Sex Allocation in a Long-Lived Monocarpic Plant

Abstract

Hermaphroditic plants with perfect flowers often show within-inflorescence flower differentiation, lower female success (and therefore female investment) as the inflorescence develops, and size-dependent sex allocation to male and female functions. Here, I present the results of a descriptive and experimental study in the long-lived monocarpic Saxifraga longifolia, a sequentially blooming plant showing a large variation in the size of the inflorescence. Natural patterns of relative investment in male and female reproductive components were explored, and flowers were removed from different positions, in order to test two models on sex allocation which predict that female investment increases with resource availability. Results of this study agree with this prediction at the flower level (within inflorescences), but not at the plant level. Pre- and post-mating female allocation declined from early to late-position flowers, while the pollen : ovule increased. Removal of flowers indicated that architectural effects do not prevent full compensation for overall seed production, although the participation of terminal flowers in female reproduction was low in most cases. There seem to be some ontogenic differences in specialization among early- and late-produced flowers, so that the progressive maleness over time is reinforced after fertilization by a sink-source effect, possibly combined with selective abortion. Overall seed production was significantly correlated with plant size; nevertheless, female success was not maximum for the largest plants, but for intermediate sized plants.

Key words

Flower position - reproductive success - functional gender - resource translocation - non-fruiting flowers

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