Changing genetic covariance
In contrast to genetic variance, we observed a clear trend in changing
genetic covariances. Specifically, the correlation between Z11-16:OH and
Z11-16:OAc changed in both sign and magnitude. Since both Z11-16:OH and
Z11-16:OAc reduce heterospecific mate attraction (Vetter and Baker,
1983; Vickers and Baker, 1997), and both traits covary with fitness and
are condition-dependent (Blankers et al., 2021), the negative genetic
correlation in the starting population could be the result of a
trade-off that is selected against when artificial selection favors
higher rates of acetates.
Tracking changes in G matrices through time, we observed another
interesting phenomenon: after selection, the genetic variance in
Z11-16:OAc was more strongly associated with genetic (g) PC2 compared to
before selection, while genetic variance described by gPC1 increased
relative to the other gPCs. Thus, more of the genetic variance was
allocated in fewer dimensions of genetic variation, while the component
under selection was uncoupled from the major dimension of genetic
variance. We acknowledge that the observed changes are subtle and that
they cannot be unequivocally attributed to selection. However, we
observed similar patterns of G matrix evolution in the high and low line
and these patterns fit the prediction that genetic variances and
covariances are reoriented to align the phenotype with the dominant
direction of selection (Melo and Marroig, 2014). These changes in the G
matrix can likely facilitate a more specific response where only
Z11-16:OAc evolves in the absence of indirect selection responses:
relative to the selection regime, the modularity (i.e. the genetic
independence of trait modules) of the pheromone increased.