Local adaptation to salinity in the three-spined stickleback?

Area of Science:

• Marine biology
• Evolutionary biology
• Ecology

Background:

• Local adaptation may be more common in marine environments than previously assumed.
• Mobile, long-lived vertebrates with complex life cycles can exhibit local adaptation.
• Salinity is a key environmental factor driving adaptation in aquatic ecosystems.

Purpose of the Study:

• To investigate local adaptation to salinity in Baltic Sea sticklebacks (Gasterosteus aculeatus).
• To test the hypothesis that stickleback populations are adapted to their native salinity regimes.
• To assess the role of salinity in shaping genetic variation and fitness in marine fish.

Main Methods:

• A common garden experiment was conducted using sticklebacks from three native salinity regimes (high, mid, low).
• Fish were subjected to three experimental salinity treatments (high, mid, low) in a full-factorial design.
• Juvenile survival, growth, and body condition were measured across treatments.

Main Results:

• Fish generally performed better in low and mid-salinity treatments, regardless of origin.
• A significant interaction between native and treatment salinities was observed, indicating local adaptation.
• Poor performance of low-salinity natives in high salinity provided clear evidence of local adaptation.

Conclusions:

• Baltic Sea sticklebacks exhibit local adaptation to salinity, challenging previous assumptions about adaptation in high gene flow marine systems.
• Genetic differentiation in osmoregulatory genes supports the observed adaptive responses.
• Population-specific responses to salinity treatments exceed expectations from random genetic drift, reinforcing adaptive divergence.