2018 Volume 83 Issue 1 Pages 109-114
Flagellar movement and mating behavior of the biflagellate gametes of the marine green macroalga, Chaetomorpha spiralis were studied using high-speed video microscopy and field emission scanning electron microscopy (FE-SEM) to clarify the role of flagella during the rapid fertilization of marine green macroalgae. Discharged isogametes always swung their flagella backward during forward swimming. The beat pattern was flagellar beat with undulatory waves produced at the flagellar base being propagated toward the tip. One beat cycle took 15 ms. When the suspension of the gametes was mixed with that of the opposite mating types, the gametes immediately agglutinated to form gamete clumps or mating pairs within 10–20 s. Initial contacts between the two gametes took place at one of the flagellar tips. In the mating gamete pair, the two gametes maintained mutual contact at the flagellar tips and subsequently at their anterior end of the cell bodies. The gametes stuck together, even though they continued to move their flagella and oscillate their cell bodies. Then the two flagella derived from the opposite mating types became a pair and gradually beat synchronously. Finally, the gamete pair lay side-by-side with their longitudinal axes nearly parallel mutually and became a quadriflagellate planozygote. Such features of gamete behavior and their flagellar movement during fertilization resemble those of Ulva.