Departamento de Ecología Evolutiva, Instituto de Ecología, Universidad Nacional Autónoma de México, México, D. F. México.
J Evol Biol. 2013 Nov;26(11):2458-66. doi: 10.1111/jeb.12241. Epub 2013 Sep 10.
Senescence, a decline in survival and reproductive prospects with age, is controlled by hormones. In insects, juvenile hormone (JH) is involved in senescence with captive individuals, but its effect under natural conditions is unknown. We have addressed this gap by increasing JH levels in young and old wild males of the damselfly Hetaerina americana. We assessed survival in males that were treated with a JH analogue (methoprene), which is known to promote sexual activity, and an immune challenge, which is known to promote terminal investment in reproduction in the studied species. We replicated the same procedure in captivity (to control for environmental variation), where males were deprived of any activity or food. We expected old males to show the lowest survival after being treated with JH and immune-challenged, because the effect of terminal investment on senescence would be exacerbated by JH. However, this should be the case for wild animals, but not for captive animals, as the effects of JH and immune challenge should lead to an increase in high energetic-demanding activities only occurring in the wild. Old animals died sooner compared with young animals in both the wild and captivity, confirming that males are subject to senescence. In wild but not captive animals, JH decreased survival in young males and increased it in old males, confirming that JH is sensitive to the environment when shaping animal senescence. Immune challenge had no effect on survival, suggesting no effect of terminal investment on senescence. Additionally, contrary to the expected effects of terminal investment, with an immune challenge, recapture rates increased in young males and decreased in old males. Our results show that male senescence in the wild is mediated by JH and that terminal investment does not cause senescence. One explanation is that animals undergoing senescence and terminal investment modify their feeding behaviour to compensate for their physiological state.
衰老，即随着年龄的增长，生存和繁殖前景的下降，受到激素的控制。在昆虫中，保幼激素（JH）参与衰老，而在自然条件下其作用尚不清楚。我们通过增加美洲长尾蜻蜓年轻和年老野生雄性个体的 JH 水平来解决这一差距。我们评估了用 JH 类似物（灭幼脲）处理的雄性个体的存活率，灭幼脲已知可促进雄性个体的性行为，并用免疫挑战来评估，这在研究物种中已知可促进繁殖的终末投资。我们在圈养中复制了相同的程序（以控制环境变化），在圈养中，雄性个体被剥夺了任何活动或食物。我们预计，用 JH 和免疫挑战处理后，年老雄性个体的存活率最低，因为终末投资对衰老的影响会因 JH 而加剧。然而，这应该是野生动物的情况，而不是圈养动物的情况，因为 JH 和免疫挑战的影响只会导致在野外发生的高能量需求活动的增加。与年轻动物相比，无论是在野外还是在圈养中，年老动物都更早死亡，这证实了雄性个体受到衰老的影响。在野外而非圈养动物中，JH 降低了年轻雄性个体的存活率，增加了年老雄性个体的存活率，这证实了 JH 在塑造动物衰老时对环境敏感。免疫挑战对存活率没有影响，这表明终末投资对衰老没有影响。此外，与终末投资的预期影响相反，免疫挑战后，年轻雄性个体的再捕获率增加，而年老雄性个体的再捕获率降低。我们的结果表明，野外雄性衰老受 JH 调节，终末投资不会导致衰老。一种解释是，正在衰老和进行终末投资的动物会改变其进食行为来补偿其生理状态。
