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http://crossmark.crossref.org/dialog/?doi=10.1007/s00709-016-0974-y&domain=pdf
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Web End = Protoplasma (2017) 254:547555 DOI 10.1007/s00709-016-0974-y
ORIGINAL ARTICLE
Chemotactic movement in sperm of the oogamous brown algae, Saccharina japonica and Fucus distichus
Nana Kinoshita1 & Chikako Nagasato2 & Taizo Motomura2
Received: 23 January 2016 /Accepted: 11 April 2016 /Published online: 23 April 2016 # Springer-Verlag Wien 2016
Abstract In oogamous species of brown algae such as Saccharina japonica and Fucus distichus, the sperm possess an unusual long posterior flagellum, which oscillates actively and produces a propulsive force during swimming. In this study, we quantitatively analyzed the effect of chemotactic responses on sperm swimming and flagellar waveforms by high-speed video recordings. We found that the thigmotactic response to the chemo-attractant was not enhanced during chemotactic swimming and that the swimming velocity of sperm did not decrease. As concentration of the chemoattractant decreased, the sperm performed drastic U-turn movements, which was caused by a rapid and large bend of the posterior flagellum. Unilateral bending of the posterior flagellum when sensing a decrease in the concentration of the chemo-attractant may be a common response in male gametes during fertilization of brown algae both oogamous and isogamous species.
Keywords Anterior flagellum . Brown algae . Chemotaxis . Flagellar waveform . Oogamy . Posterior flagellum . Sperm
Introduction
Sperm chemotaxis in response to sex pheromones (or the chemical attractant) released from eggs is a crucial factor during species-specific recognition and the fusion of both reproductive cells during the initial stage of fertilization. Sex pheromones have been identified in mammals, marine invertebrate and vertebrate animals (Kaup 2010; Yoshida and Yoshida 2011; Yoshida 2014), land plants (Higashiyama and Takeuchi 2015), and seaweeds and diatoms (Maier and Mller 1986; Frenkel et al. 2014). Chemotactic mechanism and pheromone receptors of sperm have also been elucidated in several organisms. For instance, in marine animals, such as sea urchins, ascidians, and starfish, uniflagellate sperm sense the sex pheromone gradient, change their flagellar waveform, and finally modify their swimming direction toward the egg (Kaupp et al. 2003; Bhmer et al. 2005; Shiba et al. 2008).
Brown algae belong to the major linage of Heterokontophyta or Stramenopiles, and their swarmers usually possess two heterogeneous flagella, a long, mastigonema-bearing anterior flagellum (AF) and a short, posterior flagellum (PF). Mller et al....