Humans and most other mammals cannot see ultraviolet (UV) light, whereas some rodents can. A Chilean-German research team has now reported UV vision in the South-American degu, a distant relative of the guinea pig. In a search for behaviourally relevant UV signals in the habitat of these rodents, the researchers found that fresh degu urine reflects the UV parts of the spectrum most strongly, while dry old urine has only marginal UV reflectance. The socially active degus use urine extensively to scent mark their communal trails and wallowing places. The researchers postulate that such scent marks represent visual as well as olfactory cues for the UV-sensitive degus (Investigative Ophthalmology & Visual Science, vol. 44, pp. 2290-2296, May 2003).

For humans and most other mammals, the visible spectrum extends from short-wave blue to long-wave red, ultraviolet (UV) is invisible to them. In contrast, many fish, reptiles and birds can see UV and use it in the identification of conspecifics: In some birds, e. g. blue tits, males and females have different UV patterns in their plumage. UV vision is also important for bird foraging: the waxy cover of many berries has a high UV reflectance. UV vision is part of the sensory equipment of many vertebrates and invertebrates (e. g., honeybees), but has been lost in the evolution of mammals. Not completely, however, as some rodents like mice and rats have retained UV vision. The adaptive reasons for this specialization are largely unknown.

A plausible ecological explanation has now been offered by Leo Peichl at the Max Planck Institute for Brain Research in Frankfurt/Main, Francisco Bozinovic at the Pontifica Catholic University Santiago (Chile), and Andrs Chvez and Adrin Palacios at the University of Valparaso (Chile). They studied the rodent degu (Octodon degus), a distant relative of the guinea pig, which is endemic to Chile and kept as pets worldwide. The strongly diurnal degus inhabit open bushland, where they
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Contact: Dr. Leo Peichl, Max Planck Institute for Brain Research
49- 69-96769-219
Max-Planck-Gesellschaft
10-Jun-2003

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