Assessment strategy varies with resource ownership, individual and species identity in mantis shrimp

In contests over resource access, competitors aim to win, gaining or retaining the resource while minimizing the costs of fighting. Considerable research has tested contest “assessment strategies”, which describe how animals gather information about fighting ability, resource ownership, resource value, and other factors, and how this information informs fighting effort. Historically, assessment strategies were considered fixed within a population or species, yet in recent years there has been a push to quantify how strategies vary according to resource ownership or inherently among individuals. We tested for variation in the assessment strategy of competing Gonodactylus childi, an Indo-Pacific species of mantis shrimp (Stomatopoda) that exchanges high-force strikes during contests over access to protective burrows: holes in dead coral or rock. By staging contests over access to a mock burrow, we found that larger individuals won more often, but “residents” already in the burrow were most likely to win. Our results most closely supported a self-assessment fighting strategy in residents only: losers based their fighting effort on their own body size, and not that of eventual winners. Analyses of contest behavioral progressions showed little ability to discriminate assessment strategies. Finally, we revealed among-individual variation that was unexplained by factors like resource ownership. We compare our results to a prior study of an ecologically similar and closely related mantis shrimp that assesses both own and opponent fighting ability. Overall, our results highlight multiple axes of variation that, while informing future theory, form the substrate for behavioral evolution in contests.