Light
What is light?
Light is electromagnetic radiation within a specific portion of the entire electromagnetic spectrum (from long-wavelength radio waves to short-wavelength gamma rays). The sun is the main source of light on earth. Sunlight is a portion of the electromagnetic radiation emitted by the sun, particularly infrared, visible, and ultraviolet light. Light that is visible to the human eye has wavelengths ranging from 400 to 700 nm on the electromagnetic spectrum.
How does light vary?
Light can vary in both intensity (the amount of energy transmitted, measured in lux or other units) and quality (spectral composition, measured in nm). Both light intensity and quality can vary with time (daily, seasonally) and with location.
Water also intercepts considerable amounts of light. The amounts and wavelengths of light that are absorbed change with increasing depth.
How do animals sense light?
Animals sense light with a wide variety of photoreceptors, or light-sensing organs (Freeman et al. 2014). These photoreceptors could be in the form of an eye or an extraocular receptor (e.g. dermal and ganglionic sense organs) (Cronin 1986). All photoreceptors share the common characteristic of light-sensitive pigments, which absorb light energy as the first step in initiating light-induced, or photic reactions. The energy absorbed excites the light-sensitive pigments, triggering a chain of molecular processes that result in a neural signal (Stavenga 2006). The sensation of light perceived by these receptors can range from simply perceiving light intensity or direction, to forming high-resolution and colour images.
How do animals respond to variation in light intensity?
Why is light biologically important?
Light is the ultimate source of energy for living systems and provides organisms with information about their physical environment that is essential to survival, growth and reproduction (Russell et al. 2019). Light can damage biological molecules (e.g. UV light [200 – 400 nm] can damage DNA). It also affects many physiological (e.g. body temperature, metabolic processes, cell division) and behavioral phenomena (e.g. foraging for food, mating) through the rhythmic cycle of light and darkness. The light environment in a habitat plays an important role in adaptation, affecting behavior and interactions with other organisms. |
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How do animals respond to variation in light intensity? Animals respond to variations in light intensity through behavioural responses ranging from changes in orientation (taxis) to changes in rates of movement of part or all of the animal. Phototaxis is a kind of taxis, or locomotory movement that occurs when an organism moves towards or away from the stimulus of light.
Key search terms: Light · Intensity · Wavelength · Photoreceptor · Phototaxis
References Cited
Cronin TW. 1986. Photoreception in marine invertebrates. Amer. Zool. 26:403–415. [accessed 2018 May 18]. https://academic.oup.com/icb/article/26/2/403/117330.
Freeman S, Harrington M, Sharp J. 2014. Biological Science. 2nd Canadian ed. Toronto: Pearson.
Russell PJ, Hertz PE, McMillan B, Fenton MB, Maxwell D, Haffie T, Milsom B, Nickle T, Ellis S. 2019. Exploring the diversity of life. Biology. 4th Canadian edition. Toronto: Nelson.
Stavenga DG. 2006. Invertebrate photoreceptor optics. In: Warrant E, Nilsson DE, editors. Invertebrate vision. Cambridge University Press. 547 p.
Cronin TW. 1986. Photoreception in marine invertebrates. Amer. Zool. 26:403–415. [accessed 2018 May 18]. https://academic.oup.com/icb/article/26/2/403/117330.
Freeman S, Harrington M, Sharp J. 2014. Biological Science. 2nd Canadian ed. Toronto: Pearson.
Russell PJ, Hertz PE, McMillan B, Fenton MB, Maxwell D, Haffie T, Milsom B, Nickle T, Ellis S. 2019. Exploring the diversity of life. Biology. 4th Canadian edition. Toronto: Nelson.
Stavenga DG. 2006. Invertebrate photoreceptor optics. In: Warrant E, Nilsson DE, editors. Invertebrate vision. Cambridge University Press. 547 p.
To learn more:
Bruce-White C, Shardlow M. 2011. A review of the impact of artificial light on invertebrates. Buglife. [accessed 2018 May 17]. https://www.buglife.org.uk/sites/default/files/A%20Review%20of%20the%20Impact%20of%20Artificial%20Light%
20on%20Invertebrates%20docx_0.pdf.
Jékely G, Colombelli J, Hausen H, Guy K, Stelzer E, Nédélec F, Arendt D. 2008. Mechanism of phototaxis in marine zooplankton. Nature. 456(7220):395-399.
Menzel R. 1979. Spectral sensitivity and color vision in invertebrates. In: Autrum H, editor. Handbook of sensory physiology, Vol. 7/6/6A. Comparative physiology and evolution of vision in invertebrates. A: Invertebrate photoreceptors, Chapter 9. Berlin: Springer-Verlag. pp. 503–580. [accessed 2018 May 18]. https://link.springer.com/chapter/10.1007/978-3-642-66999-6_9.
Note: Any edition of the above book or other biology textbook could be useful.
Bruce-White C, Shardlow M. 2011. A review of the impact of artificial light on invertebrates. Buglife. [accessed 2018 May 17]. https://www.buglife.org.uk/sites/default/files/A%20Review%20of%20the%20Impact%20of%20Artificial%20Light%
20on%20Invertebrates%20docx_0.pdf.
Jékely G, Colombelli J, Hausen H, Guy K, Stelzer E, Nédélec F, Arendt D. 2008. Mechanism of phototaxis in marine zooplankton. Nature. 456(7220):395-399.
Menzel R. 1979. Spectral sensitivity and color vision in invertebrates. In: Autrum H, editor. Handbook of sensory physiology, Vol. 7/6/6A. Comparative physiology and evolution of vision in invertebrates. A: Invertebrate photoreceptors, Chapter 9. Berlin: Springer-Verlag. pp. 503–580. [accessed 2018 May 18]. https://link.springer.com/chapter/10.1007/978-3-642-66999-6_9.
Note: Any edition of the above book or other biology textbook could be useful.