Post-Diapause DNA Replication during Oogenesis in a Capital-Breeding Copepod

Area of Science:

• Marine Biology
• Reproductive Biology
• Arthropod Physiology

Background:

• High-latitude arthropods enter diapause (dormancy) to survive harsh conditions and optimize reproduction.
• Neocalanus flemingeri, a subarctic copepod, has decoupled feeding from oogenesis, necessitating resource regulation for egg production.
• The mechanism by which N. flemingeri limits oocyte formation remains uninvestigated.

Purpose of the Study:

• To investigate the timing and regulation of oocyte production in post-diapause Neocalanus flemingeri females.
• To determine if and how N. flemingeri limits oocyte formation to ensure egg quality.

Main Methods:

• Females were incubated with 5-Ethynyl-2'-deoxyuridine (EdU) to label cells undergoing DNA replication.
• Ovary and oviduct DNA replication was assessed post-diapause termination.
• EdU incorporation was quantified over time to determine the phase of oocyte production.

Main Results:

• Both oogonia and oocytes incorporated EdU, indicating DNA replication during oogenesis.
• EdU labeling peaked at 72 hours post-diapause and remained high for two weeks.
• No labeling was detected by four weeks post-diapause, preceding spawning.

Conclusions:

• Oogenesis in N. flemingeri is sequential, with oocyte formation initiated within 24 hours of diapause termination and limited to the first few weeks.
• This sequential strategy separates oocyte production from provisioning, ensuring fully provisioned eggs.
• This contrasts with the concurrent oocyte maturation seen in most copepods, suggesting a unique reproductive strategy.