Crematogaster larreae, 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 : 917-918

CREMATOGASTER LARREAE BUREN, 1968 , STAT. REV.

( FIG. 22 )

Crematogaster larreae Buren, 1968: 117 . Holotype male, Franklin Mts. , El Paso, Texas (W. F. Buren) (LACM) (examined).

Junior synonym of C. depilis: Morgan & Mackay, 2017: 155 ; here overturned.

Worker measurements (N = 5): HW 0.74–1.05, HL 0.71– 0.99, SL 0.59–0.78, WL 0.80–1.09, MtFL 0.63–0.87, MSC 0, A4SC 0, PP-SL/HW 0.10–0.13, CI 1.00–1.06, OI 0.27–0.31, SI 0.74–0.80, MtFL/HW 0.83–0.85, SPL/ HW 0.19–0.23, SPTD/HW 0.48–0.53.

Discussion: Crematogaster larreae was described by Buren (1968) as a ‘cryptic’ species closely related to and sympatric with C. depilis , having distinctive queens and males but workers that are very similar to those of C. depilis . The primary difference between the workers of the two species is their colour: C. larreae workers have the head and mesosoma dark brown and the gaster brownish-black, while in C. depilis the head and mesosoma vary from yellowish-brown to reddishbrown (the head may be darker than the mesosoma), and the gaster is medium to dark brown. However, this distinction is tenous and difficult to ascertain in older, faded specimens. Buren (1968) also provided evidence of differences in biology, with C. larreae apparently confined to nesting at the base of creosote bush ( Larrea tridentata ), in contrast to the generalized ground-nesting habits of C. depilis . Because they could not distinguish the workers of these two forms, Mackay & Morgan (2017) synonymized C. larreae under C. depilis , while making no comment about the male and queen differences. We have sequenced sympatric samples taken in Chihuahuan desert near Portal, Arizona, corresponding to the C. depilis colour phenotype (PSW14684) and the C. larreae colour phenotype (PSW15960 and PSW16636), and we find that they are positioned in different parts of the UCE phylogeny ( Fig. 1 ). The C. larreae -like samples are sister to C. mutans, while the C. depilis - like sample clusters with other C. depilis populations from New Mexico, Arizona and California. Thus we have provisional evidence that there are indeed two species, with C. larreae actually being more closely related to C. mutans (with which it is allopatric) than to C. depilis . On the basis of univariate observations and bivariate plots we have been unable to discover diagnostic morphometric differences between the workers of C. depilis and C. larreae , but it is possible that a more detailed, multivariate analysis would permit discrimination of the workers of these two species. This was found to be effective, for example, to separate two closely similar sister-species in Europe, C. scutellaris and C. schmidti (Mayr, 1853) that also differ subtly in colour ( Seifert, 2018).

Distribution and biology: Crematogaster larreae was recorded by Buren (1968) from desert localities in west Texas, Arizona and California, nesting in the lower stems and roots of Larrea divaricata . The one nest series that we have collected (PSW15960) was in a similar situation in south-eastern Arizona. Buren (1968) further noted that C. larreae was often absent from localities with Larrea , and he suggested that competition with other desert-dwelling ants may restrict it to harsher, rockier sites. It is also interesting to note that the queens and males of C. larreae are smaller and shinier than those of C. depilis , suggesting perhaps an unusual mode of colony foundation.

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 19–24. Crematogaster workers, showing lateral view of body (A), full-face view of head (B) and dorsal view of body (C). 19, C. mutans worker (CASENT0922736); 20, C. colei (CASENT0922726); 21, C. detecta holotype (CASENT0863461); 22, C. larreae paratype (CASENT0005943); 23, C. depilis (CASENT0005668); 24, C. californica lectotype (CASENT0923319). Images courtesy of AntWeb (www.antweb.org); photographers Wade Lee (19, 20), Zachary Griebenow (21), April Nobile (22, 23), Michele Esposito (24).