FLORAL TRAITS IN CASTILLEJA: HOW MORPHOLOGICAL TRAITS AND VOLATILE ORGANIC COMPOUND EMISSIONS DIFFERENTIATE SPECIES, AFFECT INSECT INTERACTIONS, AND INFLUENCE PLANT FITNESS

Evan T Hilpman

doi:10.7273/000004338

One of the major goals of evolutionary biology is to explain trait variation within and among species. Much of the tremendous diversity in floral traits across angiosperm lineages is thought to reflect a history of close ecological associations with animals. While pollinator mediated selection on morphological traits has received much attention, surprisingly few have included floral scent into ecological or evolutionary analyses. Fewer still have compared the relative importance of such traits in mediating both animal pollination and predation using linear, quadratic and correlational models. Finally, this dissertation serves to document the first analysis of floral scent in the genus Castilleja. The purpose of this dissertation was to study plant-animal interactions mediated by morphological traits and floral scent. Data collected from natural populations were used to address the following questions in the genus Castilleja: 1) Does interspecific variation in plant traits predict pollinator visitation?; 2) To what extent does intraspecific variation in plant traits mediate both mutualistic and antagonistic interactions?; and 3) What forms of selection result from multiple plant-animal interactions affecting floral scent and morphological traits? We demonstrated that variation in floral morphological and scent traits among five species of Castilleja differentiated species and pollination syndromes, but did not reliably predict pollinator visitation. Extremely low rates of pollinator visitation across Castilleja species reduced statistical power of analyses reliant on direct observational data. However, using direct observations of antagonist seed predator visitation and indirect measures of seed predator and pollinator activity we detected associations between plant traits and animal behavior within a large population of Castilleja sessiliflora. While pollinator and seed predator activity was correlated with both morphology and scent, their activities were predicted by distinct traits. Directional, stabilizing, disruptive, and correlational selection were detected; and traits that experienced selection were evident during the seed initiation stage, suggesting a potential role of pollinators. However, marked changes in the direction and magnitude of selection were evident following visitation by seed predators. Overall, these results demonstrate that both scent and morphological traits mediate plant-animal interactions, and that both mutualists and antagonists significantly contribute to selection on plant traits.

FLORAL TRAITS IN CASTILLEJA: HOW MORPHOLOGICAL TRAITS AND VOLATILE ORGANIC COMPOUND EMISSIONS DIFFERENTIATE SPECIES, AFFECT INSECT INTERACTIONS, AND INFLUENCE PLANT FITNESS

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