A comparative analysis of gamete production in distylous <i>Primula</i>: Associations with floral traits and elevation

Abstract Despite the importance of gamete production this topic has rarely been investigated in angiosperms using comparative approaches. Here, we investigated pollen and ovule numbers per flower in 73 species and 99 populations of Primula comprising both distylous and homostylous reproductive systems. We investigated whether phylogenetic relationships influenced associations between variation in gamete production, floral traits and elevation, and whether the evolutionary breakdown of distyly to homostyly resulted in parallel changes to gamete production. We used a Bayesian approach facilitated by the MCMCglmm method to model pollen and ovule traits across species and determined whether they exhibited phylogenetic signals. We detected significant positive correlations between pollen number and elevation in both the long‐styled and short‐styled morphs (L‐morph and S‐morph, respectively), whereas ovule number was not influenced by elevation. Pollen production was significantly higher in the L‐morph than in the S‐morph, but there was no significant difference between morphs in ovule number. Pollen volume exhibited a positive correlation with the style length of compatible morphs. The transition from distyly to homostyly was associated with significant decreases in pollen production but not ovule number. Our findings demonstrate the importance of elevation on pollen production, perhaps because of selection to improve pollen‐transfer efficiency in uncertain pollinator environments. In contrast, ovule number variation appears to be more constrained by phylogenetic relationships. Our comparative analyses of a well defined angiosperm lineage highlight the complex interactions between intrinsic and extrinsic factors influencing gamete production in plants and emphasize the importance of considering pollen and ovule data separately.