Female fertility per flower and trade-offs between size and number in Claytonia virginica (Portulacaceae)

A consistent and paradoxical feature in flowering plants is the production of many more flowers than appear required for female fertility through fruit and seed production. Many mechanistic hypotheses for this observation share key assumptions about (1) limited resources available for reproduction and (b) greater female fertility benefits from larger flowering-time investment. Here I investigate these assumptions in two populations of Claytonia virginica. I also test predictions from theoretical analyses, comparing patterns of flowering allocation and fertility per flower in 18 populations of C. virginica. Results support the assumption that larger benefits accrue from greater flowering-time investment. The between-population pattern of flowering allocation and fertility per flower is also consistent with theoretical expectation, although not statistically significant. Not supported is the assumption that reproduction occurs under strong resource constraint. Possible reasons for this discrepancy are discussed.     

Sex allocation under simulated herbivory in the generalist perennial herb Paeonia broteroi (Paeoniaceae)

Theories of optimal resource allocation in flowering plants postulate that allocation to sexual functions are balanced. While many studies have found such evidence in hermaphroditic species among flowers, plants or populations, or at different phenological stages, it has not been supported by other studies. This has been explained by differences among genotypes in ability to acquire resources, resource partitioning among traits unrelated to reproduction or strong selection to maintain positive genetic correlation among traits. I studied how herbivory affected resource allocation to sexual functions in the perennial herb Paeonia broteroi (Paeoniaceae) by measuring a number of floral traits in control plants and in experimental plants under simulated herbivory. The species shows very little plasticity in resource allocation between sexual structures and functions, and appears to be highly sensitive to alterations in the balance of resource acquisition and allocation, with an immediate outcome in terms of seed production and a mid-term response in terms of sprouting and flowering. Plants' ability to collect resources for growth and reproduction before their senescence at the end of the reproductive season, are compromised. This may limit their reproductive potential, the maintenance and growth of their populations, and may influence their demographic state and the plants' ability to respond to selective pressures by external biotic agents.     

Does the relative importance of resource competition and architectural effect in floral variation vary with stages of floral ontogeny?

Variation in floral allocation within inflorescences has been attributed to resource competition and/or architectural effect.The two hypotheses were extensively studied and both hypotheses were partly ...     

EVOLUTIONARILY STABLE SELFING RATES OF HERMAPHRODITIC PLANTS IN COMPETING AND DELAYED SELFING MODES WITH ALLOCATION TO ATTRACTIVE STRUCTURES

I present a resource-allocation model to analyze how patterns of allocation to reproductive structures influence the evolution of selfing rates in hermaphrodites subject to competing and delayed forms of self-fertilization. The evolutionarily stable state does not depend on the mode of pollination. In contrast to previous models in which the number and the size of flowers were not considered, intermediate selfing is not evolutionarily stable with linear constraints on flower number and size. In contrast, intermediate selfing can be evolutionarily stable with nonlinear constraints on flower number and size. Optimal allocations to attractive structures increase and selfing rates decrease in the presence of inbreeding depression. In particular, stable intermediate levels of selfing may be favored when flower number is strongly constrained. Thus, nonlinear constraints on flower number and size could favor the evolution of intermediate selfing in either the delayed or the competing modes of selfing. Outcrossing is not favored in the absence of inbreeding depression, a result inconsistent with Holsinger's results in which allocation to attractive structures was not considered.