SPECIES DELIMITATION AND THE EVOLUTION OF HIGHLY VARIABLE MORPHOLOGICAL TRAITS IN THE HOLARCTIC SOCIALLY PARASITIC BUMBLEBEE, BOMBUS FLAVIDUS

Open Access
Author:
Williams, Sarah Danielle
Area of Honors:
Biology
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Heather M Hines, Thesis Supervisor
  • James Harold Marden, Honors Advisor
Keywords:
  • bombus flavidus
  • coi
  • species delimitation
  • psithyrus
  • bombus fernaldae
Abstract:
Bombus flavidus is a socially parasitic bumble bee with contentious species status. Multiple separate species within Bombus flavidus have been suggested, both on local and global scales. Until recently recognition of a Nearctic B. fernaldae and Palearctic B. flavidus was favored, but limited genetic data suggested that even these could be a single widespread species, B. flavidus. A combination of COI sequencing, color pattern, wing morphometric, and genitalia morphology analysis were used to resolve the species status of this lineage. In an initial analysis, male Bombus flavidus from Oregon, U.S.A. were determined to be part of one species. These individuals have high polymorphism in color but exhibit darker phenotypes in the darker Pacific mimicry zone. A broader analysis including Bombus flavidus specimens from Europe and Russia (“Old World” specimens) and North America (“New World” Bombus fernaldae), revealed that B. fernaldae is a distinct lineage, either a species or subspecies. However, B. fernaldae is not broadly Nearctic, but rather confined to the eastern Appalachian and boreal regions of the United States and far southeastern Canada, whereas B. flavidus occurs throughout the western U.S., Canada, and the Old World, a distribution broader than that achieved for any host bumble bee species. Analysis of phenotype data revealed that color polymorphisms are retained across the B. flavidus/fernaldae range and genitalic morphology is highly variable compared to other species.