Chemosensory tracking of scent trails by the planktonic shrimp, Acetes sibogae australis, Townsville, north Queensland

Acetes sibogae australis, a planktonic sergestid shrimp was collected at night with light traps suspended about 2 m deep in the harbour off Townsville, north Queensland, as well as in shallow water off the nearby beach and transferred to aquaria at the Australian Institute of Marine Science.Experiments were conducted in unaerated aquaria (15 x 22 x 60 cm) and water was changed every 2 days. Each aquarium was illuminated from both sides, by fluorescent light and the backs and bottoms of the tanks were painted black to make the transparent shrimps more visible. The front pane was marked at 5 cm intervals to estimate swimming speed and distance. Between 8 and 12 shrimps were placed in each aquaria and they were fed on Artemia, prior to commencement of experiments.During experiments, diced banana prawns (Penaeus merguiensis) or freshly killed and crushed Acetes, soaked in fluorescein dye were dropped into the aquariums and left to sink to the bottom, leaving thin trails of highly visible dye in the water. The movement patterns and swimming speed of the shrimps in response to the presence of trails was recorded. Additional experiments were carried out using meat and meat extract. Sensitivity to these food odours was also monitored over the time that individuals were exposed to the scent trails.The sensitivity of Acetes sibogae australis to specific chemical stimuli also was tested with pieces of blotting paper soaked in saturated solutions of 17 different L-amino acids.The importance of vision in following trails was tested by providing undyed meat and undyed blotting paper soaked in millipore filtered prawn juice as food stimuli. To determine whether Acetes sibogae australis generally swims downward when following a vertical trail or if they follow a chemical gradient, dyed meat tied to a string near one side of the aquarium was lowered and then slowly pulled it up near the opposite side and the response of the shrimps recorded.Experiments were also carried out to determine the anatomical location of the chemoreceptors on the shrimp. The role of the antennules was investigated by testing the behavioural response of shrimp to dyed stimuli, 18 hours after their antennules were excised. Other possible receptor sites, such as the setae in antennae were identified after ultrastructure analysis. This research was undertaken to investigate the importance of chemosensitivity to planktonic animals. Using the planktonic sergestid shrimp, Acetes sibogae australis, experiments were conducted to examine behavioural responses to scent trails and the precision with which this species can follow these trails.

本研究的实验对象为南方莹虾（Acetes sibogae australis），一种浮游樱虾。样本于夜间采集：在昆士兰州北部汤斯维尔附近港湾内水深约2米处悬挂的灯光诱捕器，以及附近海滩的浅水区均捕获到该虾，随后被转移至澳大利亚海洋科学研究所的水族箱中暂养。实验在规格为15×22×60 cm的未充气水族箱中开展，每2天更换一次饲养用水。每个水族箱均从两侧以荧光灯照明，同时将箱壁与箱底喷涂为黑色，以提升透明虾体的可视性。水族箱前玻璃板以5 cm为间隔标注刻度，用于估算虾的游泳速度与移动距离。实验开始前，每个水族箱投放8~12只莹虾，并以卤虫（Artemia）作为饵料进行投喂。实验过程中，将浸泡于荧光素（fluorescein）染料中的切丁墨吉对虾（Penaeus merguiensis），或是新鲜致死并捣碎的莹虾投入水族箱，待其沉至箱底后，会在水体中留下清晰可见的染料示踪轨迹。研究人员记录了莹虾在示踪轨迹存在时的运动模式与游泳速度。后续实验还采用了肉类及肉提取物作为刺激源，同时监测了个体在接触气味轨迹过程中对这类食物气味的敏感性。此外，研究人员采用浸泡于17种不同L-氨基酸（L-amino acid）饱和溶液中的吸水纸纸片，测试了南方莹虾对特定化学刺激的敏感性。为验证视觉在追踪轨迹中的作用，实验设置了未染色的肉类，以及经微孔滤膜（millipore）过滤的虾汁浸泡的未染色吸水纸作为食物刺激源。为明确南方莹虾在追踪垂直轨迹时是否通常向下游动，或是通过追踪化学梯度移动，研究人员将系有染色肉块的细绳悬挂于水族箱一侧附近，随后缓慢将其拉至水族箱另一侧，并记录虾群的行为反应。此外，实验还旨在确定莹虾化学感受器（chemoreceptor）的解剖学定位。研究人员通过在切除小触角（antennules）18小时后，测试莹虾对染色刺激的行为反应，探究了小触角的作用。后续通过超微结构分析，确定了其他潜在的受体位点，例如触角上的刚毛（seta）。本研究的核心目标为探究化学感受敏感性在浮游动物中的重要性，具体而言，本研究以浮游樱虾——南方莹虾（Acetes sibogae australis）为实验对象，开展了一系列实验，以探究其对气味轨迹的行为响应，以及该物种追踪此类轨迹的精准度。