Crematogaster nosibeensis

A polydomous, polygynous ant that constructs arboreal cartoon nests.

Identification
Blaimer (2010, 2012c) - A member of the Crematogaster hova group.

Distribution
Madagascar: This species shows a distribution mostly restricted to low and mid-elevation rainforests of the Sambirano Region of Madagascar’s northwest, including the island of Nosy Bé, the Ampasindava peninsula and the Manongarivo massif. Isolated populations of Crematogaster nosibeensis exist in the transitional dry forests of the R.S. Ambre in the foothills of the Montagne d’Ambre massif in the far north of Madagascar and the R.S. Ambohitantely in the central highlands. (Blaimer 2010)

Distribution based on Regional Taxon Lists
Malagasy Region: Madagascar.

Biology
Blaimer (2010) - In the R.S. Manongarivo, I collected workers of Crematogaster nosibeensis from a trunk of Calantica (Salicaceae; vernacular name “Janganito”) that were transporting wood fibers to a carton nest out of reach for any of my collection methods. I therefore assume that this species makes carton nests in the Manongarivo region, although it has never been collected from a carton nest at any of the northern localities. Fisher et al. collected workers of C. nosibeensis with various ground-sampling techniques, but never in association with its nest site. In R.S. Manongarivo this species certainly belongs to the rarer and less dominant species of Crematogaster, since I was able to make no more than two collections during a period of four collecting days.

In striking contrast however, C. nosibeensis is a conspicuous and dominant element of the canopy ant fauna in R.S. Ambohitantely, side by side with the Crematogaster hova-complex. Here I found the species nesting exclusively in carton nests, mostly constructed high up (ca. 15–25m) in the canopy. One remarkable collection event involved two very large, polydomous carton nest colonies that had nests in neighbouring trees of the endemic genus Sarcolaena (Sarcolaenaceae). Each colony consisted of two large (15x15cm – 20x25cm) nests housing either workers, reproductives and brood, or just workers and brood. Close to the main nests, 4–6 smaller (ca. 2x1cm – 5x5cm) satellite carton nests or shelters were present, containing worker ants and mealybugs of an undescribed species in the genus Tylococcus (Pseudococcidae), which were morphologically close to but distinct from those collected with C. mahery in P.N. Andringitra (P.J. Gullan, pers. comm.). The sole function of these satellite carton shelters appears to be the protection of the mealybugs. Besides workers, a dealate queen (each) and brood, both of these colonies also contained massive numbers of alates, both queens and males. This suggests that this was the height of reproduction for this species in the region (month of February). In contrast, none of the colonies of the C. hova-complex collected in Ambohitantely possessed alates – the temporal separation of reproduction may act as an important mechanism of reproductive isolation between these sympatric species.

Morphology
This species displays interesting bimodal variation in coloration, similar to that expressed in Crematogaster grevei. Workers of populations from northern Madagascar (R.N.I. Lokobé, R.S. Manongarivo, Ampasindava, R.S. Ambre) are brown or black, whereas the isolated population from the central highlands of Madagascar (R.S. Ambohitantely) is bi-coloured red-orange and black. Individuals from the latter are also generally larger. Queens lack the variation in colour. (Blaimer 2010)

Nomenclature

 *  nosibeensis. Crematogaster hova r. nosibeensis Forel, 1891b: 181 (q.) MADAGASCAR.
 * Blaimer, 2010: 25 (w.).
 * Combination in C. (Decacrema): Wheeler, W.M. 1922a: 1026.
 * Subspecies of hova: Dalla Torre, 1893: 84; Wheeler, W.M. 1922a: 1026; Emery, 1922e: 138; Bolton, 1995b: 158.
 * Status as species: Blaimer, 2010: 25 (redescription).

Worker
Blaimer (2010) - Measurements (n=13). HW 0.86–1.04; HL 0.75–0.94; EL 0.19–0.24; SL 0.64–0.81; WL 0.80–1.05; SPL 0.13–0.21; PTH 0.17–0.22; PTL 0.24–0.30; PTW 0.26–0.37; PPL 0.17–0.22; PPW 0.23–0.31; LHT 0.65–0.88; CI 1.12–1.18; OI 0.23–0.27; SI 0.81–0.90; SPI 0.15–0.20; PTHI 0.69–0.79; PTWI 1.07–1.37; PPI 1.26–1.53; LBI 1.17–1.28.

Small to medium size (HW 0.86–1.04, WL 0.80–1.05).

Masticatory margin of mandibles with 5 teeth; posterior margin of head straight, laterally forming round corners; antennae with scapes easily surpassing posterior margin; midline of eyes situated at midline of head in full face view.

Pronotum laterally subangular; promesonotal suture varying from completely impressed to absent; outline of promesonotum flat in lateral view; antero-medial portion of mesonotum either slightly raised over pronotum (but never tuberculate), or indistinguishable from pronotum; dorsal face of mesonotum flat, lateral portions broadly angular; mesonotum postero-laterally angular and usually with a distinct posterior face; dorsal face of propodeum absent to very short; propodeal spines small-medium sized (SPI 0.15–0.20), between half and full the width between their bases, thin and needle-shaped, slowly tapering, straight or down-curved, in dorsal view weakly diverging (<20º); propodeal spiracle large, much larger than base of spines; petiole in dorsal view weakly to distinctly lobed; subpetiolar process articulated as broad, rounded protuberance.

Head sculpture aciculate; promesonotum dorsally aciculate with shiny parts; mesopleuron largely shiny, metapleuron carinulate to reticulate; posterior face of propodeum largely shiny; petiole dorsally mostly shiny, laterally and ventrally coarsely rugulose-reticulate; postpetiole dorsally rugulose, ventrally rugulose-reticulate; helcium carinulate; erect pilosity on face reduced to 2 setae at base of frontal carinae; ventral pilosity on head reduced, ventral suberect pilosity absent; pilosity on dorsum of mesosoma usually confined to 2 erect humeral setae; petiole lacking erect pilosity; postpetiole with or without short postero-lateral setae.

Two variants. Either colour brown to black, with mesosoma usually lighter coloured than head and metasoma (R.N.I. Lokobé, R.S. Manongarivo, Ampasindava, R.S. Ambre; as shown in Fig 32 & 38), or distinctly bi-coloured with head, mesosoma and part of A4 reddish to orange and rest of metasoma dark brown (R.S. Ambohitantely; specimen image on Antweb: CASENT0423447).

Queen
Blaimer (2010) - Measurements (n=3). HW 1.64–1.72, HL 1.37–1.39, EL 0.43–0.45, SL 0.92–0.94, MSNW 1.33– 1.37, MSNL 2.06–2.07, PTH 0.34–0.38, PTL 0.41–0.47, PTW 0.44–0.54, PPL 0.39–0.43, PPW 0.47–0.54, SPL 0.12–0.16, WL 2.20–2.29, LHT 1.06–1.10, CI 1.20–1.24, OI 0.31–0.33, SI 0.66–0.68, MSNI 0.64–0.66, PTHI 0.71–0.93, PTWI 0.95–1.33, PPI 1.18–1.26, SPI 0.05–0.07, LBI 2.08–2.09.

Medium size (HW 1.64–1.72; WL 2.20–2.29). With worker characters except as described below.

Antennal scapes not surpassing posterior margin of head; midline of eyes situated below midline of head in full face view; posterior margin straight.

Mesosoma short and compact (MSNI 0.64–0.66, WL 2.20–2.29); mesoscutum in dorsal view subcircular, short, about as long as wide; scutellum in lateral view greatly projecting over postscutellum; mesopleuron with episternal groove weakly impressed; in lateral view mesepisternum meeting pronotum in nearly perpendicular angle; dorsal face of propodeum very short; propodeal suture shallow, but laterally reaching level of propodeal spiracle; propodeal spines ranging from denticles to very sharp points, never reduced to tubercules; petiole somewhat flattened anteriorly in lateral view; dorsal face of petiole flat; subpetiolar process reduced to small angular antero-ventral tooth; metasoma oval-shaped in dorsal view, shorter and broader than in other Decacrema species; abdominal segment 4 narrowed anteriorly.

Propodeum with a single transverse ridge or carinae marking the border to posterior face; petiole reticulate throughout; postpetiole feebly reticulate throughout; 10–12 erect setae on face; mesonotum with 20–24 erect setae, but leaving median portion of mesonotum devoid of erect pilosity; dorso-posterior short, erect setae on petiole and postpetiole present, in addition petiole and postpetiole with lateral suberect to erect setae and scattered appressed pubescence. Meso- and metasoma brown, head reddish brown, legs brown to dark brown, metasoma brown to dark brown.

Type Material
Blaimer (2010) :

Queen syntypes from Madagascar, Nosibé (O’swald) [Hamburg Museum] [not examined, destroyed in WWII].

Neotype queen. Madagascar: Nosy Bé, R.N.I. Lokobé: -13.41944, 48.33117, 30m, 19.–24.iii.2001, at light, rainforest, B.L. Fisher et al. #3420 (CASENT0436030; specimen image on Antweb) (deposited in ).

1) A name-bearing type is necessary to support the rank elevation of C. nosibeensis and to clearly demarcate this species from the C. hova-complex. Both queens and workers of this species are easily distinguished from the C. hova-complex by a combination of characters. Diagnostic for queens is the short and compact mesosoma, the short propodeum with a transverse ridge or carinae bordering the propodeal declivity, and the acute propodeal spines compared to queens in the C. hova-complex. Workers are recognizable by means of their blunt or broadly rounded subpetiolar process, the postero-lateral angular promesonotum, and their reduced sculpture.

2) Confirmation has been obtained from the “Zoologisches Museum” in Hamburg, Germany that the queen syntypes of C. hova nosibeensis collected by M. O’swald were among the collections of this museum destroyed in World War II (R. Peters, pers comm.).

3) The conspecificity of the neotype with the former name-bearing types seems secured since it agrees perfectly with the original description. Moreover, this is the only species in the Decacrema-group that occurs at the type locality, the island of Nosy Bé [= Nosibé, the old spelling in the original description (United States Board on Geographical Names, 1989)], from where the collections of M. O’swald are documented (Forel, 1891).

A queen collected from the type locality Nosy Bé is hereby chosen as the neotype and a full description is presented above. For the benefit of having a comprehensive type collection in one place, the neotype is deposited together with the other type material in the CASC, not in Hamburg.