Data from: Effect of juvenile hormone on senescence in males with terminal investment

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.

衰老是指随年龄增长而出现生存与繁殖能力下降的生理现象，其调控与激素密切相关。在昆虫中，保幼激素（juvenile hormone, JH）已被证实与圈养个体的衰老过程相关，但其在自然环境中的作用仍不明晰。本研究以美洲美蟌（Hetaerina americana）的野生年轻与年老雄性个体为研究对象，通过提升其体内JH水平来填补这一研究空白。我们对两类处理组雄性个体的存活情况进行了评估：一是施用可提升性活动水平的保幼激素类似物——烯虫酯（methoprene），二是施加免疫应激，而后者在本研究物种中已被证实可诱导繁殖终端投资（terminal investment）行为。为控制环境变量的影响，我们在圈养条件下重复了相同实验流程，此时雄性个体被剥夺了所有活动能力与食物供给。我们曾提出假说：经JH处理并施加免疫应激的年老雄性个体存活率最低，因为JH会加剧终端投资对衰老过程的负面影响。但该假说仅适用于野生个体，而非圈养个体——因为JH与免疫应激的联合效应仅会在自然环境中触发高能耗的生理活动，圈养环境下并无此类条件。无论是在自然环境还是圈养条件下，年老个体的死亡时间均早于年轻个体，这证实了雄性美洲美蟌存在衰老现象。仅在野生个体中，JH会降低年轻雄性的存活率、提升年老雄性的存活率，这证实了JH在调控动物衰老过程中会受到环境因素的影响。免疫应激对存活率无显著影响，这表明终端投资并未对衰老过程产生作用。此外，与终端投资的预期效应相反，施加免疫应激后，年轻雄性的重捕率（recapture rates）有所上升，而年老雄性的重捕率则出现下降。本研究结果表明，野生雄性个体的衰老过程由JH介导，而终端投资并不会引发衰老。一种可能的解释是：处于衰老状态并发生终端投资的动物会调整其取食行为，以弥补自身的生理状态损耗。