Continuous reproduction of planktonic foraminifera in laboratory culture

Abstract

Planktonic foraminifera were long considered obligate sexual outbreeders but recent observations have shown that nonspinose species can reproduce by multiple fission. The frequency of multiple fission appears low but the survival rate of the offspring is high and specimens approaching fission can be distinguished. We made use of this observation and established a culturing protocol aimed at enhancing the detection and frequency of fission. Using this protocol, we selectively cultured specimens of Neogloboquadrina pachyderma and raised the frequency of reproduction by fission in culture from 3% in randomly selected specimens to almost 60%. By feeding the resulting offspring different strains of live diatoms, we obtained a thriving offspring population and during the subsequent 6 months of culturing, we observed two more successive generations produced by fission. This provides evidence that in nonspinose species of planktonic foraminifera, reproduction by multiple fission is likely clonal and corresponds to the schizont phase known from benthic foraminifera. We subsequently tested if a similar culturing strategy could be applied to Globigerinita glutinata, representing a different clade of planktonic foraminifera, and we were indeed able to obtain offspring via multiple fission in this species. This work opens new avenues for laboratory‐based experimental work with planktonic foraminifera.

Single-cell transcriptomics highlights sexual cues among reproductive life stages of uncultivated Acantharia (Radiolaria)

“…The combined expression of OG0018738 and OG0018740 proteins may contribute to furnishing the newly fertilized cell with the requisite information to facilitate the vegetative growth of the acantharian zygote. We sustain the hypothesis that these putative acantharian zygotes are not issued from multiple fission, like commonly documented in the sister lineage of Foraminifera (Meilland et al, 2024), since the expression of gamete fusion genes in cells capable of development without fertilization wouldn’t be expected. Instead, the expression of these gamete specific genes could be explained by an incomplete gene suppression, as it has been described in zygotes of the green microalgae Chlamydomonas (Joo et al, 2017).…”

“…We sustain the hypothesis that these putative acantharian zygotes are not issued from multiple fission, like commonly documented in the sister lineage of Foraminifera (Meilland et al, 2024), since the expression of gamete fusion genes in cells capable of development without fertilization wouldn't be expected. Instead, the expression of these gamete specific genes could be explained by an incomplete gene suppression, as it has been described in zygotes of the green microalgae…”