“…Oogamy is thought to be advantageous because a species can maximize the number of gametes and, as a result, successful copulation encounters by producing many small and highly motile male gametes, as well as zygote survivorship by producing one or a few large (and immobile) female gametes (Parker et al, 1972;Maynard Smith, 1978;Matsuda & Abrams, 1999;Bulmer & Parker, 2002;Togashi et al, 2012). In pennate diatoms, however, the flagellum of male gametes was lost, and dimorphism between gametes diminished, such that gametes in a copulation pair converged towards a similar, intermediate size (reviewed in Kaczmarska et al, 2013), but differed in their behavior (Drebes, 1977), with male gametes that moved by pseudopodia to search for a nonmotile female gamete (Davidovich et al, 2010(Davidovich et al, , 2017Sato et al, 2011;Kaczmarska et al, 2017). The evolution of the raphe and active motility in vegetative cells enabled gametangia, rather than gametes, to search for mating partners, promoting further reduction in sexual dimorphism and gamete mobility.…”