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The Sap Also Rises Ity of DNA Sequence More Accurately Composed of a Whole Limb ( Crustacean ALL Plants Are Pumps

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The Sap Also Rises Ity of DNA Sequence More Accurately Composed of a Whole Limb ( Crustacean ALL Plants Are Pumps NEWS AND VIEWS DAEDALUS-------------. are thought to be largely unaffected by the appendages corresponding to the second environment, with the result that similar­ antennae of crustaceans, and a mandible The sap also rises ity of DNA sequence more accurately composed of a whole limb ( crustacean ALL plants are pumps. They take in water reflects relationships. The reality of se­ mandibles are formed from a limb base). through their roots and transpire it as quence evolution is more complex than Friedrich and Tautz argue that the first vapour from their leaves. How do they lift this statement suggests, making difficult four of these characters are shared the water? Capillary rise is limited to a the retrieval of phylogenetic signals from through convergence due to both groups metre or so, and an atmospheric suction such ancient divergences. Friedrich and being terrestrial; structures similar to the pump cannotliftwater above 10 metres; Tautz2 have analysed the largest arthro­ first three are even found in some terrest­ yettrees can grow 100 metres high. pod DNA sequence data set so far from rial arachnids. Finally, recent gene ex­ Furthermore, aquatic plants cannot use the small and large subunit ribosomal pression data argues against a whole limb either mechanism, but still thrive; and RNA genes of a carefully selected range mandible in the insects. The gene Distal­ even land plants survive flooding. of taxa. Importantly, they have also less, generally expressed in the tip of Daedalus reckons that plants move taken pains to test for and control several insect appendages, is not expressed in the their internal fluids just as we do: by factors known to bias the recovery of insect mandible 10 . This suggests that the mechanical pumping. Their internal the correct phylogeny. appendage tip is missing and that the channels form a distributed peristaltic Boore et al. 1 use molecular data in a insect mandible is, in fact, similar to that pump, driven by the ceaseless shaking of manner more familiar to traditional syste­ of the crustaceans. Indeed, Kukalova­ the wind. On this view, the gallant waving matists. They have looked for gene rear­ Peck6 claims that a limb-base mandible is of a wind-blown field of corn, the rangements within the small mitochond­ present in all arthropods. ceaseless rustling of forest leaves, even rial genomes of animals (37 genes, usual­ Other lines of evidence support a sister Wordsworth's daffodils "tossing their ly) and used gene boundaries as characters group relationship between insects and heads in sprightly dance" have stern to produce a phylogenetic tree. These crustaceans 11 . Nervous system develop­ biological purpose in their movements. rearrangements occur only rarely and are ment in the two groups is strikingly This theory is supported by a recent considered to be immune to selective similar 12 , with no equivalent similarity yet finding that many commercial plants, pressures. The vast number of potential seen in myriapods or chelicerates and, such as tomatoes, aubergines and rearrangements makes identical novel again on a cellular level, crustacean and cucumbers, benefit from the repeated arrangements in unrelated taxa extremely insect eyes are more similar to each other bending of their stems by stroking. They unlikely. Events such as these provide than either are to those of myriapods or develop a darker green, and grow more ideal characters for phylogenetic analysis. chelicerates 13 • compactly, as if the added massage Both studies provide further strong sup­ Despite their convincing congruence, saved them from having to grow port for a monophyletic Arthropoda, a these results are unlikely to be immediate­ extended fronds to catch the wind. concept particularly strengthened by the ly generally accepted and many questions DREADCO gardeners are now testing this novelty of the data of Boore et al., who remain. More needs to be done to pin notion. They are shaking selected plants also tentatively include the lobopods in down the position of the lobopods, as well in a range of frequencies and vibrational this assemblage. as the positions of other less well known modes to discover the most effective The one grouping common to virtually groups such as the tardigrades and pycno­ pumping regimes. Control plants are all previous schemes relating the arthro­ gonids (sea spiders). The monophyly or being clamped rigidly immobile to see if pods is the close relationship of the otherwise of both the myriapods and the their growth is stunted. Once the myriapods and insects; a group united by crustaceans also remains uncertain. The technique has been optimized, vibro­ the common possession of several adult position of the chelicerates is still not clear horticulture should speed the sap characteristics and often referred to as the and will determine whether a revised through crops of all kinds, boosting their atelocerates. The existence of the Atelo­ concept of the Mandibulata survives. It metabolism and growth. cerata is disputed by the study by Fried­ seems unlikely that we will have to wait For the smaller plants, a standard rich and Tautz, who suggest that it is the another 150 years for answers to these laboratory shaker should be ideal. Trays crustaceans and not the myriapods that questions and with them will come a much of seedlings could easily be vibrated at are the sister group of the insects (inciden­ improved understanding of the evolution whatever frequency and amplitude tally placing the origin of the myriapods ofarthropod body form. D optimized their growth. Very large single earlier than their fossil record suggests) ( b plants, such as trees, might also be in the figure). Boore et al. also present Maximilian J. Telford and Richard H. Thom­ driven mechanically by ropes or data that support this conclusion. Their as are in the Department of Zoology, The hydraulic rams under programmed interpretation of their data is cautious, Natural History Museum, Cromwell Road, control. But for crops such as corn, maize however, and they do not separate the London SW7 580, UK. and oats, wind seems the best shaker. A traditional atelocerate clades on their field could be set with big baffles to summary diagram. The closeness of the 1. Boore,J. L., Collins, T. M .. Stanton, D .. Daehler, L. L. & funnel and direct it, spring-loaded vanes insects and crustaceans had been sup­ Brown, W. M. Nature 376, 163-165 (1995). to release a stream of vortices downwind, ported by some, but not all, previous 2. Friedrich, M. & Tautz, D. Nature 376. 165-167 (1995). 3. Manton, S. M. The Arthropoda: Habits, Functional or huge tuned pipes to resonate atthe molecular analyses7- 9 . Morphology and Evolution (Clarendon. Oxford, 1977). best frequencies. As the crop matured, If the close relationship of the crusta­ 4. Cisne,J. L. Science 186. 13-18 (1974). 5. Wills, M.A., Briggs, D. E.G .. Fortey, R. A. &Wilkinson, M. these could be adjusted to maintain the ceans and insects is accepted, features Verh. dt. zoo/. Ges. (in the press). optimum pattern of vibration. shared by myriapods and insects, but not 6. Kukalova-Peck,J. Can. J. Zoo/. 70, 236-255 (1992). Aquatic plants would be easier to 7. Turbeville, J. M .. Pfeifer. D. M .. Field. K. G. & Raff, R. A. the crustaceans, must be shown either to Mo/ec. Biol. Evo/. 8, 669-686 (1991). vibrate. Daedalus is designing special be shared as a result of convergence, most 8. Ballard. J. W. 0. eta/. Science 258, 1345-1348 (1992). stirrers for watercress beds, and a 9. Wheeler, W. C.. Cartwright. P. & Hayashi, C. Y. C/adistics likely because both are terrestrial groups, 9, 1-39 (1993). central wave machine to spread waves or to be primitive characteristics secon­ 10. Panganiban. G.. Nagy, L. &Carroll, S. B. Curr. Biol. 4, out into a rice paddy-field. He also darily lost in the Crustacea. 671-675 (1994). advocates the planting of seaweed on 11. Averof. M. &Akam, M. Phil. Trans. R. Soc. Lond. B347, The following characters have tradi­ 293-303 (1995). breakwaters and sea defences. The tionally been used to unite the myriapods 12. Whitington, P. M .. Leach. D. &Sandeman. R. rougher the waves, the more the weed Development 118, 449-461 (1993). and insects: unbranched legs, a tracheal 13. Paulus, H.F. in Arthropod Phylogeny (ed. Gupta. A. P.) would grow to damp them. David Jones system, malphigian tubules, absence of 299-383 (Van Nostrand Reinhold. New York, 1979). 124 NATURE · VOL 376 · 13 JULY 1995 .
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