Integrative taxonomic analysis to reveal the species status of Bombus flavidus, combining COI and nuclear sequencing, wing morphometrics and secretions used for mate attraction as well as patterns of color polymorphism

Bumble bees, due to their morphological monotony and color diversity, have
presented difficulties with species delimitation. Recent bumble bee
declines have made it ever more imperative to resolve the status of
species to address conservation concerns. Some of the taxa found to be
most threatened are the often-rare socially parasitic bumble bees, which
have additional trophic requirements. Among the socially parasitic bumble
bees, Bombus flavidus Eversmann has contentious species status. While
multiple separate species allied with Bombus flavidus have been suggested,
until recently, recognition of two species, a Nearctic Bombus fernaldae
(Franklin) and Palearctic B. flavidus, was favoured. Limited genetic data,
however, suggested that even these could be a single widespread species,
B. flavidus. We addressed the species status of this lineage using an
integrative taxonomic approach, combining COI and nuclear sequencing, wing
morphometrics and secretions used for mate attraction. We also explore
patterns of color polymorphism that have previously confounded taxonomy in
this lineage. Our results support the conspecific status of Bombus
fernaldae and Bombus flavidus, however, sampling specimens from across the
range of these two taxa revealed a distinct population within this broader
species confined to eastern North America. This makes the distribution of
the social parasite B. flavidus the broadest of any bumble bee, broader
than the known distribution of any non-parasitic bumble bee species.
Analysis of color phenotypes revealed that color polymorphisms are
retained across the range of the species, but may be influenced by local
mimicry complexes. Following these results, Bombus flavidus Eversmann,
1852 is synonymized with Bombus fernaldae (Franklin, 1911) syn. nov. and a
subspecific status, Bombus flavidus appalachiensis ssp. nov., is assigned
to the distinct lineage ranging from the Appalachians to the eastern
boreal regions of the United States and far southeastern Canada.