Cannibalism and Infectious Disease: Friends or Foes?

Abstract

Cannibalism occurs in a majority of both carnivorous and noncarnivorous animal taxa from invertebrates to mammals. Similarly, infectious parasites are ubiquitous in nature. Thus, interactions between cannibalism and disease occur regularly. While some adaptive benefits of cannibalism are clear, the prevailing view is that the risk of parasite transmission due to cannibalism would increase disease spread and, thus, limit the evolutionary extent of cannibalism throughout the animal kingdom. In contrast, surprisingly little attention has been paid to the other half of the interaction between cannibalism and disease, that is, how cannibalism affects parasites. Here we examine the interaction between cannibalism and parasites and show how advances across independent lines of research suggest that cannibalism can also reduce the prevalence of parasites and, thus, infection risk for cannibals. Cannibalism does this by both directly killing parasites in infected victims and by reducing the number of susceptible hosts, often enhanced by the stage-structured nature of cannibalism and infection. While the well-established view that disease should limit cannibalism has held sway, we present theory and examples from a synthesis of the literature showing how cannibalism may also limit disease and highlight key areas where conceptual and empirical work is needed to resolve this debate.

The underappreciated extent of cannibalism and ophiophagy in African cobras

“…Its occurrence in populations is thought to be the result of the trade‐off between the costs (including risk of injury, reduction of inclusive fitness, or risk of parasite infection) and benefits (including energetic gains, reduction in competitors for food or mates, or potentially the reduction of parasite infection risk) of the behavior (reviewed in Van Allen et al. ). Ecologically, cannibalism can have important size‐dependent impacts on the demography of populations (Claessen et al.…”

Do scavengers prevent or promote disease transmission? The effect of invertebrate scavenging on Ranavirus transmission

“…Despite long‐standing interest about how scavengers might reduce infectious disease transmission (e.g. vultures; Beasley et al, , Bellan, Turnbull, Beyer, & Getz, , Fischer et al, ), and many studies on individual disease systems (Houston & Cooper, ; Hugh‐Jones & DeVos, ; Ogada, Torchin, Kinnaird, & Ezenwa, ), there is no consensus on whether scavengers generally reduce infections from carcasses or spread pathogens throughout the environment and thus increase transmission (Van Allen et al, ; Beasley et al, ). This is in large measure because of the observational nature of the previous studies and focus on the potential for transmission (but see Bellan et al, ).…”

Exposure to potentially cannibalistic conspecifics induces an increased immune response

“…S2). These results, in conjunction with previous work (Duong and McCauley, ; Van Allen et al ., ), suggest that, similar to predators, potentially cannibalistic conspecifics may have indirect beneficial effects on their potential prey by decreasing their risk of future pathogen infections (Moret and Siva‐Jothy, ) via immune enhancement. Alternatively, individuals exposed to potential cannibals that induce an immune priming response could be disadvantaged if the priming is costly and reduces the resources available for other life history challenges (e.g.…”

“…Similarly, the volume of water in which the experiments were conducted was five times greater in the density experiment compared with the cannibalism experiments, which likely diluted any conspecific chemical cues. Our results indicate that dragonfly larvae are consistently exhibiting DDP in one aspect of their immune response, however, whether DDP in this system is a response to density‐dependent cannibalism/wounding risk (Van Buskirk, ), increased pathogen risk (Wilson and Reeson, ) or both (Van Allen et al ., ) remains unclear.…”