Direct and correlated responses to selection on JHE activity in adult and juvenile Gryllus assimilis: implications for stage-specific evolution of insect endocrine traits

Abstract

Two-way selection on the activity of the endocrine regulator, juvenile hormone esterase (JHE), in adults of the cricket, Gryllus assimilis, resulted in a realized JHE heritability of 0.059<0.001. This heritability was significantly lower than the realized JHE heritability measured previously during selection on the last juvenile stadium (0.26<0.04). We observed strong correlated responses to selection on JHE activity during different periods of adulthood but very weak correlated responses in the last juvenile stadium. The additive genetic correlation between JHE activities in adults and juveniles, measured from the two pairs of correlated and direct responses obtained from the present adult and the previous juvenile selection studies, did not differ significantly from zero. Lines from the earlier juvenile selection study, reassayed for correlated responses after an additional five generations of selection, exhibited only weak correlated responses for JHE activity in adult and penultimate stages. Results from the present adult and the previous juvenile selection studies provide a consistent picture of strong withinstage JHE correlated responses in either adult or juvenile stages. By contrast, only weak JHE correlated responses occur in contiguous developmental stages, irrespective of whether the stages are physiologically or morphologically similar or dissimilar, or whether JHE activity was selected before or after the stage in which the correlated responses were measured. The regulation of a particular life cycle stage by JHE (juvenile development) can be modified by selection without necessarily altering its regulatory role in other stages (adult reproduction).