So Young, So Rich: Habitat Shifts Combined With Trait Evolution Promoted Species Radiation in Senecio in the Andes

Aim

The outstanding Andean biodiversity has been linked to the occurrence of evolutionary radiations that are common among high-elevation plant lineages. One of the most iconic examples is found in the species-rich genus Senecio, with an impressive variation in growth forms and habitat preference. Here, we use Hyb-Seq to overcome the lack of phylogenetic resolution found in previous studies with the aim of disentangling the processes shaping Senecio's hyper-diversity in the Andes, including the evolution of woodiness, growth form and habitat preference.

Location

Central and Northern Andes.

Taxon

Senecio ser. Culcitium.

Methods

Hyb-Seq data for 104 accessions of Senecio were newly generated and analysed using a data analysis workflow that utilises paralogs for phylogenetic reconstruction. The robustness of the species tree under different missing data treatments was investigated, and the phylogeny was dated. The role of hybridisation in the diversification of this lineage was addressed. The evolution of morphological key features and changes in habitat preferences were evaluated. In addition, the association of these features with diversification rate heterogeneity was tested.

Results

Senecio ser. Culcitium is a monophyletic lineage, likely of a Pleistocene origin. Hybridisation, possibly promoted by altitudinal range shifts during the Pleistocene climatic oscillations, played an important role in its evolution. We found evidence for several events of south-to-north migration from the puna on the Central Andes to the páramo on the Northern Andes. One of these migrations to the páramo resulted in a dramatic species diversification. Habitat changes from the páramo to the montane forest occurred multiple times and were associated with growth form shifts.

Main Conclusions

With a net diversification rate of 2 species per million years, high-elevation Andean Senecio is among the fastest diversifying lineages documented so far in the region. Frequent shifts in woodiness, growth form, and habitat played a crucial role in the diversification of this lineage.