Morph-Dependent Cyclic JH Titer in a Wing-Polymorphic Insect: Adaptive Significance and Underlying Causes

一些昆虫，如蟋蟀（Gryllus firmus），是翅膀多态的（即，它们包含有飞行能力和无飞行能力的变体）。 翅的多态性已被广泛地用于研究昆虫扩散的激素控制和内分泌调节的进化。 然而，所有以前的研究都只集中在飞行能力的激素控制上（例如，翅膀和飞行肌肉的生长）。 没有研究调查飞行本身的内分泌调节，也没有研究调查翅膀多态性的激素调节。 最近的研究表明，形态特异性性状的内分泌调控比以前预期的要复杂得多。 保幼激素（juvenile hormone，JH）是翅型多态性的关键调节因子。 在蟋蟀Gryllus firmus中，JH的平均浓度在有飞行能力和无飞行能力的变体中是相似的，但是变体在这种激素的水平如何随时间变化方面有所不同。 在有飞行能力的变体中，JH滴度在白天变化10-50倍，但在无飞行能力的变体中相对恒定。 本研究着重探讨JH滴度每日变化的根本原因和适应意义。 JH滴度的长期升高与卵巢生长和飞行肌肉的分解有关-这些变化对飞行不利。 本研究将检验以下假设：JH滴度的短暂升高持续时间足以引起飞行行为的表达，但持续时间不足以引起卵巢生长或飞行肌肉的分解。 研究将涉及在白天和晚上直接比较变体之间的激素滴度。 将通过实验操作JH滴度，并监测其对飞行倾向的影响。 最后，生理过程（激素的生物合成和降解），调节形态特异性的每日变化的JH滴度将进行研究。 重要的是，这些研究将在实验室和实地进行。 这一研究将极大地加深我们对昆虫扩散的内分泌调节和扩散进化的理解。

Some insects, such as the cricket (Gryllus firmus), are wing polymorphic (i.e., they contain both flight capable and flightless morphs). Wing polymorphism has been extensively used to investigate the hormonal control of dispersal and the evolution of endocrine regulation in insects. However, all previous studies have focused exclusively on the hormonal control of flight capability (e.g., growth of wings and flight muscles) in the laboratory. No study has investigated the endocrine regulation of flight itself, and no study has investigated the hormonal regulation of wing polymorphism in the field. Recent studies indicate that the endocrine regulation of morph-specific traits is more complex than previously expected. The key regulator of wing polymorphism is juvenile hormone (JH). In the cricket, Gryllus firmus, the mean concentration of JH is similar in the flight capable and flightless morphs, but the morphs differ in how the level of this hormone varies over time. The JH titer changes 10-50 fold during the day in the flight capable morph, but it is relatively constant in the flightless morph. This study focuses on the underlying causes and adaptive significance of daily changes in the JH titer. Prolonged elevation of the JH titer is associated with ovarian growth and with the breakdown of flight muscles--changes that are detrimental with respect to flight. This study will test the hypothesis that brief elevation of the JH titer is of sufficient duration to cause the expression of flight behaviors but of insufficent duration to cause ovarian growth or the breakdown of flight muscles. Studies will involve direct comparisons of hormone titers between morphs throughout the day and evening. The JH titer will be experimentally manipulated, and its effect on flight propensity will be monitored. Finally, physiological processes (hormone biosynthesis and degradation) that regulate morph-specific daily changes in the JH titer will be investigated. Importantly, these studies will be undertaken in both the laboratory and the field. This study will substantially enhance our understanding of the endocrine regulation of dispersal and evolution of dispersal in insects.