Phylogenetic signal in flowering phenology weakens over elevation in the high Andes of Chile: evidence for evolutionary convergence in a harsh habitat

TL;DR

This study finds that harsh high Andes environments drive similar flowering times in plants, not just inherited traits.

Contribution

Shows that evolutionary convergence, not ancestral traits, shapes flowering phenology in high alpine zones.

Findings

High alpine sites show earlier flowering after snowmelt and greater functional convergence in phenological traits.

Phylogenetic signal is weaker in high alpine sites compared to subalpine ones.

High alpine communities exhibit significant terminal phylogenetic clustering.

Abstract

High elevation plants experience cold temperatures and short growing seasons that constrain their flowering window. These environmental limitations are expected to promote strong overlap in flowering phenology among co-occurring species. Whether similarity in flowering times arises from environmental filtering of lineages preadapted to cold conditions or from evolutionary convergence in response to shared selective pressures remains unclear. We hypothesize that flowering phenology of high alpine communities is the result of convergence due to strong selective pressure imposed by the environment rather than environmental filtering for conserved ancestral traits.

To test this hypothesis, we analyzed the functional and phylogenetic structure of phenological traits, as well as their phylogenetic signal, using a molecular phylogeny across four sites spanning subalpine to high alpine zones in the central Chilean Andes. A total of 86 species were included. Observed patterns were compared against null model expectations to evaluate functional convergence, phylogenetic structure, and trait conservatism.

High alpine sites exhibited earlier flowering following snowmelt, greater functional convergence in phenological traits, and significant phylogenetic signal in a smaller subset of floral traits compared to subalpine sites. Additionally, both high alpine communities showed significant terminal phylogenetic clustering.

Our results suggest that environmental filtering of preadapted lineages plays a minor role in shaping high alpine community structure. Rather, intense environmental pressures at higher elevations appear to drive trait convergence in flowering phenology. We conclude that the general trend for phylogenetic conservatism in floral phenology has been overridden by the harsh environmental conditions in the high Andes. The high alpine environment can be seen as an evolutionary promoter of convergent phenological strategies rather than a gatekeeper of lineages preadapted to cold conditions.

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