Phylogeny and population genetic analyses reveals cryptic speciation in the Bombus fervidus species complex (Hymenoptera: Apidae)

Abstract

Bumble bees (Bombus Latrielle) are significant pollinators of flowering plants due to their large body size, abundant setae, and generalist foraging strategies. However, shared setal coloration patterns among closely and distantly related bumble bee species makes identification notoriously difficult. The advent of molecular genetic techniques has increased our understanding of bumble bee evolution and taxonomy, and enables effective conservation policy and management. Individuals belonging to the North American Bombus fervidus species-complex (SC) are homogenous in body structure but exhibit significant body color phenotype variation across their geographic distribution. Given the uncertainty of the genealogical boundaries within the SC, some authors have synonymized all members of the B. fervidus SC within a single taxon, while others propose an alternative two taxa hypothesis. Operating under the phylogenetic species concept, our analysis supports the hypothesis that there are two independent lineages of bumble bees within the B. fervidus SC. With the current evidence, however, it is not possible to assign valid names to either of them, because both lineages include the color phenotypes found in the original species descriptions of B. fervidus and B. californicus. Cryptic speciation does not seem to be the product of Müllerian mimicry between the clades, because diverging coloration patterns are observed when the distribution of the clades overlaps. Furthermore, within each lineage there is evidence for strong population differentiation that is correlated with geographic distribution rather than color phenotype. In our study, we demonstrate the importance of obtaining a broad sample of multiple populations when conducting lower-level phylogenetic analyses. In addition to improving our knowledge of bumble bee diversification patterns, characterizing the evolutionary history of these pollinators provides the foundation needed to guide contemporary conservation assessments and management strategies.

Substantial genetic divergence and lack of recent gene flow support cryptic speciation in a colour polymorphic bumble bee (Bombus bifarius) species complex

“…Some species historically described by discrete colour differences have been revealed to be conspecific, as discrete morphologies can be generated from diallelic Mendelian traits (Owen & Plowright, ; Rasmont et al ., ; De Meulemeester et al ., ). Failure to fully sort ancestral colour polymorphisms by species also has led to false inferences of species boundaries (Hines, ; Carolan et al ., ; Koch et al ., ; Williams et al ., ). In this instance, bifarius s.s. is a monomorphic red‐banded bee species and nearcticus is a polymorphic species that follows a continuum of variation from black to red from west to east (excepting island populations).…”

“…By contrast, coloration of thoracic and abdominal setae can be highly variable, leading to a historical focus on colour traits for species diagnosis. Colour patterns, however, can be poor traits for diagnosis in bumblebees (Carolan et al ., ; Hines & Williams, ; Koch et al ., ). One of the major reasons for this colour variation is Müllerian mimicry, which has driven many Bombus species towards nearly identical colour patterns within a geographical region, while promoting diverse colour forms within species across their distributions (Williams, ).…”

“…One of the major reasons for this colour variation is Müllerian mimicry, which has driven many Bombus species towards nearly identical colour patterns within a geographical region, while promoting diverse colour forms within species across their distributions (Williams, ). Such high variation and convergence, the general unreliability of colour traits, and the lack of morphological characters on which to base species decisions has led to many cases of taxonomic misclassification (Ellis et al ., ; Bertsch, ; Koch et al ., ), contributing to bumble bees being one of the most highly synonymized lineages (Williams, ).…”

Bombus (Pyrobombus) johanseni Sladen, 1919, a valid North American bumble bee species, with a new synonymy and comparisons to other “red-banded” bumble bee species in North America (Hymenoptera, Apidae, Bombini)

“…vancouverensis nearcticus Handlirsch, 1888 were recognized as molecularly dis-tinct from B. bifarius Cresson, 1878(Ghisbain et al 2020; B. sylvicola Kirby, 1837 was recognized as a subspecies of the Holarctic B. lapponicus (Fabricius, 1793); and a new species of Pyrobombus with close affinities to B. lapponicus, B. interacti Martinet, Brasero & Rasmont, 2019 was described from Alaska (Martinet et al 2019). At this point, 48 species of bumble bee are now recognized in North America north of Mexico, though the taxonomic status of some species is still unresolved (e.g., Yanega 2013;Koch et al 2018).…”

An integrative approach to delimit species in the Eulaema cingulata and Eulaema pseudocingulata pair (Hymenoptera: Apidae) using morphometric and molecular evidence

“…Variation is broadly present in bees. Bumble bees, for example, are known for presenting high variability in its coloration pattern (e. g. Carolan et al, 2012;Huang et al, 2015;Koch et al, 2018). Color variation in Eucerini bees was reported by Grando et al, (2018) that found two distinct color patterns in sympatric populations of Melissodes nigroaenea in Brazil.…”