# Conserved genetic markers reveal widespread diatom sexual reproduction in the global ocean

## TL;DR

This study identifies genetic markers that reveal widespread sexual reproduction in diatoms across the global ocean, challenging previous assumptions about their rarity.

## Contribution

The study introduces conserved genetic markers for detecting sexual reproduction in diatoms using a lab-to-field approach.

## Key findings

- Conserved marker genes indicate widespread sexual reproduction in nine diatom genera in natural populations.
- Sexual reproduction occurs in both dominant bloom-forming and rare diatom species in response to environmental changes.
- Metatranscriptomic data and imaging resources confirm coordinated sexual activity across diverse diatom taxa.

## Abstract

Sexual reproduction is a nearly universal characteristic of the eukaryotic life cycle, yet it is rarely observed in natural populations of micro-eukaryotes. Sex is particularly relevant for diatoms, a key group of marine and freshwater phytoplankton, where sexual reproduction counters a progressive cell size reduction due to cellular division. Here, we leveraged controlled sex transcriptome experiments of four diatom species to develop a robust method for in situ monitoring of sexual reproduction events. The resulting panel of conserved marker genes was validated for specificity and sensitivity using metatranscriptomic profiling of a natural estuarine community undergoing massive sexual reproduction of multiple species in response to increased salinity. Analysis of metatranscriptomic data linked with Metagenome-Assembled Genomes from the Tara Oceans expedition revealed widespread and coordinated expression of these markers across nine diatom genera, complemented by observations of sexual stages in automated imaging resources. Our results reveal that diatom sexual reproduction is more widespread in the global ocean than previously thought, encompassing both dominant bloom-forming species and rare taxa. Our panel of markers to detect sexual reproduction in natural environments paves the road to better understand the interplay between endogenous and environmental controls of this pivotal process, essential for the diatoms’ evolutionary success.

Diatoms dominate the oceans, yet sexual reproduction - key to bloom dynamics and species evolvability - is rarely observed. Using a lab-to-field approach, this study presents conserved markers applicable across datasets, revealing widespread sex in both abundant and rare taxa in diatom natural populations.