Stenamma pelophilum, Branstetter, Michael G., 2013

Branstetter, Michael G., 2013, Revision of the Middle American clade of the ant genus Stenamma Westwood (Hymenoptera, Formicidae, Myrmicinae), ZooKeys 295, pp. 1-277 : 175-180

Stenamma pelophilum sp. n. Worker: Figures 138, 139; Queen: Figure 140; Map: Figure 141

Stenamma mgb27 Branstetter, 2012: phylogeny.

Type material.

Holotype worker. HONDURAS: Cortés, PN Cusuco, 15.48335°N, 88.22810°W ± 50m, 1290m, 2 Jun 2010 (M. G. Branstetter, collection MGB1595) [USNM, specimen CASENT0622838]. Paratypes: same data as holotype [1w, CAS, CASENT0623452], [1w, EAPZ, CASENT0622839], [1w, ECOSCE, CASENT0622840], [1w, FMNH, CASENT0622841], [1w, ICN, CASENT0622842], [1w, INBio, CASENT0622843], [2w, JTLC, CASENT0622336], [2w, LACM, CASENT0622335], [2w, MGBPC, CASENT0622337], [1w, MCZ, CASENT0623449], [1w, MZSP, CASENT0623450], [1w, UCD, CASENT 0623451], [1w, UNAM, CASENT0623453], [1dq, 2w, USNM, CASENT0622334, CASENT0623455 [1w, UVGC, CASENT0623454].

Worker diagnosis.

Integument mostly black to brown-black and shining; small to medium-sized species (see HL, ML, PrW below); anterior margin of clypeus with a shallow median emargination; basal margin of mandible straight to slightly curving, but without a distinct basal notch or depression; head and body almost entirely smooth and shiny, except for faint punctae on waist and sometimes on propodeum; pronotum in profile usually distinctly asymmetrical, with a long, steep posterior face, that forms a distinct angle with dorsal surface, and a short anterior face; eye of moderate size (EL 0.11-0.17, REL 19-23), oval-shaped, with 6-8 ommatidia at greatest diameter; propodeal spines reduced to small tubercles or short points (PSL 0.06-0.10, PSI 1.1-1.7); setae on gastral tergites sparse, moderately long, and mostly suberect; frontal lobes narrow (FLD 0.13-0.18, FLI 24-27), not obscuring torular lobe in full-face view. Similar species: Stenamma llama , Stenamma tiburon .

Geographic range.

Mexico (Atlantic slope) to Honduras.

Worker description.

(17 measured) HL 0.58-0.83 (0.66) HW 0.51-0.73 (0.58) FLD 0.13-0.18 (0.15), PCW 0.03-0.05 (0.04), SL 0.49-0.76 (0.54), EL 0.11-0.17 (0.13), ACL 0.47-0.65 (0.54), ML 0.74-1.06 (0.86), PrW 0.38-0.47 (0.44), PSL 0.06-0.10 (0.09), SDL 0.05-0.09 (0.07), PL 0.27-0.39 (0.32), PH 0.18-0.24 (0.22), PW 0.12-0.17 (0.15), PPL 0.14-0.21 (0.18), PPH 0.14-0.19 (0.17), PPW 0.14-0.20 (0.18), MFL 0.52-0.86 (0.62), MTL 0.41-0.67 (0.48), CI 86-92 (89), SI 89-107 (92), REL 19-23 (21), FLI 24-27 (26), PSI 1.1-1.7 (1.2), PI 51-58 (54), MFI 83-105 (94), ACI1 64-71 (66), ACI2 84-99 (99)

Small- to medium-sized species; general body color black to brown-black, with mandibles and appendages brown to yellow-brown, lighter toward extremities; setae translucent brown; mandible with 4-6 teeth, consisting of 3 distinct apical teeth, a basal tooth, and 2 inner teeth, which are very often effaced; masticatory margin of mandible sometimes gently curving inward (perhaps due to wear), causing basal tooth to appear more robust; basal margin of mandible straight to slightly curving, without a distinct notch or depression; some specimens with basal section of mandible, where mandible inserts under clypeus, distinctly expanded and thin; dorsal surface of mandible mostly smooth and shining, with scattered piligerous punctae and a few basal striae; median lobe of clypeus somewhat obliquely flattened, and sometimes angled more ventrally than average, creating distinct dorsal and anterior faces; median lobe with faint to absent longitudinal carinulae, middle of lobe often slightly concave, apex of lobe with a short transverse carinula, usually present near anterior margin, remainder of clypeus mostly smooth and shining; posterior extension of clypeus between frontal lobes of moderate width (PCW 0.03-0.05), with subparallel sides; frontal lobes very narrow (FLD 0.13-0.18, FLI 24-27), not obscuring torular lobes in full-face view; head somewhat longer than broad (CI 86-92), roughly oval-shaped, posterior margin flat, never strongly depressed medially, lateral corners gently curving; eyes of moderate size (EL 0.11-0.17, REL 19-23), oval-shaped, with 6-8 ommatidia at greatest diameter; face almost entirely smooth and shiny, except for a variable number of carinulae around frontal carinae and on genae; scape of moderate to somewhat long length (SI 89-107), just reaching or slightly surpassing posterior margin of head when laid back; dorsal surface of scape with scattered piligerous punctae and a few faint striae, otherwise smooth and shining; funiculus with distinct 4-segmented antennal club; mesosoma usually almost entirely smooth and shiny, except for some longitudinal carinulae along metanotal groove, and transverse carinulae on dorsal and declivitous faces of propodeum; in some populations propodeum with more developed rugulae and punctae; promesonotum in profile usually asymmetrically domed and somewhat bulging, with posterior slope distinctly longer and straighter than anterior slope, and forming a more well-defined angle with dorsal surface, apex of promesonotum offset toward posterior margin; lateral and posterior margins of promesonotum in dorsal view, usually well defined, with relatively sharp transitions; one population (from high-elevation) with promesonotum in profile low-domed and roughly symmetrical; propodeal spines forming tubercles, or small projecting points (PSL 0.06-0.10, PSI 1.1-1.7); petiole of moderate length (PL/HW 0.51-0.58), node of variable height (PH/PL 0.59-0.69) and volume, usually pointing slightly posteriad, anterior face longer than posterior face and rising from about midpoint of petiole, posterior face nearly vertical, dorsum in profile usually narrowly rounded, but sometimes forming a defined apex; postpetiole in profile slightly to distinctly smaller than petiolar node (PPH/PH 0.76-0.89), roughly symmetrical, with anterior face slightly longer and more sloping than posterior face; petiole mostly smooth and shining, except for light punctae on venter and lateral portions of peduncle; postpetiole with anterior face smooth, shiny and shield-like, venter and posterior half of postpetiole lightly punctate; gaster mostly smooth and shiny, with scattered piligerous punctae; most of body with a thin layer of moderately long standing setae; setae on gastral tergites sparse and uniformly suberect; facial setae mostly decumbent with a few erect hairs; setae on scape subdecumbent to appressed; setae on legs mostly decumbent to appressed, with coxae and ventral surfaces of the femora with some suberect setae.

Queen description.

(3 Measured) HL 0.63-0.69 (0.69), HW 0.58-0.63 (0.63), FLD 0.14-0.16 (0.16), PCW 0.03-0.06 (0.06), SL 0.54-0.56 (0.56), EL 0.17-0.19 (0.18), ACL 0.53-0.56 (0.56), ML 0.91-1.02 (1.02), PrW 0.52-0.56 (0.56), PSL 0.09-0.14 (0.10), SDL 0.08-0.09 (0.09), PL 0.33-0.39 (0.37), PH 0.20-0.24 (0.24), PW 0.17-0.20 (0.19), PPL 0.17-0.20 (0.20), PPH 0.19-0.20 (0.20), PPW 0.19-0.23 (0.22), MFL 0.60-0.67 (0.67), MTL 0.45-0.53 (0.53), CI 91-93 (91), SI 89-92 (89), REL 23-30 (29), FLI 24-26 (26), PSI 1.1-1.7 (1.2), MFI 94-105 (94), ACI1 65-67 (65), ACI2 94-101 (100).

Same as worker except for standard queen modifications and as follows: scutellum with irregular longitudinal rugulae/carinulae; metapleuron with longitudinal carinulae; dorsum of propodeum with transverse carinulae; petiolar node usually same as in workers, but one queen (Huejutla population) with node dorsum in posterior/anterior view forming two sharp points, separated by a steep concavity.

Male.

Unknown.

Biology.

This is a rare species that inhabits montane wet forests from 1000 to 1800 m elevation. Most collections are from Winkler or Berlese extracts of sifted leaf litter. However, at Cusuco National Park in Honduras, I found two nests in a mud bank bordering a stream. The surface of the bank was rocky with an overlying layer of dense mud. The first nest was located by haphazardly cutting into the bank in an area where I saw lots of worker activity. This nest had a single chamber with about 35 workers and some brood. The second nest was located by following a returning forager. This nest had a nearly undetectable entrance (2 mm diameter) consisting only of a small hole, without any surrounding structure or excavated substrate. Behind the entrance was a very short tunnel leading to a single, small chamber. This contained 46 workers, some brood and a single dealate queen. When the nest chamber was disturbed, the queen immediately absconded out onto the clay bank followed by a series of workers carrying brood. Before excavation, foragers outside the nest were observed to be slow moving and solitary, similar to behavior in most other Stenamma species.

Comments.

Molecular phylogenetic data show that Stenamma pelophilum is sister to the lobinodus species group, which includes Stenamma llama , Stenamma lobinodus , and Stenamma tiburon (Branstetter unpublished data). Although Stenamma pelophilum does not have the distinguishing features of this group, it does bear some similarity to Stenamma llama and Stenamma tiburon . It can be easily separated from these species by its distinctive promesonotum shape and average looking postpetiole, which lacks a distinctive dorsal lobe.

There is minimal morphological variation amongst most populations of Stenamma pelophilum , and I interpret this variation to be intraspecific. One population, however, is significantly divergent from the type population and I describe it here as variant 1 (Figure 139 A–C). This variant is known from above 2000 m in Oaxaca, Mexico, on the wet, eastern slope of the Sierra Juarez. It is larger, has more sculpture on the mesopleuron and propodeum, and has the promesonotum in profile low-domed and roughly symmetrical. Also, it has a relatively longer scape and metafemur than other populations of standard Stenamma pelophilum (SI ≥ 100 vs. ≤ 96, MFI ≤ 86 vs. ≥ 93). It could be that this variant is a mountaintop endemic, derived from the Stenamma pelophilum populations found lower on the mountain. I choose, however, to include variant 1 within Stenamma pelophilum , because I have found specimens with intermediate phenotypes (Figure 139 D–F). These have been collected from intermediate elevations, and from the same samples as variant 1. The morphological differences might be due to environmental effects on development, rather than reproductive isolation and divergence. It would be interesting to investigate the population dynamics between these two forms along the elevational gradient.

Material examined.

GUATEMALA:Zacapa: 2km SE La Unión, 14.94681°N, 89.27583°W, 1550m, 12 May 2009 (LLAMA); HONDURAS: Cortés: PN Cusuco, 15.48335°N, 88.22810°W, 1290m, 2 Jun 2010 (M. G. Branstetter); MÉXICO: Hidalgo: 43km SW Huejutla, [ca. 20.988°N, 98.662°W], 14 Jun 1983 (S. & J. Peck); Oaxaca: 20.6km SW Valle Nacional, 17.60404°N, 96.37786°W, 1730m, 13 Aug 2009 (M. G. Branstetter); 26km SW Valle Nacional, 17.58667°N, 96.44948°W, 2160m, 11 Aug 2009 (M. G. Branstetter); 27km SW Valle Nacional, 17.59582°N, 96.47572°W, 2290m (M. G. Branstetter); 27.4km SW Valle Nacional, 17.59635°N, 96.47449°W, 2280m, 12 Jun 2009 (M. G. Branstetter); 47.5km SW Valle Nacional, km100.5, [ca. 17.590°N, 96.410°W], 2125m, 26 Jul 1992 (R. S. Anderson); Querétaro: 7km NE Pinal de Amoles, 21.17601°N, 99.57341°W, 1700m, 18 Aug 2009 (M. G. Branstetter); San Luis Potosí: Taman, 20km SW Tamazunchale, [ca. 21.153°N, 98.947°W], 11 Jun 1983 (S. & J. Peck); 20km W Xilitla, [ca. 21.293°N, 99.194°W], 1600m, 12 Jun 1983 (S. & J. Peck); 40km W Xilitla, [ca. 21.259°N, 99.194°W], 1700m, 12 Jun 1983 (S. & J. Peck); Tamaulipas: Sa. de Guatemala, Rancho del Cielo, [ca. 23.062°N, 99.209°W], 1070m, 4 Jul 1969 (S. & J. Peck); Veracruz: Cordoba, Paraje Nuevo, Nacimiento, [ca. 18.88°N, 96.86°W], 7 Aug 1969 (S. & J. Peck).