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Data from: The consequences of demand-driven seed provisioning for sexual differences in reproductive investment in Thalictrum occidentale (Ranunculaceae)


Ida, Takashi Y.; Harder, Lawrence D.; Kudo, Gaku (2015), Data from: The consequences of demand-driven seed provisioning for sexual differences in reproductive investment in Thalictrum occidentale (Ranunculaceae), Dryad, Dataset,


Many iteroparous angiosperms may benefit from flexible annual resource allocation in response to variable reproductive opportunities induced by external conditions. If maximal reproductive investment is fixed, lack of reproductive sinks would cause resource redistribution to other sinks. Alternatively, reproductive investment may vary depending on the demand of reproductive sinks, changing source-sink relations. In particular, differential responses by males and females to the demands of flower and seed production may cause sexual dimorphism. We assess the occurrence of demand-driven seed allocation by females and its implications for sexual differences in reproductive investment, including the dynamics of mass and carbon allocation and the physiological cost of reproduction, for a dioecious, perennial herb, Thalictrum occidentale. We specifically quantified allocation responses to partial defoliation, which reduced current resource supply, and partial flower/fruit removal, which reduced the aggregate demand of reproductive sinks. During flowering, males preferentially invested carbon and mass in flowers at the expense of vegetative organs, whereas females allocated less mass to flowers and invested more in new-rhizome production for future performance than males. In contrast, during early fruiting, both sexes had new rhizomes of similar size and a doubling of reproductive mass by females after flowering resulted in similar total reproductive investment for both sexes. Manipulation of the source-sink balance did not influence carbon allocation, except that partial fruit removal increased new-rhizome mass compared to intact plants. Females with many fertilized ovules invested proportionally more in seed number and mass per seed than females with few fertilized ovules, indicating both demand-driven seed maturation and its elimination of seed size-number trade-off. Furthermore, males consistently exhibited size-dependent flower production, whereas females exhibited size-dependent flower production only if they had not reproduced during the previous year. Synthesis: This study demonstrates that sexual differences in policies of reproductive investment and the timing of the physiological costs of reproduction impose contrasting allocation schedules. Males invested in reproduction proportionally with their size, whereas females invested flexibly in seeds in response to the demand of developing embryos. Thus, the contrasting certainty and timing of reproductive resource requirements between the sexes contribute to sexual dimorphism.

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