required reading:
Chiao C-C, Cronin TW, Marshall NJ. 2000. Eye design and color signaling in a stomatopod crustacean Gonodactylus smithii. Brain Behav Evol 56:107-122.
pdf-file

Questions:

1. Describe the general design of the mantis shrimp eye. What are some of its distinguishing features?
2. What are two ideas about why mantis shrimp have so many different photoreceptors?
3. Describe the general methods used by the authors in the paper to assess absorbance in Figure 2. What general properties of the stomatopod eye in terms of organization and distribution of photoreceptors are confirmed by the data in figure 2?
4. What does the data in Figure 3 suggest about the functions of the tiers and filters in the stomatopod eye. Speculate on how these structures achieve this.
5. What is reflectance? What is chromaticity? What do they measure? How are they determined? What are the limitations to this approach? From figures 4, 6, and 7 what observations can be made about how color information is processed by stomatopods?
6. Based on the data in Figures 8 and 9, are there any differences in the way color information from other organisms and conspecifics is detected by mantis shrimp?
7. At the level of the retina, how does human color vision differ from that found in the mantis shrimp? Speculate on how this might translate into differences in color perception.
8. In biology, no organism can "have it all." What appears to be the trade-offs for the enhanced color perceptual abilities of the mantis shrimp eye?
9. Longer wavelengths (e.g. red) are absorbed before they reach deeper levels in the ocean. In some stomatopod species found at these deeper levels, receptors have been found to degenerate or contain no measurable pigment. Based on the data in this paper, which row would you predict these receptors are likely to be found? Based on what you know about the general eye design in the mantis shrimp, speculate on how color tuning might be achieved in mantis shrimp larvae to accommodate spectral ranges at different depths.

Susy's comments and useful background reading

I knew nothing about mantis shrimp before approaching this formidable paper. So for the fellow uninitiated, here are a few tempting tidbits I collected from random websites and other papers:

· Mantis shrimp are more than just another pretty sparkly marine animal. Despite their size, they are ferocious predators that lash out raptorial claws like ballistic instruments to either spear or smash their prey (fish, crabs, shrimp, clams, snails) to death. In the West Indies, they are known as toe splitters or thumb splitters due to the severe lacerations and occasional amputation they've inflicted on unwitting human victims.

· The species studied in the paper, G. smithii is classified as a "smasher." The striking force of its calcified appendage is equivalent to that of a fired 22-calibre bullet and has been reported to be able to break the double paned safety glass of an aquarium wall. It uses this appendage to perform such aggressive feats as smashing the claws, legs and carapace of a crab before dragging its victim into a burrow to feed upon it. A dreaded pest in reef aquarium tanks, a single mantis shrimp can devastate the population of fish, crustaceans, and other species on display. (Tiny shrimp terrorizes aquarium)

· The telson is the flexible tail the mantis shrimp uses to defend itself against the crushing blows of rival shrimp. In a duel, it can curl its tail under itself and use the telson as a shield while it throws punches from behind it.

· The meral spot is located on the inside of each raptorial claw and is speculated to be an aid to assess the fighting ability of an opponent. In battle with a rival, the claws are raised to the side to display the colorful meral spots.

· Mantis shrimp have a visual system which enhances their ability to catch fast moving prey. The upper and lower eye parts are believed to act together to optimize distance vision, whereas the middle part is used for color vision. The movements of its predatory claws are among the fastest known in the animal kingdom. They can unfold their claw and lash out at prey in less than 8 milliseconds.

· While humans color vision isn't too shabby with our ability to distinguish roughly 10,000 different colors, the mantis shrimp can differentiate approximately 110,000 including those in the UV range.

· The color filters in rows 2 and 3 of the stomatopod eye are actually electron dense vesicles containing carotenoid pigments. In cryosection, they appear brightly coloured (red, yellow, orange, pink, blue and purple.) In G. smithii: Row2: F1 = Yellow, F2 = Orange and Row 3: F1 = Salmon, F2 = Blue. (from NJ Marshall. "A unique colour and polarization vision system in mantis shrimps." Nature vol. 333, June 9, 1988). pdf-file

I found the following paper very helpful in further clarifying features of the mantis shrimp eye. It is brief (< 4 pages of text) and available online: T.W. Cronin et al., "Spectral tuning and the visual ecology of mantis shrimp." Philosophical Transactions of the Royal Society of London: B. Biological Sciences. (2000) 355, 1263-1267.
pdf-file

Here are some useful excerpts to accompany figure 1 of our paper du jour:

· "The apposition compound eyes of stomatopods….are always divided into three distinct parts: the dorsal region (or hemisphere), the midband and the ventral region….the midbands are composed of six parallel rows of ommatidia, and each ommatidial row has unique specializations that enhance the analysis of spectral and polarizational features of light." What our paper refers to as the "peripheral regions" are the dorsal and ventral parts of the stomatopod eye.

· Stomatopod "retinas…include four classes of intrarhabdomal filters, two each in all ommatidia of midband rows 2 and 3. These act as long-pass spectral filters, with those of row 2 transmitting light in a shorter wavelength range than those of row 3. Since each filter lies above its own photoreceptor tier, they alone are sufficient to produce a well-tuned, spectrally diverse receptor set. Additional complexity, however, is afforded by the diverse assortment of visual pigments present in the same retina. Each tier of of the main rhabdoms in rows 1 to 4 has its own visual pigment [8 visual pigments are accounted for by the tiers of rows 1-4]." Main rhabdoms of rows 5 and 6 use a ninth (the same) visual pigment and a tenth visual pigment class occurs throughout the main rhabdoms of all peripheral (dorsal and ventral region) ommatidia.

· "In midband rows 1 to 4, the visual pigments of the distal tiers themselves act as long pass filters for the proximal tiers. Thus, in every case the distal [closest to cornea] pigment absorbs at shorter wavelengths than the proximal pigment by about 25 nm. The arrangement sharpens spectral sensitivity functions of proximal tier photoreceptors and the effect is augmented by the action of the filters in rows 2 and 3. Receptors in rows 1 and 4, which are sensitive at the shortest wavelenghts, are tuned by the tiering of visual pigments alone. Receptors in rows 2 and 3 are more strongly influenced by the presence of the intrarhabdomal filters."

PDF-file of power-point lecture (about 1.4 MB)

background reading

NJ Marshall (1988). A unique colour and polarization vision system in mantis shrimps. Nature vol. 333, June 9. pdf-file

TW Cronin, NJ Marshall (1989). A retina with at least ten spectral types of photoreceptors in a mantis shrimp. Nature 339:137-140. pdf-file

T.W. Cronin et al. (2000) Spectral tuning and the visual ecology of mantis shrimp." Phil. Trans. R Soc. Lond. B: 355, 1263-1267.
pdf-file

Links
The Lurker's guide to Stomatopods
Mantis shrimp
Justin Marshall's Sensory Ecology Lab

Human Color Vision