Bocher Aurélie, Doums Claudie, Millot Laurence, Tirard Claire
Laboratoire de Parasitologie Evolutive CNRS 7103, Université Pierre et Marie Curie, 7 quai Saint Bernard, 75005, Paris, France.
Evolution. 2008 Jan;62(1):123-34. doi: 10.1111/j.1558-5646.2007.00273.x. Epub 2007 Dec 6.
In many species of social Hymenoptera, totipotency of workers induces potential conflicts over reproduction. However, actual conflicts remain rare despite the existence of a high reproductive skew. One of the current hypotheses assumes that conflicts are costly and thus selected against. We studied the costs of conflicts in 20 colonies of the queenless ant Diacamma sp. "nilgiri" by testing the effects of conflicts on labor and worker immunocompetence, two parameters closely linked to the indirect fitness of workers. In this species, the dominant female is the only mated worker (gamergate) and monopolizes reproduction. We experimentally induced conflicts by splitting each colony into two groups, a control group containing the gamergate and an orphaned group displaying aggressions until a new dominant worker arises. Immunocompetence was assessed by the clearance of Escherichia coli bacteria that we injected into the ants. Time budget analysis revealed a lower rate of labor and especially brood care in orphaned groups, supporting the existence of a cost of conflicts on labor. Fifteen days after splitting, a lower immunocompetence was also found in orphaned groups, which concerned workers involved and not involved in conflicts. We propose that this immunosuppression induced by conflicts could stem from stress and not directly from aggression.
在许多群居膜翅目昆虫物种中，工蚁的全能性引发了繁殖方面的潜在冲突。然而，尽管存在高度的繁殖偏斜，但实际冲突仍然很少见。当前的一种假设认为，冲突代价高昂，因此会被自然选择淘汰。我们通过测试冲突对劳动和工蚁免疫能力的影响，研究了无蚁后蚂蚁Diacamma sp. “nilgiri”的20个蚁群中的冲突代价，这两个参数与工蚁的间接适合度密切相关。在这个物种中，占主导地位的雌性是唯一交配的工蚁（生殖蚁后），垄断繁殖。我们通过将每个蚁群分成两组进行实验性诱导冲突，一组是包含生殖蚁后的对照组，另一组是孤儿组，该组会表现出攻击性，直到出现新的主导工蚁。免疫能力通过我们注射到蚂蚁体内的大肠杆菌的清除情况来评估。时间分配分析显示，孤儿组的劳动率较低，尤其是育幼率较低，这支持了冲突对劳动存在代价的观点。分开15天后，在孤儿组中也发现免疫能力较低，这涉及参与和未参与冲突的工蚁。我们认为，冲突诱导的这种免疫抑制可能源于压力，而不是直接源于攻击行为。
