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

Grazing alters network architecture during interspecific mycelial interactions

The changes that occur in mycelial architecture of Phanerochaete velutina interacting with Hypholoma fasciculare mycelium in soil microcosms in the presence and absence of the collembola Folsomia candida are investigated employing tools developed in graph theory and statistical mechanics. There was substantially greater overgrowth of H. fasciculare by P. velutina mycelium when grazed than when un-grazed. There was a marked disappearance of hyphal links in all un-grazed systems between 8 d and 34 d, predominantly in areas distant from the interaction, but this was much less evident in grazed systems. Further, new tangential cross-links connecting radial cords distant from the inoculum formed in grazed systems. The thickness of cords increased with time, and more so in grazed systems. There was no significant difference in transport efficiency between the grazed and un-grazed systems. The ability of the mycelial network to modify dynamically link strengths is crucial to achieving a balance between transport capacity/robustness to damage and overall cost of production. © 2008 Elsevier Ltd and The British Mycological Society