The effect of ecological context and relatedness on larval cannibalism in a fungus-associated beetle

The fitness consequences of extreme competitive interactions such as cannibalism are often governed by the environment because the costs and benefits of such behaviors depend on the ecological and social context of the participants. However, most studies of context-dependent cannibalism are conducted under extreme circumstances or examine only a single environmental context, conditions that are unlikely to exist in natural populations. In this study, we tested the effect of multiple environmental contexts on the frequency of cannibalism in forked fungus beetle larvae (Bolitotherus cornutus), which develop in 1 of 3 different fungus species. We paired larvae in laboratory trials and measured the effect of 1) ecological context (the 3 fungi) and 2) the relatedness of the paired larvae on the frequency of cannibalism. We found a strong effect of ecological context on cannibalism: larvae in 1 fungus cannibalized nearly twice as often as larvae in the other two. We did not detect an effect of relatedness on cannibalism in the 1 species of fungus in which trials were conducted. Cannibalism conferred benefits in the form of accelerated growth rates in all measured traits relative to noncannibals. However, contrary to most studies, cannibalism was most common in the highest quality fungus, contradicting the hypothesis that cannibalism occurs in poor environments to compensate for resource deficiencies. We discuss alternative mechanisms that may drive the ecological context dependence of cannibalism in B. cornutus and emphasize the importance of studying context-dependent behavior in naturally occurring environments.