is from Pelican Key, and it is very similar in appearance to the `Shepherd Island' type. Photographs by K. Summers, except for Bocas Island and Solarte Island images, which were taken by Marcos Guerra.

View larger version (14K): [in a new window]   Fig. 2. Representative reflectance spectra from leaves used as backgrounds for spectral comparisons. (A) Purple leaf from Zebrina pendula. (B) Red leaf from Neoreglia carolinae. (C) Yellow dry leaf. (D) Green leaf of Aglaonema commutatum.

View larger version (25K): [in a new window]   Fig. 3. Spectra used in data analyses of spectral discriminability. See text for a description of the model used for this analysis. (A) Irradiance spectra. D65 (standard daylight), D55 (direct sunlight) and D75 (`north' skylight), from Wyszecki and Stiles (1982). Green (light under the natural forest canopy in D. pumilio habitat, Pelican Key), from Summers et al. (2003). (B) Templates representing cone visual pigments of D. pumilio. (C) Spectral sensitivities of avian cones, taken from Parus caeruleus (generously provided by N. Hart). Thin lines indicate visual pigments, while thick lines represent spectral sensitivities computed taking cone oil droplet absorption into account, used for actual analyses. (D) Normalized absorptance of an avian double cone, including the contribution of the associated oil droplet, used in achromatic analyses (provided by N. Hart). UVS, ultraviolet sensitive; SWS, short-wavelength sensitive; MWS, medium-wavelength sensitive; LWS, long-wavelength sensitive.

View larger version (37K): [in a new window]   Fig. 4. Results from microspectophotometric analyses of photoreceptors of D. pumilio, together with best-fit rhodopsin templates (smooth lines; from Lipetz and Cronin, 1988). (A) Rod photoreceptors (max=491 nm; N=16). (B) SWS cone photoreceptors (max=466 nm; N=5). (C) MWS cone photoreceptors (max=488 nm; N=14). (D) LWS cone photoreceptors (max=560 nm; N=20). (E) Single oil droplet from a single LWS cone inner segment, showing no significant absorption throughout the visual spectrum.

View larger version (23K): [in a new window]   Fig. 5. Results of analyses comparing frog spectral reflectances as discriminated by frog or bird visual systems. Each panel is a histogram plot of the number of comparisons (each a pair of spectra) vs. jnds (`just-noticeable-differences'); see text for details. Data plotted here represent results for the `Green' illuminant, but overall results were similar for all illuminants; see also Table 1. (A) Frog spectral pairs, as seen by frog vision. (B) Frog spectra compared to background spectra, as seen by frog vision. (C) Frog spectral pairs, as seen by bird vision. (D) Frog spectra compared to background spectra, as seen by bird vision.

View larger version (22K): [in a new window]   Fig. 6. Results of analyses comparing frog spectral reflectances within single color morphs, as viewed by frog or bird visual systems. Each panel plots the discriminability (in jnds; just-noticeable-differences) of spectral pairs, each indicated by a dot, for color morphs indicated along the abscissa. Al, Almirante; Ag, Aguacate; Ba, Bastimentos; Bo, Bocas; Ca, Cayo Agua; Cg, Chiriqui Grande; Gu, Guabo; Po, Pope; Ra, Rambala; Rb, Robalo; Rd, Roldan (Pelican Key); Sc, San Cristobal; Sh, Shepherd; So, Solarte; Uy, Uyama. Results plotted here are for the `Green' illuminant, but similar results were found for all illuminants. See also Table 2. (A) Frog spectral pairs, as seen by frog vision. (B) Frog spectra compared to background spectra, as seen by frog vision. (C) Frog spectral pairs, as seen by bird vision. (D) Frog spectra compared to background spectra, as seen by bird vision. Note that there are many more points in the panels for frogs vs. backgrounds, because each frog color was compared to all background colors, not only to the few colors present in any given frog color morph as in A and C.

View larger version (22K): [in a new window]   Fig. 7. Results of analyses comparing frog spectral reflectances as discriminated by frog or bird visual systems, using only `bright' frog colors in the analysis. Each panel is a histogram plot of the number of comparisons (each a pair of spectra) vs. jnds (`just-noticeable-differences'); see text for details. Data plotted here represent results for the `Green' illuminant, but overall results were similar for all illuminants; see also Table 3. (A) Frog spectral pairs, as seen by frog vision. (B) Frog spectra compared to background spectra, as seen by frog vision. (C) Frog spectral pairs, as seen by bird vision. (D) Frog spectra compared to background spectra, as seen by bird vision.

View larger version (12K): [in a new window]   Fig. 8. Results of analyses comparing spectral reflectances from dorsal or ventral frog body regions, as discriminated from backgrounds by frog or bird visual systems. All discriminations plotted here are for the `Green' illuminant, but results were similar for all illuminants. Open bars, dorsal frog colors; solid bars, ventral frog colors. (A) Frog visual systems, (B) bird visual systems.

View larger version (28K): [in a new window]   Fig. 9. Results of analyses comparing frog spectral reflectances as discriminated by only the achromatic channel of frog or bird visual systems. Data plotted here represent results for the `Green' illuminant, but overall results were similar for all illuminants; see also Table 4. (A) Frog spectral pairs, as seen by frog vision. (B) Frog spectra compared to background spectra, as seen by frog vision. (C) Frog spectral pairs, as seen by bird vision. (D) Frog spectra compared to background spectra, as seen by bird vision.

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