Morphological Variance in Mouthparts and Foraging Behavior in Bumblebees

Author (Your Name)

Ye Jin Lee, Colby CollegeFollow

Date of Award

2021

Document Type

Honors Thesis (Open Access)

Department

Colby College. Biology Dept.

Advisor(s)

David R. Angelini

Second Advisor

Devin O'Brien

Third Advisor

Judy Stone

Abstract

Bumblebees (Hymenoptera: Apidae: Bombus) show an incredible degree of size variation within and between species. Individuals from the same hive may vary up to 10-fold in mass. This variation allows individuals to specialize in foraging on different flowers suited to their morphology. However, as different species have different foraging behaviors, their variation in mouthparts and scaling of mouthparts to body size may have been under different kinds of stabilizing selection as they adapted to collect nectar from flowering plants over evolutionary time. Here, we examined the scaling relationships between body size and mouthpart structures, and the variation in mouthpart shape between species to determine whether there is any relationship to foraging behavior. In addition, the wings were also analyzed as a reference trait to compare the trends seen in the mouthparts to. We sampled 8 bumblebee species throughout Maine, a region of high bumblebee species diversity, biogeographic variation, and diverse land-use histories. Variation in the size and shape of mouthparts was analyzed for each species using multivariate morphometric analyses to identify species and caste differences. Landmark based geometric morphometrics was used to study the wings. Our results indicate that there is significant correlation between morphological variance in mouthparts and foraging specialization in bumblebees. Specialist bumblebees such as B.ternarius and B.terricola have shallower scaling of tongue lengths to body size and lower variation in mouthpart shape than generalist species such as B.bimaculatus, B.impatiens, and B.vagans. Overall, these patterns support the hypothesis that different bumblebee species with different pollination strategies were under different stabilizing selection to result in different mouthpart morphology.

Keywords

Bumblebees, Bombus, Morphometrics, Scaling, Evolution

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