Syscia Roger, 1861

Borowiec, Marek L., 2016, Generic revision of the ant subfamily Dorylinae (Hymenoptera, Formicidae), ZooKeys 608, pp. 1-280 : 174-177

Taxon classification Animalia Hymenoptera Formicidae

Syscia Roger, 1861 gen. rev.

Type-species.

Syscia typhla , by monotypy.

Syscia is the only doryline genus with a disjunct distribution between the Old and New World, and includes many cryptic, undescribed species.

Diagnosis.

Worker. Syscia workers have 11- or 9-segmented antennae, eyes small to absent, and are usually heavily sculptured with abundant body pilosity. Body is usually uniformly colored and ranges from yellow through reddish to dark brown but never black. They possess apparently autapomorphic characters that serve to easily distinguish this lineage from all other dorylines: basal segment of hind tarsus widening distally with a light patch of cuticle on the inner (flexor) side, and abdominal tergite IV anteriorly folding over sternite. This combination is unique to Syscia and although species in other lineages may have similar habitus ( Ooceraea , Parasyscia ), none of these possess these characteristics.

Male. The males of Syscia have the number of antennal segments reduced to 12. They can be difficult to distinguish from Ooceraea (see under diagnosis for that genus), but a lack of constrictions between abdominal segments IV, V, and VI, presence of a spur on middle tibia, and no costal vein (C) in the fore wing will distinguish them from the other genera where a reduction in the number of antennal segments is currently known, which include Acanthostichus , Eusphinctus , and Simopone .

Description.

Worker.Head: Antennae with 9 or 11 segments. Apical antennal segment conspicuously enlarged, much broader than and longer than two preceding segments combined. Clypeus with cuticular apron. Lateroclypeal teeth present. Parafrontal ridges reduced. Torulo-posttorular complex vertical. Antennal scrobes absent. Labrum with median notch or concavity. Proximal face of stipes projecting beyond inner margin of sclerite, concealing prementum when mouthparts fully closed. Maxillary palps 2-segmented. Labial palps 2-segmented. Mandibles triangular, edentate. Eyes absent or present, composed of 1-5 ommatidia. Ocelli absent. Head capsule with differentiated vertical posterior surface above occipital foramen. Ventrolateral margins of head without lamella or ridge extending towards mandibles and beyond carina surrounding occipital foramen. Posterior head corners dorsolaterally immarginate. Carina surrounding occipital foramen ventrally present. Mesosoma: Pronotal flange not separated from collar by distinct ridge. Promesonotal connection with Pronotomesopleural suture completely fused. Pronotomesopleural suture visible, unfused up to notal surface. Mesometapleural groove not impressed. Mesometapleural groove weakly impressed. Transverse groove dividing mesopleuron present or absent. Pleural endophragmal pit concavity present. Mesosoma dorsolaterally immarginate. Metanotal depression or groove on mesosoma absent. Propodeal spiracle situated low on sclerite. Propodeal declivity without distinct dorsal edge or margin and rectangular in posterior view. Metapleural gland with bulla visible through cuticle. Propodeal lobes present, well developed. Metasoma: Petiole anterodorsally immarginate, dorsolaterally immarginate, and laterally above spiracle immarginate. Helcium in relation to tergosternal Pronotomesopleural suture placed at posttergite and axial. Prora forming a U-shaped margin with median ridge. Spiracle openings of abdominal segments IV–VI circular. Abdominal segment III anterodorsally immarginate and dorsolaterally immarginate. Abdominal segment III more than half size of succeeding segment IV, which is weakly constricted at presegmental portion (uninodal waist). Girdling constriction of segment IV present, i.e. pre- and postsclerites distinct. Cinctus of abdominal segment IV gutter-like, not sculptured or cross-ribbed. Abdominal segment IV not conspicuously largest segment or conspicuously largest segment. Abdominal tergite IV folding over sternite, anterior portion of sternite concealing tergite in lateral view. Girdling constriction between pre- and posttergites of abdominal segments V and VI absent. Girdling constriction between pre- and poststernites of abdominal segments V and VI absent. Pygidium medium-sized, with impressed medial field, and armed with modified setae. Hypopygium unarmed or armed with modified setae. Legs: Mid tibia with single pectinate spur. Hind tibia with single pectinate spur. Hind basitarsus widening distally, oval in cross-section. Posterior flange of hind coxa not produced as raised lamella. Metatibial gland present as oval patch of whitish cuticle. Metabasitarsal gland present. Hind pretarsal claws simple. Polymorphism: Monomorphic.

Male.Head: Antennae with 12 segments. Clypeus with cuticular apron. Parafrontal ridges present. Torulo-posttorular complex vertical. Maxillary palps 4-segmented. Labial palps 2-segmented. Mandibles triangular, edentate. Ventrolateral margins of head without lamella or ridge extending towards mandibles and beyond carina surrounding occipital foramen. Carina surrounding occipital foramen ventrally present. Mesosoma: Pronotal flange not separated from collar by distinct ridge. Notauli present. Transverse groove dividing mesopleuron present. Propodeal declivity reduced, without distinct dorsal edge or margin. Metapleural gland opening absent. Propodeal lobes present. Metasoma: Petiole anterodorsally immarginate, dorsolaterally immarginate, and laterally above spiracle marginate. Helcium in relation to tergosternal Pronotomesopleural suture placed at posttergite and axial. Prora forming a U-shaped margin with median ridge. Spiracle openings of abdominal segments IV–VI circular. Abdominal segment III more than half size of succeeding segment IV; latter weakly constricted at presegmental portion (uninodal waist). Abdominal segment III about half size of succeeding segment IV or less; latter strongly constricted at presegmental portion (binodal waist). Girdling constriction of segment IV present, i.e. pre- and postsclerites distinct. Cinctus of abdominal segment IV gutter-like and cross-ribbed. Girdling constriction between pre- and postsclerites of abdominal segments V and VI absent. Abdominal segment IV conspicuously largest segment. Abdominal sternite VII simple. Abdominal sternite IX distally armed with two spines. with lateral apodemes about as long as medial apodeme, directed anteriorly (towards head). Genitalia: Cupula long relative to rest of genital capsule and shorter ventrally than dorsally. Basimere broadly fused to telomere, with no sulcus trace at junction, and ventrally with left and right arms abutting. Telomere gradually tapering toward apex. Volsella not tapering much toward apex, relatively broad. Penisvalva laterally flattened, at apex hooked ventrally, in Neotropical forms also apparently curving outwards. Legs: Mid tibia with single pectinate spur. Hind tibia with single pectinate spur. Posterior flange of hind coxa not produced as raised lamella. Metatibial gland present as oval patch of whitish cuticle. Metabasitarsal glands absent. Hind pretarsal claws simple. Wings: Tegula present, broad, demiovate in shape. Vein C in fore wing absent. Pterostigma broad. Abscissa R·f3 absent. Abscissae Rs·f2-3 absent. Cross-vein 2r-rs present, forming base of 'free stigmal vein’ (2r-rs&Rs·f4-5) in absence of Rs·f3 and 2rs-m. Abscissae Rs·f4-5 present, fused in absence of 2rs-m. Abscissa M·f2 in fore wing contiguous with Rs+M. Abscissa M·f4 in fore wing present, short, not reaching wing margin. Cross-vein 1m-cu in fore wing absent. Cross-vein cu-a in fore wing present, arising from M+Cu and proximal to M·f1. Vein Cu in fore wing absent past M+Cu. Vein A in fore wing with abscissae A·f1 and A·f2 present. Vein C in hind wing absent. Vein R in hind wing absent. Vein Sc+R in hind wing present. Abscissa Rs·f1 in hind wing present, longer than 1rs-m. Abscissa Rs·f2 in hind wing present, not reaching wing margin. Cross-vein 1rs-m in hind wing absent or present, about as long as M·f1. Vein M+Cu in hind wing present. Abscissa M·f1 in hind wing absent. Abscissa M·f2 in hind wing absent. Cross-vein cu-a in hind wing absent. Vein Cu in hind wing absent. Vein A in hind wing with abscissa A·f1 present.

Gyne. Alate, brachypterous, or ergatoid with eyes of variable size and with or without ocelli. Gynes are known for Syscia augustae , Syscia honduriana , Syscia humicola , and Syscia typhla . In Syscia typhla the gynes have well-developed flight sclerites on the mesosoma but I have never examined a specimen with wings. Field observations of Syscia augustae or a closely related species suggest that virgin queens may be brachypterous (Michael Branstetter pers. comm.). Ergatoid queens have been reported in Syscia humicola ( Ogata 1983), and their morphology is very similar to that of the worker, except for larger size, presence of compound eyes and a single ocellus in some but not all gynes. Confirmed alate or apparently dealated gynes are so far known only in undescribed forms from both Old and New World.

Larva. Described for Syscia augustae ( Wheeler 1903b). Cocoons absent.

Distribution.

This is the only doryline genus with a disjunct distribution between the New and Old Worlds (except for tramp Ooceraea biroi ), with one center of diversity in Central America, with records from the Antilles (Cuba and Dominican Republic) and as far north as Arkansas, United States, and the other center in Southeast Asia west of Wallace’s Line, especially Borneo, reaching Japan to the north and southern India to the west.

Taxonomy and phylogeny.

Syscia was described by Roger (1861) in his paper on ' Ponera -like ants’. Forel (1893a) included it in his newly erected ‘Cerapachysii’ and subsequently it was treated as either a genus (e.g. Forel 1900b, Bingham 1903) or a subgenus of Cerapachys (e.g. Wheeler 1902, Emery 1911 e) until Kempf (1972) treated it as a synonym of the latter.

Syscia is here recognized as a valid genus, following the molecular evidence that Neotropical and Indomalayan species form a clade ( Brady et al. 2014, Borowiec, in prep.) and because species related to typhla are easily distinguished from a closely related group, Ooceraea . There are five species currently described but at least fifteen additional morphospecies present in collections from the Old World and more than 30 undescribed species in the New World (Theodore Sumnicht pers. comm.).

This lineage belongs to a clade with Eusphinctus and Ooceraea (Borowiec, in prep.). No attempts of reconstructing the internal phylogeny have been made.

Biology.

Syscia species are found in leaf litter samples and soil cores. The foraging habits are not known. Syscia augustae , a species present in southern United States, has been observed on diurnal emigrations and briefly studied under laboratory conditions (Clint Penick pers. comm.). The brood production in Syscia augustae is synchronized. Gyne morphology varies in this lineage, with ergatoid, brachypterous, and fully winged individuals known. There is an observation of a brachypterous gyne aggregation under a stone (Michael Branstetter pers. comm.). It is unknown whether this represents cooperative colony foundation.

Species of Syscia

Syscia augustae (Wheeler, W. M., 1902): United States, comb. n.

Syscia honduriana (Mann, 1922): Honduras, comb. n.

Syscia humicola (Ogata, 1983): Japan, comb. n.

Syscia tolteca (Forel, 1909a): Guatemala, comb. n.

Syscia typhla Roger, 1861: Sri Lanka, comb. rev.