Bombus (Alpigenobombus) angustus Chiu, 1948

Williams, Paul H., An, Jiandong, Dorji, Phurpa, Huang, Jiaxing, Jaffar, Saleem, Japoshvili, George, Narah, Jaya, Ren, Zongxin, Streinzer, Martin, Thanoosing, Chawatat, Tian, Li & Orr, Michael C., 2023, Bumblebees with big teeth: revising the subgenus Alpigenobombus with the good, the bad and the ugly of numts (Hymenoptera: Apidae), European Journal of Taxonomy 892 (1), pp. 1-65 : 47-48

11. Bombus (Alpigenobombus) angustus Chiu, 1948

Figs 104‒105

Bombus (Alpigenobombus) angustus Chiu, 1948: 59 .

Species-taxon concept and variation

Evidence for the taxon concept of the species B.angustus here provides further support for the interpretation ( Williams et al. 2022b) that this is separate from the taxon concept of the species B. breviceps ( Williams 1998) , based on: (1) our PTP analysis supports independent species-level coalescents in the COI gene ( Fig. 12 ); corroborated by (2) diagnostic morphological character states (see the keys).

The PTP and morphological results ( Fig. 12 , keys) support the interpretation that B. angustus and B. breviceps are separate species ( Williams et al. 2022b). The available COI-barcode-like sequences may all be low-divergence neonumts ( Fig. 11 ).

The female mandible of B. angustus has been imaged by Starr (1992: fig. 6a).

No substantial colour-pattern variation of B. angustus is known (Figs 104‒105). Bombus angustus , with its black with red-tailed colour pattern from Taiwan, appears to mimic the commoner local B. (Megabombus) trifasciatus Smith, 1852 ( Williams 2007: fig. 5e).

Type material

Bombus (Alpigenobombus) angustus Chiu, 1948: 59 . Holotype by original designation: ♁ Taiwan ( TARI). Photographic images examined .

Morphological diagnosis

Female

Wings very weakly clouded with brown, nearly clear, with the veins dark brown (cf. B. genalis , B. breviceps , B. grahami ), hair of medium length, oculo-malar area shorter than broad, clypeus in its central area with many small punctures (cf. B. genalis , B. grahami ); mid and hind tibiae with the exoskeleton and hair predominantly black, hair of the thoracic dorsum and T1‒3 black, T4‒6 orange-red.

Male

Examined from photographic images, also described and genitalia illustrated by Chiu (1948: fig. 1) (genitalia of the type not found by C.-F. Lee, pers. com.): wings very weakly clouded with brown, nearly clear, with the veins light brown; genitalia with the gonostylus nearly equally short on both its outer side and its inner side but with the distal lobe projecting inwards as a long broadly triangular pointed process; hair of the thoracic dorsum and T1‒3 ‘black’ (on the type specimen, which is in poor condition, hair of the thorax in part?faded to brown), T4‒7 orange-red.

Material sequenced in Fig. 12

TAIWAN • 1 ♀ (worker); Chiayi, Alishan ; [23.446° N, 120.794° E]; 14 Jul. 2020; Y. Lin leg.; GenBank seq: MZ831894; TFRI: AG#074 .

Global distribution

Taiwan endemic ( Williams et al. 2022b): PW, TARI, TFRI.

This is a rare species with few individuals recorded: Chiu (1948) lists three individuals from three localities; Starr (1992) lists 21 individuals from eight localities (mapped in Starr: fig. 7) among a total sample of 4555 Taiwanese bumblebees (<0.5%; from his map fig. 7, most B. angustus appear to be from elevations around 1000‒2000 m, although one individual in the north may be from ca 100 m).

Behaviour

Male behaviour not seen.

Figures

Figs 19–105 (see pages 28–29). Simplified diagrams for the colour patterns of the hair on the dorsum for particular female (f) and male (m) specimens of the species from Fig. 12. The dorsum is divided into regions, each of which shows only the predominant or most apparent colour for that region, using a simplified colour palette, with olive indicating a mixture of black and yellow hair, and grey indicating a mixture of black and white hair.

Fig. 12. Interpretation of filtered MrBayes estimate of phylogeny as a metric tree (outgroup B. festivus Smith, 1861, not shown) for the subgenus Alpigenobombus Skorikov, 1914, from COI-like sequences from the sequences identified in black and orange in Fig. 11 together with Bayesian Poisson-tree-process (PTP) models re-applied for assessing support for species’ gene coalescents by maximum likelihood (for the 11 most likely candidate species). The scale bar is calibrated in substitutions per nucleotide site. Sequence labels and branch colours as in Fig. 10. Numbers above nodes are the Bayesian support values that all daughter haplotypes are parts of a single species. Grey spots show likely mitochondrial-to-nuclear transfers of the low-divergence numts accepted for estimating this tree. Asterisks mark sequences used as informal proxies for the type specimens of each of the taxon names in Table 2. To the right in grey are shown the interpretations of the PTP results as candidate species using the oldest available names for the species.

Fig. 11. Re-interpretation of sequences from Fig. 10, re-drawn with the percentage of nucleotides A and T at codon position 3 (AT3%) for each sequence given after the sequence label. Sequences are classified: (a) in purple – earlier-diverging groups of sequences without unique morphology that often have lower AT3% and shorter sequences that appear to duplicate species as pseudospecies in Fig. 10 – these sequences are interpreted as older, more divergent numts; (b) red – remaining sequences with low AT3% (<95%) – these are interpreted as younger, less divergent numts; (c) orange – sequences from the red group but with the highest AT3% available for some taxa, selected to retain these taxa in the analysis; (d) grey and brown – sequences that are duplicate haplotypes for the black and orange sequences above and often shorter; (e) black – likely orthologous sequences with high AT3% (≥ 95%) and unique haplotypes.