Davis Andrew K, Gloege Helen
Odum School of Ecology, University of Georgia, Athens, GA 30602, USA.
Department of Biological Science, Mount Holyoke College, South Hadley, MA 01075, USA.
Microorganisms. 2024 Jun 18;12(6):1219. doi: 10.3390/microorganisms12061219.
When animals perceive an acute stressor like a predator, they typically undergo a suite of physiological changes that function to improve survival during the encounter, such as elevation in cardiac output, to supply more energy to muscles. If bodily energy is limited, such as by parasites or infections, these functions could become less efficient and lessen host survival. In the aquatic world of microorganisms, individuals can become colonized by other organisms on their surface (epibionts), which could sap energy from their host from their weight, or even compete with the host for food. Here, we tested if one epibiont (a ciliated protozoan, spp.) affects its hosts' ability to mount a physiological stress reaction. We collected wild daphnia () that had varying burdens of these on their bodies and exposed them to a simulated stressor (crushed daphnia, to simulate nearby predation) under a microscope while monitoring for changes in their heart rates in real time. Out of 121 daphnia, those with no epibionts showed no meaningful changes in their heart rate after exposure, but those with light or heavy burdens showed immediate elevations (within 5 min). Moreover, the heart rates of heavily burdened daphnia continued to rise for 1.5 h thereafter, to as much as 17% higher than at baseline. These patterns were unexpected, as they suggest that the ciliated epibionts act to elevate their hosts' physiological reaction, rather than dampen it, perhaps by churning the water column around the host, thereby enhancing the chemical alarm cue. The procedures used in this study may be useful for future investigations into the acute stress reactions of daphnia or other microorganisms.
当动物感知到像捕食者这样的急性应激源时，它们通常会经历一系列生理变化，这些变化的作用是在遭遇期间提高生存几率，比如心输出量增加，以便为肌肉提供更多能量。如果身体能量有限，比如受到寄生虫或感染的影响，这些功能可能会变得效率更低，从而降低宿主的生存几率。在微生物的水生世界中，个体的体表可能会被其他生物（体表共生生物）定殖，这些生物可能会因其重量从宿主身上消耗能量，甚至与宿主争夺食物。在这里，我们测试了一种体表共生生物（一种纤毛原生动物， 属）是否会影响其宿主产生生理应激反应的能力。我们收集了体表带有不同数量这种生物的野生水蚤（ ），并在显微镜下将它们暴露于模拟应激源（碾碎的水蚤，以模拟附近的捕食行为）中，同时实时监测它们心率的变化。在121只水蚤中，那些没有体表共生生物的水蚤在暴露后心率没有明显变化，但那些体表带有少量或大量共生生物的水蚤心率立即升高（在5分钟内）。此外，体表共生生物负担重的水蚤的心率在随后的1.5小时内持续上升，比基线水平高出多达17%。这些模式出人意料，因为它们表明这种纤毛体表共生生物的作用是提高其宿主的生理反应，而不是抑制它，也许是通过搅动宿主周围的水柱，从而增强化学警报信号。本研究中使用的程序可能对未来关于水蚤或其他微生物急性应激反应的研究有用。
