ZERA, Anthony J.; University of Nebraska, Lincoln: Regulation of wing polymorphism by juvenile hormone: State of the art and new perspectives

For over four decades the endocrine mechanisms that underlie morph development and reproduction in wing polymorphic insects have been the subject of extensive experimentation and speculation. Yet little is known about the details of these mechanisms. The “classic” hypothesis postulates that a juvenile hormone (JH) titer consistently above or below a threshold causes the expression of morph-specific traits. Most data supporting this hypothesis are weak, having been derived almost exclusively from gross-level hormone manipulation experiments. Recent, direct JH titer measurements in the wing-polymorphic cricket, Gryllus firmus, indicate a more complex situation with the JH titer exhibiting dramatic morph-specific diurnal variation. No morph exhibits a consistently higher or lower JH titer than the other. In this species, JH may regulate the expression of antagonistic, morph-specific traits such as flight propensity, retention of flight muscles, ovarian growth and flight muscle histolysis by the duration of time above a threshold level rather than being consistently above or below a threshold. Future studies of the endocrine mechanisms of morph development and reproduction should focus on direct measurement of hormonal traits (titers, rates of hormone biosynthesis and degradation, receptor characteristics) rather than relying primarily or exclusively on gross-level hormone manipulation experiments (e.g. topical application of hormones). Since very little is known about the role of hormones other than JH (e.g. neuropeptides) in morph development and reproduction, future studies should also focus on the regulatory role of these non-JH hormones.