Relationship between death-feigning behavior and population density in a beetle

Death feigning is an anti-predator behavior that is found in many animal taxa. Death feigning is thought to inhibit further attacks by predators and reduce the perceived need of the predator to subdue prey further. One of the hypotheses regarding the function of mimicry in death is the “selfish-prey hypothesis” where the prey sacrifices of other individuals of the same species. That is, the optimal intensity of death feigning may depend on the prey population density. Reported variations in the intensity of death feigning among wild populations may arise from differences in the prey population density. Here, I investigated the relationship between the intensity of death feigning and population density in the red flour beetle, Tribolium castaneum. Beetles were randomly collected from six wild populations and the prey population density was estimated. I also observed death-feigning behavior when the beetles were stimulated by artificial stimuli. The results showed that the duration of death feigning differed significantly among wild populations. However, this difference was not associated with the population density of T. castaneum. Although body mass differed within the wild population, there were no significant effects of body mass on death feigning. Therefore, the effects of prey population density on death-feigning behavior in T. castaneum are small.