Evolutionary change in developmental trajectories (heterochrony) is a major mechanism of adaptation in plants and animals. However, there are few detailed studies of the variation in the timing of developmental events among wild populations. João Costa e Silva and colleagues aimed to identify the climatic drivers and measure selection shaping a genetic-based developmental cline among populations of an endemic tree species complex on the island of Tasmania.
Seed lots from 38 native provenances encompassing the clinal transition from the heteroblastic Eucalyptus tenuiramis to the homoblastic Eucalyptus risdonii were grown in a common-garden field trial in southern Tasmania for 20 years. The authors used 27 climatic variables to model the provenance variation in vegetative juvenility as assessed at age 5 years. They then used a phenotypic selection analysis to measure the fitness consequences of variation in vegetative juvenility based on its impact on the survival and reproductive capacity of survivors at age 20 years.
Costa e Silva et al. show that increased vegetative juvenility is associated with increasing home-site aridity, and that directional selection at the mesic trial site favours reduced vegetative juvenility. They suggest that developmental plasticity and heterochrony are under-appreciated processes, contributing to populations of long-lived organisms, such as trees, persisting and ultimately adapting to environmental change.