Sperm storage induces an immunity cost in ants

Area of Science:

• Insect reproductive biology
• Animal behavior
• Immunology

Background:

• Ant queens are exceptionally long-lived insects, mating once and storing sperm for years.
• Queen reproductive success is limited by stored sperm, but the reasons for storage limits are unclear.
• Sperm storage is crucial for long-term reproduction in species with single mating events.

Purpose of the Study:

• To investigate the costs associated with sperm storage in ant queens.
• To determine if sperm storage impacts immune function during the critical colony founding stage.
• To explore the relationship between sperm load, mating diversity, and queen immunity.

Main Methods:

• Studied newly mated queens of the leaf-cutting ant Atta colombica during colony founding.
• Assessed queen immune response at different time points post-colony initiation.
• Quantified sperm load and the number of contributing males to stored sperm.
• Correlated immune markers with sperm storage parameters.

Main Results:

• Queen immune response initially increases post-nest burrow completion but decreases by day nine.
• A negative correlation exists between the amount of stored sperm and immune response nine days after colony founding.
• Increased genetic diversity of stored sperm (more males) is associated with a lower immune response.

Conclusions:

• Sperm storage incurs a significant cost in the form of reduced immunity during colony founding.
• This trade-off suggests a balance between short-term survival and long-term reproductive potential.
• Mating with multiple males may impose an additional immunological cost on sperm storage.