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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

Citation

Lhomme, Patrick et al. (2021), 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 , Dryad, Dataset, https://doi.org/10.5061/dryad.cvdncjt3t

Abstract

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.

Methods

The full dataset includes 9 files :

1- file "COI_phylogeny_flavidus.nex" : We constructed a COI Bayesian phylogeny of 62 specimens of both the Nearctic and Palearctic lineages of Bombus flavidus, including 59 newly sequenced individuals spanning its range, and 3 sequences from North America obtained from GenBank. We included exemplar COI sequences of B. barbutellus (n = 4), B. bohemicus (n = 4), B. norvegicus (n = 7), B. quadricolor (n = 3), B. skorikovi (n = 1), B. sylvestris (n = 6), B. vestalis (n = 4) and Bombus citrinus (n = 1) as an outgroup, using both newly sequenced individuals and sequences extracted from GenBank.

2- file "Haplotypes_flavidus.nex" : TCS haplotype network using inferred haplotypes from a subset of the COI sequences (n=65 individuals, including 61 B. flavidus s.l. and 4 B. norvegicus).

3- file "ITS_flavidus.nex" : Nuclear Internal Transcribed Spacer (ITS) gene sequenced on 10 individuals of Bombus flavidus, and 2 outgroups B. skorikovi and B. norvegicus.

4- file "PEPCK_flavidus.nex" : Sequence data for the PEPCK gene including 13 individuals of Bombus flavidus, and the two closest relatives as outgroups, B. skorikovi and B. norvegicus, using sequences for these available on Genbank.

5- file "CLGS_matrix_flavidus.xslx" : Matrix showing chemical composition of the cephalic labial gland secretions (CLGS) of males of Bombus flavidus. We extracted CLGS of 23 specimens of the Nearctic lineage from Alaska (n = 4), Yukon (n = 5), Wyoming (n = 1) and Pennsylvania (n = 13) and 11 specimens of the Palearctic lineage from Siberia (n = 8) and Sweden (n = 3).

6- file "wing_morpho_file1_flavidus.TPS" : Digitization of the 18 homologous landmarks on the veins and cells of the bumble bee wings if Bombus flavidus males with 2D Cartesian coordinates. Geometric morphometric analysis of wing venation includes 103 total male specimens, 94 males of the Nearctic lineage from Oregon (n = 78), Alaska (n = 2), Pennsylvania (n = 12) and Maine (n = 2) and 9 specimens of the Palearctic lineage from Scandinavia (n = 5) and Russia (n = 4).

7- file "wing_morpho_file2_list_name_specimens.txt" : List of the species names of the 103 individuals used in the geometric morphometric analysis.

8 - file "wing_morpho_file3_list_location_specimen.txt" : List of the location of the 103 individuals used in the geometric morphometric analysis.

9- file "Color_pattern_oregon_flavidus.xslx" : Quantification of color pattern differences of Bombus flavidus across Oregon (77 males collected from 16 different localities across Oregon). Each specimen had their color pattern recorded for the head, dorsal thorax, pleuron (lateral thorax), and abdomen. The color patterns were partitioned into 68 total squares for each individual. Each square was given a score representing the color percentage of the pile (black, yellow or orange). The percentages of each color were summed, and each individual was given a total body pile percent black, yellow and orange.

Funding

National Science Foundation, Award: CAREER DEB-1453473

Fonds De La Recherche Scientifique - FNRS

Vetenskapsrådet, Award: 2018-06238