Brans Victor, Manzi Florent, Jacob Staffan, Schtickzelle Nicolas
Biodiversity Research Centre, Earth and Life Institute Université catholique de Louvain Louvain-la-Neuve Belgium.
Centre National de la Recherche Scientifique (CNRS) Station d'Ecologie Théorique et Expérimentale (UAR2029) Moulis France.
Ecol Evol. 2024 Apr 23;14(4):e11291. doi: 10.1002/ece3.11291. eCollection 2024 Apr.
In freshwater habitats, aerobic animals and microorganisms can react to oxygen deprivation by a series of behavioural and physiological changes, either as a direct consequence of hindered performance or as adaptive responses towards hypoxic conditions. Since oxygen availability can vary throughout the water column, different strategies exist to avoid hypoxia, including that of active 'flight' from low-oxygen sites. Alternatively, some organisms may invest in slower movement, saving energy until conditions return to more favourable levels, which may be described as a 'sit-and-wait' strategy. Here, we aimed to determine which, if any, of these strategies could be used by the freshwater ciliate when faced with decreasing levels of oxygen availability in the culture medium. We manipulated oxygen flux into clonal cultures of six strains (i.e. genotypes) and followed their growth kinetics for several weeks using automated image analysis, allowing to precisely quantify changes in density, morphology and movement patterns. Oxygen effects on demography and morphology were comparable across strains: reducing oxygen flux decreased the growth rate and maximal density of experimental cultures, while greatly expanding the duration of their stationary phase. Cells sampled during their exponential growth phase were larger and had a more elongated shape under hypoxic conditions, likely mirroring a shift in resource investment towards individual development rather than frequent divisions. In addition to these general patterns, we found evidence for intraspecific variability in movement responses to oxygen limitation. Some strains showed a reduction in swimming speed, potentially associated with a 'sit-and-wait' strategy; however, the frequent alteration of movement paths towards more linear trajectories also suggests the existence of an inducible 'flight response' in this species. Considering the inherent costs of turns associated with non-linear movement, such a strategy may allow ciliates to escape suboptimal environments at a low energetic cost.
在淡水生境中，需氧动物和微生物可通过一系列行为和生理变化对缺氧作出反应，这些变化或是性能受阻的直接后果，或是对缺氧条件的适应性反应。由于水柱中氧气的可利用性会有所不同，因此存在不同的策略来避免缺氧，包括从低氧区域主动“逃离”。另外，一些生物可能会选择移动得更慢，节省能量直至条件恢复到更适宜的水平，这可被描述为一种“坐等”策略。在此，我们旨在确定当面对培养基中氧气可利用性降低的情况时，淡水纤毛虫会采用这些策略中的哪一种（如果有的话）。我们控制进入六个品系（即基因型）克隆培养物的氧气通量，并使用自动图像分析跟踪它们数周的生长动力学，从而能够精确量化密度、形态和运动模式的变化。氧气对种群统计学和形态的影响在各品系间具有可比性：降低氧气通量会降低实验培养物的生长速率和最大密度，同时大幅延长其稳定期的持续时间。在指数生长期取样的细胞在缺氧条件下更大且形状更细长，这可能反映了资源投资从频繁分裂转向个体发育的转变。除了这些一般模式外，我们还发现了对氧气限制的运动反应存在种内变异性的证据。一些品系的游泳速度降低，这可能与“坐等”策略有关；然而，运动路径频繁改变为更线性的轨迹也表明该物种存在一种可诱导的“逃离反应”。考虑到与非线性运动相关的转向的内在成本，这样一种策略可能使纤毛虫能够以较低的能量成本逃离次优环境。
