The grass shrimp Palaemon pugio is an abundant and ecologically important species in estuarine habitats in the northwest Atlantic and is commonly used as an indicator species for environmental contamination, but little is known about its behavior. We examined aggression and dominance in P. pugio by using experimental arenas and groups of five shrimp that were observed an hour at a time for three days in the laboratory. Female shrimp showed high levels of initial aggression that quickly decreased over time, suggesting the formation of a dominance hierarchy. The dominance hierarchy between groups of females appeared linear, with shrimp at five distinct ranks in most replicates and higher-ranked individuals dominating lower-ranked ones. Dominance was significantly correlated with cheliped size but not body size, suggesting that larger chelipeds in female P. pugio may have evolved as a tool to establish dominance, perhaps to gain access to shelter in salt marshes, seagrass beds, or oyster reefs. Grass shrimp are preyed upon by a wide range of estuarine fish, and females are especially vulnerable; so securing access to shelter may provide a major selective advantage, with the dominance hierarchy evolving to save energy through a long-term reduction in fighting over resources.

中文翻译：

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雌性草虾 Palaemon pugio 的线性优势等级

草虾Palaemon pugio是大西洋西北部河口栖息地中丰富且具有重要生态意义的物种，通常用作环境污染的指示物种，但对其行为知之甚少。我们研究了P. pugio 的攻击性和优势通过使用实验场地和五只虾为一组，在实验室中连续观察一小时，持续三天。雌虾表现出高水平的初始攻击性，随着时间的推移迅速减少，表明形成了优势等级。雌性群体之间的优势等级呈现线性，在大多数重复中，虾处于五个不同的等级，而较高等级的个体主导较低等级的个体。优势与螯足的大小显着相关，但与体型无关，这表明雌性P. pugio中较大的螯足可能已经进化为一种建立支配地位的工具，也许是为了在盐沼、海草床或牡蛎礁中获得庇护。草虾被各种河口鱼类捕食，雌性尤其容易受到伤害；因此，确保获得庇护所可能会提供一个主要的选择优势，随着支配等级的演变，通过长期减少对资源的争夺来节省能源。