Pseudomyrmex comitator

Pseudomyrmex comitator is an apparent workerless social parasite of Pseudomyrmex cognatus, and is currently known only from two adjacent sites in high-elevation forest (1,520 m) of Chiapas, Mexico. The holotype was collected by Jack Longino in a nest of P. cognatus that contained workers, alate males, alate queens, and brood (larvae, prepupae) of the presumed host. Only a single dealate queen of P. comitator was found in the nest. The paratype queen was encountered as a stray on the ground, in a nearby locality.

Identification
Small species (see HW, HL, and LHT measurements), with elongate head (CI 0.77–0.80); upper surface of mandible finely reticulate with scattered punctures, lacking striae; eyes relatively short (REL 0.40–0.42, REL2 0.51–0.54); frontal carinae separated by slightly less than basal scape width; petiole stout and short, the height and width of petiole about 0.8× the length (less so in the paratype); in profile, petiole with flat to convex anterodorsal face, ascending to summit in posterior quarter of node, then rounding into more steeply descending posterior face; profemur slender; hind leg relatively short (LHT/HL 0.69). Head sublucid, densely punctulate-coriarious. Standing pilosity sparse and short on most of body (MSC 4–7). Dark brown to brownish-black, head and gaster darker than rest of body.

This species, known only from two dealate queens, bears some resemblance to Pseudomyrmex cognatus, but differs in ways that suggest it represents a workerless inquiline (see also notes on Distribution and Biology below). The P. comitator queens are notably smaller than those of P. cognatus (HW 0.77–0.81, HL 1.00–1.01, vs HW 0.99–1.11, HL 1.28–1.42 in queens of P. cognatus), lack striae on the mandibles, have reduced mesosomal pilosity (MSC 4–7 vs 15–22 in P. cognatus queens), and possess an oddly swollen and foreshortened petiole (PLI 0.67–0.83, vs 0.45–0.53 in P. cognatus queens) (Figs. 8 and 9). The two specimens of P. comitator do not show the same degree of modification of the petiole (compare PLI and PWI values), with the holotype being more extreme, indicating some instability in the expression of this character. Both individuals of P. comitator were sequenced; they are sister taxa in our UCE tree and embedded phylogenetically within the putative host species (Fig. 1). They are more closely related to P. cognatus populations from Honduras and Nicaragua, however, than to samples from Chiapas.

Distribution based on Regional Taxon Lists
Neotropical Region: Mexico.

Nomenclature

 * ''. Pseudomyrmex comitator Ward & Branstetter, 2022: 21, figs. 9, 24 (dq.) MEXICO (Chiapas).

Type Material

 * Holotype dealate queen, MEXICO Chiapas: 29 km E La Trinitaria, 1,520 m, 16° 06′ N 91° 46′ W, 21 Jul 2007, ex nest of P. cognatus in dead stick, pine oak scrubby forest, J. Longino JTL6094 (UNAM) (JTLC000010310).
 * Paratype dealate queen, MEXICO Chiapas: Lagos de Montebello, 1,520 m, 16° 08′ N 91° 44′ W, 21 Jul 2007, on ground, pine oak Liquidambar forest, J. Longino JTL6093-s (UCDC) (JTLC000010349).