Quantitative genetic evidence that the timing of vegetative phase change in Eucalyptus globulus ssp globulus is an adaptive trait

Quantitative genetic analysis of six field trials suggests a complex pattern of adaptive significance for the timing of the abrupt change in leaf form in Eucalyptus globulus Labill. spp. globulus. Data from one small trial demonstrated a genetic basis to a steep local cline in habit, in the size of plants flowering and in the height of the change in foliage type. Thus, slow growth, early phase change and precocious flowering appear to be maintained in exposed coastal environments by current selection. This contrasts with results from five large trials that contained open-pollinated progeny from across the whole geographic range of this taxon. On this broad scale, early phase change appears to promote growth, a fitness surrogate, in two trials but not the others, implying differential selection for the timing of phase change. In these cases, early phase change may have been favoured in warm, wet environments by reducing damage by leaf fungi. There was marked genetic variation in the timing of vegetative phase change among broad regions, consistent with either adaptation to broad-scale environmental variation or historical differentiation.