Why spawning salmon return to their natal stream: the immunological imprinting hypothesis

Area of Science:

• Comparative immunology
• Fish biology
• Neuroscience and behavior

Background:

• Salmonids possess immune systems similar to mammals, with B and T lymphocytes and diverse antibodies.
• Unlike mammals, salmonids develop immune cells in the anterior kidney, which also contains long-lived plasma cells (LLPCs).
• LLPCs are crucial for protecting adult salmon from pathogens encountered during spawning migrations.

Purpose of the Study:

• To propose a novel hypothesis connecting immune memory in salmonids to their navigational abilities.
• To explore the role of long-lived plasma cells (LLPCs) in salmon homing behavior.
• To link immunological memory with chemical imprinting and high return rates to natal streams.

Main Methods:

• This study presents a theoretical hypothesis, not experimental data.
• It synthesizes existing knowledge on salmonid immunology and behavior.
• The hypothesis posits a functional link between LLPCs and navigational cues.

Main Results:

• The hypothesis suggests that LLPCs, formed during early life, may retain memory of natal stream chemical signatures.
• This immune memory could contribute to the highly accurate homing behavior observed in adult salmon.
• The proposed mechanism offers a new perspective on the integration of immune and sensory systems in fish.

Conclusions:

• The hypothesis provides a potential explanation for the remarkable navigational accuracy of salmon.
• It highlights the underappreciated role of the immune system, specifically LLPCs, in complex behaviors like homing.
• Further research is needed to experimentally validate the proposed link between immune memory and chemical imprinting in salmon migration.