BACKGROUND To understand variation in resistance to parasites within host populations, researchers have examined conditions under which immunity is induced and/or is costly. Both host sex and age have been found to influence immune expression and subsequently are likely factors influencing the costs of resistance. The purpose of this study was to examine immune expression and associated survival costs for two age groups (newly emerged and sexually mature individuals) of the damselfly, Enallagma boreale Selys. Survival was assessed for experimentally challenged and control damselflies, housed initially at 22 degrees C and then subjected to low temperatures (15 degrees C) associated with reduced foraging activity and food deprivation. Experimental conditions emulated natural local variation in bouts of good weather followed by inclement weather (successions of days with hourly mean temperatures around 15 degrees C and/or rainy weather). RESULTS At least one of three immune traits was induced to higher levels for both newly emerged and mature E. boreale challenged by Lippopolysaccharide (LPS) relative to saline-injected controls, when housed at 22 degrees C. The immune traits assayed included haemocyte concentration, Phenoloxidase activity and antibacterial activity and their induction varied among ages and between males and females. For matures, those injected with LPS had lowered survivorship compared to saline-injected controls that were housed initially at 22 degrees C and subsequently at 15 degrees C. Newly emerged LPS-injected damselflies did not show reduced survivorship relative to newly-emerged controls, despite showing immune induction. CONCLUSION Reduced longevity following induction of immunity was observed for reproductively mature damselflies, but not for newly emerged damselflies. Costs of resistance depend only partly on the immune trait induced and more on the age (but not sex) of the host. In four years, we often observed bouts of inclement weather following good days and these bouts occurred primarily during the emergence periods, but also during the flight periods, of E. boreale. The duration of these bouts appear sufficient to compromise survival of mature damselflies that responded immunologically to LPS challenge. We further suggest the environmental conditions likely experienced by different ages of damselflies, following resistance expression, has influenced optimal immune investment by individuals in different age classes and the likelihood of detecting costs of resistance.

中文翻译：

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温带豆娘的雄性和雌性的年龄依赖性诱导免疫力和随后的生存成本。

背景技术为了理解宿主种群中对寄生虫的抗性变化，研究人员研究了诱导免疫力和/或成本高昂的条件。已发现宿主性别和年龄均会影响免疫表达，因此可能是影响耐药性成本的因素。这项研究的目的是检查豆娘Enallagma boreale Selys的两个年龄组（新出现和性成熟的个体）的免疫表达和相关的生存成本。对存活率进行了评估，以适应实验挑战性和控制性的蜻蜓，它们最初居住在22摄氏度，然后处于低温（15摄氏度），与觅食活动和食物匮乏相关。实验条件模拟好天气的自然局部变化，随后是恶劣天气（连续数天，每小时平均温度在15摄氏度左右和/或阴雨天气）。结果相对于生理盐水注射的对照组，当在22摄氏度下饲养时，通过脂多糖（LPS）攻击的新出现和成熟的大肠杆菌的三种免疫性状中的至少一种被诱导为更高的水平。检测的免疫性状包括血红细胞浓度，酚氧化酶活性和抗菌活性及其诱导作用随年龄的增长以及男女之间的差异而变化。对于成熟者而言，注射LPS的人的存活率要比最初注射于22摄氏度，然后容纳于15摄氏度的注射生理盐水的对照要低。尽管出现了免疫诱导作用，但新出现的注射LPS的豆娘相对于新出现的对照组没有表现出降低的存活率。结论生殖成熟的豆娘观察到免疫诱导后的寿命降低，而新出现的豆娘则没有。抗药性成本仅部分取决于诱导的免疫特征，而更多取决于宿主的年龄（而非性别）。在四年中，我们经常观察到好天气后出现暴风雨，这些暴风雨主要发生在E.boale的出苗期和飞行期。这些回合的持续时间似乎足以损害对LPS攻击产生免疫反应的成熟豆娘的生存。我们进一步建议不同年龄的豆娘可能经历的环境条件，