Meeting Abstract
Juvenile hormone (JH) has been a major focus of studies investigating the endocrine regulation of wing-polymorphism. The most general model postulates a single threshold, above which JH causes the expression of traits that define the short-winged, flightless morph (SW), and below which JH causes the expression of traits that define the long-winged, dispersing morph (LW). Early studies in aphids and crickets produced ambiguous results due to the small size of aphids or to the very low JH titer in nymphal crickets. Detailed studies in adult Gryllus firmus morphs uncovered an unexpected, and novel morph-specific JH titer circadian cycle (cycling in LW but not in SW) in both the laboratory and field. This finding clearly contradicts the classic model. Morph-specific daily rhythms in global gene expression are strongly associated with and are possibly caused by the morph-specific JH titer rhythm. Daily rhythms for hormonal traits and gene expression, which have largely been ignored in studies of life history evolution, may be common, and may play an important role in adaptation. JH likely has evolved a specialized within-morph function in Gryllus, regulating aspects of daily flight in the LW morph, which exhibits circadian flight. Other hormones, such as insulin-like peptides and ecdysteroids exhibit large-magnitude, non-cyclic differences between the morphs. These hormones possibly regulate the expression of chronic (long-term, non-circadian) differences between LW and SW morphs, such as the much greater ovarian growth of the SW, flightless morph, and the much greater biosynthesis of triglcyeride (flight fuel) in the LW morph. Future studies need to investigate JH titers in more detail, and other hormones, most notably peptides and biogenic amines, which, until very recently, have been largely ignored in endocrine studies of wing polymorphism.
