Breeding systems and seed size in a neotropical flora: testing evolutionary hypotheses

Area of Science:

• Plant reproductive ecology
• Evolutionary biology
• Biodiversity research

Background:

• A key prediction in plant reproductive ecology suggests dioecious taxa (species with separate male and female individuals) should produce superior seeds compared to cosexual taxa (species with both sexes on the same individual).
• This prediction, while widely accepted, has remained largely untested across diverse plant communities.
• Understanding the relationship between breeding systems and seed traits is crucial for plant evolution and ecology.

Purpose of the Study:

• To evaluate the prediction that dioecious plant species produce larger seeds than cosexual species.
• To examine the ecological and evolutionary associations between plant breeding systems and mean seed size.
• To investigate these relationships across different growth forms (woody and nonwoody) within a tropical flora.

Main Methods:

• Utilized a dataset of 972 species from 104 families in the Tambopata Wildlife Reserve, Peru.
• Conducted cross-species analyses to compare mean seed size between dioecious and cosexual species.
• Employed phylogenetically independent contrasts using a hypothesized phylogeny to assess evolutionary changes in seed size associated with breeding system divergence, controlling for growth form.

Main Results:

• Cross-species analyses showed dioecious species produced significantly larger seeds than cosexual species in woody species, shrubs, lianas, and pooled taxa, but not in trees.
• Phylogenetically independent contrasts confirmed a significant association between breeding system and seed size in woody taxa, lianas, and pooled taxa.
• The relationship between breeding system and seed size was not significant among shrubs in the phylogenetic analysis.

Conclusions:

• The findings support the prediction that dioecy is associated with larger seed size, particularly in woody plant lineages.
• This study provides empirical evidence for the evolutionary link between breeding system and seed trait evolution in plants.
• The results have implications for understanding the diversification and ecological strategies of plants with different reproductive systems.