A Global Analysis of the Distribution Patterns of Style-Length Polymorphisms Across Angiosperms

Area of Science:

• Evolutionary Biology
• Biogeography
• Plant Reproductive Biology

Background:

• Style-length polymorphisms (SLP) are recurrently evolved outcrossing traits in angiosperms, optimizing pollination efficiency.
• The Rubiaceae family, predominantly tropical and diverse, harbors over 50% of SLP genera, suggesting potential tropicality or diversity drivers.
• Previous hypotheses proposed that specialized tropical pollinators or high species richness might drive SLP evolution and distribution.

Purpose of the Study:

• To investigate the biogeographical factors, specifically tropicality and species diversity, influencing the global distribution of SLP.
• To test the tropicality-driven and diversity-driven hypotheses for SLP evolution.
• To evaluate the role of phylogenetic conservatism and the Rubiaceae family in SLP distribution patterns.

Main Methods:

• Global-scale analysis of angiosperm genera to identify SLP occurrence.
• Phylogenetic logistic regression models to assess SLP prevalence in tropics and biodiversity hotspots.
• Inclusion of phylogenetic relatedness, genus species richness, and Rubiaceae family as covariates.

Main Results:

• Phylogenetic conservatism was the predominant factor shaping SLP distribution, challenging previous hypotheses.
• A significant association between SLP and tropical habitats was observed, but this was largely driven by the Rubiaceae family.
• No positive association was found between SLP and biodiversity hotspots; however, genus-level species richness showed a positive relationship with SLP.

Conclusions:

• The tropicality- and diversity-driven hypotheses for SLP evolution are not supported when phylogenetic relatedness is considered.
• Phylogenetic conservatism, rather than specific biogeographical factors, primarily explains the distribution of SLP.
• Future research should explore the impact of SLP on diversification and species richness patterns.