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Questions and answers should be concise. We reserve the right to edit items for clarity and style. Include a daytime telephone number and email address if you have one. Restrict questions to scientific enquiries about everyday phenomena. The writers of published answers will receive a cheque for £25 (or US$ equivalent). Reed Business Information Ltd reserves all rights to reuse question and answer material submitted by readers in any medium or format. New Scientist retains total editorial control over the content of The Last Word. Send questions and answers to The Last Word, New Scientist, Lacon House, 84 Theobald’s Road, London WC1X 8NS, UK, by email to [email protected] or visit www.last-word.com (please include a postal address in order to receive payment for answers). For a list of all unanswered questions send an SAE to LWQlist at the above address. THE LAST WORD Happy feet The blue-footed booby is an extraordinary-looking bird. It has fairly dull plumage but strikingly coloured blue legs and feet. What could be the evolutionary benefit of such a conspicuous feature? Both sexes have blue feet so they don’t seem to be for impressing potential mates. n Although not obvious at first sight, during courtship blue- footed boobies (Sula nebouxii) are dimorphic in terms of their feet: male feet are brighter and more of a greenish-blue, while the females have duller feet that are bluish. The birds exhibit their feet to prospective partners in a series of courtship displays. These include a kind of ritualised strutting around that allows them to show off their feet, plus stylised or “salute” landings which serve the same purpose. I am a member of a research group that studies the sexual behaviour of the blue-footed booby. In one experiment, we altered the colour of the courting males’ feet and recorded the females’ response. Females paired to males with duller feet were less enthusiastic about courtship and less likely to copulate compared with females paired to males with normal, brightly coloured feet. Similarly, when we altered the females’ feet to a dull blue, males became less interested in courting them. Birds in poor health often have dull blue feet. What’s more, females whose mates had dull blue feet produced smaller eggs, and their chicks had a poorer immune response compared with normal females. This may sound surprising, but it is in accordance with theoretical expectations. All this suggests that males are probably under strong selection pressure to maintain greenish- blue feet during courtship. This will ensure not only that they copulate successfully but also that their mates will lay big, healthy eggs. Overall, our results suggest that foot colour is a trait maintained by mutual male and female preferences. Roxana Torres Institute of Ecology National Autonomous University of Mexico n Both male and female Sula nebouxii have blue feet, but it is the male that presents his feet prominently in courtship. This, in effect, is a way of saying that he is of the same species as the female. I cannot offer any specific reason why the blue-footed booby has blue feet, but I would point out that foot colour does seem to be significant in the genus – there is an equally striking red- footed booby, Sula sula. This suggests that as members of the genus evolved, they adapted to different ecological niches which, in turn, meant that there was an advantage in the birds splitting into different “tribes” which could only mate with their own kind. This is as an example of what is called sympatric evolution, where one species evolves into two within a shared territory. In contrast, allopatric evolution occurs because populations become isolated from each other. For sympatric evolution to succeed, it is essential that some sort of difference between the species arises so that a bird can distinguish between a bird of a related species and one of its own kind. Guy Cox Associate Professor Australian Centre for Microscopy & Microanalysis University of Sydney, Australia This week’s questions GERROFF What are the noises of protest that people make when you disturb them in their sleep? Are they inarticulate attempts at speech or something else? Sumit Paul-Choudhury London, UK NO SKIDDING Your question on motorcycle-tyre tread patterns prompts me to pose another motorcycle-related query. I was watching motorcycle racing at the weekend and noticed that the bikes were taking corners while tilting at well over 45 degrees from the vertical, in fact probably by as much as 60 degrees. Most of the time the bikes managed this without sliding and crashing. How do the bikes lean so steeply and corner on what looks like the side of their tyres without sliding? Chris Grant Wakefield, West Yorkshire, UK WATER MARKED I was boiling chunks of potatoes when I noticed that they were surrounded by a correspondingly shaped outline on the water’s surface (see photo). The pan had been on the stove for only a couple of minutes so the water was not yet boiling. What causes the lines on the surface to form and why do they follow the outlines of the potato pieces? Harry Simon Windsor, Berkshire, UK “Female boobies paired to males with duller feet were less enthusiastic about courtship” Last words past and present, plus questions, at last-word.com The latest collection: witty, brilliant, intelligent and packed with insight Available from booksellers and at www.newscientist.com/elephants Why can’t elephants jump? “Foot colour does seem to be significant in boobies – there is an equally striking red-footed booby”
