Data from: Support for the immunocompetence handicap hypothesis in the wild: hormonal manipulation decreases survival in sick damselflies

The immunocompetence handicap hypothesis (ICHH) states that hormones enhance sexual trait expression but impair immunity. Previous tests of the ICHH have been hampered by experimental design problems. Here we report on an experimental test of the ICHH that includes manipulations of both hormones and infections in males of the territorial damselfly, Hetaerina americana, with accurate survival measurements. We conducted a fully factorial experiment subjecting each individual to one of three topical treatments: methoprene (a juvenile hormone analog), acetone, or control, and one of three injection treatments: bacteria, PBS, or control. We measured survival of manipulated males in both the wild and in captivity. As predicted, survival was most heavily impaired in methoprene-bacteria males than in the other groups in the wild, and no survival differences emerged in captive animals. This result confirms that survival is one cost an animal pays for increased hormonal levels. This corroborates theoretical predictions of the ICHH.

免疫能力妥协假说（immunocompetence handicap hypothesis, ICHH）提出，激素可增强性征表达，但会损害免疫功能。此前针对该假说的相关检验均受限于实验设计层面的缺陷。本研究针对领地性豆娘美洲珈蟌（Hetaerina americana）的雄性个体，开展了同时操控激素与感染状态的实验检验，并对其存活情况进行了精准测定。本实验采用完全析因设计，为每只受试个体施加三类体表处理之一：甲氧普林（一种保幼激素类似物）、丙酮，或空白对照；同时施加三类注射处理之一：细菌、磷酸缓冲盐溶液（PBS），或空白对照。我们分别在野外与笼养环境下，测定了经实验操控的雄性个体的存活情况。正如理论预期，野外环境中，甲氧普林+细菌联合处理组的雄性个体存活受损程度显著高于其余各组；而笼养环境下未出现显著的存活差异。该结果证实，动物体内激素水平升高会以存活作为其代价之一，这一结果验证了免疫能力妥协假说的理论预测。