PHENOTYPIC PLASTICITY IN POLLEN AND OVULE PRODUCTION OF NICOTIANA LONGIFLORA AND N. PLUMBAGINIFOLIA (SOLANACEAE): IMPLICATIONS FOR PLANT MATING SYSTEM VARIABILITY pp. 255-272
Authors: (Figueroa-Castro Dulce Marķa, Timothy Holtsford, Angela Etcheverry, Division of Biological Sciences, University of Missouri, Columbia, Missouri, USA, and others)
Abstract: Phenotypic plasticity in floral traits associated with mating systems has been demonstrated for many species. However, few studies have explored the existence of plasticity in pollen and ovule production. This is important because plant mating systems are often estimated as pollen:ovule ratio. In this chapter we determine the existence of phenotypic plasticity in gamete production and in mating system as estimated through pollen:ovule ratio in Nicotiana longiflora and N. plumbaginifolia. We measured several morphological traits of flowers and then counted pollen and ovules directly on plants from greenhouse and natural environments. Then we developed regression models for both environments, using morphological traits to predict pollen and ovule number. We then applied both regression models to eight and six natural populations of N. longiflora and N. plumbaginifolia, respectively. We found that pollen production is plastic in N. longiflora but not in N. plumbaginifolia. There was a general trend towards a decrease in number of pollen grains in natural populations of N. longiflora; but it was significant in only four out of the eight populations sampled. In N. plumbaginifolia that trend was inverted, with natural populations producing more pollen grains; however this pattern was not significant for any of the six populations studied. Ovule production was not significantly different between environments in N. longiflora and data did not show any particular trend. In N. plumbaginifolia, ovule production had a general trend towards a decrease in natural populations, but this trend was significant in only three out of the six populations studied. Pollen:ovule ratio had a general trend towards a decrease in natural populations of N. longiflora, but this trend was significant in only one population, suggesting the existence of a trend towards selfing for that population. On the contrary, pollen:ovule ratio in N. plumbaginifolia tended to be higher in natural populations compared to greenhouse, however, it was not significant in any of the populations studied. Our results showed that plastic responses are population- and species- specific, possibly as a consequence of local adaptations to dominant selective pressures in each population.