Crematogaster grevei Forel 1891
Creators: name: Blaimer, Bonnie B.
Publisher: name: Zenodo
Year: 2010
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Hymenoptera
Formicidae
Crematogaster
Crematogaster grevei

description: Crematogaster grevei Forel 1891
(Fig. 37 & 43)
Crematogaster grevei Forel, A. 1891:183. Syntypes, 2 workers, Morondava (Grevé) (MHNG) [examined] [The two MHNG syntypes are also imaged on AntWeb: CASENT0101572, CASENT0101558]. One syntype (CASENT0101572) hereby designated the LECTOTYPE.
Crematogaster (Decacrema) grevei Forel, Forel 1910a:18. Combination in Crematogaster (Decacrema). Crematogaster (Decacrema) grevei Forel, Forel 1910b:9. Combination in Crematogaster (Decacrema).
Material examined. (BBBC, CASC, PSWC, MHNG) MADAGASCAR Fianarantsoa: P.N. Isalo: - 22.29833, 45. 35167, 990m (B.L.Fisher et al.); near P.N Isalo: -22.62667, 45.35817, 700-825m (R.Harin’Hala); Mahajanga: P.N. Namoroka: -16.37667, 45.32667, 100m (B.L.Fisher et al.); Mahavavy River: -16.05167, 45.90833, 20m (B.L.Fisher et al.); Rés. forest. Beanka: -18.02649, 44.05051, 250m (B.L.Fisher et al.); Morondava: -20.28333, 44.28333 (M. Grevé); 50km N Morondava: -20.06670, 44.58330 (A.Pauly), 48km ENE Morondava: -20.29650, 44.28150, 30m (D.M.Olson); 3.7km 102º ESE Belo-sur-mer: - 20.73472, 44.04000, 10m (B.L.Fisher et al.); Bemeraha: -18.65000, 44.71670 (D.C.Lees); P.N. Baie de Baly: -16.01000, 45.26500, 10m (B.L.Fisher et al.); F Tsimembo-19.02139, 44.44067, 20m, -18.99528, 44.44350, 50m (B.L.Fisher et al.); Toliara: P.N. Kirindy-Mite: -20.79528, 44.14700, 80m (B.L.Fisher et al.); Kirindy: - 20.04500, 44.66222, 100m (B.L.Fisher et al.); P.N. Zombitse: -22.84330, 44.71000, 770m (B.L.Fisher et al.); Isoky-Vohimena: -22.68330, 44.83330, 730m (B.L.Fisher et al.); F Vohibasia: -22.46670, 44.85000, 780m (B.L.Fisher et al.); 15km E Sakaraha: -22.90000, 44.68333, 760m (P.S.Ward); Ranobe: -23.03975, 43.61090, 30m (Frontier Project, MGF); Rés. Berenty (F Bealoka): -24.95694, 46.27150, 35m (B.L.Fisher et al.); Rés. Berenty (F Malaza): -25.00778, 46.30600, 40m (B.L.Fisher et al.); Rés. Berenty: -25.02100, 46.30550, 35m (R.Harin’Hala), -25.01670, 46.30000 (P.S.Ward); F Mahavelo: -24.75830, 46.15717, 110m, -24.75000, 46.16670, 115m (B.L.Fisher et al.); P.N. Andohahela: -24.93000, 46.64550, 300m (B.L.Fisher et al.); P.N. Andohahela: -25.01366, 46.64650, 160m (B.B.Blaimer); F Beroboka: -22.23306, 43.36633, 80m (B.L.Fisher et al.); Mahafaly Plateau: -24.65361, 43.99667, 80m (B.L.Fisher et al.); F Tsimanampetsotsa: -24.10056, 43.76000, 25m (B.L.Fisher et al.); Cap St. Marie: -25.59444, 45.14683, 160m (B.L.Fisher et al.); F Mite: - 23.52417, 44.12133, 75m (B.L.Fisher et al.); Manderano: -23.52417, 44.09278, 75m (Frontier Project, MGF); Fiheranana: -23.23528, 43.87083, 65m (B.L.Fisher et al.); F Tsinjoriaky: -22.80222, 43.42067, 70m (B.L.Fisher et al.); Rés. Beza-Mahafaly: -23.65000, 44.63333, 135m (B.L.Fisher et al..), -23.68650, 44.59100, 165m (R. Harin’Hala); Rés. Beza-Mahafaly, parcel 1: -23.65000, 44.63330, 130m (P.S.Ward); Manombo: -22.81092, 43.73440, 165m (Frontier Project, MGF); F Vohidava: -24.24070, 46.28780, 500m, - 24.23900, 46.28230, 850m (B.L.Fisher et al.); F Mikea: -22.90367, 43.47550, 35m (R. Harin’Hala).
Worker measurements (n=12). HW 0.82–0.89; HL 0.72–0.78; EL 0.16–0.21; SL 0.66–0.74; WL 0.79– 1.07; SPL 0.13–0.18; PTH 0.18–0.22; PTL 0.24–0.29; PTW 0.26–0.31; PPL 0.15–0.20; PPW 0.27–0.32; LHT 0.57–0.63; CI 1.11–1.18; OI 0.21–0.27; SI 0.92–0.98; SPI 0.13–0.22; PTHI 0.74–0.79; PTWI 1.01–1.20; PPI 1.43–1.84; LBI 1.29–1.71.
Worker description. Small species (HW 0.82–0.89, WL 0.79–1.07).
Masticatory margin of mandibles with 4 teeth; posterior margin of head in full-face view with subangular corners, sometimes medially depressed; antennal scapes surpassing posterior margin of head easily; midline of eyes situated well above midline of head in full face view.
Promesonotum medially depressed and laterally with raised shoulders, these transitioning into lateral carinae and terminating in small denticles that abruptly demarcate promesonotum from propodeum; in lateral view outline of promesonotum flat; promesonotal suture absent; promesonotum without a distinct posterior face medially; propodeal spines small-medium sized (SPI 0.13–0.22), length roughly a third of the width between their bases, quickly tapering, in lateral view more or less straight, in dorsal view almost parallel and barely diverging; petiole in dorsal view suboval, with dorso-lateral margins carinate, terminating in small postero-lateral tubercules; subpetiolar process developed as broad, rounded protuberance; postpetiole distinctly bilobed and broadly medially impressed.
Head sculpture reduced aciculate to aciculate-reticulate, more pronounced in darker coloured form than in orange-red variety; mesosoma with promesonotum dorsally irregularly carinulate-reticulate; meso- and metapleuron carinulate-areolate; propodeum with dorsal face carinulate and first half of posterior face reticulate, otherwise shiny; legs shiny to reticulate; dorsal face of petiole mostly reticulate, centrally shiny; postpetiole dorsally feebly reticulate; lateral and ventral face of petiole and postpetiole coarsely reticulate; helcium dorsally shiny or reticulate, at most feebly carinulate; promesonotum with 4-8 erect humeral setae, rarely with 2 additional setae on lateral carinae; petiole with single stiff, long erect setae on each posterolateral tubercle; postpetiole with a pair of erect dorso-posterior setae; abdominal tergites 4–7 with scattered erect pilosity.
Two distinct colour variants: first variant distinctly bi-coloured, with pale to bright orange-red head, mesosoma, legs, petiole and postpetiole that contrast with a brown to almost black gaster (as shown in Fig. 37 and 43); second variant (to which the lectotype belongs) uni-coloured, from reddish brown to brown to dark brown, to entirely black (specimen image on Antweb: CASENT0454184).
Queen measurements (n=3). HW 1.26–1.33, HL 1.06–1.15, EL 0.36–0.39, SL 0.87–0.93, MSNW 0.92– 1.05, MSNL 1.71–1.93, PTH 0.31–0.36, PTL 0.41–0.42, PTW 0.48–0.53, PPL 0.30–0.34, PPW 0.46–0.53, SPL 0.03–0.08, WL 2.06–2.23, LHT 0.88–0.96, CI 1.11–1.26, OI 0.32–0.37, SI 0.76–0.83, MSNI 0.51–0.55, PTHI 0.74–0.87, PTWI 1.15–1.28, PPI 1.54–1.58, SPI 0.01–0.04, LBI 2.33–2.38.
Queen description. Small (HW 1.26–1.33, WL 2.06–2.23). With worker characters, except as follows. Antennal scapes just barely surpassing posterior margin of head; eyes situated at midline of head in full face view; posterior margin of head straight.
Mesosoma slender (MSNI 0.51–0.55, WL 2.06–2.23); mesoscutum in dorsal view oval, about half as wide as long; mesopleuron with episternal groove carinulate to broadly carinate; in lateral view mesepisternum meeting pronotum at an oblique angle; postscutellum with posterior face rounded to flattened; propodeal suture deep and laterally reaching until level of propodeal spiracle; dorsal face of propodeum short, about one third of the size of posterior face; propodeal spines reduced, ranging from tubercule to denticles to very sharp points; petiole and postpetiole as in worker, but less prominently shaped and dorso-posterior tubercule on petiole lacking; antero-ventral subpetiolar tooth present, but reduced with respect to worker.
Propodeum with vertical carinulae on dorsal and posterior face; petiole reticulate throughout; postpetiole feebly reticulate throughout; face with 10–12 erect setae and abundant appressed pilosity; mesonotum with 20–26 erect setae; petiole and postpetiole with dorso-posterior setae and further with appressed pilosity throughout.
Colour brown to dark brown, or orange-red with gaster dark brown or black.
Comments. This species is recognizable by a combination of the following characters. The lateral portions of the promesonotum are raised with respect to the median portion and end in postero-lateral carinate denticles. Lateral carinae border the metanotal groove. The petiole has postero-lateral tubercles dorsally that each bear a single, stiff and long erect seta; the postpetiole is distinctly bilobed and broadly medially impressed, and also bears a pair of dorso-posterior stiff, long erect setae. Further noteworthy are the short and straight spines, the erect pilosity on abdominal tergites 4–7, and the mandibles that possess only 4 teeth. C. grevei is strongly supported by both nuclear and mitochondrial molecular data.
Both syntype specimens in the MHNG correspond well with the brown and black coloured variants in the CASC material, and with the type description. One of the MHNG syntypes carries matching locality data and collector information with the type description and is hence chosen as the lectotype.
Variation. Apart from colouration, the two variants of C.grevei exhibit slight variations in head sculpture. Some size polymorphism is exhibited in the workers of this species. Larger workers that have a disproportionately larger mesosoma than head are often found among colony samples of normal-sized workers.
Distribution and biology. Crematogaster grevei occurs throughout the seasonally dry forests and spiny forests of western and southwestern Madagascar (Fig. 54). Among members of the Malagasy Decacrema - group, these habitats are almost exclusively inhabited by C. grevei, its range is parapatric or allopatric in regard to most other species in the group. Narrow sympatry exists with the C. hova -complex in the Isalo Range, where isolated pockets of dry forest occur at higher elevations, in remnants of western subhumid forest in the P.N. Zombitse, and in the “tsingy” of P.N. Namoroka. In the Andohahela Range C. grevei occurs at low elevation in drier habitats, and the C. hova- complex and C. mahery take over at higher elevation in the humid forest. Fisher et al. frequently collected this species nesting in dead twigs on and above the ground, in rotten logs, from leaf litter samples, and also found it occasionally nesting under stones or in stems of live plants. Carton nesting has not been recorded for this species. The absence of this behaviour is probably related to the drier habitat of this species, as rotting plant material here may simply lose moisture too quickly to be implemented in carton fabrication.
The two colour variants of C.grevei have nearly allopatric distributions. The nature of these distributions suggests that the orange variant is associated with the spiny forests of the far south and southwest parts of Madagascar, while the brown or black variant is adapted to western dry and western subhumid forest habitats. Very likely some environmental variables play a role in stabilizing this colour dimorphism, at the moment however too little is known about the ecology of the species to make further assumptions.
description: Published as part of Blaimer, Bonnie B., 2010, Taxonomy and Natural History of the Crematogaster (Decacrema) - group (Hymenoptera: Formicidae) in Madagascar, pp. 1-39 in Zootaxa 2714 on pages 14-17, DOI: 10.5281/zenodo.199681