Trade-offs between immunity and competitive ability in fighting ant males

Area of Science:

• Ecology
• Evolutionary Biology
• Animal Behavior

Background:

• Male ants compete for mating opportunities with queens, facing trade-offs between fighting and disease resistance.
• The fungal pathogen Metarhizium robertsii can infect males, potentially affecting their competitive abilities.
• Colony workers may interfere in male-male competition, influencing outcomes.

Purpose of the Study:

• To investigate how infection stage and intensity by Metarhizium robertsii affect fighting success in Cardiocondyla obscurior ant males.
• To understand the trade-offs between immune response and competitive ability in infected males.
• To explore the role of worker aggression in disease management within the colony.

Main Methods:

• Experimental infection of male ants with Metarhizium robertsii at varying stages and intensities.
• Observation and quantification of male-male fighting behavior and success.
• Monitoring of male survival rates and immune responses.

Main Results:

• Severe infection significantly reduced male fighting success and survival.
• Early-stage severe infection, despite a strong immune response, led to increased mortality during combat, suggesting an immune-related trade-off.
• Late-stage severe infection resulted in high morbidity and increased aggression from workers towards infected males.

Conclusions:

• Cardiocondyla obscurior males can tolerate mild infections due to a rapid immune response, preserving mating opportunities.
• Severe infections compromise fighting ability and survival, with workers actively removing infected individuals.
• Worker aggression towards infected males represents a novel social immunity mechanism protecting the colony from disease spread.