Crematogaster sisa, Blaimer, Bonnie B., 2010

Blaimer, Bonnie B., 2010, Taxonomy and Natural History of the Crematogaster (Decacrema) - group (Hymenoptera: Formicidae) in Madagascar, Zootaxa 2714, pp. 1-39 : 29-37

Crematogaster sisa NEW SPECIES

( Fig. 33 & 39 )

Holotype worker. MADAGASCAR: R.S. Manongarivo, -14.02167, 48.41833, 1580m, 27.x.1998, sifted litter (leaf mold, rotten wood), montane rainforest, B.L.Fisher#1970(49)-2 (CASENT0193556, specimen image on antweb) (deposited in CASC).

Paratypes. 4w, same locality and collection data as holotype (B.L.Fisher#1970(49)-2, CASENT0193557, CASENT0193542 and CASENT0193543; #1972(11)-1, CASENT0193009) (deposited in MCZC, SAMC, MHNG, UCDC).

Material examined. ( CASC) MADAGASCAR: Antsiranana: R.S. Manongarivo: -14.02167, 48.41833, 1580m; -14.04667, 48.40167, 1860m (B.L.Fisher).

Worker measurements (n=10). HW 0.89–1.14; HL 0.81–1.08; EL 0.21–0.27; SL 0.73–0.84; WL 0.91– 1.12; SPL 0.16–0.24; PTH 0.16–0.23; PTL 0.24–0.31; PTW 0.26–0.35; PPL 0.17–0.22; PPW 0.24–0.33; LHT 0.71–0.90; CI 1.05–1.17; OI 0.22–0.28; SI 0.78–0.90; SPI 0.17–0.21; PTHI 0.65–0.83; PTWI 0.91–1.24; PPI 1.33–1.53; LBI 1.23–1.30.

Worker description. Medium to large species (HW 0.89–1.14, WL 0.91–1.12).

Masticatory margin of mandibles with 5 teeth; posterior margin of head straight or medially depressed, laterally forming gentle round corners; 1–3 ocelli sometimes present on large workers; antennal scapes just surpassing posterior margin of head; midline of eyes situated at midline of head in full face view.

Pronotum laterally angular; promesonotal suture usually complete, and distinctly and broadly impressed, continuing laterally to mesopleural spiracle and thereby constricting mesonotum in relation to pronotum; dorsum of promesonotum more or less flat in lateral view; antero-medial portion of mesonotum slightly raised with respect to pronotum, but not tuberculate; dorsum of mesonotum flat, lateral portion broadly angular; mesonotum postero-laterally angular or tuberculate, and with a distinct to indistinct posterior face; propodeal spines small to medium sized (SPI 0.17–0.21), half as long to as long as width between their bases, evenly tapering, straight or weakly down-curved, in dorsal view weakly diverging; petiole in dorsal view trapezoidal or suboval, weakly lobed or rounded, laterally weakly carinate, with weak postero-lateral tubercle; dorsum of petiole weakly concave; subpetiolar process articulated as acute and distinct antero-ventral tooth, but rarely may be present as only a minute tooth.

Head sculpture aciculate; mesosoma with mesopleuron costulate, and metapleuron partly costulate, partly aciculate; dorsal face of propodeum weakly carinulate; posterior face largely shiny; otherwise mesosoma largely aciculate; dorsal face of petiole mostly shiny; lateral and ventral face of petiole coarsely reticulate; postpetiole dorsally and ventrally rugulose; helcium carinulate; face usually with 4-6 erect setae; promesonotum with 0-2 erect humeral setae; petiole and postpetiole lacking erect pilosity.

Colour brown to dark brown.

Variation. There seems to be considerable gradual size variation in workers, but sampling of this species is too sparse to give a general statement.

Comments. This species is easily distinguished morphologically by its uniquely shaped subpetiolar process in form of an acute tooth. The species status of C. sisa is further well supported by both mitochondrial and nuclear DNA sequences.

Distribution and biology. Crematogaster sisa has to be regarded as a high-elevation endemic, known to date only from two localities in the rugged and isolated Manongarivo massif ( Fig. 59 ) that were visited during a biological inventory in 1998 by B.L. Fisher (see Fisher, 2002). Collections of foraging workers were made while sifting litter and beating vegetation in montane rainforest habitats at 1580 and 1860 m. No nest collections have yet been recorded for this species, thus reproductives and natural history are entirely unknown. The Manongarivo massif lies in the Sambirano Region of Madagascar’s northwest and is part of a mountain complex spanning much of northern Madagascar ( Gautier & Goodman, 2002) – probably one of the least accessible and least studied regions of the island. Further inventory efforts in this region may therefore result in expanding the known distribution of C. sisa and lead to the discovery of colonies and their nesting habits. The species occurs in sympatry with the C. hova -complex, but appears to be parapatric in distribution to C. nosibeensis by virtue of elevation, since the latter is found in northwest Madagascar only in lowland forests.

Etymology. “ Sisa ” is Malagasy for “remnant” and this species is named in allusion to its isolated distribution. “ Sisa ” is used in this combination as a noun in apposition.

Figures

FIGURES 32 – 37. Malagasy Crematogaster (Decacrema) species; a: full-face view, b: lateral view, c: dorsal view. 32: C. nosibeensis; 33: C. sisa; 34: C. sabatra; 35: C. mahery; 36: C. malala; 37: C. grevei.

FIGURES 38 – 43. Malagasy Crematogaster (Decacrema) species; a: petiole & postpetiole in dorsal view, b: petiole & postpetiole in lateral view. 38: C. nosibeensis; 39: C. sisa, 40: C. sabatra; 41: C. mahery; 42: C. malala; 43: C. grevei.

FIGURES 58 – 61. Distributions of Malagasy Crematogaster (Decacrema). 58: C. sabatra; 59: C. sisa; 60: C. hovacomplex, entire distribution; 61: C. hova- complex morphotype 1.