Huang Z Y, Robinson G E
Department of Entomology, University of Illinois, Urbana 61801, USA.
J Comp Physiol B. 1995;165(1):18-28. doi: 10.1007/BF00264682.
Honey bee colonies can respond to changing environmental conditions by showing plasticity in age related division of labor, and these responses are associated with changes in juvenile hormone. The shift from nest tasks to foraging has been especially well characterized; foraging is associated with high juvenile hormone titers and high rates of juvenile hormone biosynthesis, and can be induced prematurely in young bees by juvenile hormone treatment or by a shortage of foragers. However, very few studies have been conducted that study plasticity in division of labor under naturally occurring changes in the environment. To gain further insight into how the environment and juvenile hormone influence foraging behavior, we measured juvenile hormone titers and rates of biosynthesis in workers during times of the year when colony activity in temperature climates is reduced: late fall, winter, and early spring. Juvenile hormone titers and rates of biosynthesis decreased in foragers in the fall as foraging diminished and bees became less active. This demonstration of a natural drop in juvenile hormone confirms and extends previous findings when bees were experimentally induced to revert from foraging to within-hive tasks. In addition, endocrine changes in foragers in the fall are part of a larger seasonally related phenomenon in which juvenile hormone levels in younger, pre-foraging bees also decline in the fall and then increase the following spring as colony activity increases. The seasonal decline in juvenile hormone in foragers was mimicked in summer by placing a honey bee colony in a cold room for 8 days. This suggests that seasonal changes in juvenile hormone are not related to photoperiod changes, but rather to changes in temperature and/or colony social structure that in turn influence endocrine and behavioral development. We also found that active foragers in the late winter and early spring had lower juvenile hormone levels than active foragers in late spring. In light of recent findings of a possible link between juvenile hormone and neuroanatomical plasticity in the bee brain, these results suggest that bees can forage with low juvenile hormone, after previous exposure to some threshold level of juvenile hormone leads to changes in brain structure.
蜜蜂蜂群可以通过在与年龄相关的劳动分工中表现出可塑性来应对不断变化的环境条件，而这些反应与保幼激素的变化有关。从巢内任务到觅食的转变已经得到了特别充分的研究；觅食与高保幼激素滴度和高保幼激素生物合成速率相关，并且通过保幼激素处理或觅食者短缺可以在幼蜂中过早诱导出觅食行为。然而，很少有研究在自然发生的环境变化下研究劳动分工的可塑性。为了进一步深入了解环境和保幼激素如何影响觅食行为，我们在温带气候下蜂群活动减少的一年中的几个时期，即深秋、冬季和早春，测量了工蜂体内的保幼激素滴度和生物合成速率。随着秋季觅食活动减少且蜜蜂变得不那么活跃，觅食者体内的保幼激素滴度和生物合成速率下降。保幼激素自然下降的这一证明证实并扩展了之前的研究结果，即在实验诱导蜜蜂从觅食转变为巢内任务时的发现。此外，秋季觅食者的内分泌变化是一个更大的季节性相关现象的一部分，在这个现象中，较年轻的、尚未开始觅食的蜜蜂体内的保幼激素水平在秋季也会下降，然后在次年春天随着蜂群活动增加而上升。在夏季，将一个蜜蜂蜂群置于冷室中8天，可模拟出觅食者体内保幼激素的季节性下降。这表明保幼激素的季节性变化与光周期变化无关，而是与温度和/或蜂群社会结构的变化有关，而这些变化反过来又会影响内分泌和行为发育。我们还发现，冬末和早春的活跃觅食者的保幼激素水平低于晚春的活跃觅食者。鉴于最近发现保幼激素与蜜蜂大脑中的神经解剖可塑性之间可能存在联系，这些结果表明，在先前接触到一定阈值水平的保幼激素导致大脑结构发生变化后，蜜蜂可以在低保幼激素水平下进行觅食。
