File:Image from page 304 of "The Biological bulletin".jpg

English: Title: The Biological bulletin

Identifier: biologicalbullet193mari Year: (s) Authors: Marine Biological Laboratory (Woods Hole, Mass. ); Marine Biological Laboratory (Woods Hole, Mass. ). Annual report 1907/08-1952; Lillie, Frank Rattray, 1870-1947; Moore, Carl Richard, 1892-; Redfield, Alfred Clarence, 1890-1983 Subjects: Biology; Zoology; Biology; Marine Biology Publisher: Woods Hole, Mass. : Marine Biological Laboratory Contributing Library: MBLWHOI Library Digitizing Sponsor: MBLWHOI Library

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Text Appearing Before Image: Reference: Bio/. Bull. 193: 199-201. (October, 1997) Introduction to Featured Article: The Lateral Eyes of Two Species of Horseshoe Crabs Are Similar, but Not Quite the Same The lateral eye of the horseshoe crab has been a useful and productive model for vision research; it is complex enough to be interesting, yet simple enough to be understood. Extensive studies of this eye have yielded fundamental insights about how eyes of other animals, including humans, encode and process visual information. Lateral inhibition, light adaptation, and efferent-mediated circadian rhythms are just a few of the numerous physiological properties that were first uncovered through experiments on the horseshoe crab eye. We always speak about "THE horseshoe crab." and indeed, all of the studies and advances have been made with the eye of a particular species, Limulns polyphemus, which inhabits the waters along the eastern shores of North and Central America. But there are actually four extant species of horseshoe crabs—one of them. Tachypleus tnilentatiix. inhabits the shores of Japan. In the following article, T. Saito and his colleagues compare the properties of the eyes of Tachypleus with those of the standard model, Limulns. Saito et al. have found that, although the retinal sensitivity of the lateral eyes of Tachypleus and Limulns shows nearly the same circadian rhythms, the underlying mechanisms are different. The Limulns eye increases in sensitivity at night primarily by catching more photons, whereas the Tachypleus eye shows, in addition, a substantial increase in photoreceptor gain: i.e., an enhanced response of the photoreceptors to absorbed photons. This difference could be explained by the fact that the lateral eyes of Tachypleus are smaller than those of Limulns (see Fig. 1); moreover these smaller eyes contain fewer, smaller ommatidia that cannot catch as many photons as those of Liiniilux. So the increased response of the Tachypleus photoreceptors to each photon they absorb may be a compensatory adaptation. In short, what the small Tachypleus eye lacks in photon catch, it may make up in gain. Once again we rind that although the functions of homologous tissues and cells are similar, they are never exactly the same, and that important and unexpected lessons can be learned in even small species differences. —Robert B. Barlow August 1997 ..- .. -r (-r••:%••»•-• • ' •-. . ».!V '-.».«* -•

Text Appearing After Image: Figure 1. 77/c lateral eyes o/Tachypleus (rig/;/) urn/ Limulus (/f/tj. The photographs are at the same maxiiijiculitiir, the Lnnulus eye is 1 cm wide. 199

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