Clonal expansion behind a marine diatom bloom.

Area of Science:

• Marine biology
• Microbial ecology
• Population genetics

Background:

• Genetic diversity is crucial for population adaptation and evolution.
• Planktonic diatoms, like Pseudo-nitzschia multistriata, are key primary producers with significant ecological roles.
• Understanding micro-evolutionary dynamics in phytoplankton is essential for predicting ecosystem responses.

Purpose of the Study:

• To investigate the micro-evolutionary patterns of the diatom Pseudo-nitzschia multistriata.
• To determine the interplay of sexual reproduction and vegetative growth in shaping genetic diversity.
• To analyze long-term changes in the genetic fingerprint of this diatom species.

Main Methods:

• Long-term sampling of Pseudo-nitzschia multistriata over 6 years.
• Genotyping of isolates using 22 microsatellite markers.
• Analysis of demographic and clonal expansion events.

Main Results:

• Both sexual reproduction and vegetative growth significantly influence intraspecific diversity.
• A brief, massive demographic and clonal expansion was driven by strains of the same mating type.
• Nonlinear changes in the genetic fingerprint of P. multistriata were observed over 6 years, linked to periods of clonal predominance.

Conclusions:

• Micro-evolutionary dynamics in diatoms are complex, involving interactions between sexual and asexual reproduction.
• Clonal expansions can temporarily override sexual recombination, leading to significant shifts in genetic diversity.
• These findings enhance our understanding of diatom bloom formation and microevolutionary mechanisms in phytoplankton.