No abstract

Comparing the genetic diversity of wild and cultivated accessions suggested the absence of a genetic bottleneck during carrot domestication. In conjunction with historical documents, our results suggest an origin of domesticated carrot in Central Asia. Wild carrots from North America were likely introduced as weeds with European colonization. These results provide answers to long-debated questions of carrot evolution and domestication and inform germplasm curators and breeders on genetic substructure of carrot genetic resources.

In plants whose flowers develop in a sequence, different flowers may exhibit temporal variation in pollen donation and receipt such that the fitness contributions through male and female functions can vary among flowers. Dichogamy, or directional pollinator movements within inflorescences, can create situations where flowers in different stages in the sequence may differ in the numbers of flowers in the female stage available as potential mates. We present an evolutionarily stable strategy (ESS) analysis of the resource allocations expected in different flowers in hermaphroditic plants when the mating environments vary among flowers. This introduces a modular element into sex-allocation models. Our analysis shows that such variation in the mating environments of flowers can select for differences in sex allocation between flowers. When male and female fertilities are nonlinear functions of the allocations, variation in resource availability can also select for variation in sex allocation among flowers. The influence of dichogamy and pollinator directionality on floral sex allocation is discussed, and the empirical evidence supporting the predictions derived from the model is briefly reviewed. The implications of our results for the evolution of andromonoecy and monoecy are discussed.

The timing of fruit initiation and the proximity of fruits to resources influence the probability of fruit and seed initiation in many hermaphroditic plants. In two populations of Aquilegia caerulea, both fruit and seed set decreased significantly between early and late flowers. Low fruit and seed set of late flowers was not due to pollen limitation. Fruit and seed set of late flowers remained low when extra pollen was added to these flowers (pollen quantity), or when all flowers on an inflorescence received self or outcross pollen (pollen quality). While competition for resources occurred among flowers, resource limitation was not responsible for the low fruit and seed set of late flowers. Indeed, preventing pollination of late flowers significantly increased both fruit and seed set of early flowers, but fruit and seed set of late flowers remained low when early flowers were prevented from setting fruits. Late flowers were not just smaller or larger replicates of early flowers, as they allocated more reproductive resources to male function relative to early flowers. Neither herbivory nor architectural constraints could explain the low fruit and seed set of late flowers. While previously published adaptive explanations proposed to explain the low fruit and seed set of late flowers have emphasized a positive aspect to female reproductive success, it is suggested here that both male and female functions should be considered. Morphological data and estimates of male and female reproductive success demonstrate how, both morphologically and functionally, late flowers on inflorescences of A. caerulea specialize as males, early flowers as females. It will be argued that protandry in this sequential bloomer is expected to select for an increase in relative male allocation between early and late flowers, and that the observed pattern of resource allocation and the decrease in fruit and seed set between early and late flowers is consistent with this prediction.