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

一些昆虫，如蟋蟀(Gryllus Firus)，翅膀是多形性的(即，它们既有能飞的，也有不能飞的)。翅的多态已被广泛用于研究昆虫扩散的激素控制和内分泌调节的进化。然而，以前的所有研究都集中在实验室中荷尔蒙对飞行能力的控制(例如，翅膀和飞行肌肉的生长)。还没有研究过飞行本身的内分泌调节，也没有研究过飞行中翅膀多态的激素调节。最近的研究表明，特定形态性状的内分泌调节比之前预期的要复杂得多。保幼激素(JH)是翅型多态的关键调节因子。在蟋蟀中，JH的平均浓度在能飞行和不能飞的变种中是相似的，但这种荷尔蒙的水平随着时间的变化而不同。在有飞行能力的变种中，JH滴度在白天变化10-50倍，但在不能飞行的变种中相对恒定。本研究的重点是JH滴度日变化的潜在原因和适应意义。JH滴度的长期升高与卵巢生长和飞行肌肉的崩溃有关--这些变化对飞行是有害的。这项研究将检验这样一种假设，即JH滴度的短暂升高足以导致飞行行为的表达，但持续时间不足以导致卵巢生长或飞行肌肉崩溃。研究将包括直接比较白天和晚上不同形态的激素效价。将对JH效价进行实验操作，并将监测其对飞行倾向的影响。最后，将研究调节特定形态的JH滴度每日变化的生理过程(激素生物合成和降解)。重要的是，这些研究将在实验室和实地进行。这项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.