Bombus kluanensis Williams & Cannings, 2019

Williams, Paul H., Berezin, Mikhail V., Cannings, Sydney G., Cederberg, Björn, Ødegaard, Frode, Rasmussen, Claus, Richardson, Leif L., Rykken, Jessica, Sheffield, Cory S., Thanoosing, Chawatat & Byvaltsev, Alexandr M., 2019, The arctic and alpine bumblebees of the subgenus Alpinobombus revised from integrative assessment of species’ gene coalescents and morphology (Hymenoptera, Apidae, Bombus), Zootaxa 4625 (1), pp. 1-68 : 39-42

7. Bombus kluanensis Williams & Cannings

( Figs. 10 , 104‒115 , 135 , 149 )

[ Megabombus (M.<egabombus>) strenuus (Cresson) ; Milliron 1973:110, misidentification.]

[unnamed Williams et al. 2015: 3]

Bombus (Alpinobombus) kluanensis Williams & Cannings in Williams et al. 2016:5 , type-locality citation ‘Outpost Mtn’. Holotype queen (#16) by original designation, NHMUK examined PW, ‘ Outpost Mtn’ (Yukon, Canada).

Taxonomy and variation. Bombus kluanensis has long been considered part of B. neoboreus but was recognized as a separate species based on evidence of a species coalescent in the COI gene and differences in the PEPCK gene as well as from differences in morphology ( Williams et al. 2015; Williams, Cannings, et al. 2016). Support from bGMYC analysis for separation of B. kluanensis , B. natvigi , and B. hyperboreus , was not as high as for the other species of Alpinobombus ( Williams et al. 2015), but B. kluanensis is easily distinguished from B. natvigi and B. hyperboreus by its social behaviour with abundant workers.

Bombus kluanensis was first collected in 1913 by A. Pattison and H. Lambart as two queens from the Klutlan Glacier (Yukon), which are now in the CNC (#2305, 2306). These specimens were included in Milliron’s review of the western hemisphere bumblebee fauna ( Milliron 1973) as part of B. strenuus Cresson (a junior secondary homonym in Bombus of Apis strenuus Harris ), the name used by Milliron (1973) for B. neoboreus . According to labels on the two specimens, both were also identified by R.B. Miller in 1987 as ‘ B. strenuus Cresson’ (see the comments on B. neoboreus ).

In 1971 and 1972, L.W. Macior collected a series of 18 queen and 222 worker specimens of B. kluanensis from Kluane (Yukon), which are now in the NMNH collection (#4409‒4454, 4457‒4468, 4473, 4475‒4507, 4509‒4518, 4530‒4554, 4556‒4613, 4615‒4621, 4625‒4628, 4637‒4661, 4664, 4666, 4670‒4675, 4681‒4684, 4686, 4689, 4691‒4692, 4696‒4697, 4700). These specimens were not included by Milliron (1973). According to labels on these specimens, they were again identified by R.B. Miller in 1986 as ‘ B. strenuus Cresson’ (= B. neoboreus ). The Kluane specimens were not examined by one of us (PW) until 2015.

Bombus kluanensis was first recognized as different from B. neoboreus by one of us (PW) from the COI barcodes of two specimens collected by SC in the Saint Elias Mountains of the Yukon during 2010 (#16, 17). These barcodes were later matched with others for specimens from Alaska (#4392‒4394). In a subsequent guide to North American bumblebees, Williams et al. (2014:105) described this observation as ‘Evidence from DNA barcodes appears to show that this species [then B. neoboreus s. l.] is not a single natural group (i.e., it is paraphyletic [when including B. kluanensis ]) without including B. hyperboreus [s. l., including B. natvigi ]’.

Six specimens collected in 2010‒2016 (#16, 17, 4392‒4394, 4870: geographical distribution mapped in Fig. 10 : green spots) were sequenced for COI barcodes and found to differ from B. neoboreus at 18 COI base positions and at three PEPCK base positions ( Williams et al. 2015; Williams, Cannings, et al. 2016). These specimens were described under the name B. kluanensis (holotype specimen #16, Fig. 107 ), along with many of the specimens col- lected earlier that had not previously been recognized as a separate species. Females of B. kluanensis identified from COI have the oculo-malar area (cheek) longer (1.31‒1.40 times longer than the breadth of the mandible at its base) than in B. neoboreus (1.12‒1.21 times longer than broad) as reported by Williams et al. (2016). Compared to the pale colour pattern of B. neoboreus (colour pattern strenuus ), for B. kluanensis females have the upper two thirds of the side of the thorax is yellow but with few or many black hairs intermixed, T3 is yellow but often with black hairs intermixed anteriorly (whereas both of these areas have few black hairs in many B. neoboreus ), and T4‒6 are usually entirely black ( Figs. 107‒109 ), rarely with many orange hairs on T5‒6 (e.g. L. Macior specimens in Figs. 105‒106 ) (T5‒6 usually have at least a few orange hairs in B. neoboreus : Figs. 90, 92‒93 ). The first worker recognised of B. kluanensis (#17) has the hair of T6 predominantly orange. Compared to the dark colour pattern of B. neoboreus ( neoboreus s. str.), for B. kluanensis the scutellum always has a broad yellow band (Williams, Cannings, et al. 2016). Two older females (L. Macior specimens in Figs. 110‒111 ), tentatively associated with B. kluanensis , have T3 and the side of the thorax almost entirely black, resembling B. natvigi . For an analysis of the principal aspects of the colour polymorphism see Williams et al. (2015).

Another 15 specimens collected in 2015‒2017, (#4849‒4855, 4869, 4872, 4873, 4979‒4984: distribution mapped in Fig. 10 : red spots) that appeared from morphology to be B. kluanensis were barcoded but found to differ from the earlier sequences of B. kluanensis s. str. at 10 COI base positions. This is sufficient for the PTP analysis to show that they might represent a separate candidate species ( Fig. 9 ), which is labelled here ‘unnamed2’.

Morphological and colour characters in the keys distinguish all species of Alpinobombus but do not distinguish between individuals with the two COI alleles. Furthermore, differences in 16S distinguish among all species of Alpinobombus but do not distinguish between individuals with the two COI alleles, B. kluanensis s. str. and ‘unnamed2’ (see the Results).

The most likely explanation is paralogy in COI ( Figs. 9 , 11 ) with incomplete lineage sorting and mitochondrial heteroplasmy (see the Results). In our data, B. kluanensis s. str. and ‘unnamed2’ uniquely within Alpinobombus show two gel bands and one individual (#4850) appears to have yielded both the kluanensis s. str. (as sequence NHM-CT-4850) and the ‘unnamed2’ (as sequence CCDB-25141-A05) alleles. The geographical distributions of the two alleles are broadly coincident, showing no obvious pattern of geographical segregation ( Fig. 10 ). Consequently, until more information is available, we regard ‘unnamed2’ as likely to be conspecific with B. kluanensis s. l. ( Fig. 13 ). Further investigation of this taxon is needed.

Description of the male. Morphology. Body length 16‒20 mm. Hair (pubescence) moderately long and even, wings clear. Mandible with the posterior fringe (‘beard’) unusually sparse, the outer surface of the mandible nearly covered with an extremely dense thick brush of moderately long, plumose, pale orange hair (which may appear dark if matted) forming a pronounced thick dense rounded pad extending from the basal mandibular articulations to just short of the apical mandibular teeth ( Fig. 149 : it is unknown whether this unique structure has a special function). Oculo-malar area long, 2.1× longer (length measured between the ventral edge of the compound eye and the edge of the malar area at the articulation of the mandible midway between the mandibular condyles) than the breadth of the mandible at its base (breadth between and including the mandibular condyles). Eye similar in relative size and shape to the eye of any female bumblebee. Antenna of medium length, the flagellum 3× longer than the scape. Genitalia ( Fig. 135 ) with the gonostylus inner (medial) edge between the anterior and posterior inner corners nearly straight dorsally, ventral to the submarginal groove with three broad shallow inner (medial) lamellate projections, the inner corners projecting slightly; volsella in ventral view broad in its mid section, narrowing gradually in its posterior section to just anterior to the inner process; penis-valve head on its outer edge proximal to the apex by a distance approximately equal to the breadth of the penis-valve head without a tooth. Colour pattern of the hair ( Figs. 112‒115 ). Hair of the body predominantly black. Head ventral to the antennal base with a large patch of yellow with black hairs intermixed; top of the head posterior to the ocelli with a large patch of yellow. Thoracic dorsum with broad anterior and posterior yellow bands, each less broad than the black band between the wing bases (with some yellow hairs intermixed), some black hairs intermixed posteriorly on the scutellum; side of the thorax with black and yellow hairs intermixed. Foreleg and midleg with pale hairs posteriorly; hind femur ventrally with pale hairs, tibia and tarsus with long fringing hairs pale orange. Metasomal T1‒3 yellow ( Fig. 112 ), T3 anteriorly often with many black hairs intermixed ( Fig. 113‒114 ), predominating on T3 anteriorly in one individual ( Fig. 115 ); T4 black sometimes with yellow hairs intermixed in the posterior lateral corners; T5‒7 black with a few hairs laterally with pale tips.

Material examined. 30 queens 244 workers 8 males (plus 3 females with caste undetermined), from Canada and the USA ( Fig. 104 : CNC HUM NHMUK NMNH PW RBCM RSKM UAM YPM), with 22 specimens barcoded.

Habitat and distribution. Flower-rich alpine tundra and subalpine meadows of the St Elias Mountains near Kluane in the Yukon and in the Denali National Park in the Alaska Range of Alaska ( Figs. 10 , 104 ).

Food plants. Unknown.

Behaviour. Unknown.

Conservation status. Unassessed.

Figures

FIGURE 9. Estimate of the metric gene tree for the 54 longest unique COI-barcode alleles of the subgenus Alpinobombus from MrBayes combined with the Bayesian Poisson-tree-process (PTP) solution with the highest support with spots showing the nodes with the strongest support as coalescents for candidate species (outgroup B. ignitus not shown). Values above the nodes are Bayesian posterior probabilities showing branch support for groups; values below the nodes are PTP Bayesian support values that all daughter alleles are parts of a single species (probabilities within candidate species are all ≤ 0.44). The scale bar is calibrated in substitutions per nucleotide site. Each unique allele is represented by one of the longest available sample sequences, labelled with: the sequence length in number of nucleotides, a taxon name or name describing an unpublished colour pattern, and then a code that consists of a specimen identifier (AL#n) from the project database and (after the hyphen) a sample identifier from BOLD or GenBank, followed with its geographic origin (for simplicity Greenland is included without Denmark).

FIGURE 10. Map of the entire global distribution of records of B. kluanensis s. l.. Grey crosses are records for any Alpinobombus species; black crosses are records of B. neoboreus; overlayed with small white spots for specimens of B. kluanensis s. l.; large green spots for sequenced samples with the kluanensis s. str. alleles (collected 2010‒2016); small red spots for sequenced samples with the ‘unnamed2’ allele (collected 2015‒2017). Relief map with hill shading, with a Polar projection, and with the Arctic Circle and the USA (Alaska) / Canada (Yukon) international boundary shown as grey lines. North pointer and scale bar below, with an inset that shows the location of the detailed area of the global map. Image created in ArcGIS using World_Shad- ed_Relief basemap which is Copyright: © 2014 Esri.

FIGURES 104‒115. 104: Bombus kluanensis global distribution (as for Fig. 15). 105‒115 colour patterns (as for Figs. 16‒21): 105 (#4473) Canada-Yukon; 106 (#4689) Canada-Yukon; 107 (#16) Canada-Yukon; 108 (#4393) USA-Alaska; 109 (#4466) Canada-Yukon; 110 (#4700) Canada-Yukon; 111 (#3130) Canada-Yukon; 112 (#4876) Canada-Yukon; 113 (#4882) Canada- Yukon; 114 (#4852) Canada-Yukon; 115 (#4881) Canada-Yukon.

FIGURES 129‒137. Morphology of the male genitalia for species of the subgenus Alpinobombus from the dorsal aspect, anterior to the left of the image, posterior to the right: 129 B. alpinus (#3824); 130 B pyrrhopygus (#3833); 131 B. polaris (#73); 132 B. balteatus (#3843); 133 B. kirbiellus (#3768); 134 B. neoboreus (#4387); 135 B. kluanensis (#4876); 136 B. natvigi (#81); 137 B. hyperboreus (#3821).

FIGURES 148‒149. Anterior / left lateral aspect of the lower part of the clypeus, the labrum, and the mandibles of males of: (148) B. neoboreus (#4867), showing the small orange hair patches at the base of the mandibles and the long dense posterior fringing black beard; (149) B. kluanensis (#4876), showing the large dense orange hair pads on the mandibles and the sparse orange hairs in the posterior fringing beard.

FIGURES 89‒103. 89: Bombus neoboreus global distribution (as for Fig. 15). 90‒103 colour patterns (as for Figs. 16‒21): 90 (#68) USA-Alaska; 91 (#4706) Canada-Nunavut; 92 (#3816) Canada-Yukon; 93 (#3819) USA-Alaska; 94 (#2055) Canada-Nunavut; 95 (#2058) Canada-Nunavut; 96 (#2071) Canada-Nunavut; 97 (#2051) Canada-Nunavut; 98 (#4406) Canada-Nunavut; 99 (#90) Canada-Nunavut; 100 (#92) Canada-Nunavut; 101 (#93) Canada-Yukon; 102 (#3762) Canada-Nunavut; 103 (#91) Canada-Nunavut.

FIGURES 11‒13. 11: gene trees for COI; 12: gene trees for 16S; and 13: species trees from *BEAST analysis of data from Thanoosing (2017) displayed using Densitree. Each plot shows the background density of trees from samples of 10,000 Bayesian trees, with the summary ‘root canal’ tree superimposed as a thick line, and the branches exclusively linking samples of B. kluanensis s. l. (#4850, 4869, 4870, 4873) traced in red.