Turbidity affects stomatopod contest behaviours and response to UV cues

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Environmental conditions change the effectiveness of animal signals by affecting the contrast between the signal and the background. In aquatic environments, fluctuations in water clarity likely drive the evolution of signalling systems by affecting signal conspicuousness. However, the effects of turbidity on signalling in many aquatic organisms remain largely unstudied. Stomatopods (mantis shrimp) are marine crustaceans known to use chromatic and achromatic signals during territorial contests over refuges. Here, we investigate how turbidity affects Neogonodactylus oerstedii contest behaviours and response to visual cues. We manipulated water clarity by adding bentonite clay, and altered visual cues by painting refuges with UV reflective (UV+) or non-UV reflective (UV-) paint. In turbid conditions, intruder stomatopods won contests less frequently. In UV+ treatments, intruders increased their rate of coils, a behaviour where the stomatopod curls so that the hard telson (tail) is facing the opponent. This result supports previous research suggesting that UV reflectance is a component of stomatopod threat displays. Intruders also increased their rate of offensive behaviours in response to UV, but only in the turbid treatment. Although this result contradicts our prediction that turbidity would reduce stomatopod response to UV cues, it suggests that turbidity does affect the transmission and perception of chromatic cues. Our results indicate that turbidity can impact assessment of visual cues and contest outcomes in aquatic organisms. To our knowledge, this study is the first to assess the effect of environmental light conditions on stomatopod communication as well as the effect of turbidity on intraspecific contest behaviours generally.