Genes Suggest Ancestral Colour Polymorphisms Are Shared across Morphologically Cryptic Species in Arctic Bumblebees

Abstract

Our grasp of biodiversity is fine-tuned through the process of revisionary taxonomy. If species do exist in nature and can be discovered with available techniques, then we expect these revisions to converge on broadly shared interpretations of species. But for the primarily arctic bumblebees of the subgenus Alpinobombus of the genus Bombus, revisions by some of the most experienced specialists are unusual for bumblebees in that they have all reached different conclusions on the number of species present. Recent revisions based on skeletal morphology have concluded that there are from four to six species, while variation in colour pattern of the hair raised questions as to whether at least seven species might be present. Even more species are supported if we accept the recent move away from viewing species as morphotypes to viewing them instead as evolutionarily independent lineages (EILs) using data from genes. EILs are recognised here in practice from the gene coalescents that provide direct evidence for their evolutionary independence. We show from fitting both general mixed Yule/coalescent (GMYC) models and Poisson-tree-process (PTP) models to data for the mitochondrial COI gene that there is support for nine species in the subgenus Alpinobombus. Examination of the more slowly evolving nuclear PEPCK gene shows further support for a previously unrecognised taxon as a new species in northwestern North America. The three pairs of the most morphologically similar sister species are separated allopatrically and prevented from interbreeding by oceans. We also find that most of the species show multiple shared colour patterns, giving the appearance of mimicry among parts of the different species. However, reconstructing ancestral colour-pattern states shows that speciation is likely to have cut across widespread ancestral polymorphisms, without or largely without convergence. In the particular case of Alpinobombus, morphological, colour-pattern, and genetic groups show little agreement, which may help to explain the lack of agreement among previous taxonomic revisions.

Site fidelity by bees drives pollination facilitation in sequentially blooming plant species

“…We follow the plant nomenclature in Hartman and Nelson () and bee nomenclature in Williams et al. ().…”

“…During this study, bees foraged mainly for nectar. We follow the plant nomenclature in Hartman and Nelson (2001) and bee nomenclature in Williams et al (2014Williams et al ( , 2015.…”

Adding attractive semio-chemical trait refines the taxonomy of Alpinobombus (Hymenoptera: Apidae)

“…The Alpinobombus subgenus has been the focus of systematic studies using morphological characters (e.g., color pattern) that have since been highly criticized (Bickford et al 2007;Batalha-Filho et al 2010;Carolan et al 2012;Lecocq et al 2015). Indeed, due to their morphological similarities and their circum-polar distribution (i.e., isolated populations with relict populations in southern mountain ranges), many different taxa could show doubtful taxonomic status (Løken 1973;Williams et al 2015). Several authors have examined the species of Alpinobombus , but no consensus on the number of valid species could be found (Richards 1931;Skorikov 1914;Løken 1973;Milliron 1973).…”

“…Several authors have examined the species of Alpinobombus , but no consensus on the number of valid species could be found (Richards 1931;Skorikov 1914;Løken 1973;Milliron 1973). Acknowledging the need of taxonomic revision, a recent study has used a more accurate trait than only morphological diagnose: DNA markers (Williams et al 2015 Williams et al, 2016;B. natvigi Richards, 1931;B.…”

“…Here, we propose to compare the DNA-based taxonomic conclusions on Alpinobombus to CLGS differentiation pattern in order to confirm or to reassess the taxonomic conclusions proposed by Williams et al (2015).…”