Leptomyrmex relictus

The only extant member of the genus from the New World. Its unusual distribution is paired with a preference for a xeric habitat, the dry savannah of the Brazil cerrado. This contrasts with the mesophilic habitats preferred by its Australasian congeners.

Identification
Boudinot et al. (2016) - With diagnostic characters of genus from Shattuck (1992), notably with medial hypostomal notch (synapomorphy of genus) and lacking pterostigmal appendage in male (synapomorphy of macro-Leptomyrmex). Distinguished from all Leptomyrmex by the following characters: (i) short, thick, erect setae present on the head capsule, mesosoma (legs included) and metasoma; (ii) clypeal setae comparatively more numerous; (iii) anterior clypeal margin strongly convex; (iv) lateral hypostoma weakly flanged; (v) worker with convexity subtending subapical mandibular tooth; (vi) worker petiole lateromedially narrow; (vii) worker gaster strongly lateromedially compressed; (viii) male scape elongate (SI 1.26–1.40 versus 0.19–1.05 in other Leptomyrmex); (ix) male wing with five closed cells (costal, basal, subbasal, submarginal 1, marginal 1); (x) male petiole dorsal margin concave; (xi) male petiolar spiracles situated on tubercles; (xii) several features of male genitalia (see description).

Distribution based on Regional Taxon Lists
Neotropical Region: Brazil.

Biology
Boudinot et al. (2016) - Although males of L. relictus have been collected as far back as 1956 – remaining unidentified for over half a century – workers were only recently discovered in 2013 from nest samples of Cornitermes silvestrii and in 2012 from epigaeic and arboreal pitfall traps in typical cerrado (Brazilian savannah) habitat. It is unknown whether workers are nocturnal or diurnal, but hypothetical nocturnal habits and/or their Camponotus-like habitus may account for the low encounter rate of this species. It is interesting to note that at least three of the specimens were captured in arboreal pitfall traps, suggesting that workers may forage both on the soil and in the vegetation strata. The collection of workers and brood inside termitaria suggests that L. relictus may live in association with Cornitermes silvestrii. One termite nest measuring 1.30m wide and about 40–50 cm tall inhabited by L. relictus was found in northeast Goiás state under a tree, and was also occupied by another ant species, Camponotus blandus (Smith, F.), which is known to be a facultative termite inquiline (Gallego-Ropero & Feitosa, 2014). The other termite nest with L. relictus specimens was found in southeast Tocantins state, along a trail edge. Unfortunately, no data are available on how the Leptomyrmex occupy the termitaria or if they were sharing galleries with the termites. A potential association with C. silvestrii is compelling as the termitaria of C. silvestrii are large, environmentally-stable clay mounds and may house several other ant and termite species (see Appendix S2). In addition to describing and comparing the sociometric and sociogenic patterns (Tschinkel, 1991, 2011) of L. relictus with the Australian species, future studies should test the association of the species with C. silvestrii.

A potential association with Cornitermes silvestrii is compelling as the termitaria of Co. silvestrii are large, environmentally-stable clay mounds and may house several other ant and termite species. For example, termites collected in the Goiás nest include Rhinotermitidae (Heterotermes Hagen), Serritermitidae (Serritermes serrifer [Hagen]), and Termitidae (Apicotermitinae: Grigiotermes sp.; Nasutitermitinae: Nasutitermes cf. kemneri; Syntermitinae: Curvitermes minor [Silvestri], Silvestritermes Rocha & Cancello; and Termitinae: Spinitermes robustus [Snyder]), while the nest in Tocantins contained Serritermitidae (Serritermes serrifer with alates), and Termitidae (Apicotermitinae; Syntermitinae: Silvestritermes; Nasutitermitinae: workers of Angularitermes Emerson; Termitinae: Amitermes and Spinitermes cf. robustus with a queen).

Termitaria in the structurally simple cerrado are an important ecological component as the hard, permanent nests provide shelter for a wide range of organisms and provide protection from fire regimes (Abensperg-Traun & Milewski, 1995; Joseph et al., 2013), particularly in environments where either natural or man-induced fires occur in a roughly annual frequency (Eiten, 1972), and are normally of moderate intensity (DeSouza et al., 2003). Given that the known, extant Australian Leptomyrmex are reported to occupy preformed cavities (Lucky & Ward, 2010), a permanent and protective clay shelter may have enabled L. relictus to survive regional extinction(s). Redford (1984) evaluated the ecological role displayed by Cornitermes cumulans (Kollar) termitaria, and found at least 17 termites and 10 ant species nesting in different mounds; Mathews (1977) found eight species of termites living in a rotten C. snyderi mound. Redford (1984) argued that termite nest structure and size increases the number of obligate inquilines found in the cerrado. These observations were corroborated by Gallego-Ropero et al. (2013) who recorded 61 ant species belonging to 32 genera living inside several C. cumulans nests, suggesting that those inquilines must play a fundamental role on the dynamics of this ecosystem. Indeed, termite mounds are local biodiversity hotspots in African savannah (Pringle et al., 2010), with insect abundance and biomass decreasing with the distance from the nearest termite mound.

Nomenclature

 *  relictus. Leptomyrmex relictus Boudinot, Probst et al. 2016: 663, figs. 1-5, S1, S2 (w.m.) BRAZIL.

Worker
(n=4): HL 1.53–1.66, HW 0.94–1.20, MDL 0.72–0.78, MFC 0.10–0.17, IOD 0.55–0.67, SL 3.35–3.53, EL 0.34–0.36, EW 0.22–0.28, WL 2.85–3.01, PW 0.75-0.81, HTL 4.00–4.25, HTw 0.09–0.14, HTW 0.12–0.16, PTL 0.41–0.46, PTW 0.20–0.23, GL 1.52–2.06, TL 7.04–7.77; indices: CI 0.57–0.78, SI 2.92–3.76, ESI 0.10, 0.10–0.30, OI 0.08-0.10, HTC 0.67–0.86. Note: Head left side crushed in one specimen reducing IOD; head of other specimen crushed reducing HL and increasing HW. Very thin integument. Body surface weakly sculptured, mostly very finely and densely coriarious, denser on head and mesosoma dorsa. Medium-sized among Leptomyrmex Mayr species (TL 7.04–7.77, WL 2.85-3.01, HL 1.53-1.66).

Head: Elongate (CI 0.57–0.78), oblong; sides straight in full-face view, gently narrowing anteriorly, widest at compound eyes and abruptly tapered posteriorly in direction of posterolateral corners; posterior border almost straight medially, in lateral view narrowing to neck-like constriction. Palpal formula 6,4; first maxillary palpomere half-length of second, third palpomere slightly shorter than second, fourth to sixth palpomeres subequal. Third labial palpomere slightly shorter than other palpomeres; other palpomeres subequal. Mandibular dorsa with longitudinal carina following the masticatory margin shape, from the basal insertion and slightly surpassing the masticatory margin midlength, this carina creating longitudinal canaliculi between the dorsum and inner margin of mandibles. Mandibular basal angle broadly angulated; apical mandibular tooth largest; subapical tooth smaller and subtended by convexity followed by row of finely serrate denticles; basal margin very finely serrate. Anterior clypeal margin convex; posterior clypeal margin slightly concave and depressed anterad antennal toruli. Hypostoma anterolaterally flanged; flange angulate, lamellar, weak; medial hypostoma notched. Frontal carinae narrowing posteriorly. Median longitudinal frontal impression superficial, extending from frontal carina anterior margin to slightly beyond posterior compound eye margin. Antennae elongate, slender (SI 2.98-3.76), not compressed; scape surpassing posterior head margin in full-face view by nearly 1/2 scape length; pedicel and flagellomeres subequal in length. Compound eyes situated posterad head midline; eyes convex, reaching but not surpassing lateral head margins glabrous. Mesosoma: Pronotum slender, saddle-shaped, distinctly elongated anteriorly; anterodorsal margin rounded projecting over propleurae; humeral angles ill-defined; dorsal face very weakly convex in profile view. Mesonotum dorsal profile anteriorly slightly above the pronotum level, with up to 2/3 of its length; dorsal profile feebly concave. Metanotal spiracle dorsal. Propodeal dorsum with a strongly convex anterior bulge followed by a shallow concavity; propodeal declivity predominantly flat and discretely inclined. Legs very long and slender (HTL 4–4.25), not compressed (HTC 0.67–0.86). Protibial calcar short. Meso- and metatibiae each with one simple spur.

Metasoma: Petiole wedge-shaped, posteriorly elongate; node strongly convex, dorsal face rounded in profile, highest before midlength; anterior face slightly convex in profile view, posterior and ventral faces convex in side view; in dorsal view, apex arching evenly anteroposteriorly; lateral and dorsal faces flat, sides straight; ventral margin convex near posterior third. Gaster strongly compressed lateromedially, elliptical in profile view. First gastral tergum without distinct anterior and dorsal faces; tergum tapering posterodorsally, almost linear in profile view. Second gastral spiracle situated in dorsal third of segment. Gastral sternum 5 strongly keeled medially, sternum 4 with posteromedian notch for reception of keel. Setation: Extremely fine and short pubescence densely present on virtually all of body, more dilute on gaster; somewhat dilute short pubescence present across body surfaces. Erect setae on head, mesosoma, legs, and metasoma short and coarse. Mandibular setae short to elongate, yellow; longer at apex and near the masticatory border. Anterior clypeal margin with about 10 yellowish-brown to brown setae, clypeal disc with 30–40 sparse setae. Brown to black shorter setae distributed all over the body, more abundant on ventral and frontal face of head, anterolateral portion of procoxae and gaster; scarce on mesosoma and rest of legs; setal length varies according to position; one to two pairs present on petiolar dorsum, two pairs posteroventrally. Short, bristle-like standing hairs present on posterior face of femora and tibiae.

Colouration: Body unicolourous yellowish brown; gaster entirely brown.

Male
(n=4): HL 1.25–1.30, HW 0.74–0.88, MDL 0.50–0.64, MFC 0.07–0.11, IOD 0.46–0.50, SL 1.04–1.14, LA2 0.16, LA3 0.47, EL 0.35–0.38, EW 0.28–0.31, WL 2.13–2.38, PW 0.59–0.87 [two specimens broader due to distortion], HTL 3.00–3.20, HTw 0.08–0.09, HTW 0.09–0.10, PTL 0.30–0.34, PTW 0.15–0.20, GL 1.30–1.50, TL 5.66–5.87; indices: CI 0.59–0.67, SI 1.23–1.40, SI2 1.67–1.78, ESI 0.35–0.44, OI 0.12–0.13, HTC 0.81–0.99. Integument, sculpture, and size similar to worker.

Head: Elongate (CI 0.59–0.67), head posterad eyes tapering to occiput. Head dorsoventrally broad, in profile view dorsally convex, ventral margin sublinear. Palpal formula 5,3; palps short, not reaching postgenal bridge midlength. Maxillary palpomere 1 shortest, 5 second shortest, 4 third shortest, and 2 and 3 longest and subequal. Second labial palpomere longest. Mandibles well developed, long (MDL 0.50–0.64); basal and masticatory margins curving into one another; these margins very finely serrate. Dorsal mandibular sulcus distinct, extending from mandalus to almost mandibular apex near masticatory margin. Mandalus small, concealed. Anterior clypeal margin strongly convex. Antennal toruli distant from posterior clypeal margin. Hypostoma laterally flanged, medially notched. Compound eyes globular, glabrous, situated at about head midlength. Clypeus longer than broad. Supraclypeal area obtusely triangular, anterior margin convex and slightly longer than sides. Frontal carinae strongly developed, narrowly set (MFC 0.07–0.11). Frontal carinae and medial torular arches raised well above frons in posterior view. Antennae 13-merous; scapes elongate, slightly shorter than head length (SI 1.23–1.40); pedicel short, about 1/5th to 1/6th length of antennomere 3; antennomeres 3–13 subequal in length. Ocelli small, greatest diameter less than half pedicel width.

Mesosoma: Mesosoma elongate. Mesepimeron neither expanded nor completely concealing metapleural spiracle. Mesonotum anterodorsally produced as variable cone; mesonotal dorsum evenly convex lateromedially. Parapsidal lines very faint, diverging anteriorly, not contacting transscutal line posteriorly. Scutoscutellar sulcus narrow. Mesoscutellum small, strongly convex. Upper metapleuron anteroposterior width about 1/4th dorsoventral length. Dorsal metapleural gland flange well-developed, glabrous. Propodeal spiracle small, circular. Propodeal profile convex, weakly angulate; dorsal face slightly longer than posterior face. Legs elongate and slender, femora and tibiae linear, without bends. Tibial spur formula 1s,1s.

Forewing: Costal vein present, meeting pterostigma. Pterostigma small, situated in apical half of wing. Pterostigmal appendage absent. Rsf1 and Mf1 situated slightly past half wing length; these abscissae subparallel. Rs+M and Rsf2-3 enclosing submarginal cell 1; Mf2-3 absent. 2r-rs present. 2rs-m+Mf4–6 retained, juncture with Rsf distal to 2r-rs. Marginal cell 1 closed. Rf extending distally beyond marginal cell 1. 1m-cu absent (discal cell 1 open). 1A extending for only a short way beyond cu-a, apex well basad Mf1.

Hindwing: R+Rs extending beyond 1rs-m+M. Rf extending to but not meeting costal margin. R+Rs and 1rs-m+M curving into one another. Subbasal cell about 1/6th basal cell length.

Metasoma: Petiole cylindrical, node absent; in profile view, dorsal margin weakly concave and ventral margin convex; petiole lateromedially narrow; petiolar spiracles situated on variably-developed tubercles. Gaster not reduced.

Genitalia: Pygostyles digitate, about 3 x longer than broad. Abdominal sternum IX posterior margin bilobate and medially concave; posterior lobes shallow, length from cranial apodeme to lobe apex approximately 0.2 x lobe width (estimated). Spiculum absent. Cupula dorsal and lateral surfaces extremely narrow, thread-like. Cupula ventral disc absent. Cupula anterior margins unswollen. Genital foramen extremely broad. Cupula in dorsal view with anterior margin linear. Basimere dorsomedial margins rounded, broadly curving posterolaterally to truncate posterior margins around where volsellae insert in dorsal view. Basimeral posterodorsal and posterolateral margins carinate and inflexed. Basimere dorsal posteromedial margin with a sclerotized bridge joining basimeres dorsal to aedeagus. Basimere ventromedial margin ecarinate and lacking subrectangular medial process. Basimeral-penisvalvar corium membranous, not sclerotized. Telomere in profile view lobate. Basivolsellar process and cuspis absent. Digitus very strongly falcate, with ventral margin curving dorsally before arcing apicoventrally. Digitus apicodorsal process absent; apical margin evenly rounded; ventroapical process broadly tapering to apex. Penisvalvar bridge present, fused with the basimeres (autapomorphy of the species). Valviceps ventral-to-lateral carina broadly sclerotized and bent at two angles. Setation: Pubescence as in worker, but equally dense on gaster as elsewhere. Setation as in worker, but setae on postgenal bridge and propleurae long and fine; gastral tergites lacking erect setae.

Colouration: Unicolourous; light yellow to light brownish-yellow.

Pupae
Similar to the mature conspecific worker, translucent.

Larva
(Integument partially damaged): length (through spiracles) about 4.0 mm. Body shape dolichoderoid; thirteen differentiated somites visible;. thoracic segments stout, slightly curved; body anterior region formed by the enlarged dorsal portion of the prothorax; posterior region slender and presenting a small, curved postanal projection. Integument thin, dorsal surface covered by minute papillae (= scobinations) isolated in short rows, denser on prothorax. Head subheptagonal, ventrally placed on body anterior end; lateral margins broadly rounded. Antennae relatively large, elliptical. Labrum subtrapezoidal. Hypopharynx spinulose, spinules arranged longitudinally, converging anteriorly. Maxillae large, inflated. Mandibles short, subtriangular. Abdomen curving ventrally, posteriorly elongate; anus ventral. Ventral segments surfaces with numerous rows of spinules). Body tubercles scarce, mostly located in a row of frustums posterior to anus aperture. Body hairs unbranched, short and stout, sparsely present on head dorsum. Dorsa of thoracic segments bearing very peculiar pilosity, coral branch-like.

Type Material
Type material. Holotype worker. BRAZIL, Goiás: Niquelândia, Serra da Mesa, 14∘20′39.5′′S, 48∘10′21.1′′W, 16.xi.2013, cerrado, inside nest of Cornitermes silvestrii (D. E. Oliveira, R. G. Santos & T. Carrijo) (sample code DEO2013-030; specimen code CASENT0106501).

Paratype workers (w) and males (m). Same data and colony as holotype; sample code R06 1w, 1w (CASENT0730400) 1m ; sample code TC08, 1w , 1w MZSP; sample code DEO2013-030, 1 w , 1 m MZSP.

Etymology
The specific epithet ‘relictus’ (from Latin: abandoned, relinquished) is a reference to the geographical isolation of this taxon in comparison with known extant Leptomyrmex species, believed to be a remaining lineage from an ancestral group once more widespread.