Vasey Gabrielle, Lukeman Ryan, Wyeth Russell C
*Department of Mathematics, Statistics and Computer Science, St Francis Xavier University, P.O. Box 5000, Antigonish, Nova Scotia, Canada B2G 2W5;
Department of Biology, St Francis Xavier University, P.O. Box 5000, Antigonish, Nova Scotia, Canada B2G 2W5
Integr Comp Biol. 2015 Sep;55(3):447-60. doi: 10.1093/icb/icv073. Epub 2015 Jun 26.
The navigation strategies animals use to find sources of odor depend on the olfactory stimuli, the properties of flowing fluids, and the locomotory capabilities of the animal. In high Reynolds number environments, animals typically use odor-gated rheotaxis to find the source of turbulent odor plumes. This strategy succeeds because, although turbulence creates an intermittent chemical cue, the animal follows the (continuous) directional cue created by the flow that is transporting the chemical. However, in nature, animals may lose all contact with an odor plume as variations in the direction of bulk flow cause the plume to be rotated away before the animal reaches the source of the odor. Our goal was to use a mathematical model to test the hypothesis that strategies that augment odor-gated rheotaxis would be beneficial for finding the source of an odor plume in such variable flow. The model links a stochastic variable-direction odor plume with a turbulence-based intermittent chemical signal and four different movement strategies, including: odor-gated rheotaxis alone (as a control), odor-gated rheotaxis augmented by further rheotaxis in the absence of odor, odor-gated rheotaxis augmented by a random walk, and odor-gated rheotaxis augmented by movement actively guided by the heading of the flow when the odor was still present. We found that any of the three augmented strategies could improve on strict odor-gated rheotaxis. Moreover, variations in performance caused the best strategy to depend on the speed of movement of the animal and the magnitude of the variation in flow, and more subtly on the duration over which the augmented strategy was performed. For most combinations of parameters in the model, either augmenting with a random walk or following the last-known heading were the best-performing strategies. Overall, our results suggest that marine animals that rely on odor cues to navigate in turbulent environments may augment odor-gated rheotaxis with additional movements that will increase the probability of finding the sources of odors. Moreover, we believe our approach to modeling odor plumes in variable flows is a valuable step toward mathematically capturing the key conditions experienced by animals navigating on the basis of odors carried by flows.
动物用于寻找气味源的导航策略取决于嗅觉刺激、流动流体的特性以及动物的运动能力。在高雷诺数环境中，动物通常利用气味门控趋流性来寻找湍流气味羽流的源头。这种策略之所以成功，是因为尽管湍流会产生间歇性的化学信号，但动物会跟随由携带化学物质的流动所产生的（连续的）方向信号。然而，在自然界中，由于总体流动方向的变化，动物可能会在到达气味源之前就与气味羽流完全失去接触，导致气味羽流转向离开。我们的目标是使用数学模型来检验这样一个假设：增强气味门控趋流性的策略将有助于在这种多变的流动中找到气味羽流的源头。该模型将一个随机可变方向的气味羽流与基于湍流的间歇性化学信号以及四种不同的运动策略联系起来，这四种策略包括：仅气味门控趋流性（作为对照）、在没有气味时通过进一步的趋流性增强气味门控趋流性、通过随机游动增强气味门控趋流性，以及在气味仍然存在时通过由流动方向主动引导的运动增强气味门控趋流性。我们发现，这三种增强策略中的任何一种都能比严格的气味门控趋流性有所改进。此外，性能的差异导致最佳策略取决于动物的移动速度和流动变化的幅度，更微妙的是还取决于执行增强策略的持续时间。对于模型中的大多数参数组合，要么通过随机游动增强，要么跟随最后已知的方向是表现最佳的策略。总体而言，我们的结果表明，在湍流环境中依靠气味线索导航的海洋动物可能会通过额外的运动来增强气味门控趋流性，这将增加找到气味源的概率。此外，我们相信我们在可变流动中对气味羽流进行建模的方法是朝着数学上捕捉基于流动携带的气味进行导航的动物所经历的关键条件迈出的有价值的一步。
