Streblognathus peetersi

Colonies are small, averaging 95 workers, and reproduction is exclusively via gamergates.

Identification
Robertson (2002) - In the worker, scape, mesosoma and legs are shorter relative to width measurements in Streblognathus peetersi than in Streblognathus aethiopicus with scape index being the easiest measurement to separate the two species. The relatively longer body and appendages of S. aethiopicus, combined with its larger size results in Scape length, Meso-propodeal length and tibia length being longer in this species than in S. peetersi. There is also only a slight degree of overlap in Eye length. Mandibles in S. aethiopicus are castaneous with a black border whereas in S. peetersi they are generally black although there is a small proportion of specimens with some castaneous colouration. In the male, the subgenital plate in S. peetersi has convex lateral margins and the apex is broadly rounded, whereas in S. aethiopicus the lateral margins are concave and the apex is flat. The barbed apices of the penis valves are oriented vertically in S. peetersi whereas in S. aethiopicus, they splay outwards. In contrast, the barbs along the outer margins of the penis valves, behind the apices, are splayed outwards in S. peetersi whereas in S. aethiopicus they are oriented vertically.

There are two species of Streblognathus

Streblognathus aethiopicus - Scape both absolutely and relatively longer (Scape length 4.32-5.11 mm; Scape index 102-113); Eye length 0.86-1.03 mm; Mesonotal-propodeal length 5.56-6.32 mm; hind tibia length 4.80-5.54 mm

Streblognathus peetersi - Scape both absolutely and relatively shorter (Scape length 3.28-4.12 mm; Scape index 87-98); Eye length 0.62-0.85 mm; Mesonotal-propodeal length 4.34-5.47 mm; Hind tibia length 3.80-4.80 mm.

Distribution
Streblognathus peetersi has a wide distribution in the grassland regions of eastern South Africa, Lesotho and Swaziland.

Distribution based on Regional Taxon Lists
Afrotropical Region: Lesotho, South Africa, Swaziland.

Biology
Robertson (2002) - Distribution of the genus is limited to grassland and southern karoo regions of southern Africa, and it has the largest worker ants in Africa, measuring up to 2.5 cm long. Like many large southern African ponerine ants, Streblognathus has lost the queen caste and instead, reproduction is undertaken by a single, mated worker, termed a gamergate (Ware et al.  1990; Peeters 1991). Mandibular glands of workers contain three types of pyrazines which, in a study based on two colonies, were found to occur in smaller quantities and in different proportions in the gamergate compared with the mated workers (Jones et al. 1998). Colony size of S. aethiopicus is moderately small ranging from 9 to 51 workers (Ware et al. 1990). Workers stridulate, apparently for alarm purposes, by moving the presclerite of the second gastral segment, which has ridges on it, against the posterior edge of the first gastral segment (Lewis 1896, Ware 1994).

Schmidt and Shattuck (2014) - Relatively little is known about most aspects of Streblognathus ecology. They occur in arid thorn scrub and grasslands in extreme southeastern Africa, and apparently are specialist predators of tenebrionid beetles (Brown, 2000; Robertson, 2002). Workers stridulate when disturbed (Ware, 1994) and are able to differentiate nestmates from non-nestmates (Schlüns et al., 1996).

In contrast, a fair bit is known about the reproductive and social behavior of the genus. Colonies are small, with usually around 100 workers or fewer (mean = 35 for Streblognathus aethiopicus; mean = 95 for Streblognathus peetersi; Ware et al., 1990; Peeters, 1993). The queen caste is entirely absent, with reproduction instead being performed by a single mated gamergate worker. This gamergate, or alpha worker, is morphologically indistinguishable from the other workers but differs from them in its ovarian development (Ware et al., 1990), hormone levels (Brent et al., 2006), neurochemistry (Cuvillier-Hot & Lenoir, 2006), cuticular hydrocarbons (Cuvillier-Hot et al., 2005), and relative proportions of mandibular gland secretions (Jones et al., 1998). Within a colony, workers are behaviorally differentiated into foragers, nest workers and the sole reproductive gamergate (Ware et al., 1990).

A dominance hierarchy exists among the workers in a colony, with high-ranking workers subordinate to the alpha but dominant over the low-ranking individuals. Gamergates inhibit reproduction by subordinate workers through chemical signaling (Cuvillier-Hot et al., 2004b). The reproductive division of labor within the colony is further maintained by the low-ranking workers, who identify the alpha worker and aggressively prevent sub-alpha workers from ascending to dominance unless the alpha senesces. In such instances, high-ranking workers aggressively compete until a single alpha ascends to dominance; this is usually the previous beta, or second ranked, worker (Cuvillier-Hot et al., 2004a, 2004b).

Castes
Queens have been lost in Streblognathus; reproduction is carried out by gamergate workers.

Nomenclature

 *  peetersi. Streblognathus peetersi Robertson, 2002: 11, figs. 1, 2, 3b, 3d, 4 (w.m.) SOUTH AFRICA.

Worker
Matching description of genus (see Streblognathus ) but with the following specimen-specific characters.

Size. Head width 3.87 mm; Head length 3.93 mm; Eye length 0.71 mm; Scape length 3.54 mm; Pronotal width 2.54 mm; Mesonotal-propodeal length 4.66 mm; Hind tibia length 4.04 mm; Cephalic index 99; Scape index 91; Eye index 18.

Head. Mandibles glossy smooth with sparsely distributed punctures containing hairs. Fringe of black hairs on anterior surface, behind basal margin and basal tooth. Anterior clypeal margin with middle section broadly concave, projecting beyond the outer margins and meeting them in a right angle. Compound eyes situated slightly anterior to mid-length of head. Fine puncturing on head poorly defined and smeared in appearance. Golden pubescence on head sparse to absent, limited mainly to the posterior, the central region and anterior to eyes. Antennal scapes with sparse golden pubescence overlaid by sparse decumbent black hairs. Venter of head smooth to shagreenate with sparse golden pubescence and uniformly distributed short, black hairs.

Mesosoma. Propodeal dorsum in profile mainly flat but curving down slightly to the metanotal groove and terminating posteriorly in dorsally projecting short spines. Slight indentation present about one quarter of the way from the metanotal groove. No distinct lateral margins to propodeal dorsum. A hairless shallow furrow passes from the dorsal edge of the propodeal spiracle, round its posterior edge, and across to above the dorsal edge of the metapleural gland opening. Mesosoma dorsum covered in fine, ill-defined punctate sculpture, some of the punctures flowing into one another. Sides with shagreenate sculpture. Mesosoma covered in sparse, fine, golden pubescence and dorsum with scattered subdecumbent short, black, pointed hairs.

Petiole. Appearing as in description of genus. Covered in sparse golden pubescence and uniformly distributed subdecumbent short black hairs.

Gaster. As described for genus.

PARATYPE WORKERS. Matching the description of the genus and the holotype but with the following additional variation. Size. Head width 3.83-4.12 mm; Head length 3.79-4.11 mm; Eye length 0.70-0.77 mm; Scape length 3.54-3.77 mm; Pronotal width 2.82-2.70 mm; Mesonotal-propodeal length 4.55-4.93 mm; Hind tibia length 3.91-4.26 mm; Cephalic index 98-102; Scape index 89-94; Eye index 18-19 (n=6).

ALL WORKERS. Size. Head width 3.43-4.46 mm; Head length 3.60-4.50 mm; Eye length 0.62-0.85 mm; Scape length 3.28-4.12 mm; Pronotal width 2.30-2.84 mm; Mesonotal-propodeal length 4.34-5.47 mm; Hind tibia length 3.80-4.80 mm; Cephalic index 95-102; Scape index 87-98; Eye index 17-21 (n=38).

Male
PARATYPES. Size. Head width 2.26-2.42 mm; Head length 1.83-1.90 mm; Eye length 1.25-1.32 mm; Ocellus diameter 0.55-0.69 mm; Forewing length 13.46-13.81 mm; Hind tibia length 4.02-4.12 mm; Cephalic index 122-128; Eye index 53-57 (n = 6).

ALL MALES. Size. Head width 2.02-2.51 mm; Head length 1.62-1.97 mm; Eye length 1.12-1.41 mm; Ocellus diameter 0.42-0.69 mm; Forewing length 13.46-14.83 mm; Hind tibia length 3.83-4.38 mm; Cephalic index 121-130; Eye index 53-57 (n = 12).

Type Material
HOLOTYPE: worker, SOUTH AFRICA, Limpopo Province: next to Magoebaskloof Hotel, 23º53'S 29º59E, 8.iv.2001, C. Peeters, SAM-HYMC017887a (SAMC). PARATYPE: workers (unless otherwise indicated): same locality as holotype, and collector is C. Peeters unless otherwise indicated: 24.i.2000, 'MAGOE #A', SAM-HYM-C015165; 24.i.2000, 'MAGOE#B', SAM-HYM-C015166; 24.i.2000, 'ZH-2', SAM-HYM-C015168; 24.i.2000, 'ZH-3', SAM-HYM-C015169 (males); 24.i.2000, SAMHYM-C017879; 24.i.2000, 'ZH-1', SAM-HYM-C017880; v.2000, 'ZH-5', SAM-HYMC017882; v.2000, 'ZH-6a', SAM-HYM-C017883; v.2000, 'ZH-7', SAM-HYM-C017884; J de Oliveira, 9.ii.2001, 'ZH-9', SAM-HYM-C017885; J de Oliveira, 10.ii.2001, 'ZH-10', SAM-HYM-C017886; 8.iv.2001, SAM-HYM-C017887 (workers and males). Some duplicate specimens of above paratype material have been deposited in The Natural History Museum, London and at the California Academy of Sciences, San Francisco.

Etymology
Named after Christian Peeters who drew my attention to this new species and collected the type material. It is also named after him in recognition of the substantial contribution he has made to our understanding of ponerine reproductive biology.