A shift in developmental allometry underlies the transition to a multi-ovulate strategy from a single-ovulate ancestral state in Phlox (Polemoniaceae)

ABSTRACT The number of seeds produced per flower is influenced by many pre- and post-pollination factors and varies enormously across taxa, from one to thousands. This diversity has obvious implications for fitness and often reflects a tradeoff between investment in allocation per seed vs. the number of seeds produced. However, we know remarkably little about the developmental basis for variation in seed number, which, at its origin, is fundamentally variation in ovule number. In this study, we have used between and within species variation in the genus Phlox to explore the developmental basis of a shift between an ancestral state of producing only one ovule per locule and a derived state of producing two or more ovules per locule. Our results demonstrate that a change in the allometric relationships between ovary size, ovule size and ovule number has repeatedly evolved in this genus. This is the first study to demonstrate a relationship between ovule primordia size and ovary size and the first to find that the relative size of ovule primordia correlates with ovule number variation.