ZERA, Anthony J.; University of Nebraska: Artifical selection on juvenile hormone esterase activity: Insights into the microevolution of endocrine regulation

Although considerable information is available on the physiology and biochemistry of hormonal regulation, little is known about the microevolution of endocrine regulatory mechanisms. A key step in understanding endocrine microevolution is documenting the existence, characteristics, and phenotypic consequences of endocrine variation and covariation. To this end we directly selected on a key in vivo endocrine regulator in insects, the blood activity of juvenile hormone esterase (JHE) in a recently founded laboratory stock of the cricket, Gryllus assimilis. JHE degrades and partially regulates the titer of the key developmental and reproductive hormone, juvenile hormone. After 10 generations of selection during the juvenile stage, upward-selected and downward-selected lines diverged 10-fold in JHE activity. The response to selection was due to variable genes in the base population that controlled both the total amount of enzyme produced as well as the tissue distribution of enzyme activity. No significant kinetic differences were observed between JHE enzymes from the high- or low-selected lines. Lines did not differ in JHE activity during the adult stage indicating that the response to selection during the juvenile stage was due to selection on stage-specific regulators. The JHE gene is being cloned to identify these regulators. The evolution of the endocrine control of development can evolve independently of the endocrine regulation of adult reproduction. Selection on JHE activity altered whole-organism JH degradation, and various phenotypic traits such a duration of development and size of flight muscles. This is the first artifical selection study of an insect endocrine regulator and is currently the most intensive artificial selection study of endocrine regulation (involving biochemical/endocrine analyses of over 30,000 individuals) in any organism.