Grooming behaviors and fouling of the spider crab Libinia dubia (Decapoda: Epialtidae)

Abstract Body fouling has been reduced by grooming behaviors. In decapods, grooming has been focused on gills, sensory structures, and jointed appendages. In this study, grooming behaviors of the spider crab, Libinia dubia H. Milne-Edwards, 1834, were examined; this brachyuran crab decorates and camouflages body regions by attaching materials onto hooked setae. The relationship between grooming and these camouflaged body regions was unknown. Six observational and experimental studies examined the grooming frequency, duration of grooming behaviors, body regions groomed, variance of these behaviors in the presence of another individual, and the efficiency of these grooming behaviors at removing gill fouling. Sensory and respiratory structures were groomed most frequently and for the longest duration, not body regions with decorations and hooked setae. Crabs in isolation exhibited the highest grooming time budget (5.22%). The presence of another conspecific decreased the grooming time budget (0.67%), and primary actions (e.g., fighting, displaying, mating) became priority. Ablation of a gill-grooming appendage did not impact fouling on gills. Grooming as a secondary action was supported. Reasons for not grooming body regions with hooked setae were discussed. Spider crabs had a lower time budget for grooming compared to most decapods, but similar to another brachyuran.

摘要：体表污垢可通过梳理行为得到有效清除。在十足目（Decapoda）动物中，以往的梳理行为研究多集中于鳃、感官结构以及分节附肢。本研究针对1834年H. Milne-Edwards定名的端庄蜘蛛蟹（Libinia dubia）的梳理行为展开系统调查；该种短尾蟹（Brachyura）会通过将外源材料附着于钩状刚毛（hooked setae）之上，对躯体区域进行装饰与伪装，而此前对于梳理行为与这类带有伪装的躯体区域之间的关联尚不明确。本研究共开展6项观测与实验，对梳理行为的发生频率、持续时长、受梳理的躯体部位、同种个体存在时该类行为的变异特征，以及梳理行为清除鳃部污垢的效能进行了考察。结果显示，感官与呼吸结构的梳理频率最高、单次持续时长最长，而非带有装饰结构与钩状刚毛的躯体区域。孤立状态下的蜘蛛蟹，其梳理行为的时间预算占比最高，达5.22%；当存在另一同种个体时，梳理行为的时间预算占比降至0.67%，此时打斗、行为展示、交配等主要行为成为优先级更高的活动。切除鳃梳理附肢并不会对鳃部的污垢附着情况产生显著影响。本研究支持“梳理行为可作为次要行为”这一观点，并对蜘蛛蟹未对带有钩状刚毛的躯体区域开展梳理行为的潜在原因进行了讨论。与多数十足目动物相比，蜘蛛蟹的梳理行为时间预算占比更低，但与其他短尾蟹类则较为相近。