狂蟻食物取回小組的共識決策機制

Abstract

對於表現集體移動的動物而言，在移動方向上達成共識是重要的課題。許多蟻種會表現的合作取回（cooperative retrieval）即是集體移動的一個例子。藉由形成食物取回小組（Food-retrieving group, FRG），螞蟻能夠運回體積太大而無法由單一個體搬運的食塊。然而在搬運過程中，若突然有障礙物在FRG前方出現，FRG將需要達成共識以決定後續行進的方向。此外，若障礙物的其中一側被阻擋而無法通過，FRG更需要能夠選擇沒有被阻擋的一側以通過障礙。本研究以狂蟻(Paratrechina longicornis )為研究對象，探討FRG如何在繞過障礙物的方向上取得共識，並且驗證FRG是否有能力選擇沒有被阻擋的一側來繞過障礙物。本研究同時觀察群體與個體階層的行為表現，並且透過分析、整合兩個階層的結果，釐清FRG取得共識以繞過障礙物的行為機制。結果顯示，在FRG遭遇單一障礙物的50次重複中，FRG成員在其中36次達成共識繞過障礙物。在這36次達成共識的重複中，其中25次有部份成員離開小組，在障礙物附近探索，並且在返回小組後，往先前探索過的一側拉動食塊，進而幫助小組達成共識，選擇該側繞過障礙物。此外，若障礙物的一側無法讓FRG通過，個體會根據其探索的一側是否被阻擋而有不同的行為表現，進而幫助FRG選擇沒有被阻擋的一側繞過障礙物。

Reaching consensus on moving direction is important for gregarious animals performing collective movement. As an example of collective movement, cooperative retrieval is performed by many ant species to cooperatively carry food items too large to be carried by single individuals. When a food-retrieving group (FRG) encounters a barrier, it is necessary for the group members to reach consensus on moving direction so as to bypass the barrier. In addition, if one of the two sides of the barrier is blocked, it will be better for the FRG to choose the more passable side. This study was set to investigate how FRG members of crazy ants Paratrechina longicornis reach consensus on moving direction, and to verify whether FRGs are able to choose the more passable side to bypass the barrier. To answer these questions, a series of experiments using barrier device were conducted, and data of both individual-level as well as group-level behaviors were integrated to investigate the behavioral mechanism of FRG members to reach consensus on moving direction. The results show that in 36 of 50 cases members of FRG reached consensus when encountering a barrier. In 25 of the 36 cases where consensus was reached, some members would leave FRGs and explore either side of the barrier. After exploration some of these individuals returned to FRGs, leading the group toward the side they had explored by performing tugs. In this way, these individuals assisted the group in bypassing the barrier. Furthermore, when one of the two sides of the barrier was blocked, individuals behaved differently according to whether the side they had explored was blocked, and hence assisted FRGs in choosing the unblocked side.