Circadian Clock Involvement in Zooplankton Diel Vertical Migration

Area of Science:

• Marine biology
• Chronobiology
• Zooplankton ecology

Background:

• Biological clocks are crucial for anticipating environmental cycles in organisms.
• Circadian clocks in marine organisms, especially those with large-scale rhythms like diel vertical migration (DVM), are poorly understood.
• DVM by abundant species like Calanus finmarchicus significantly impacts marine ecosystems.

Purpose of the Study:

• To investigate exogenous cycles and endogenous rhythms of DVM in Calanus finmarchicus.
• To analyze the expression of core circadian clock genes in relation to DVM.
• To explore the link between circadian clock gene expression and DVM in a key marine species.

Main Methods:

• Laboratory experiments on Calanus finmarchicus to observe DVM, metabolism, and clock gene rhythms.
• Field assessments of clock gene expression in wild-caught C. finmarchicus at different depths.
• Correlation analysis of clock gene expression timing with DVM peak migration times.

Main Results:

• Calanus finmarchicus displays circadian rhythms in DVM, metabolism, and core clock genes (clock, period1, period2, timeless, cryptochrome2, clockwork orange) in laboratory settings.
• Most clock genes exhibited cyclical expression in wild animals, with reduced rhythmicity at greater depths (50-140 m) compared to shallow waters (0-50 m).
• Peak expression of clock genes generally coincided with sunset or sunrise, aligning with peak DVM periods.

Conclusions:

• Circadian clock gene expression is strongly correlated with diel vertical migration in Calanus finmarchicus.
• Biological clocks likely enhance zooplankton fitness by optimizing the trade-off between feeding and predator avoidance, particularly when environmental cues are weak.
• This study provides insights into the role of circadian clocks in regulating one of the planet's largest daily migrations of biomass.