Crematogaster hespera, BUREN, 1968

Ward, Philip S. & Blaimer, Bonnie B., 2022, Taxonomy in the phylogenomic era: species boundaries and phylogenetic relationships among North American ants of the Crematogaster scutellaris group (Formicidae: Hymenoptera), Zoological Journal of the Linnean Society 194, pp. 893-937 : 917

CREMATOGASTER HESPERA BUREN, 1968 , STAT. REV.

( FIG. 28 )

Crematogaster hespera Buren, 1968: 98 . Holotype worker, Phoenix , Arizona, 20 Jul 1918 (A. W. Morrill) (USNM) ( USNMENT00529501 ) (examined).

Crematogaster hespera a junior synonym of C. laeviuscula: Morgan & Mackay, 2017: 197 ; here overturned.

Worker measurements (N = 18): HW 0.82–1.16, HL 0.79–1.05, SL 0.67–0.90, WL 0.90–1.20, MtFL 0.72– 1.03, MSC 3–14, A4SC 9–26, PP-SL/HW 0.13–0.21, CI 1.04–1.11, OI 0.22–0.26, SI 0.76–0.83, MtFL/HW 0.82– 0.89, SPL/HW 0.19–0.22, SPTD/HW 0.42–0.52.

Discussion: The synonymy of C. hespera under C. laeviuscula is not supported by our phylogenomic analyses, which indicate that C. hespera is sister to C. cerasi and more distantly related to C. laeviuscula ( Fig. 1 ). Buren (1968: 99) described differences in sculpture and shape between C. hespera and C. laeviuscula as follows: ‘This form [ hespera ] may be easily distinguished from laeviuscula by the finely striate thorax, the evenly but not strongly convex profile of the promesonotum without mesonotal declivity, the less divergent, often incurved epinotal [= propodeal] spines with the little oblique impressions at base, the differently shaped postpetiole and by the fact that the larger workers do not exhibit as much allometry as in laeviuscula .’ Buren noted the apparent allopatry of the two species while at the same time identifying areas in northern Mexico and west Texas that could be investigated to determine if the two taxa overlap. We have found that larger workers of C. laeviuscula (HW> 1.00 mm) differ from those of C. hespera by the greater relative length of their propodeal spines: SPL/HW 0.23–0.27 and SPL/WL 0.22–0.25, compared to SPL/HW 0.19–0.22 and SPL/WL 0.18–0.21 in C. hespera ( Fig. 45 ). In smaller workers this distinction does not hold up. Crematogaster hespera differs from its sister-species, C. cerasi , by having a more smooth and shiny promesonotum which is, moreover, convex not flattened, in profile.

Crematogaster hespera is typically a bright, bicoloured ant with orange-brown or reddish-brown head and mesosoma and dark brown gaster, but in coastal California there is a tendency for workers to become more uniformly dusky in colour. These could be confused with workers of C. coarctata from southern California that have comparable coloration and a similarly shiny head and mesosoma (more typical C. coarctata from northern California have dense reticulate-foveolate sculpture on the head, which readily distinguishes them from shiny-headed C. hespera ). Workers of C. hespera can generally be distinguished from those of C. coarctata by their shorter legs (MtFL/HL 0.89–0.98 vs. 0.97–1.07 in C. coarctata ) and shorter scapes (SL/HL 0.79–0.89 vs. 0.87–0.96 in C. coarctata ). Measurements taken from throughout the ranges of the two species overlap slightly, but in south-central California and northern Baja California, where the two species might be confused, the differences in leg length are diagnostic (MtFL/HL 0.90–0.96 in C. hespera and 0.97–1.03 in C. coarctata ). In addition, C. hespera workers usually lack the longitudinal striae on the lower mesopleuron that are present in C. coarctata , and they have a mesosoma dorsum that is more convex in profile and without a pronounced mesonotal declivity, compared to workers of C. coarctata .

Distribution and biology: Crematogaster hespera has a wide distribution across the South-West, from Chihuahua and west Texas to California and Baja California. It is commonly found in riparian woodland; other recorded habitats include coastal scrub, maritime chaparral, sand dunes, grassland, sagebrush-riparian vegetation and mixed coniferous forest. Colonies are typically located under tree bark, in dead branches of trees and shrubs or in dead stalks of perennial plants. Although this species is predominantly arboreal, nests are sometimes found in or under fallen logs on the ground and under stones.

Figures

Figure 1. Phylogeny of the North American Crematogaster scutellaris group. Maximum likelihood phylogenetic tree estimated from the 90% taxon completeness matrix after application of spruceup trimming with a 0.98 cut-off (90%-0.98-spruceup), using a combined best tree and ultrafast bootstrap (N = 1000) search in IQ-TREE v.1.6.12 and implementing 746 partitions. The analysis was rooted using the most distantly related outgroup taxon C. cf.rogenhoferi; the long branch leading to this taxon has been shortened for space-saving purposes. All nodes have bootstrap support = 100% unless labelled otherwise. Species images courtesy of AntWeb (www.antweb.org).

Figures 25–30. Crematogaster workers, showing lateral view of body (A), full-face view of head (B) and dorsal view of body (C). 25, C. opuntiae (CASENT0922738); 26, C. marioni (CASENT0922734); 27, C. coarctata (CASENT0005667); 28, C. hespera holotype (USNMENT00529501); 29, C. browni (CASENT0922722); 30, C. emeryana (CASENT0922729). Images courtesy of AntWeb (www.antweb.org); photographers Wade Lee (25, 26, 29, 30), April Nobile (27), Michele Esposito (28).

Figures 40–47. Bivariate plots of selected worker measurements in the Crematogaster scutellaris group. 40, PP-SL (postpetiole seta length) by HW (head width) in C. browni (N = 16) and C. cerasi (N = 17); 41, ED (eye diameter) by MtFL (metafemur length) in C. californica (N = 22) and C. coarctata (N = 21); 42, MtFL (metafemur length) by HW (head width) in C. californica (N = 22), C. colei (N = 12) and C. opuntiae (N = 10); 43, MtFL (metafemur length) by HW (head width) in C. depilis (N = 15), C. detecta (N = 11) and C. larreae (N = 5); 44, MtTL (metatibia length) by HW (head width) in C. depilis (N = 15), C. detecta (N = 11) and C. larreae (N = 5); 45, SPL (propodeal spine length) by HW (head width) in workers of C. hespera (N = 18), C. laeviuscula (N = 25) and C. parapilosa (N = 15); 46, SL (scape length) by HW (head width) in C. emeryana (N = 12) and C. marioni (N = 18); 47, SPTD (propodeal spine tip distance) by HW (head width) in C. lineolata (N = 26) and C. punctulata (N = 15).