Habitat complexity and predator odours impact the escape performance of fish through a stress-related mechanism

Abstract [Related publication]: Mass coral bleaching events coupled with local stressors have caused regional-scale loss of corals on reefs globally. Following the loss of corals, the structural complexity of these habitats is often reduced, increasing the predation risk of many reef inhabitants. By obscuring visual information and physically impeding predators, habitat complexity can influence predation risk and the perception of risk by potential prey. Yet, little is known on how habitat complexity and risk assessment interact to influence predator-prey interactions on coral reefs. To better understand how these interactions may shift in degraded ecosystems we reared juvenile whitetail damselfishes (Pomacentrus chrysurus) in environments of various habitat complexity levels (low, medium, and high) and then exposed them to olfactory risk odours before simulating a predator strike. We found that the fast-start escape response of whitetail damselfish were enhanced when forewarned with olfactory cues of a predator and in environments of increasing level of complexity. However, no interaction between complexity and olfactory cues was observed. As hormonal changes in cortisol can prime the body to cope and respond to stressors, we conducted whole-body cortisol analysis via enzyme-linked immunosorbent assay (ELISA) to discern if the mechanisms used to modify these escape responses were facilitated through hormonal pathways. Cortisol concentrations were influenced by an interaction between complexity and risk, in that the whitetail damselfish had elevated cortisol concentrations when forewarned with predator odours, but only when complexity levels were low. Our study suggests that as complexity is lost, prey may more appropriately assess predation risk, likely as a result of receiving additional visual information. Prey ability to modify their responses depending on the environmental context could suggest that they may partly alleviate the risk of increased predator-prey interactions as structural complexity is reduced.
The full methodology is available in the Open Access publication from the Related publications link below.
Software/equipment used to create/collect the data:

Kinematic trials (Quicktime used to analyze videos)
Cortisol (Caymen Chemical cortisol EIA kits spreadsheets)

Software/equipment used to manipulate/analyse the data:

SPSS to explore data and analyze kinematic variables
R Studio used to analyze cortisol data and create all figures
Illustrator used to make figures more presentable

摘要 [相关出版物]：大规模珊瑚白化事件叠加局部环境压力，已造成全球珊瑚礁区域范围内的珊瑚大面积消亡。珊瑚消亡后，这些栖息地的结构复杂度往往随之降低，进而提升了诸多礁栖生物的被捕食风险。栖息地复杂度可通过遮蔽视觉信息、物理阻挡捕食者的方式，影响被捕食风险以及潜在猎物的风险感知。然而，目前学界对珊瑚礁栖息地复杂度与风险评估如何共同作用，进而调控捕食者-猎物互作的机制仍知之甚少。
为进一步明确退化生态系统中这类互作关系的变化规律，本研究将白尾雀鲷（Pomacentrus chrysurus）幼体饲养于不同复杂度梯度（低、中、高）的栖息地环境中，随后在模拟捕食者攻击前，使幼体暴露于嗅觉风险气味中。研究结果显示，当白尾雀鲷接收到捕食者的嗅觉预警信号，且所处栖息地复杂度升高时，其快速启动逃逸反应会得到增强。但未观测到栖息地复杂度与嗅觉预警信号之间存在交互效应。
由于皮质醇（cortisol）的激素变化可激活机体以应对并响应环境压力，本研究通过酶联免疫吸附测定（enzyme-linked immunosorbent assay, ELISA）对全身皮质醇含量进行检测，以探明调控上述逃逸反应改变的机制是否通过激素通路介导。研究发现，皮质醇浓度受栖息地复杂度与风险信号的交互作用影响：仅当栖息地复杂度较低时，接收到捕食者气味预警的白尾雀鲷体内皮质醇浓度才会升高。
本研究表明，随着栖息地复杂度丧失，猎物或可更精准地评估被捕食风险，这可能得益于其获取了更多视觉信息。猎物可依据环境背景调整自身响应的能力，意味着当栖息地结构复杂度降低时，它们或可在一定程度上缓解捕食者-猎物互作加剧带来的风险。
完整实验方法可查阅下方相关出版物链接中的开放获取论文。
用于生成/采集数据的软件与设备：
运动学试验（采用Quicktime对视频进行分析）
皮质醇检测（使用Caymen Chemical公司皮质醇EIA试剂盒及配套电子表格）
用于处理/分析数据的软件与设备：
SPSS：用于数据探索与运动学变量分析
R Studio：用于皮质醇数据的分析与所有图表的绘制
Illustrator：用于优化图表的视觉呈现效果