Bau Josep, Cardé Ring T
*Department of Systems Biology, University of Vic-Central University of Catalonia, 08500 Vic, Spain;
Department of Entomology, University of California, Riverside, CA 92521, USA
Integr Comp Biol. 2015 Sep;55(3):461-77. doi: 10.1093/icb/icv036. Epub 2015 May 16.
Male moths locate females by navigating along her pheromone plume, often flying hundreds of meters en route. As the first male to find a calling female is most apt to be her mate, this can be termed "a race to find the female" and it is assumed to be under strong selective pressure for efficiency and rapidity. Locating a distant, odor-linked resource involves two strategies. The first is to contact the outer envelope of the odor plume. When wind direction is relatively invariant, the plume stretches and then crosswind flights may be favored, although when wind direction shifts over 60°, upwind and downwind paths may be optimal. Alternatively, the path may be random with respect to the direction of wind flow, with periodic changes in direction, as in either Lévy or Random Walks. After first detecting the pheromone, a second strategy follows: moths navigate along the plume by heading upwind when the pheromone is detected, with crosswind casting to re-establish contact if the plume is lost. This orientation path is not straightforward in nature, however, because atmospheric turbulence fragments the plume, thereby creating large odor gaps. Furthermore, a shifting wind direction can lead the responder out of the plume. One way to explore which strategies are optimal for enabling initial contact with the plume and subsequent navigation is through modeling of plumes' dispersal and of insects' flight strategies. Our simulations using the flight characteristics of the male gypsy moth (Lymantria dispar) suggest that search strategies similar to Lévy Walks are most apt to result in a high probability of contact with plumes. Although a searching trajectory aimed predominately crosswind performed almost as well as those with a random orientation when wind direction was relatively stable, downwind biased trajectories were least successful. A random orientation with respect to immediate wind flow, as used in our simulations of Lévy and Random Walks, seems optimal both for initial discovery of the plume and likelihood of locating an odor source. In the two available direct field observations, moths adopted a random orientation with respect to concurrent wind direction.
雄性飞蛾通过沿着雌蛾的性信息素羽流导航来定位雌蛾，在此过程中它们常常要飞行数百米。由于第一个找到正在求偶雌蛾的雄性最有可能成为其配偶，这可以被称为“寻找雌蛾的竞赛”，并且人们认为它处于强大的选择压力之下，以确保效率和速度。定位一个遥远的、与气味相关的资源涉及两种策略。第一种是接触气味羽流的外层。当风向相对不变时，羽流会伸展，此时可能更有利于进行侧风飞行，不过当风向转变超过60°时，逆风或顺风路径可能是最优的。或者，飞行路径可能相对于风流方向是随机的，伴有方向的周期性变化，就像在 Lévy 飞行或随机漫步中那样。在首次检测到性信息素之后，第二种策略随之而来：当检测到性信息素时，飞蛾通过逆风飞行沿着羽流导航，如果羽流丢失则通过侧风搜索来重新建立接触。然而，这种定向路径在本质上并非是直接的，因为大气湍流会使羽流破碎，从而产生大的气味间隙。此外，风向的变化可能会使响应者偏离羽流。探索哪种策略对于与羽流进行初始接触以及随后的导航最为最优的一种方法是通过对羽流扩散和昆虫飞行策略进行建模。我们利用雄性舞毒蛾（Lymantria dispar）的飞行特征进行的模拟表明，类似于 Lévy 飞行的搜索策略最有可能导致与羽流接触的高概率。尽管当风向相对稳定时，主要以侧风为主的搜索轨迹的表现几乎与随机定向的轨迹一样好，但偏向顺风的轨迹最不成功。在我们对 Lévy 飞行和随机漫步的模拟中所采用的相对于即时风流的随机定向，对于羽流的初始发现和定位气味源的可能性似乎都是最优的。在两项现有的直接野外观察中，飞蛾相对于同时存在的风向采用了随机定向。
