Data from: Shelter availability mediates decorating in the majoid crab, Camposcia retusa

While numerous aquatic and terrestrial species adorn their surface with items secured from their surroundings, termed decorating, the physical and environmental factors that drive this behaviour are often unclear. One of the best-known examples of this phenomenon are the decorator crabs (Majoidea), with almost 75% of species known to decorate. Here, we examined patterns of decorating in a coral reef-associated majoid, Camposcia retusa, to identify what factors determine patterns of, and investment in, decorating. Observations of natural decoration patterns indicate this species primarily decorate with sponges, fleshy and filamentous algae, and detritus. Decorations were primarily distributed on the carapace and hind walking legs which may reflect exoskeleton morphology. However, decoration cover did not decline with size, as is observed in some other majoid species, suggesting the factors driving decoration investment remain consistent throughout growth stages. From behavioural experiments, we determined that non-uniform decorating is a result of active selection, with crabs preferentially decorating their hind legs and carapace, with only small items placed on the carapace. Decorating in C. retusa appears to function primarily as an anti-predator response, with crabs decorating at higher rates when access to shelter is limited. This study is the first to quantify the decorating habits of C. retusa and suggests that behaviourally-mediated decorating has a primary anti-predator function. This study also highlights the value of manipulative behavioural experiments as a tool for assessing the behavioural mechanisms that drive decorating in animals.

尽管众多水生与陆生物种会利用周遭环境获取的物品装点体表，该行为被称为装饰行为（decorating），但驱动这一行为的物理与环境因素往往尚不明确。该现象最广为人知的例证之一是菱蟹总科（Majoidea）的装饰蟹，已知该总科近75%的物种会进行装饰行为。本研究针对一种与珊瑚礁共生的菱蟹总科物种钝额菱蟹（Camposcia retusa）展开分析，旨在明确决定其装饰行为模式与投入程度的相关因素。对其自然装饰模式的观测结果显示，该物种主要以海绵、肉质藻类、丝状藻类以及碎屑作为装饰材料。装饰主要附着于头胸甲与后步足之上，这一分布特征或与其外骨骼形态相关。但与部分其他菱蟹总科物种不同，该物种的装饰覆盖率并未随体型增长而降低，这表明驱动其装饰投入的因素在整个生长阶段均保持稳定。通过行为实验，本研究证实非均匀的装饰分布是主动选择的结果：该蟹类优先对其后步足与头胸甲进行装饰，且仅将小型装饰物料附着于头胸甲之上。钝额菱蟹的装饰行为主要发挥反捕食防御功能，当可获取的遮蔽物有限时，其装饰频率会显著提升。本研究首次量化了钝额菱蟹的装饰习性，研究结果表明行为介导的装饰行为具备核心的反捕食功能。同时，本研究也凸显了操控性行为实验作为探究动物装饰行为驱动机制的研究工具的重要价值。