title: The walk and jump of Equisetum spores.
abstract: Equisetum plants (horsetails) reproduce by producing tiny spherical spores that are typically 50 µm in diameter. The spores have four elaters, which are flexible ribbon-like appendages that are initially wrapped around the main spore body and that deploy upon drying or fold back in humid air. If elaters are believed to help dispersal, the exact mechanism for spore motion remains unclear in the literature. In this manuscript, we present observations of the 'walks' and 'jumps' of Equisetum spores, which are novel types of spore locomotion mechanisms compared to the ones of other spores. Walks are driven by humidity cycles, each cycle inducing a small step in a random direction. The dispersal range from the walk is limited, but the walk provides key steps to either exit the sporangium or to reorient and refold. Jumps occur when the spores suddenly thrust themselves after being tightly folded. They result in a very efficient dispersal: even spores jumping from the ground can catch the wind again, whereas non-jumping spores stay on the ground. The understanding of these movements, which are solely driven by humidity variations, conveys biomimetic inspiration for a new class of self-propelled objects.
authors.affiliation: Laboratoire Interdisciplinaire de Physique, CNRS and University Grenoble I, , B.P. 87, 38402 St Martin d'Hères Cedex, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Marmottant
authors.forename: Alexandre
authors.initials: A
authors.lastname: Ponomarenko
authors.forename: Diane
authors.initials: D
authors.lastname: Bienaimé
mesh_terms: D000392:Air Movements; D020829:Equisetum / Q000502:physiology*; D006813:Humidity; D009038:Motion; D012098:Reproduction; D013170:Spores / Q000502:physiology*
keywords: Equisetum; elastic energy; hygroscopic; locomotion; spores
references.citation: J Exp Biol. 2009 Sep 1;212(17):2835-43
references.pmid: 19684219
references.citation: PLoS One. 2008 Sep 17;3(9):e3237
references.pmid: 18797504
references.citation: Science. 2011 Sep 23;333(6050):1726-30
references.pmid: 21940888
references.citation: Phys Rev E Stat Nonlin Soft Matter Phys. 2011 Mar;83(3 Pt 2):035301
references.pmid: 21517551
references.citation: J Exp Biol. 2011 Feb 15;214(Pt 4):521-9
references.pmid: 21270299
references.citation: Science. 2010 Jul 23;329(5990):406
references.pmid: 20651145
references.citation: J R Soc Interface. 2009 Oct 6;6(39):951-7
references.pmid: 19570796
references.citation: Nature. 2001 Feb 1;409(6820):618-22
references.pmid: 11214320
references.citation: Science. 2012 Mar 16;335(6074):1322
references.pmid: 22422975
references.citation: Science. 2007 May 11;316(5826):884-6
references.pmid: 17495170