Autogamic reproductive behavior and sex cell structure in Thalassiosira angulata (Bacillariophyta)

Abstract

Our understanding of diatom reproduction is limited, especially for marine planktonic centric diatoms. This project aimed to elucidate sexual behavior and gametogenesis in the mediophycean diatom, Thalassiosira angulata, and to determine the fine structure of its reproductive cells. A monoclonal culture of T. angulata was successfully induced and enumerated, and all stages of auxosporulation documented. Spermatogenesis was absent in all inductions. Nuclear behavior of the auxospore mother cell (AMC) during auxosporulation indicated that reproduction was autogamic. In our clone, reproduction began with a differentiating mitosis and subsequent pervalvar expansion of the AMC, a meiocyte. The smaller cell often continued normal vegetative growth. In the AMC, meiosis I was acytokinetic and resulted in one viable haploid and one pycnotic nucleus. Meiosis II resulted in the production of two viable haploid nuclei, which we postulate later fused to produce the zygotic nucleus. Cell expansion was observed in very young AMCs both prior to and following autosyngamy. The initial cell valves were produced after at least two acytokinetic and pycnotic mitotic divisions, after which the cell was capable of undergoing its first normal mitosis involving production of two sibling hypovalves.

Auxosporulation in Paralia guyana MacGillivary (Bacillariophyta) and Possible New Insights into the Habit of the Earliest Diatoms

“…Apomixis is the simplest of the processes explaining our observations, similar to that reported for other centrics ([ 8 ] p. 262; [ 9 ] p. 129) and pennate diatoms [ 8 , 41 ]. A less likely possibility, the extremely reduced form of autogamy [ 42 ], could not be completely discounted, because the second nuclear division (meiosis II) and subsequent fusion of haploid, sister nuclei might have been very rapid and thus the trinucleated stage (two sister nuclei following second meiosis plus a lasting pyknotic [homolog] product of the first division) in the young (small) auxospores difficult to capture. However, given the considerable number of auxospores we examined, reduced autogamy seems less likely.…”

“…The final stage, the development of the heavily silicified initial cell, was relatively lengthy compared to such diatoms as Thalassiosira angulata (Gregory) Hasle or Tabularia fasciculata (C. Agardh) D.M. Williams & Round ([ 42 , 49 ] respectively), and took days rather than hours. This lengthy final stage allowed numerous older auxospores to accumulate in the culture, rendering this stage suitable for detailed SEM examination.…”

“…Developing a typical vegetative valve in more derived diatoms thus far examined is comparatively prompt and involves only 1–2 post-auxospore mitoses [ 42 , 62 – 64 ]. Building the typical vegetative valve in P .…”

Thalassiosira sundarbana sp. nov. (Bacillariophyta), an estuarine diatom from Sundarbans mangrove ecoregion based on morphology and molecular phylogeny

“…Several studies based on physiology, reproductive behavior, and cell wall morphogenesis of Thalassiosira have been undertaken to date to unravel adaptive mechanisms that has resulted in its success as a major bloom forming genus across different ecosystems globally (Chepurnov et al . ; Mills & Kaczmarska ; Hildebrand et al . ; Hockin et al .…”

Morphological and transcriptomic evidence for ammonium induction of sexual reproduction inThalassiosira pseudonanaand other centric diatoms

“…The proportions of oogonia and 187 auxospores increased with light up to moderate intensities (70-100 µE) but decreased at high 188 (220 µE) intensities ( Table 1), suggesting that photon flux has an important role in meeting the 189 energetic demands of sexual reproduction. Other work showed sexualization was more prevalent 190 at light <50 µE [31] or with the addition of a dark period [13,32,33]. Likely, the optimum light 191 intensity or need for a dark period to precede sexual induction [34] is species-specific and linked 192…”