Parallel evolution of arborescent carrots (Daucus) in Macaronesia

Area of Science:

• Evolutionary biology
• Plant anatomy
• Island biogeography

Background:

• The evolution of woodiness on oceanic islands is poorly understood.
• The genus Daucus, primarily herbaceous, features endemic rosette treelets in Macaronesia, suggesting independent evolution of woodiness.
• Investigating Daucus offers insights into the pathways and drivers of derived woodiness.

Purpose of the Study:

• To elucidate the evolutionary pathways to derived woodiness in the genus Daucus.
• To examine phylogenetic relationships, habit, and secondary xylem evolution in Daucus and related taxa.
• To understand the factors driving the evolution of woodiness in island environments.

Main Methods:

• Phylogenetic analysis of 60 taxa using molecular markers.
• Reconstruction of trait evolution (life history, habit, wood anatomy) using parsimony and maximum likelihood.
• Dated phylogeny estimated using Bayesian methods.

Main Results:

• Daucus independently colonized Macaronesian islands multiple times.
• Rosette treelets evolved independently in different island lineages, with rapid evolution observed in some cases.
• Wood anatomy was not significantly different between treelets and herbaceous forms and was linked to reproductive strategy (polycarpy) rather than life form.

Conclusions:

• Life span and life form in Daucus are evolutionarily labile and can change independently of wood anatomy.
• Wood anatomy in Daucus is primarily related to reproductive strategy, not directly to derived woodiness or island habit.
• Insular woodiness can evolve rapidly and may not be solely an adaptation to reduce xylem embolism risk.