Department of Zoology/ Evolutionary Biology, University of Regensburg, 93053, Regensburg, Germany.
BMC Evol Biol. 2018 Dec 27;18(1):202. doi: 10.1186/s12862-018-1320-0.
The intense interactions among closely related individuals in animal societies provide perfect conditions for the spread of pathogens. Social insects have therefore evolved counter-measures on the cellular, individual, and social level to reduce the infection risk. One striking example is altruistic self-removal, i.e., lethally infected workers leave the nest and die in isolation to prevent the spread of a contagious disease to their nestmates. Because reproductive queens and egg-laying workers behave less altruistically than non-laying workers, e.g., when it comes to colony defense, we wondered whether moribund egg-layers would show the same self-removal as non-reproductive workers. Furthermore, we investigated how a lethal infection affects reproduction and studied if queens and egg-laying workers intensify their reproductive efforts when their residual reproductive value decreases ("terminal investment").
We treated queens, egg-laying workers from queenless colonies, and non-laying workers from queenright colonies of the monogynous (single-queened) ant Temnothorax crassispinus either with a control solution or a solution containing spores of the entomopathogenic fungus Metarhizium brunneum. Lethally infected workers left the nest and died away from it, regardless of their reproductive status. In contrast, infected queens never left the nest and were removed by workers only after they had died. The reproductive investment of queens strongly decreased after the treatment with both, the control solution and the Metarhizium brunneum suspension. The egg laying rate in queenless colonies was initially reduced in infected colonies but not in control colonies. Egg number increased again with decreasing number of infected workers.
Queens and workers of the ant Temnothorax crassispinus differ in their reaction to an infection risk and a reduced life expectancy. Workers isolate themselves to prevent contagion inside the colony, whereas queens stay in the nest. We did not find terminal investment; instead it appeared that egg-layers completely shut down egg production in response to the lethal infection. Workers in queenless colonies resumed reproduction only after all infected individuals had died, probably again to minimize the risk of infecting the offspring.
动物社会中密切相关个体之间的强烈相互作用为病原体的传播提供了完美的条件。因此，社会昆虫在细胞、个体和社会层面上进化出了对策，以降低感染风险。一个引人注目的例子是利他性的自我清除，即致命感染的工蜂离开蜂巢并独自死亡，以防止传染病传播给巢内同伴。由于生殖女王和产卵工蜂的行为不如非产卵工蜂利他，例如在群体防御方面，我们想知道垂死的产卵工蜂是否会表现出与非生殖工蜂相同的自我清除行为。此外，我们还研究了致命感染如何影响繁殖，并研究了女王和产卵工蜂是否会在剩余生殖价值下降时（“终端投资”）加强繁殖努力。
我们用对照溶液或含有昆虫病原真菌绿僵菌孢子的溶液处理单巢（单女王）蚂蚁 Temnothorax crassispinus 的女王、无女王群体中的产卵工蜂和有女王群体中的非产卵工蜂。致命感染的工蜂会离开蜂巢并在远离蜂巢的地方死亡，而不论其生殖状态如何。相比之下，感染的女王从未离开过蜂巢，只有在它们死亡后才会被工蜂移除。用对照溶液和绿僵菌悬浮液处理后，女王的繁殖投资大大减少。无女王群体中的产卵率在感染群体中最初会降低，但在对照群体中不会降低。随着感染工蜂数量的减少，产卵数量再次增加。
Temnothorax crassispinus 蚂蚁的女王和工蜂对感染风险和预期寿命降低的反应不同。工蜂将自己隔离以防止在群体内部传染，而女王则留在巢内。我们没有发现终端投资；相反，产卵工蜂似乎完全停止了产卵，以应对致命感染。无女王群体中的工蜂只有在所有感染个体死亡后才会恢复繁殖，这可能是为了最大限度地降低感染后代的风险。
