Annals of Botany

Evidence that divergent selection shapes a developmental cline in a forest tree species complex

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.

Varying vegetation
Image: João Costa e Silva et al. (2018)

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.

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