Territoriality mediates atypical size-symmetric cannibalism in the Amblypygi Phrynus longipes.

Cannibalism can have important demographic and ecological effects on populations. Typically, cannibalism is size-structured, where larger individuals eat smaller conspecifics. Initial cursory observations of the whip spider, Phrynus longipes, however, suggested that cannibalism might not be size-structured in this species, perhaps because cannibalism is often a by-product of territory contests. We staged paired interactions and recorded latency to escalate to physical aggression or cannibalize to understand the dynamics of cannibalism and resource contests. We employed a multimodel comparative approach to tease apart the contest characteristics that best predicted cannibalism during behavioral trials between P. longipes opponents. We found that, while armament size symmetry predicted escalation of contests, cannibalism was best predicted by body mass asymmetry. Further, cannibalism was most likely to occur among individuals similar in armament, but dissimilar in body mass. This suggests a discrepancy between phenotypes that may have evolved to communicate resource holding potential (e.g., armaments which benefit individuals if dishonest), and body mass as a cue of resource holding potential. [ABSTRACT FROM AUTHOR]