Syllophopsis fisheri

A montane rainforest species.

Identification
See the nomenclature section below.

Distribution based on Regional Taxon Lists
Malagasy Region: Madagascar.

Nomenclature

 *  fisheri. Monomorium fisheri Heterick, 2006: 165, figs. 12, 30, 31, 78, 79 (w.q.m.) MADAGASCAR. Combination in Syllophopsis: Ward et al., 2014: 13.

Syllophopsis fisheri and its close ally, Syllophopsis hildebrandti pose the same problems within the S. hildebrandti group that Monomorium termitobium does for the Monomorium monomorium group.

Workers within S. fisheri cluster around three morphotypes.

(a) Workers of this form exhibit only a slight variation in worker size. They are uniformly pale yellow to orange and, in the northernmost population, finely microstriolate over much of the head and mesosoma. The eye is very small, with about five or six ommatidia, its diameter much narrower than the thickest length of the antennal scape. The mandible most commonly has four teeth, rarely three teeth and two denticles or four teeth and a small denticle. All workers have smoothly rounded humeri. The node is regularly shaped and not particularly thick, and the postpetiole is evenly rounded. Most specimens come from a fairly large series from Ambohitantely Reserve, Antananarivo Province, with three additional workers having been collected from Manongarivo, Antsiranana Province. No queens or males have been identified for this morphotype, whose representatives have been taken from sifted litter and leaf mould.

(b) The second morphotype is very similar, and may well simply represent a southward continuation of form (a). The eye is similarly small and the color is the same. This form has a smoother exoskeleton, and the postpetiole in smaller specimens is attenuated anteriad. Many workers have a slight promesonotal shelf, but in others the humeri are rounded. Allometric variation is apparent between workers of the same nest, and in the southernmost populations the variation becomes a genuine polymorphism, with the largest workers rivaling S. aureorugosum and S. infuscum in size. These very large workers (HW = 1mm) have massive, quadrate head capsules and proportionately very small eyes. They also have a mandibular count of five or six mandibular teeth and denticles, contrasting with a usual count of four in the smaller workers. The mesonotal sector is sculptured in the large worker as is the mesopleuron, with strong lateral striae and striolae. The petiolar node is ‘blocky’ and subcuboidal. The queens are reasonably large ants, over half a centimeter in total length, with a massive, rounded mesosoma and small tubercles or denticles at the propodeal angles. Seen in full-face view, a number of these queens have paired setae straddling the mid point of the anterior clypeal margin, rather than one seta. Queens and males (which are as large as most workers of S. fisheri) have the full complement of wing veins. The CAS has several long series of this morphotype, collected from montane rainforest in Fianarantsoa and Toliara Provinces. These tend to be nest series, which is unsurprising as S. fisheri is larger and, hence, more conspicuous than most Monomorium species. Most collections have come from sifted litter, root mats and rotten wood.

(c) Workers of the third morphotype are very smooth and shining, and the predominant base color of the head and mesosoma is a russet-brown with some smaller workers tending to ochraceous. All workers have pale legs. The promesonotum mostly has a distinctly flattened humeral shelf, which projects over the sides when the ant is seen in full-face view. The metanotal groove is weak to absent, but the postpetiole is attenuate, as with smaller workers of morphotype (b). Where present, sculpture is confined to a few dull striolae on the mesopleuron and metanotum. While workers of this form have relatively the longest scapes (SI to 107), scape length shows the same variability as that of the other morphotype. When plotted on a scattergram, moreover, the relationship between HML and SL in all morphotypes shows the same slope (r2 = 0.95). Morphotype (c) exhibits weak monophasic allometry. The queen is smaller and brown rather than dull orange-yellow, but its appearance otherwise agrees with that of morphotype (b), and there is no significant difference between the males. Collections have been made along Madagascar’s eastern half, most samples being associated with rotten wood, though a few have come from sifted litter.

In my opinion, the variation seen in S. fisheri is infraspecific, as workers of all three morphotypes show convergence of form in at least some localities and all possess a basic underlying similarity. The tendency of populations of a Monomorium species living in very moist conditions to produce a worker morphotype that is smooth and glassy with minimal sculpture and a flattened promesonotum has been previously noted in the case of the Australian species, Monomorium leae Forel (Heterick 2001). This appears to have occurred with S. fisheri, whose distribution is confined to montane rainforest. Possibly, individual microhabitats experience greater precipitation or are otherwise damper than others, over long time periods imposing selection pressure on isolated populations of individual species to produce the sort of phenotypic variation noted above. The smooth, waxy cuticle may be an adaptation to prevent pathogenic fungi from growing on the ant, or, it may prevent waterlogging. The holotype selected is a medium-sized worker of morphotype (b), which is probably the form most commonly encountered.

Worker
Holotype. HML 2.25 HL 0.76 HW 0.66 CeI 86 SL 0.64 SI 98 PW 0.46.

HML 1.78–3.58; HL 0.64–1.23; HW 0.50–1.26; CeI 76–103; SL 0.42–0.96; SI 75–107; PW 0.34–0.80 (n=60).

HEAD: Head rectangular, oval, or, quadrate (i.e., heart-shaped); vertex planar to strongly concave; frons (i) shining and smooth except for piliferous pits, or, (ii) shining and smooth except for a few striolae around antennal sockets and front carinae and piliferous pits, or, (iii) shining and finely striolate and microreticulate; pilosity of frons a mixture of incurved, semi-erect setae and slightly shorter decumbent setae. Eye moderate, eye width 1–1.5× greatest width of antennal scape to small, eye width less than 1× greatest width of antennal scape; (in full-face view) eyes set above midpoint of head capsule to set at about midpoint of head capsule; (viewed in profile) eyes set around midline of head capsule; eyes more-or-less circular, or, elliptical, curvature of inner eye margin may be more pronounced than that of its outer margin. Antennal segments 12; antennal club three-segmented. Clypeal carinae weakly to strongly defined; anteromedian clypeal margin highly variable in appearance, being either: (i) narrowly convex between weakly ridged clypeal carinae, or, (ii) straight, or, (iii) straight between strongly divergent clypeal carinae, with clypeus descending almost vertically to horizontal arc of mandibles and sometimes transversely carinate below level of antennal insertions, or, (iv) emarginate, clypeal carinae indistinct, or, (v) emarginate, clypeal carinae terminating in blunt angles; paraclypeal setae moderately long and fine, curved; posteromedian clypeal margin extending slightly beyond level of posterior margin of antennal fossae to approximately level with antennal fossae. Anterior tentorial pits equidistant from antennal fossae and mandibular insertions. Frontal lobes straight, parallel. Psammophore absent. Palp formula 2,2. Mandibular teeth either five, or, four and one or two denticles, or, four; mandibles linear-triangular and smooth (except for piliferous pits); masticatory margin of mandibles strongly oblique; basal tooth approximately same size as t4 (five teeth present), or, smaller than t4 (five teeth present), or, approximately same size as t3 (four teeth present).

MESOSOMA: Promesonotum shining and smooth on dorsum, with entire lower mesopleuron distinctly striolate, or, promesonotum shining and faintly striolate dorsally, with striolae becoming more distinct posteriad, and entire mesopleuron distinctly striolate; in profile promesonotum (i) broadly convex, or, (ii) with anterior promesonotum smoothly rounded, thereafter more-or-less flattened, promesonotum on same plane as propodeum, or, (iii) promesonotum gently convex or distinctly flattened, humeri with vestigial to strongly accentuated dorsolateral flange; promesonotal setae greater than twelve; standing promesonotal setae consisting of a mixture of incurved, semierect setae and slightly shorter decumbent setae; appressed promesonotal setulae very sparse or absent. Metanotal groove variable, from strongly impressed, with distinct transverse costulae to absent. Propodeum varying from shining, with dorsum and sides of propodeum mainly smooth with weak to strong striolae on declivitous face and on metapleuron, to uniformly finely striolate; propodeal dorsum either slightly elevated anteriad and sloping away posteriad, propodeal angles not raised, or, propodeal dorsum sloping posteriad, and depressed between raised propodeal angles; propodeum either (i) smoothly rounded or (ii) with indistinct angle, or, (iii) angulate, propodeal angle blunt, or, (iv) distinctly angulate, propodeal angle sharp; if angulate, length ratio of propodeal dorsum to its declivity is between 3:2 and 4:3; standing propodeal setae consisting of one prominent pair anteriad, with a few to many erect to decumbent setae on/around dorsal and declivitous faces of propodeum, or, consisting of two or more prominent pairs of setae anteriad, often with another pair of prominent setae posteriad, and other smaller setae on/around dorsal and declivitous surfaces of propodeum; appressed propodeal setulae well-spaced and sparse to very sparse or absent; propodeal spiracle equidistant from metanotal groove and declivitous face of propodeum, or, nearer declivitous face of propodeum than metanotal groove; vestibule of propodeal spiracle distinct in some specimens; propodeal lobes present as blunt-angled flanges, or, present as rounded flanges.

PETIOLE AND POSTPETIOLE: Position of petiolar spiracle varying from lateral and situated well anteriad of petiolar node to lateral and situated within anterior sector of petiolar node. In profile, petiolar node shape ranging from subcuboidal, vertex rounded, to subcuboidal, inclined posteriad; appearance of node shining and smooth throughout, or, shining and faintly striolate and microreticulate; ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) between 4:3 and 3:4. Anteroventral petiolar process present as a thin flange tapering posteriad, or, absent or vestigial; ventral petiolar lobe absent. Height ratio of petiole to postpetiole between 4:3 and 1:1; height–length ratio of postpetiole between 4:3 and 1:2; postpetiole shining and smooth; postpetiolar sternite either (i) depressed near its junction with gaster, and sloping anteriad at angle of 45–60 to form large conspicuous lip at its anterior end, or, (ii) not, or, only slightly depressed at midpoint, anterior process prominent, or, (iii) petiolar sternite not depressed at midpoint, its anterior end an inconspicuous lip or small carina.

GASTER: Pilosity of first gastral tergite consisting of a mixture of incurved, semi-erect setae and slightly shorter decumbent setae.

GENERAL CHARACTERS: Color usually yellow to reddish-brown, some specimens with yellow head and gaster and reddish mesosoma, dark brown specimens with pale legs. Worker caste monomorphic, or, monophasically allometric, i.e., with variable size, but not morphology among workers from same nest, or, polymorphic.

Queen
HML 3.13–4.92; HL 0.90–1.24; HW 0.83–1.34; CeI 87–111; SL 0.76–1.02; SI 76–95; PW 0.79–1.50 (n=29).

HEAD: Head rectangular; vertex weakly concave or planar; either (i) frons shining and longitudinally striolate, with some smooth areas, or, (ii) frons longitudinally finely striolate; pilosity of frons with a mixture of well-spaced, distinctly longer erect and semi-erect setae interspersed with shorter setae or setulae, which are decumbent or appressed, longer setae thickest on vertex, or, with a mixture of incurved, semi-erect setae and slightly shorter decumbent setae. Eye elliptical, curvature of inner eye margin may be more pronounced than that of its outer margin; (in full-face view) eyes set at about midpoint of head capsule; (viewed in profile) set posteriad of midline of head capsule.

MESOSOMA: Mesoscutum broadly convex, or, broadly convex anteriad, with convexity reduced posteriad; mesoscutum and mesopleuron either shining and mainly smooth, vestigial striolae, if present, confined to anterior katepisternum, or, faintly longitudinally striolate on sides of pronotum and mesoscutum, dorsum of mesoscutum mainly smooth; length–width ratio of mesoscutum and scutellum combined between 2:1 and 3:2. Axillae separated by width of at least one axilla. Standing pronotal/mesoscutal setae consisting of a mixture of incurved, semi-erect setae and slightly shorter decumbent setae; appressed pronotal, mescoscutal and mesopleural setulae few, mainly on sides of pronotum and mesopleuron. Propodeum either (i) longitudinally striolate, except for posterior sector of propodeum, which is smooth, or, (ii) shining and densely striolate over whole surface, or, (iii) shining, with strong, transverse rugae dorsally, laterally and on declivitous face; propodeum angulate, propodeal angle blunt, or, distinctly angulate, propodeal angle sharp, or, distinctly angulate, propodeal angles produced as short denticles; propodeal dorsum sloping posteriad, and depressed between raised propodeal angles; standing propodeal setae consisting of up to a dozen or more longer erect and shorter sub-erect setae; appressed propodeal setulae very sparse or absent; propodeal spiracle ranging from nearer metanotal groove than declivitous face of propodeum to equidistant from metanotal groove and declivitous face of propodeum; propodeal lobes present as bluntly angled flanges.

WING: Wing veins tubular and strongly sclerotised; vein m–cu present as an entire vein enclosing first discoidal cell; vein cu–a present.

PETIOLE AND POSTPETIOLE: Petiolar spiracle either lateral and situated well anteriad of petiolar node, or, lateral and situated slightly anteriad of petiolar node, or, laterodorsal and situated slightly anteriad of petiolar node; node, in profile cuneate, vertex tapered; appearance of node shining and weakly striolate posteriad, or, shining, rugose posteriad; ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) between 4:3 and 1:1. Anteroventral petiolar process either present as a thin flange tapering posteriad, or, absent or vestigial; height ratio of petiole to postpetiole between 4:3 and 1:1; height–length ratio of postpetiole between 3:2 and 1:1; postpetiole smooth anteriad, rugose posteriad to strongly rugose; postpetiolar sternite depressed near its junction with gaster, and sloping anteriad at angle of 45–60 to form large conspicuous lip at its anterior end.

GASTER: Pilosity of first gastral tergite consisting of a mixture of incurved, erect and semi-erect setae and slightly shorter decumbent setae.

GENERAL CHARACTERS: Color brownish-yellow, through orange to brown with lighter areas. Brachypterous alates not seen. Ergatoid or worker-female intercastes not seen.

Male
HML 2.37–2.99; HL 0.68–0.79; HW 0.66–0.80; CeI 99–102; SL 0.17–0.20; SI 23–29; PW 0.76–0.84 Male (n=7).

HEAD: Head width-mesosoma width ratio between 4:3 and 3:4; frons finely micropunctate. Compound eyes protuberant and elliptical, or, protuberant and circular or subcircular; margin of compound eye clearly separated from posterior margin of clypeus. Ocelli not turreted. Ratio of length of first funicular segment of antenna to second funicular segment between 1:2 and 1:3. Maximum number of mandibular teeth and denticles four.

MESOSOMA: Mesoscutum broadly convex; either lower pronotum and mesoscutum finely stri olate, otherwise smooth and shining, or, shining and faintly striolate throughout, striolae becoming more deeply impressed on posterior mesopleuron. Parapsidal furrows distinct, vestigial or absent; notauli absent. Axillae separated by width of at least one axilla.

WING: Wing veins tubular and strongly sclerotised; vein m–cu present as an entire vein enclosing entire discoidal cell; vein cu–a present.

PETIOLE AND POSTPETIOLE: Petiolar spiracle lateral and situated well anteriad of petiolar node. Node (viewed in profile) conical, vertex rounded, or, evenly tumular to roundly conical; appearance of node shining and smooth, or, shining, with vestigial sculpture; ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) between 4:3 and 1:1. Anteroventral petiolar process present as a thin flange tapering posteriad, or, absent or vestigial. Height ratio of petiole to postpetiole between 4:3 and 1:1; height–length ratio of postpetiole between 4:3 and 3:4; postpetiole shining and smooth, or, shining, with vestigial sculpture.

GASTER: Pilosity of first gastral tergite consisting of a mixture of incurved, semi-erect setae and slightly shorter decumbent setae.

GENERAL CHARACTERS: Color head chocolate, gaster, mesosoma brown, legs yellowish-brown.

Type Material
Holotype: worker, Prov. Toliara, P.N. Andohahela, Manantalinjo, 3.8 km 113 ESE Mahamavo 900m, Sedro, 24º46′S 46º45′E 21–25.i.2002 Fisher et al BLF#/ex rotten log montane rainforest/CASENT0430841 5087. Paratypes: Prov. Toliara (locality details as for holotype, but collected ex root mat, ground layer, montane rainforest/ collection code 5147): 12 queens ; 13 workers ; 1 worker 2 queens (CAS); 13 workers + 12 queens.

Etymology
In honour of Dr. Brian Fisher (California Academy of Sciences).