Morphometric analysis of fossil bumble bees (Hymenoptera, Apidae, Bombini) reveals their taxonomic affinities.

Manuel Dehon,Denis Michez,Guillaume Ghisbain,Paul H Williams,Pierre Rasmont,Maxence Gérard,A Murat Aytekin,Michael S Engel

doi:10.3897/zookeys.891.36027

Abstract

Bumble bees (Bombus spp.) are a widespread corbiculate lineage (Apinae: Corbiculata: Bombini), mostly found among temperate and alpine ecosystems. Approximately 260 species have been recognized and grouped recently into a simplified system of 15 subgenera. Most of the species are nest-building and primitively eusocial. Species of Bombus have been more intensely studied than any other lineages of bees with the exception of the honey bees. However, most bumble bee fossils are poorly described and documented, making their placement relative to other Bombus uncertain. A large portion of the known and presumed bumble bee fossils were re-examined in an attempt to better understand their affinities with extant Bombini. The taxonomic affinities of fossil specimens were re-assessed based on morphological features and previous descriptions, and for 13 specimens based on geometric morphometrics of forewing shape. None of the specimens coming from Eocene and Oligocene deposits were assigned within the contemporary shape space of any subgenus of Bombus. It is shown that Calyptapis florissantensis Cockerell, 1906 (Eocene-Oligocene boundary, Florissant shale, Colorado, USA) and Oligobombus cuspidatus Antropov, 2014 (Late Eocene, Bembridge Marls) likely belong to stem-group Bombini. Bombus anacolus Zhang, 1994, B. dilectus Zhang, 1994, B. luianus Zhang, 1990 (Middle Miocene, Shanwang Formation), as well as B. vetustus Rasnitsyn & Michener, 1991 (Miocene, Botchi Formation) are considered as species inquirenda. In the Miocene, affinities of fossils with derived subgenera of Bombus s. l. increased, and some are included in the shape space of contemporary subgenera: Cullumanobombus (i.e., B. pristinus Unger, 1867, B. randeckensis Wappler & Engel, 2012, and B. trophonius Prokop, Dehon, Michez & Engel, 2017), Melanobombus (i.e., B. cerdanyensis Dehon, De Meulemeester & Engel, 2014), and Mendacibombus (i.e., B. beskonakensis (Nel & Petrulevičius, 2003), new combination), agreeing with previous estimates of diversification.

Highlights

Bumble bees (Bombini: Bombus Latreille, 1802) are a lineage of corbiculate bees (Apidae: a widespread corbiculate lineage (Apinae)) dominant in many temperate and alpine ecosystems (Williams 1998; Michener 2007)
When using the first dataset, all fossils were assigned to Apidae, to Apinae (except for the second specimen of C. florissantensis described by Cockerell (1908) and B. vetustus, both assigned to Eucerinae) and to Bombini
Oligobombus cuspidatus and both specimens of C. florissantensis were close to the shape space of contemporary Bombini, while being placed outside of contemporary Bombini and fossil Electrapini (Dataset 2, Linear Discriminant Analyses (LDA) 4)

Summary

Introduction

Bumble bees (Bombini: Bombus Latreille, 1802) are a lineage of corbiculate bees (Apidae: Apinae) dominant in many temperate and alpine ecosystems (Williams 1998; Michener 2007). The pretarsal claws are cleft, with a small arolia present, and the metatibial spurs are present (Engel 2001; Michener 1990, 2007; Engel and Rasmussen in press). Both wings have strong and complete venation (Michener 1990, 2007). Bombus s. l. display interspecific diversity in structures like male genitalia, female sting, color pattern, and mandibular shape (Engel 2001; Michener 1990, 2007)

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