Beyond pollen:ovule ratios: Evolutionary consequences of pollinator dependence and pollination efficiency for pollen and ovule production in angiosperms

Premise: The relative per‐flower production of ovules and pollen varies broadly with angiosperm mating systems, with outcrossing types commonly producing more pollen grains per ovule than selfing types. The evolutionary causes of this variation are contentious, especially the relevance of pollination risk. Resolution of this debate may have been hampered by its focus on pollen:ovule (P:O) ratios rather than on the evolution of pollen and ovule numbers per se.
Methods: Using published mean ovule and pollen counts, we analyzed associations with the proportion of removed pollen that reaches stigmas (pollen‐transfer efficiency) and differences between pollinator‐dependent and autogamous forms within and among species. Analyses involved Bayesian methods that simultaneously considered variation in pollen and ovule numbers and accounted for phylogenetic relatedness. We also assessed the utility of P:O ratios as mating‐system proxies and their association with female outcrossing rates.
Results:..., Data compilation
We searched for papers that reported pollen and ovule numbers using three complementary approaches: by searching the Web of Science (WoS) for papers that included the key words “pollen:ovule”, “pollen-ovule” and “pollen/ovule”; by using Erbar and Langlotz’s (2005, Botanische Jahrbucher 126: 71-132) compilation of published pollen:ovule ratios to identify older papers not abstracted by WoS; and by using the WoS citation information to identify papers that had cited Cruden's (1977, Evolution 31: 32-46) seminal paper on pollen:ovule ratios. We also recorded information concerning species characteristics, of which those relevant for this study are pollen-vector dependence, life history (annual, biennial, or monocarpic or iteroparous perennial), female outcrossing rate and pollen-transfer efficiency. If the source reference of the pollen and ovule records did not provide this information, we sought it from supplementary sources.
Phylogeny construction
Most analyses accounted..., All data files can be opened with any text editor.