Is ovule packaging strategy in animal-pollinated plants correlated to the level of specialization of their pollination systems?

The number of ovules per flower varies over several orders of magnitude among angiosperms, with some families exhibiting remarkable conservatism and others displaying extensive variation among closely related species. Numerous hypotheses have been advanced to explain plant strategies in ovule packaging, often linking this trait to the statistical dispersion of pollen receipt. Given that, in animal-pollinated plants, the pollen load received depends on flower visitor identity, abundance, and efficiency, we hypothesized that ovule packaging should be directly related to the pollination system. Specifically, we predicted that (1) specialist plants, serviced by a few efficient floral visitors, would bet-hedge on rare visits by producing more ovules per flower and thereby maximizing seed output when pollination is successful, (2) compared to generalists that operate in more predictable pollinator environments and consequently produce fewer ovules per flower. To test our hypothesis, we analyzed literature-derived data encompassing 192 zoogamous plant species representing 61 taxonomic families. We observed fewer ovules with greater visitor diversity in trees compared to perennials, but these effects disappeared under phylogenetic models, which showed that ovule number has a strong phylogenetic signal. These findings indicate that while pollination system characteristics may influence ovule packaging strategies, they do not fully account for the observed variation. Instead, ovule number appears subject to strong and conflicting selective pressures, suggesting that the generalization/specialization of pollination systems does not singularly explain its evolution.