Crematogaster decamera

A widespread member of a group of Crematogaster species associated with Macaranga plants in Sumatra, Borneo, and Peninsula Malaysia.

Identification
Feldhaar et al. (2016) - A member of the Crematogaster decamera subgroup within the Crematogaster borneensis group. Worker: Propodeal spines absent, legs relatively long (RLEG 0.71 - 0.85), head slightly longer than wide (CI 0.94 - 1.02), postpetiole always wider than petiole (PI < 1.0). Queen: EL 0.39 - 0.45mm, REL 0.29 - 0.35, OD1 > OW, SL > 0.7 mm, CI usually > 1.0, PI < 1.0.

Distinguished from all other species in the group based on workers only by the complete lack of propodeal spines. Queens from Peninsula Malaysia tend to be smaller than from Borneo, with the largest individuals observed in Sarawak (e.g. mean HW: 1.22 in Peninsula Malaysia (n=6) and 1.35 in Sarawak (n=4)).

Distribution based on Regional Taxon Lists
Indo-Australian Region: Borneo, Indonesia, Malaysia.

Biology
Feldhaar et al. (2016) - Crematogaster decamera has a large distributional range and occurs in all geographic regions of the Macaranga- Crematogaster association (Peninsula Malaysia, Sumatra, Borneo). Queens of Crematogaster decamera only colonize saplings, and colonies have an early onset of reproduction. On Peninsula Malaysia several colonies were found that had turned secondarily polygynous or at least contained several mated queens.

This species colonizes glaucous hosts of the section Pachystemon only (Macaranga beccariana, Macaranga constricta, Macaranga havilandii, Macaranga hypoleuca, Macaranga motleyana).

Nomenclature

 *  decamera. Crematogaster (Decacrema) decamera Forel, 1910a: 18 (footnote) (w.q.m.) BORNEO.

Worker
Feldhaar et al. (2016) - Paralectotype. CI 0.96, DPPW 0.22, DPW 0.19, EL 0.13, HL 0.75, HW 0.72, LHT 0.66, (LPS not measured, no spines), MTW 0.44, PI 0.86, REL 0.18, RLEG 0.71, SI 0.71, SL 0.51, (TL 3.5), WL 0.94.

(n= 12) CI 0.95-1.0, DPPW 0.15-0.22, DPW 0.15-0.21, EL 0.09-0.13, HL 0.51-0.75, HW 0.5-0.74, LHT 0.44-0.77, (LPS not measured, no spines), MTW 0.31-0.44, PI 0.861-1.0, REL 0.15-0.2, RLEG 0.71-0.85, SI 0.68-0.76, SL 0.36-0.51, (TL 2.4-3.6), WL 0.62-0.94.

Colour medium to dark brown with head and gaster a slightly darker shade than the alitrunk. Workers monomorphic in size. Total body length of workers 2.4 mm to 3.6 mm. Head and gaster shiny with smooth surface, alitrunk slightly less shiny and faintly shagreened. All body parts bear appressed pubescent hairs. Long flexuous setae present on head, gaster and abdomen: on head especially in frons, on gaster more on the posterior margins of tergites and sternites. Only few setae on alitrunk and one pair each on petiole and postpetiole. Head subquadratic but slightly elongated (CI ≤1.0), usually longer than wide and only slightly rounded on sides. Anterior clypeal margin slightly convex and with a row of long erect setae projecting anteriorly. Occipital margin straight, occipital lobes rounded. Mandibles relatively short and with four denticles, capable of closing tightly against the clypeus. Denticles increasing continuously in size from most proximate to most distal denticle. Surface of mandibles smooth, covered with short pubescent hairs. Antennae are relatively long in comparison with head width (SI 0.68-0.78; mean 0.72) and covered in short, pubescent hair. Terminal two funicular segments form a club, sometimes the terminal three segments are clubbed.

Compound eyes elliptically shaped and not protruding over margin of head in full-face view. Pronotum and mesonotum form a convex dome in profile. Anterodorsal surface of pronotum sloping downwards less steep than posterodorsal surface of mesonotum. Metanotal groove slightly notched and clearly developed, whereas promesonotal suture visible but not prominent. Propodeal spines always absent (Fig S1.5C and S1.5D). A nodiform elevation may be present above the propodeal spiracle, albeit not very prominent. Slope of the posterior face of the propodeum similar to posterior slope of mesonotum and approximately 45°. Legs are relatively long in comparison to alitrunk length (RLEG: 0.71-0.85). Node of petiole in dorsal view rounded and distinctly longer than wide, postpetiolar node also rounded, distinctly shorter and usually wider than node of petiole (PI 0.86-1.0). Subpetiolar process usually absent. (See Table 1 for comparative overview of worker characters.)

Queen
Feldhaar et al. (2016) - Lectotype. CI 1.03, DPPW 0.42, DPW 0.38, EL 0.39, HL 1.32, HW 1.36, LHT 1.07, MTW 1.05, OD1 0.2, OD2 0.1, OW 0.14, PI 0.90, REL 0.30, RLEG 0.47, ROD 0.154, ROD2 0.082, SI 0.53, SL 0.71, (TL 7.8), WL 2.27.

(n=14) CI 0.96-1.05, DPPW 0.39-0.46, DPW 0.37-0.44, EL 0.39-0.45, HL 1.21-1.42, HW 1.16-1.41, LHT 0.83-1.08, MTW 0.9-1.06, OD1 0.15-0.2, OD2 0.08-0.1, OW 0.11-0.14, PI 0.88-1.0, REL 0.29-0.35, RLEG 0.4-0.47, ROD 0.119- 0.155, ROD2 0.056-0.082, SI 0.48-0.57, SL 0.7-0.75, (TL 6.5-7.8), WL 2.08-2.37.

Queens relatively small with total body length from a 6.5 to 7.8 mm and uniformly dark brown in colour. Surface of head and gaster smooth and shiny, alitrunk slightly less shiny and faintly shagreened. All body parts bear appressed pubescent hairs. Long flexuous setae present on head gaster and abdomen: on head especially in frons, on gaster more on the posterior margins of tergites and sternites. A row of long erect setae pointing anterior present on the clypeus. Mandibles relatively short, capable of closing tightly against the clypeus.

Head subquadratic, usually approximately as wide as long (CI: 0.96-1.05; mean 1.01). Sides of the head only very slightly convex, occipital margin of the head slightly concave. Occipital lobes rounded. Anterior clypeal margin slightly convex. Terminal four segments of funiculus continuously increasing in size forming an indistinct antennal club. Antennal scrobes strongly developed, with an acute and marked dorsal margin; the frontal carinae short.

Compound eyes small (ranging from 0.39-0.45 mm) and usually span less than one third of HL (REL 0.29-0.35). Compound eyes round to oval-shaped from lateral view and convex from dorsal view (see Fig 3.6; Fig S1.5A and S1.5B) with margins of compound eyes protruding over margin of head. Ocelli relatively small in diameter. Diameter of the median ocellus smaller than the distance between the lateral ocelli.

Mesoscutum convexly rounded anterodorsally. Mesoscutellum nearly in horizontal plane in lateral view. Propodeum flattened dorsally and then drops off at an angle of approximately 45° posterior of the propodeal spiracle. Mesoscutum stretches out over less than half of the alitrunk in lateral view. In dorsal view, the posterior margin of the propodeum forms a straight line and the mesonotum is broadly triangular. Propodeum not armed with spines.

Petiole in dorsal view elongate and not concavely rounded on sides and always less wide than postpetiole (PI: 0.88-1.0). Petiole anterodorsally flattened in lateral view and sloping downwards and distinctly longer than the postpetiole. Postpetiole round in dorsal view.

Type Material
Lectotype queen (upper individual on pin) and paralectotype worker (upper individual on pin) (both pins with blue cardboard labels) from Sarawak (Borneo), Malaysia (Haviland) (designated by Feldhaar, Maschwitz & Fiala, 2016: 661, but note that all syntypes other than lectotype are paralectotypes).

Determination Clarifications
In earlier publications by our group this species was referred to as Crematogaster morphospecies 6 (Fiala et al., 1999).

References based on Global Ant Biodiversity Informatics

 * Blaimer B. B. 2012. Acrobat ants go global  Origin, evolution and systematics of the genus Crematogaster (Hymenoptera: Formicidae). Molecular Phylogenetics and Evolution 65: 421-436.
 * Chapman, J. W., and Capco, S. R. 1951. Check list of the ants (Hymenoptera: Formicidae) of Asia. Monogr. Inst. Sci. Technol. Manila 1: 1-327
 * Feldhaar H., U. Maschwitz, and B. Fiala. 2016. Taxonomic revisions of the obligate plant-ants of the genus Crematogaster Lund (Hymenoptera: Formicidae: Myrmicinae), associated with Macaranga Thouars (Euphorbiaceae) on Borneo and the Malay Peninsula. Sociobiology 63(1): 651-681.
 * Forel A. 1910. Glanures myrmécologiques. Ann. Soc. Entomol. Belg. 54: 6-32.
 * Herwina H., R. Satria, Yaherwandi, and Y. Sakamaki. 2018. Subterranean ant species diversity (Hymenoptera: Formicidae) in educational and biological research forest of universitas andalas, Indonesia. Journal of Entomology and Zoology Studies 6(1): 1720-1724.
 * Hosoishi S. and K. Ogata. 2009. A check list of the ant genus Crematogaster in Asia (Hymenoptera: Formicidae). Bull. Inst. Trop. Agr. Kyushu Univ. 32: 43-83.
 * Murase K., S. Yamane, T. Itino, and T. Itioka. 2010. Multiple factors maintaining high species-specificity in Macaranga-Crematogaster (Hymenoptera: Formicidae) myrmecophytism: higher mortality in Mismatched ant-seedling pairs. Sociobiology 55(3): 883-898.
 * Pfeiffer M.; Mezger, D.; Hosoishi, S.; Bakhtiar, E. Y.; Kohout, R. J. 2011. The Formicidae of Borneo (Insecta: Hymenoptera): a preliminary species list. Asian Myrmecology 4:9-58
 * Wheeler W. M. 1919. The ants of Borneo. Bulletin of the Museum of Comparative Zoology 63:43-147.