Pseudomyrmex ferrugineus species group

Species

Notes

A detailed morphological diagnosis of the P. ferrugineus group, based on the species then known, was given in Ward (1993: 133). Now that two additional species have been discovered to be part of the same clade, a revised diagnosis is needed. This primarily affects the worker and queen castes, where allowance must be made for morphological differences between the mutualists (inhabiting Vachellia domatia) and generalists (nesting in dead twigs). The male diagnosis requires less revision, since features of the male morphology, including the genitalia, are evidently less variable across different life histories.

The P. ferrugineus group provides a striking example of convergent evolution of worker morphology among two separate lineages of ant-plant specialists (Ward & Branstetter 2017). The presence of more generalized (non-mutualist) species in the P. ferrugineus group necessitates a more nuanced worker-based diagnosis of the clade. The male diagnosis is less affected because features of the males, including genitalia, are shared among all species, both generalists and specialists. In effect, the male morphology better reflects phylogenetic relationships than worker morphology.

Identification

Key to Pseudomyrmex ferrugineus group species

Worker diagnosis. Medium sized species (HW 0.74–1.28, HL 0.86–1.42); head varying from somewhat elongate to rather broad (CI 0.75–1.05); eyes moderately elongate in non-mutualist species (REL 0.48–0.55), shorter in the mutualist acacia-ants (REL 0.39–0.50). Masticatory margin of mandible with 6, rarely 7, teeth; mesial tooth on basal margin closer to apicobasal angle than to proximal tooth. Palp formula 5,3, reduced to 4,3 in three species. Anterior margin of median clypeal lobe somewhat blunt-edged, in dorsal view convex, straight or concave, laterally rounded or with sharp angles. Frontal carinae separated by about basal scape width in most species but more closely contiguous in some (FCI 0.03–0.10), fusing anterolaterally with antennal sclerites. Profemur relatively robust in non-mutualist species (FI 0.42–0.46), more slender in mutualist acacia-ants (FI 0.35– 0.41). Pronotum laterally rounded. Metanotal groove weakly impressed in non-mutualists, well developed in mutualists. Basal and declivitous faces of propodeum moderately well differentiated and subequal in length, in profile the juncture between the two subangulate or gently rounded. Petiole relatively long (PL/HL 0.44–0.63), always much longer than high or wide (PLI 0.47–0. 71, PWI 0.46–0.75), small anteroventral tooth present; in four species anterior peduncle of petiole weakly differentiated and posterolateral corners of petiolar node not expanded (the presumed plesiomorphic condition), in other species petiole with distinct anterior peduncle and with expanded, subangulate posterolateral corners. Postpetiole broader than long, with small anteroventral tooth. Body sculpture varying from densely punctulate or punctulate-coriarious to coriarious-imbricate, the integument sublucid to opaque; dorsum of head never with extensive smooth, shiny interspaces (punctulae usually separated by their diameters or less); propodeum of some species overlain by a coarser but weak rugulo-punctate sculpture. Standing pilosity usually common, less abundant in non-mutualists (MSC 7–26) than mutualists (MSC 10–62), present on the scapes, head, mesosoma dorsum, petiole, postpetiole and gaster, absent from the extensor faces of tibiae (HTC 0, MTC 0). Appressed pubescence dense on most of body, including head and abdominal tergite IV. Color varying from light yellow- or orange-brown to black.

Queen diagnosis. Similar to worker except for caste-specific differences. Larger in size (HW 0.76–1.36, HL 1.00–1.81), head more elongate (Cl 0.60–0.88). Median clypeal lobe narrower and more protruding, anterior margin convex or straight, laterally rounded or subangulate. Profemur robust in non-mutualists (FI 0.46–0.51), more slender in mutualists (FI 0.39–0.44). Petiole and postpetiole generally more slender than in worker (PL/HL 0.57–0.74, PLI 0.43–0.63, PWI 0.47–0.67). Forewing with 2 submarginal cells (erroneously called “cubital cells” in Ward (1993)), i.e., cross-vein 2rs-m present.

Male diagnosis. Head varying from longer than broad to slightly broader than long (CI 0.82–1.11 in a sample of 73 males belonging to all species); compound eye large, prominent (REL2 0.46–0.62). Mandibles with 8+ teeth or denticles on masticatory margin. Palp formula as in females, but somewhat more variable (males with 5p4,3 commoner than in workers or queens). Surface of median clypeal lobe convex, its anterior margin subtriangular in shape (dorsal view) with sides converging medially to a rounded point. Petiole and postpetiole more slender than in workers (PLI 0.39–0.55, PWI 0.35–0.51) and simpler in shape. Posterolateral corners of sternites IV–VIII not notably protruding ventrally. Subgenital plate (sternite IX) with a conspicuous posteromedial concavity. Posterior margin of pygidium (tergite VIII) convex, directed posteroventrally. Paramere with several characteristic features (Ward 1993: 134): a finger-like, posterodorsally directed mediodorsal lobe; angulate or expanded posterodorsal extremity; and mesial dorsoventral ridge which joins the mediodorsal lobe posteriorly. Aedeagus with expanded posterodorsal corner, a medial protrusion on the posterior margin, numerous small teeth (15+) on the posterior margin, and on the outer face a raised ridge curving posterodorsally from a basal origin.

Related Pages

References

Ward, P.S. 2017. A review of the Pseudomyrmex ferrugineus and Pseudomyrmex goeldii species groups: acacia-ants and relatives (Hymenoptera: Formicidae). Zootaxa. 4227:524–542. (doi: 10.11646/zootaxa.4227.4.3).