Species evolution determines epiphyte evolution in Orchids

Orchid diversity and conservation are tightly linked to the evolution of orchid lifeforms (e.g., epiphytic or terrestrial) as epiphytic species are highly sensitive to environmental changes and includes super-high species diversity. However, the factors that drive the evolution of orchid lifeform remain unclear. Here, we used a global orchid phylogeny (2272 species, all five subfamilies and 302 genera) to evaluate the relative contributions of potential factors (i.e., phylogeny, climate region, pollination traits) that may drive orchid lifeform evolution using partial $R^2$ framework. Conventional correlation results indicated that orchid lifeforms are strongly associated with climate regions and weakly related to pollination traits. In contrast, partial $R^2$ analyses revealed that orchid phylogeny alone accounted for 62% of lifeform variation; pollinator attraction strategies independently explained an additional 23.9% variation, while climate region only further explained 3.4%. The discrepancies arise from variation in phylogenetic conservatism of different orchid traits: both orchid lifeform and climate region are more phylogenetically conserved than pollination traits. Specifically, our findings that species evolution plays a key role in lifeform evolution together with variation in phylogenetic conservatism among key traits provide insights into trait evolution and species conservation in orchids.