Intrinsic and extrinsic factors influence reproductive ecology in a Florida scrub plant hybrid complex

Background/Question/Methods   The Piriqueta cistoides ssp. caroliniana (Turneraceae) complex, found throughout the southeastern United States, is a conspicuous member of Florida scrub communities. This obligate outcrosser is distylous and hermaphroditic, and it has a generalist pollination syndrome. The Piriqueta group is comprised of three distinct morphotypes: a northern type, a southern type, and their late-generation heterotic hybrids. Morphotypes express variation in macrophenotypic traits that reflects both genotypic variation and habitat moisture conditions. While previous studies have shown plasticity in vegetative traits and effects of floral traits on pollinator visitation, no work has examined the influence of both endogenous (environmental) and exogenous (genetic) factors on these plants' in situ reproductive effort. We asked how gamete quantity, floral morphology, nectar reward, and degree of herkogamy varied among both style morphs and morphotypes, expecting that hybrid vigor would be reflected in these reproductive traits. Samples from 1400 Piriqueta individuals (28 populations) were collected from throughout their native range in 2008 and 2009. Plants were photographed in situ to determine degree of herkogamy, and both corolla area and symmetry were evaluated using PetalPicker v.2.0. Each flower was then sampled for nectar, and floral parts were removed and preserved in 70% ethanol. To assess reproductive effort, ovaries were dissected to count ovules, and pollen grains were counted in a hemocytometer. Results/Conclusions   Results indicated significant effects of population and time on gamete quantity, floral morphology, nectar reward, and degree of herkogamy. Pollen and ovule quantity varied among morphotypes and style morphs (P < 0.05 for all), although pollen:ovule ratios were constant within all groupings. As expected, hybrid plants produced more gametes than northern or southern types (P < 0.0001); they also exhibited larger, more symmetrical corollas with more nectar (P < 0.05 for all) than other morphotypes. Style morphs with short anthers produced significantly more pollen than style morphs with long anthers (P < 0.0001), though morphs did not vary in ovule numbers (P = 0.5269). Floral morphology and distyly varied among populations, morphotypes, and style morphs (P < 0.05 for all). Our results demonstrate differences in reproductive effort among Piriqueta types, with important implications for plant-pollinator interactions, plant demography, and the dynamics of this expanding hybrid zone. Future work in common gardens will focus on examining the separate effects of genetics and environmental factors such as moisture availability.