How does a bacterial infection affect an individual’s foraging and risk management over time?

Abstract

Abstract The effects of host-parasite interactions can be measured in ecologically relevant ways through behavioural indicators based on foraging theory. These include, assessing how parasites alter foraging aptitudes, harvest rates, and risk management of foragers. Consequences of infection can be measured from individuals to ecosystems. At the individual level, sick animals need to trade-off finding food with remaining safe from predators, while potentially facing debilitating effects from infection. This potentially results in reduced foraging efficiencies, compromised risk awareness, and increased apprehension. To investigate this, we assessed how a Mycoplasma bacterial infection impacted individual Allenby’s gerbils’ foraging aptitudes, resource harvest rates, and anti-predator responses. We monitored individuals through three stages, from uninfected, to acutely (newly) and finally chronically (long term) infected. We identified three distinct responses. While acutely infected, some individuals increased their foraging effort in patches and spent less time vigilant. This may reflect increased future value of food for these individuals. Some individuals immediately reduced their foraging effort and displayed increased apprehension while acutely infected. This likely reflects a lethargy, where sick individuals are compromised in their ability to harvest seeds efficiently while also remaining vigilant. As all individuals became progressively sicker with a chronic infection, their foraging declined and apprehension levels increased. Two individuals employed a ‘grab and go’ foraging strategy to minimize time spent in patches. Foraging costs of long-term infection increase dramatically over time. These findings point to some behavioural plasticity in response to initial infection, yet the consequences of long-term infection are similar for all individuals.