Corolla shape vs. size in flower choice by a nocturnal hawkmoth pollinator

Corolla shape is one of many floral traits used by pollinators when making foraging decisions. Corolla shape has been implicated as a factor in floral isolation and evolutionary shifts between pollinator affinities, yet few studies have investigated how quantifiable differences in corolla shape affect pollinator behaviour. 2. This study measured variation in corolla shape (primarily corolla limb dissectedness) across eight species of Nicotiana (section Alatae) and its influence on flower choice by nocturnal hawkmoths (Manduca sexta). Behavioural assays performed under simulated moonlight tested for hawkmoth preference and performance differences between the average floral shape of sphingophilous species (CHawkmoth), the average of all Nicotiana species in this study (CAll), and/or the average of hummingbird-pollinated species (CHummingbird). 3. In mixed arrays, hawkmoths preferred CHawkmoth over CAll flowers, but only when shapes were not standardized for surface area. In homogeneous arrays, hawkmoths emptied more flowers with CHawkmoth shapes, but performance did not differ when shapes were standardized by surface area. However, hawkmoths visited fewer CHummingbird flowers than other shapes when surface area was standardized. 4. Our study shows that hawkmoth behaviour can be affected by differences in corolla shape, but that floral size may be more important than true shape differences in floral discrimination by hawkmoths.