Life cycle and survival strategies of Noctiluca scintillans: Gamete physiology and reproduction

Noctiluca scintillans is a dinoflagellate species known for causing red tides in tropical and subtropical regions worldwide. Its reproductive cycle includes both asexual reproduction via binary fission and sexual reproduction through gametogenesis. Traditionally, it was believed that during sexual reproduction, Noctiluca scintillans transformed into gametocyte mother cells, which released gametes into the surrounding water. These gametes would then combine to form zygotes, maturing into trophont cells. Gametes were thought to possess only swimming ability, with no capability for reproduction or grazing. However, in this study, we observed that isolated gametes from mature Noctiluca scintillans cells exhibited signs of asexual reproduction, with increasing gamete concentration over time in closed environments. This discovery led us to investigate the reproductive and grazing behaviors of the gametes, as well as their diet and optimal cultivation condition. Due to the low natural rate of sexual reproduction (~1%), we employed previously established methods to induce gametocyte production and generate sufficient gametes for experimentation. Multiple culture experiments were conducted to assess the environmental factors influencing asexual reproduction in these gametes. Our results indicate that Noctiluca scintillans gametes are capable of reproduction and do not perform photosynthesis, suggesting that gametes represent an alternate generational form in the species’ life cycle. Further grazing experiments demonstrated that gamete concentration closely follows bacterial concentration trend, indicating that gametes feed primarily on bacteria or prey smaller than 2μm. Specifically, high rates of asexual reproduction were observed when the gametes were fed exclusively with Vibrio parahaemolyticus, showing stable population growth over 72 hours. These findings suggest that this alternate form of generation may act as a survival strategy toward the end of a bloom. When the adult form struggles to find sufficient prey, gametogenesis produces gametes that can feed on smaller-sized prey, such as bacteria, which remain abundant. This shift in feeding behavior allows the population to persist in low-prey conditions, ensuring the species' survival during periods of environmental stress.

Presentation Preference: Oral

Primary Presenter: Jeffery Lee, National Taiwan Ocean University (jl042430064@gmail.com)

Authors:

Jeffery Lee, National Taiwan Ocean University  (jl042430064@gmail.com)

Kuo-Ping Chiang, National Taiwan Ocean University  (kpchiang@mail.ntou.edu.tw)

Sheng-Fang Tsai, National Taiwan Ocean University  (stsai@mail.ntou.edu.tw)