Life Under the Sun

Life Under the Sun, a photobiology book published by Yale University Press , is a collection of science essays about organisms that sense and respond to sunlight. The book is directed toward readers interested in nature, science, or the environment.

A figure (The Organisms of Life Under the Sun) shows the evolutionary relationships of organisms featured in the book. Another figure (Daylight Spectrum) shows the wavelength spectrum of sunlight at 12 noon on a typical day. A table (Levels of Light on Earth and Biological Responses) shows the levels of light that elicit the biological responses featured in the book.

What the Critics are Saying ...

"extraordinary little volume ... held my attention right to the last page ... virtuoso review of fungi, amoebae, slugs, butterflies, bacteria, and a host of other organisms"
- Gren Lucas, New Scientist

"Like the writings of Stephen Jay Gould, Oliver Sacks, and Lewis Thomas, Ensminger's work combines hard science and entertaining prose..."
- David Pitt, BookList

"This is a quick read, full of fascinating scientific stories by an accomplished writer. Readers will put this book down enlightened and satisfied that their time with this elegant exposition of light and its biological and medical effects was enjoyable and well spent."
- Albert D. Carlson, Quarterly Review of Biology

"Life Under the Sun is vibrant and illuminating ... and is strongly recommended for general readership and specialists alike"
- Alex Waller, Biologist

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Preface. . . [ Top ]
    I wrote Life Under the Sun to share with people who have an enthusiasm for science in general and biology in particular my own fascination with the animals, plants, fungi, and microbes that respond to light. I hope that this book will appeal to professional biologists as well ...
 
[Preface, Introduction, Chapter 1 ( PDF )]

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1. Vision at the Threshold. . . [ Top ]
A rod cell in the retina of the eye can sense the absorption of a single photon. Absorption of photons by about six different rod cells allows perception of a light flash.

Two figures from the Appendix show the structual changes in retinal that follow light absorption:

• Photoisomerization of rhodopsin.
• Light and dark activation of rhodopsin.

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2. The Five Percent Solution to Vision. . . [ Top ]
The Eyeless Shrimp (Rimicaris exoculata) lives near hydrothermal vents two miles deep in the Atlantic ocean. Its eye-like organs may allow it to see the heat generated by these deep sea geysers.

Several books by Cindy Lee Van Dover, whose research is featured in this chapter, are highly recommended:

• The Octopus's Garden: Hydrothermal Vents and Other Mysteries of the Deep Sea (1996, Perseus Press).
• Deep-Ocean Journeys: Discovering New Life at the Bottom of the Sea (1997, Perseus Press).
• The Ecology of Deep-Sea Hydrothermal Vents (2000, Princeton Univ. Press).

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3. A More Delightful Vision . . . [ Top ]
Mantis shrimps, which live in tropical coral reefs, have eyes with more than a dozen different types of photoreceptors - many more than humans or any other animal.

• The Lurker's Guide to Stomatopods is a comprehensive resource on mantis shrimps, with many beautiful color photos and several digital videos.
• A recent paper discusses the ecological significance of trichromatic vision: Dominy N, Lucas PW, 2001 [PubMed ].

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4. A Burning Issue. . . [ Top ]
Recent research has shown that long wavelength ultraviolet radiation (UV-A), formerly considered rather benign, can cause skin cancer and other health problems in humans.

• A figure from the Appendix shows the most common type of UV radiation-induced structural damage to DNA: Cyclobutane pyrimidine dimer.
• The USDA UVB Monitoring Program provides information on the geographical distribution and temporal trends of ultraviolet-B radiation in the United States.
• A recent paper describes the topical application of an enzyme for reversal of DNA damage: Stege H, et al, 2000 [PubMed ].

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5. A SAD Tale. . . [ Top ]
Many people experience Seasonal Affective Disorder (SAD) during the winter due to lack of sunlight. This disease can be treated by daily exposure to a bank of bright fluorescent bulbs.

• A figure from the Appendix shows the synthesis of melatonin, a pineal hormone important in circadian rhythms: Melatonin synthesis.
• The Michigan State University Counseling Center provides information about SAD: SAD Information Search .
• Recent studies indicate that melanopsin from the retinal ganglion cells is the visual pigment that sets the human circadian clock: Hattar S, et al, 2002 [PubMed ]; Berson DM, et al, 2002 [PubMed ].

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6. The Purple Disease. . . [ Top ]
Variegate porphyria, a disease in which porphyrins accumulate and make a person's skin photosensitive, may have afflicted King George III and other members of the Royal family of England.

• A figure (Final steps of heme synthesis) and a table (Metabolic basis and characteristic features of the porphyrias) from the Appendix show the metabolic bases of the different forms of porphyria.
• Purple Secret: Genes, 'Madness' and the Royal Houses of Europe (1998, Rohl J, Warren M, and Hunt D, Bantam Press) is highly recommended.

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7. A Novel Method of Weed Control. . . [ Top ]
Farmers may be able to reduce their dependence on herbicides by applying a new method to control the germination of photosensitive weed seeds.

• A figure from the Appendix shows the structure of the light-absorbing chrompohore of phytochrome: Photoisomerization of phytochrome.
• The Weed Science Society of America promotes the development of weed science and technology.

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8. Light and Beer. . . [ Top ]
When beer is exposed to sunlight, there is a chemical change in certain chemicals that are derived from hops. This can give the beer a skunky odor.

• The Appendix shows the chemistry of the Sun-struck reaction and the structures of Photostable hop compounds.
• Skunk Defensive Secretion has information on the chemistry of skunk odor and describes the use of household chemicals to neutralize this odor.

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9. Phycomyces - The Fungus that Sees. . . [ Top ]
Physiological reactions in the fungus Phycomyces and in the visual systems of humans allows adaptation to a 10 billion fold or more change in ambient light level.

• The Appendix shows the structures of riboflavin and roseoflavin.
• The Phycomyces Web Site is a comprehensive resource for information about Phycomyces.

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10. Dictyostelium - The Amoeba and the Slug. . . [ Top ]
Dictyostelium, a cellular slime mold, begins its life as an amoeba; thousands of amoebas aggregate to form a slug. Light regulates both life cycle stages of this organism.

• The Appendix shows the biochemical reaction that underlies amoeba migration: Biochemical basis of Dictyostelium amoeba migration.
• Pattern Formation in Dictyostelium , from the Zoologisches Institut München, features many fascinating videos.
• dictyBASE is a comprehensive online resource for Dictyostelium.

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11. High Hopes for Hypericin. . . [ Top ]
The movement of Stentor coeruleus, a ciliated microorganism, is controlled by light. The pigment that controls this response is related to hypericin, which is present in St. John's wort.

• The Appendix shows the structures of hypericin and stentorin.
• Protista Tutorials has videos of Stentor coerulus and other protists.

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12. Turning on a Butterfly. . . [ Top ]
The Japanese yellow swallowtail (Papilio xuthus) and many other butterflies have photoreceptors on their genitalia. Excitation of these photoreceptors by ultraviolet radiation is necessary for copulation.

• Butterflies of Japan (Papiliionidae) provides many color photos of the various species of Papilio.

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13. Red Tides and Blue Moons. . . [ Top ]
Massive reproduction of dinoflagellates causes the well-known "red tide" that is fatal to many marine organisms. At night time, these same dinoflagellates emit blue bioluminecence.

• The Appendix shows the Biochemical basis of Gonyaulax bioluminescence.
• "What's a Blue Moon?" , from Sky and Telescope Magazine.

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14. Photosynthesis and the Great Salt Lake. . . [ Top ]
Certain highly specialized microorganisms thrive in the Great Salt Lake and similar environments. These microorganisms perform photosynthesis by using a pigment similar to the rhodopsin found in human eyes.

• The Appendix shows the Photocycle of bacteriorhodopsin.
• Introduction to the Archaea gives an overview of the Archaea.
• Recent research by Hartmut Luecke and colleagues has determined the 3-dimensional structures of bacteriorhodopsin and sensory rhodopsin.

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15. Too Much of a Good Thing. . . [ Top ]
Sunlight drives photosynthesis but too much sunlight can harm plants. Many plants use carotenoids to protect themselves from excess light.

• The Appendix shows the Xanthophyll cycle, which protects from the damage caused by excess light.
• Photosynthesis and the Web , by Larry Orr and Govindjee, provides an overview of photosynthesis web sites.