Pouebo symmetricauda, Bickel, 2008

Bickel, Daniel J., 2008, Pouebo (Diptera: Dolichopodidae), a remarkable new genus from New Caledonia, with secondary symmetry in the male postabdomen, Mémoires du Muséum national d'Histoire naturelle 197, pp. 49-56 : 51-55

Pouebo symmetricauda n. sp.

Figs 1, 2A-C

TYPE MATERIAL. — New Caledonia: holotype ♂, paratypes 4 ♂, ♀, Prov. Nord, Mt. Mandjélia , 5 km WSW of Pouébo , 20.397ºS 164.528ºE, 780 m, 2-13.XI.2000, Malaise trap, D. W. Webb, E. I. Schlinger & M. E. Irwin; paratypes 5 ♂, same but 13-27.XI.2000; ♂, ♀, same but 9-15.XII.2000 ( INHS; holotype and 1 paratype deposited MNHN) .

MATERIAL EXAMINED. — New Caledonia: ♂, 2 ♀, Prov. Nord, Réserve spéciale de faune de l’Aoupinié, 21.157ºS 165.323ºE, 550 m, Malaise trap, 30.XI-4.XII.2000, M. E. Irwin & L. J. Boultin ( INHS) .

DESCRIPTION. — Male: body length: 1.7 mm; wing: 1.5 x 0.5 mm; habitus: Fig. 1.

Head: dorsal postcranium slightly concave; vertex not excavated between ocellar tubercle; frons wide, metallic green with bronze reflections, without pruinosity; major setae black; short postvertical seta, and strong vertical and ocellar setae present; face and clypeus wide, metallic green without pruinosity; eye with anterior facets distinctly enlarged; palpus yellowish, rather narrow, with strong brown basal and apical seta; proboscis brown; scape and pedicel brown; pedicel with short dorsal and ventral setae: first flagellomere dull yellow, subrectangular; arista dorsoapical, brown, about as long as head height; ventral postcranium with long white setae; dorsal postorbital setae short and black.

Thorax: rather short and rounded in lateral view; almost entirely dark metallic blue green with little pruinosity; setae black; ac comprising one offset pair long setae near mesonotal suture, sometimes with unpaired short seta anteriad; 2 strong posterior dc setae bordering mesonotal slope, and with 2-3 weak hair-like setae anteriad (MSSC); 1 postalar seta, 1 posterior supra-alar seta, 1 sutural intraalar and shorter intraalar anteriad; 1 postpronotal seta, and 2 notopleural setae; proepisternum with fine hair; scutellum with strong median setae only; postnotum with slight bulge under scutellum.

Legs: coxae brown; trochanters I and II yellow, trochanter III brown; basal two-thirds of femora I and II, and almost all of femur III to knee dark brown with metallic green reflections; distal third of FI and FII, knee of FIII, all tibiae, basal tarsomeres yellow; t 5 of legs I and II and IIIt 3-5 dark brown; CI with pale hairs and slightly stronger pale distolateral setae; CII distally with some short anterolateral setae; CIII with single strong lateral seta in basal third; tibiae bare of major setae; I: 2.2; 2.0; 1.4/ 0.3/ 0.3/ 0.2/ 0.2; FI with av and pv rows of short pale hairs; TI with posterior row of about 9-10 erect hairs along length (MSSC); II: 2.3; 2.2; 1.6/ 0.5/ 0.5/ 0.3/ 0.2; FII with row of short pale hairs; III: 3.1; 2.8; 0.8/1.0/ 0.6/ 0.4/ 0.3; FIII with row of about 10 long pale ventral hairs along length, about as long as thickness of FIII; IIIt 3-5 not distinctly flattened, but with ventral padlike surface (MSSC).

Wing: hyaline and narrow; vein R 2+3 joining costa at 7/8; vein R 4+5 almost straight and joining margin just before wing apex; vein M unbranched, and beyond dm-cu crossvein with gentle bend towards R 4+5; both veins becoming subparallel in distal fifth of wing; crossvein dm-cu straight; CuAx ratio: 0.8; anal vein weak; lower calypter brown with fan of brown setae; halter yellow.

Abdomen (Figs 2A, B): entirely dark brown with some metallic green reflections; terga 1-6 with short black vestiture and 4 setae along tergal margins; tergum and sternum 7 each well developed, forming short peduncle and

FIG. 1. Pouebo symmetricauda n. sp., habitus, male. Scale bar = 0.5 mm.

tergum 7 setose; sternum 8 spatulate, with long basal extension, sometimes seen as bump extruding at membranous join with sternum 7, and forming cap over basal hypopygial foramen; epandrium rather short, dark brown, cercus yellow; epandrium rather short and subrectangular, and with 2 epandrial setae on ventral margin, hypandrium with hood, and with left lateral arm crossing under phallus; phallus (= aedeagus) longer than hypandrium, and with dorsal prominence (= dorsal angle) near half length; epandrial lobe enlarged, ovate with two apical setae; surstylus with massive three pronged distal pedunculate seta, and group of three median spike like setae; cercus narrow and elongate, with setae as figured.

FIG. 2. Pouebo symmetricauda n. sp.:A,hypopygium,left lateral;B,hypopygium,ventral;C,female oviscapt,left lateral.Abbreviations:cer,cercus;epl, epandrial lobe; for, hypopygial foramen; hyp, hypandrium; lah, left arm of hypandrium; pha, phallus; sur, surstylus; s, sternum; t, tergum. Scale bar = 0.1 mm.

Female: similar to male except as noted: eye facets uniform; ac also comprising single pair, but much shorter; 4 strong dc setae present; leg colouration and podomere ratios similar; TI unmodified; IIIt not ventrally padlike; oviscapt (Fig. 2C) with each hemitergite separate and with 2 strong apical setae; female cercus elongate, digitiform, extending beyond tergum 10.

REMARKS. — The specific epithet symmetricauda is from Latin and means “symmetrical tail”, a character discussed below. For further notes, see “Remarks” above, under the generic diagnosis.

MORPHOLOGY OF THE MALE POSTABDOMEN IN POUEBO

The structure of the male postabdomen in Pouebo is of particular interest. In Dolichopodidae , segment 8 is represented by the sternum only, which lies as an ovate cap over the hypopygial foramen on the left lateral or laterodorsal side of the hypopygium. Segment 7 primitively consists of both tergum and sternum although these are sometimes fused and modified.

The attachment of the postabdomen to segment 6 is variable, but two major morphological forms (not necessarily representing monophyletic assemblages) are distinguished. In the encapsulated form (e.g., Sympycninae , Diaphorinae, and Rhaphiinae ), the hypopygium at rest is partially covered by tergum 6, and segment 7 acts as a short lever to roll the genital capsule ventrally and anteriorly. In the pedunculate form (e.g., Medeterinae , Sciapodinae , and Dolichopodinae ), the hypopygium is permanently exerted, and segment 7 is developed as an external arm or peduncle. In both of these forms, the postabdomen is externally asymmetrical along the median sagittal plane, with the hypopygial foramen and sternum 8 positioned along the left side and with distal segment 7 tending towards the left. Although the epandrium is asymmetrical with respect to the left lateral position of the hypopygial foramen, various hypopygial appendages (cercus, surstyli, hypandrium, etc.) are usually symmetrical about the median sagittal plane.

External asymmetry of the postabdomen is almost universal throughout the family Dolichopodidae , and is undoubtedly the plesiomorphic condition resulting from abdominal segments being dragged during torsion and flexion (McAlpine 1981). However, external symmetry or near symmetry, with secondary modification of sclerites and a basally positioned foramen has evolved at least three times in the Dolichopodidae : Babindella Bickel (Babindellinae) ( Bickel 1987) , Plagioneurus Loew (Plagioneurinae) , and the genus described here, Pouebo . As well, many species of Thrypticus Gerstäcker (Medeterinae) have the foramen in a left basal position, whereas in most Medeterinae , the foramen is distinctly left lateral.

Therefore, although secondary hypopygial symmetry with a basal foramen is an apomorphic condition in the Dolichopodidae , it has arisen independently several times and is an autapomorphy in Pouebo .

SYSTEMATIC POSITION OF POUEBO

When I first sorted specimens of Pouebo from New Caledonian Dolichopodidae , I could not place them to subfamily. Clearly, the male postabdomen was strongly pedunculate, and the rather short compact thorax suggested Sciapodinae , a subfamily I studied for many years. However, it lacked the two diagnostic characters of the subfamily, the branched vein M and excavated vertex. Yet other sciapodine genera lack these characters, apomorphies that arose de novo in separate lineages. a) The M 2 branch has been lost independently at least six times in the subfamily, either as a male secondary sexual character, or permanently in both sexes and therefore useful for higher taxonomic definition (e.g., the genera Mesorhaga Schiner and Pilbara Bickel ). The lost vein is sometimes indicated by a trace on the membrane, but in these two genera and Pouebo there is no trace of M 2. b) The vertex is shallowly excavated in some Sciapus Zeller species and in the genus Pilbara ( Bickel 1994) .

Three character states confirm the placement of Pouebo in the Sciapodinae :

Sexual dimorphism of the dorsocentral setae (dc): the Sciapodinae have 4-6 pairs of dc, which in females are strong and well developed. However, males of the Chrysosomatini have only the posteriormost two dc strong, while the anterior dc are reduced to weak hairs. This is a MSSC known only from the Sciapodinae and occurs in 12 genera. Male Pouebo has three weak anterior hairlike dc.

Hypandrial structure: the hypandrium in most Sciapodinae is asymmetrical, with a hood and a left lateral hypandrial arm arising near its base. This structure is considered part of the sciapodine groundplan and a synapomophy for the subfamily. The left hypandrial arm usually parallels the left side of the phallus (see “lah” in Figs 2A, B) but sometimes crosses to the right side. Pouebo has such a left lateral arm on the hypandrium. Female terminalia: the oviscapt structure is varied among the Sciapodinae ( Bickel 1994) , but females in many genera have the hemitergite (division of tergum 10) long and tapering, not fused medially, and with apical setae not flattened nor bladelike. The oviscapt of Pouebo (Fig. 2C) fits this pattern and is similar to species in other sciapodinae genera (compare Figs 3C & 4A in Bickel 1994).

Therefore, although Pouebo lacks two diagnostic characters of the Sciapodinae , a branched vein M and an excavated vertex, it is placed in the subfamily based on three other characteristic subfamily structures, noted above. As well, the basic hypopygial structure is that of the Sciapodinae , and the strongly modified setae of the surstylus should not be a distraction from this fact. It must be emphasized here that all these characters are subject to reversal or nonexpression, and higher taxonomic placement is often based on a somewhat variable suite of characters states. As discussed above, the symmetrical hypopygium is uniquely derived autapomorphy and not useful in determining subfamily placement.

Finally, did Pouebo evolve in place with a more plesiomorphic sister taxon on New Caledonia, or are some of its distinctive apomorphies shared with extralimital taxa? From the 53 described species of Sciapodinae endemic to New Caledonia (Bickel 2002), I could find none that shared any unique structural modification (e.g., the surstylus or the elongate cercus) found on Pouebo . This also is the case for southwestern Pacific Sciapodinae I have seen. And, although the monotypic Australian genus Pilbara also has an unbranched vein M and unexcavated vertex, it is quite unlike Pouebo in genitalic structure, and its hypopygial foramen is distinctly left lateral. Thus, Pouebo remains a highly derived and somewhat enigmatic genus of the Sciapodinae .

ACKNOWLEDGMENTS Hannah Finlay drew the figures. Mike Irwin facilitated the sorting and shipment of specimens.

REFERENCES

BICKEL D. J. 1987. — Babindellinae, a new subfamily of Dolichopodidae BICKEL D.J.2002.— The Sciapodinae of New Caledonia (Diptera:Dolichopodidae), (Diptera) from Australia, with a discussion of symmetry in the dipteran in NAJT J.& GRANDCOLAS P.(eds),Zoologia Neocaledonica 5.Systématique male postabdomen. Entomologica scandinavica 18: 97-103. et endémisme en Nouvelle-Calédonie. Mémoires de Muséum national

BICKEL D. J. 1994. — The Australian Sciapodinae (Diptera: Dolichopodidae), d’Histoire naturelle 187: 11-83. with a review of the Oriental and Australasian faunas, and a world MCALPINE J. F. 1981. — Morphology and Terminology - Adults, p. 9-64, in conspectus of the subfamily. Records of the Australian Museum Supplement MCALPINE J. F. et al. (eds), Manual of Nearctic Diptera, Vol. 1. Research 21: 1-394. Branch Agriculture Canada Monograph 27, Ottawa, 674 p.