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Abstract Detail

Reproductive Processes

Wenzell, Katherine [1], Fant, Jeremie [2], Skogen , Krissa Ann [3].

Geographic variation in pollinators and floral traits in a widespread species Castilleja sessiliflora (Orobanchaceae).

INTRODUCTION: The process of speciation is a major focus of evolutionary biology, and is shaped by gene flow and selection. As many flowering plants rely on animal pollinators to reproduce, pollinators directly influence plant evolution, as agents of both gene flow (pollen movement) and selection (fecundity). Thus, plant-pollinator interactions provide a lens through which to study speciation. Though the exact role of pollinators in plant speciation is debated, most models of pollinator-driven speciation invoke geographic variation in pollinators driving local adaptation in floral traits. Despite this, few studies actually measure geographic variation in either plant traits or pollinators across wide scales. Here, our study tests whether a geographic pollinator mosaic relates to floral variation, and thus whether it has the potential to drive divergent selection on floral traits.
STUDY SYSTEM: The genus Castilleja (Orobanchaceae) is known for charismatic and variable inflorescences. One such species, Castilleja sessiliflora, displays intraspecific variation in floral color and morphology across its range. This study examines ecological consequences of floral trait variation within a species across a wide geographic range. We ask the questions: 1. Do floral traits and local pollinators of C. sessiliflora vary geographically? 2. Is this variation correlated at the population level? 3. Could a geographic pollinator mosaic be driving divergent selection on floral traits?
METHODS: We sampled 10-12 populations of C. sessiliflora to measure floral traits and observe pollinators. We measured morphology and color of flowers and conducted pollinator observations during daylight and dusk. Visitation rate was recorded and compared among pollinator groups and correlated with population mean floral trait values.
RESULTS: Geographic variation in floral traits was apparent in inflorescence color and corolla length. Southern populations displayed pink, and occasionally yellow, inflorescences, while northern populations were white-green. Corolla length was shorter in two far southern populations. Pollinator visitation varied among populations and regions. Southern populations were visited by more diverse assemblages of pollinators, while in the north, visitation was low and restricted to infrequent small bees and occasional hawkmoths. The most diverse pollinator assemblages were observed at populations with brightly-colored inflorescences and short corollas. We hypothesize this trait combination may attract and allow access to rewards to a wider array of pollinating insects. However, additional study is needed and is currently ongoing. Nonetheless, we find early evidence that intraspecific geographic variation in floral traits may relate to differences in local pollinators, indicating the potential for pollinator-mediated divergent selection in C. sessiliflora.

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1 - Chicago Botanic Garden, Plant Biology and Conservation, 1000 Lake Cook Road, Glencoe, Illinois, 60022, United States
2 - Chicago Botanic Gardens, Plant Biology And Conservation , 1000 Lake Cook Rd, Glencoe, IL, 60022, United States
3 - Chicago Botanic Garden, 1000 Lake Cook Road, Glencoe, IL, 60022, USA

Floral trait divergence.

Presentation Type: Oral Paper
Session: 16, Reproductive Processes I
Location: 111/Mayo Civic Center
Date: Tuesday, July 24th, 2018
Time: 9:00 AM
Number: 16005
Abstract ID:133
Candidate for Awards:None

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