Ecology Program, Huck Institutes of Life Sciences, Pennsylvania State University, University Park, Pennsylvania, United States of America.
Centre for Infectious Disease Dynamics, Huck Institutes of Life Sciences, Pennsylvania State University, University Park, Pennsylvania, United States of America.
PLoS One. 2018 Feb 23;13(2):e0193536. doi: 10.1371/journal.pone.0193536. eCollection 2018.
Social insect colonies function cohesively due, in part, to altruistic behaviors performed towards related individuals. These colonies can be affected by parasites in two distinct ways, either at the level of the individual or the entire colony. As such, colonies of social insects can experience conflict with infected individuals reducing the cohesiveness that typifies them. Parasites of social insects therefore offer us a framework to study conflicts within social insect colonies in addition to the traditionally viewed conflicts afforded by groups of low genetic relatedness due to multiple mating for example. In our study, we use the behavior manipulating fungal pathogen, Ophiocordyceps kimflemingiae (= unilateralis) and its host, Camponotus castaneus, to ask if colony members are able to detect infected individuals. Such detection would be optimal for the colony since infected workers die near foraging trails where the fungus develops its external structures and releases spores that infect other colony members. To determine if C. castaneus workers can detect these future threats, we used continuous-time point observations coupled with longer continuous observations to discern any discrimination towards infected individuals. After observing 1,240 hours of video footage we found that infected individuals are not removed from the colony and continuously received food during the course of fungal infection. We also calculated the distances between workers and the nest entrance in a total of 35,691 data points to find infected workers spent more time near the entrance of the nest. Taken together, these results suggest healthy individuals do not detect the parasite inside their nestmates. The colony's inability to detect infected individuals allows O. kimflemingiae to develop within the colony, while receiving food and protection from natural enemies, which could damage or kill its ant host before the parasite has completed its development.
群居昆虫的群体之所以能够协调一致地运作，部分原因是它们对亲缘个体表现出了利他行为。寄生虫可以通过两种截然不同的方式影响这些群体，一种是个体层面，另一种是整个群体层面。因此，群居昆虫的群体可能会与被感染的个体发生冲突，从而降低它们的协调性。寄生虫为我们提供了一个框架，除了传统上由于多配偶制等原因而导致的低遗传相关性群体所产生的冲突之外，还可以研究群居昆虫群体内部的冲突。在我们的研究中，我们使用行为操纵真菌病原体 Ophiocordyceps kimflemingiae（=unilateralis）及其宿主 Camponotus castaneus，来探究群体成员是否能够检测到被感染的个体。如果群体能够检测到被感染的个体，这对它们来说是最佳的，因为感染的工蜂会在真菌发育其外部结构并释放感染其他群体成员的孢子的觅食路径附近死亡。为了确定 C. castaneus 工蜂是否能够检测到这些潜在威胁，我们使用连续时间点观察和更长时间的连续观察来辨别它们对感染个体的任何歧视。在观察了 1240 小时的视频片段后，我们发现感染个体没有被从群体中移除，并且在真菌感染过程中持续获得食物。我们还计算了总共 35691 个数据点中工人与巢口之间的距离，发现感染工人在巢口附近花费的时间更多。综上所述，这些结果表明健康个体无法检测到巢内同伴体内的寄生虫。群体无法检测到感染个体，使 O. kimflemingiae 能够在群体内发育，同时获得食物和免受天敌的伤害，否则这些天敌可能会在寄生虫完成发育之前伤害或杀死它的蚂蚁宿主。
