Evolutionary endocrinology of juvenile hormone esterase: Functional relationship with wing polymorphism in the cricket, Gryllus firmus

The existence, nature, and physiological consequences of genetic variation for juvenile hormone esterase (JHE) activity was studied in the wing-polymo rphic cricket, Gryllus firmus. Hemolymph (blood) JHE activity was sixfold l ower in nascent short-winged (SW) females, relative to nascent long-winged (LW) females, during the last juvenile stadium (stage). Morph-associated ge netic variation for JHE activity had two causes, variation in loci: (1) reg ulating whole-organism enzyme activity; and (2) controlling the degree to w hich JHE is secreted into the blood. Reduced JHE activity in nascent SW-sel ected individuals was associated with reduced in vivo juvenile hormone cata bolism. This suggests that variation in JHE activity during juvenile develo pment may have important physiological consequences with respect to the reg ulation of blood levels of juvenile hormone and consequent specification of wing morph. This is the first definitive demonstration of genetic variatio n for hormonal metabolism in any insect and a genetic association between h ormone metabolism and the subsequent expression of morphological variation (wing morph). However, we have not yet firmly established whether these ass ociations represent causal relationships. In contrast to the clear associat ion between JHE activity and wing morph development, we observed no evidenc e indicating that variation in JHE activity plays any direct or indirect ro le in causing the dramatic differences in ovarian growth between adult wing morphs. Variation in JHE activity also does not appear to be important in coordinating the development of wing morph with the subsequent expression o f reproductive differences between adult morphs. Finally, genetic variation for the developmental profiles of JHE activity during juvenile and adult s tages are remarkably similar in three Gryllus species. This suggests that g enetic correlations between JHE activities during different periods of deve lopment, which underlie these activity profiles, have been conserved since the divergence of the three Gryllus species.