Predicting correlated responses in natural populations: changes in JHE activity in the bermuda population of the sand cricket, gryllus firmus

Quantitative genetic methods have been used to examine selection responses in domesticated organisms but there are few cases of their application to predict changes in natural populations: there are, to our knowledge, no cases in which correlated responses to selection have been predicted. In the present paper we use quantitative genetic parameters estimated from a half-sib experiment to predict the changes expected in juvenile hormone esterase (JHE) activity in the Bermuda population of the wing dimorphic cricket, Gryllus firmus. JHE activity is genetically correlated with wing form in this cricket and hence changes in the proportion of macroptery (volant morph) are predicted to bring about a correlated response in JHE activity. The Bermuda population has a higher proportion of macropterous individuals (95%) compared to the stock (35%, originally from Florida) from which the heritabilities and correlations were estimated. The quantitative genetic analysis makes three predictions which were tested both qualitatively and quantitatively. In all cases the null hypothesis that the observed results correspond to those predicted cannot be rejected. As predicted, in the Bermuda population there is: (i) an increase in the population mean JHE activity; (ii) a leftwards shift in the curve relating the probability of microptery (flightless morph) to JHE activity; and (iii) a decrease in the mean JHE activity within each morph.