Crematogaster kelleri

Crematogaster kelleri typically nests arboreally; collections of colonies are most often made from dead twigs or branches and from nests under bark or canopy moss mats. On occasion, this species has also been found on the ground under stones or in rotten logs. Colonies found under bark or canopy moss appeared to be large and spread across entire trees, while branch-nesters may well have a polydomous nest structure, occupying different parts of one tree.

Identification
A member of the Crematogaster kelleri group. Blaimer and Fisher (2013) - Workers of Crematogaster kelleri can best be separated from Crematogaster tavaratra by the absence of a distinct, complete longitudinal impression on the postpetiole (complete in the latter). Crematogaster hazolava and Crematogaster hafahafa workers can be distinguished from Crematogaster madagascariensis by the position of the propodeal spiracle, which is not confluent with the spine base. Queens of C. kelleri are recognizable from C. hazolava queens by their metanotum, which projects below the scutellum, and from C. tavaratra queens by the shorter spines (SPI 0.00–0.07; compared to C. tavaratra with SPI 0.09–0.10).

As with many widespread species within the genus Crematogaster, C. kelleri is morphologically highly variable. Character states that vary continuously between colonies and to a lesser extent also within colonies are promesonotal structure, color, pilosity and body size. The variable promesonotal structure (i.e. whether the mesonotum is elevated over the pronotum or not) and body size in this species are most likely to cause confusion in specimens not collected from nest series. Fortunately, for our study, recent colony series collections were available in sufficient quantity to estimate variation in this species. Few of these colonies, however, provided queens and even fewer provided males. We found males overall quite variable in size and promesonotal structure, and queens usually variable in size (correlated with worker size).

Color variation in C. kelleri appears to be gradual in what is subsequently referred to as the ‘‘brown form.’’ This form can be colored from very pale brown to almost black; the pale coloration is seen mostly in small specimens, whereas darker coloration is most commonly in larger individuals. Color variation in this brown form is also high within colonies, i.e. one colony often has both pale colored, small workers and darker, larger workers. A second color form, the ‘‘yellow form’’, is distinct from and not part of the variation within the brown form. This yellow color does not appear to be variable within colonies, and colonies with yellow colored workers also have queens of the same coloration. The color of males is unknown. Aside from color, no other character states separate these yellow and brown forms. The lectotype worker of C. kelleri represents the yellow form, whereas the syntypes of C. adrepens belong to the brown form.

Distribution based on Regional Taxon Lists
Malagasy Region: Madagascar, Seychelles.

Biology
Crematogaster kelleri is widely distributed throughout humid forests and dry forests in Madagascar, and has been collected at elevations ranging from sea level up to 2000 m. This species is much more common in lower elevation rainforests and littoral forests than in dry forest or at higher elevations. We therefore surmise that low- to mid-elevation humid forests provide optimal habitat for this species. The yellow form of C. kelleri occurs pre-dominantly in regions closer to the coast and at lower elevations and is often the only form found in littoral forests. There is a notable exception to this with an occurrence record at 2000 m in the Andringitra massif. However, since this record does not refer to a colony sample, we consider cross-contamination of samples or mislabeling as a possible explanation. The yellow form is entirely absent from west coast localities. The brown form of C. kelleri occurs throughout the distribution range in no particular pattern. It should be emphasized that both forms can occur in sympatry (e.g. R.N.I. Betampona), but one form usually seems to be more abundant than the other. Furthermore, the species can be found in sympatry with all other species within the C. kelleri-group, as well as Crematogaster tsisitsilo.

Nomenclature

 *  kelleri. Crematogaster kelleri Forel, 1891b: 197, pl. 6, fig. 10 (w.) MADAGASCAR. Combination in C. (Crematogaster): Wheeler, W.M. 1922a: 1022; in C. (Acrocoelia): Emery, 1922e: 147; in C. (Crematogaster): Bolton, 1995b: 166. Senior synonym of adrepens, gibba: Blaimer & Fisher, 2013: 10.
 * adrepens. Crematogaster adrepens Forel, 1897c: 197 (w.) MADAGASCAR. Combination in C. (Crematogaster): Wheeler, W.M. 1922a: 1022; in C. (Acrocoelia): Emery, 1922e: 144; in C. (Crematogaster): Bolton, 1995b: 166. Junior synonym of kelleri: Blaimer & Fisher, 2013: 10.
 * gibba. Crematogaster gibba Emery, 1894a: 70, fig. (w.) SEYCHELLES IS. Combination in C. (Crematogaster): Wheeler, W.M. 1922a: 1022; in C. (Acrocoelia): Emery, 1922e: 147; in C. (Crematogaster): Bolton, 1995b: 166. Junior synonym of kelleri: Blaimer & Fisher, 2013: 10.

Description
Blaimer and Fisher (2013) :

Worker
HW 0.60–1.16; HL 0.57–0.99; EL 0.12–0.23; SL 0.57–0.84; WL 0.65–1.12; SPL 0.07–0.22; PTH 0.13–0.21; PTL 0.16–0.27; PTW 0.19–0.33; PPL 0.11–0.20; PPW 0.16–0.27; LHT 0.52–0.93; CI 1.04–1.18; OI 0.20–0.25; SI 0.81–1.00; SPI 0.11–0.23; PTHI 0.58–0.86; PTWI 0.94–1.28; PPI 1.34–1.74; LBI 1.14–1.41.

Very small to large in size (HW 0.60–1.16, WL 0.65–1.12), but on average small (mean HW 0.81, mean WL 0.82; n =43); highly morphologically variable, with general characters of the C. kelleri-group and the following refinements.

Masticatory margin of mandibles with four, rarely five teeth (in some large specimens); posterior margin of head in full face view laterally subangular, sometimes medially slightly depressed; midline of eyes situated at or slightly above midline of head in full face view.

Promesonotal suture usually absent or indistinct, except in largest workers where mesonotum may be dorsally raised and has a median tubercule; mesonotum with a distinct dorsal and posterior face, and laterally angulate or subangulate; mesonotum with or without posterolateral angular tubercules or denticles, propodeal spines short to medium-sized (SPI 0.11–0.23), spiniform, straight or slightly downcurved, moderately diverging in dorsal view; propodeal spiracle situated below and not confluent with base of spines; postpetiole bilobed, but median impression not fully complete, rather posteriorly deep, anteriorly superficial.

Pilosity highly variable; color yellow or light to dark brown, rarely reddish brown with dark abdominal segments four to seven.

Queen
HW 1.15–1.42, HL 1.04–1.29, EL 0.31–0.39, SL 0.71–0.88, MSNW 0.86–1.13, MSNL 0.93–1.21, WL 1.70–2.08, SPL 0.00–0.12, PTH 0.27–0.35, PTL 0.33–0.44, PTW 0.38–0.47, PPL 0.28–0.34, PPW 0.35–0.47, LHT 0.82–1.04, CI 1.05–1.15, OI 0.27–0.32, SI 0.65–0.74, MSNI 0.75–0.98, SPI 0.00–0.07, PTHI 0.66–0.92, PTWI 0.97–1.37, PPI 1.15–1.64, LBI 2.01–2.32.

Small (HW 1.15–1.42, WL 1.70–2.08), with characters of the C. kelleri-group and the following refinements.

Masticatory margin of mandibles with five teeth; antennal scapes usually not reaching head margin (SI 0.65–0.74); eyes situated at or slightly below midline of head in full face view. Metanotum projecting from below scutellum in lateral and dorsal view; propodeal spines absent to short (SPI 0.00–0.07), spiniform or dentiform.

Queen
HW 1.15–1.42, HL 1.04–1.29, EL 0.31–0.39, SL 0.71–0.88, MSNW 0.86–1.13, MSNL 0.93–1.21, WL 1.70–2.08, SPL 0.00–0.12, PTH 0.27–0.35, PTL 0.33–0.44, PTW 0.38–0.47, PPL 0.28–0.34, PPW 0.35–0.47, LHT 0.82–1.04, CI 1.05–1.15, OI 0.27–0.32, SI 0.65–0.74, MSNI 0.75–0.98, SPI 0.00–0.07, PTHI 0.66–0.92, PTWI 0.97–1.37, PPI 1.15–1.64, LBI 2.01–2.32.

Small (HW 1.15–1.42, WL 1.70–2.08), with characters of the C. kelleri-group and the following refinements.

Masticatory margin of mandibles with five teeth; antennal scapes usually not reaching head margin (SI 0.65–0.74); eyes situated at or slightly below midline of head in full face view. Metanotum projecting from below scutellum in lateral and dorsal view; propodeal spines absent to short (SPI 0.00–0.07), spiniform or dentiform.

Male
(n= 11). HW 0.47–0.60, HL 0.39–0.48, EL 0.18–0.33, SL 0.07–0.11, MSNW 0.45–0.72, MSNL 0.42–0.69, WL 0.85–1.19, SPL 0.00, PTH 0.13–0.18, PTL 0.13–0.21, PTW 0.14–0.23, PPL 0.11–0.17, PPW 0.17–0.24, LHT 0.55–0.66, CI 1.17–1.33, OI 0.40–0.68, SI 0.19–0.26, MSNI 0.84–1.39, SPI 0.00, PTHI 0.77–1.11, PTWI 0.84–1.30, PPI 1.16–1.66, LBI 1.63–1.90.

Small to medium body size (HW 0.47–0.60, WL 0.85–1.19), with characters of the C. kelleri-group and the following refinements.

Masticatory margin of mandibles with two to three teeth; antennae with second and third funicular segment not globular, longer than wide, sixth to eleventh funicular segment distinctly wider than second to fifth segment; occipital carinae distinct, sometimes forming a thin flange projecting backwards.

Scutellum in dorsal view distinctly tapering from anterior to posterior end, dorsoposterior portion truncate; metanotum projecting at least slightly below scutellum in dorsal and lateral view; dorsal face of propodeum very short.

Head sculpture rugulose; scutellum mostly shiny. Color pale yellow to brown, with head darker.