Food Searching Strategy of Amoeboid Cells by Starvation Induced Run Length Extension

Food searching strategies of animals are key to their success in heterogeneous environments. The optimal search strategy may include specialized random walks such as Levy walks with heavy power-law tail distributions, or persistent walks with preferred movement in a similar direction. We have investigated the movement of the soil amoebae Dictyostelium searching for food. Dictyostelium cells move by extending pseudopodia, either in the direction of the previous pseudopod (persistent step) or in a different direction (turn). The analysis of ��4000 pseudopodia reveals that step and turn pseudopodia are drawn from a probability distribution that is determined by cGMP/PLA2 signaling pathways. Starvation activates these pathways thereby suppressing turns and inducing steps. As a consequence, starved cells make very long nearly straight runs and disperse over ��30-fold larger areas, without extending more or larger pseudopodia than vegetative cells. This ��win-stay/lose-shift�� strategy for food searching is called Starvation Induced Run-length Extension. The SIRE walk explains very well the observed differences in search behavior between fed and starving organisms such as bumble-bees, flower bug, hoverfly and zooplankton.

动物的觅食策略是其在异质环境中取得生存成功的核心要素。最优觅食策略可包含特定的随机游走模式，例如服从重幂律尾分布的列维游走（Levy walks），或是倾向于沿单一方向持续移动的持久游走。我们针对土壤变形虫盘基网柄菌（Dictyostelium）的觅食运动开展了研究。盘基网柄菌细胞通过伸出伪足完成位移：伪足可沿此前伪足的方向伸出（持续步），或转向其他方向（转向步）。对近4000个伪足的分析表明，持续步与转向步的概率分布由cGMP/PLA2信号通路决定。饥饿状态会激活该通路，进而抑制转向步并促进持续步的产生。由此，饥饿状态下的细胞会形成极长的近乎直线的运动轨迹，其扩散范围较营养生长状态的细胞扩大近30倍，且伪足的数量与尺寸并未出现明显变化。这种“赢留输变”（win-stay/lose-shift）的觅食策略被称为饥饿诱导运动长度拓展（Starvation Induced Run-length Extension，SIRE）游走。SIRE游走能够很好地解释已观测到的饱食与饥饿状态下各类生物的觅食行为差异，涉及的生物包括熊蜂、花蝽、食蚜蝇以及浮游动物。