Drosophila spinipes, Lamb, 1914

Grimaldi, David A. & Jones, Lance E., 2020, A Revision of the Drosophila spinipes Species Group (Diptera: Drosophilidae), Zootaxa 4809 (1), pp. 1-28 : 3-8

The Drosophila spinipes Species Group

Diagnosis: Arista with 1 ventral terminal branch, 2 short dorsal branches (fig. 1A); labellum with 15–16 pseudotracheae and apical-marginal row of stout microsetae on each lobe (fig. 1C); cibarium simple, with ca. 10 sensilla (none of them trichodea), not in rows; proximal end of cibarium without bend, bulb or sclerotization (fig. 1B). Face narrow, flat, no carina, with median cleft on oral margin; 2 pairs of vibrissae (second pair 0.5–0.9X the size of true vibrissae); anterior reclinate orbital large, ~0.7–1.1X the size of proclinate; ocellar setae lateral to anterior ocellus (fig. 1A). Notum and dorsal portion of pleuron usually dark (except for spinipes Lamb ); pleuron ventrally light (rarely dark) (figs. 2A, 3); anterior spiracle deeply recessed, with large posterior channel (fig. 2C); anterior dorsocentral setae barely larger than acrostichals; 2 small tubercles near notopleural suture, one bearing notopleural seta, another with supra-alar seta (fig. 2C). Profemur and protarsomere 1 very short, profemur stout; protarsus with 7–9 black, spine-like setae on tarsomeres 1 and 2 in both sexes (figs. 2E, F; 5). Wing: costal spinules ending slightly beyond apex of R 2+3; anal lobe and veins CuA+CuP, A 1 highly reduced (fig. 2D). Oviscapt with stout apical pegs (3 dorsal, 2 ventral), emarginate gap between dorsal and ventral ones (fig. 7); spermathecae not present or highly vestigial, ventral receptacle well developed but membranous; oviprovector membrane without scales; female tergite 8 narrow, dorsally long and sloping, lateral portions strap-like; 1–2 large eggs matured at a time, devoid of filaments (fig. 6E). Male genitalia simple, without pair of lateral postgonites (paraphyses); cercus not laterally attached/fused to epandrium; ventral lobe of epandrium long, narrow, apex with 1-3 short, spine-like setae; surstylus long, with row of spine-like prensisetae (no peg-like ones) (figs. 8–10). Anthophilous.

Description: Coloration: The following structures always dull blackish-brown, except in spinipes (which is overall dark yellowish-ochre): lateral surfaces of labellum; palps, clypeus, face, cheeks, antennae; frons, occiput; mesoscutum (sometimes with pair of faint, incomplete, lighter paramedian vittae [fig. 3E), scutellum, subscutellum, postnotum; on pleuron: anepisternum, anepimeron, katatergite, haltere (in nigrospinipes n. sp. the katepisternum and meron are also dark); dorsal (not lateral) portions of tergites. Terminal tergites (7, 8) in both sexes variable (either dark blackish brown or yellowish) (fig. 4).

The following structures are yellowish: portions of the pleuron other than those mentioned above; coxae and legs (generally lighter yellow); prosternum; abdominal sternites, lateral portions of tergites; sometimes tergites 7, 8 and cerci; oviscapt valves.

Wing without patterning, membrane always with faint smoky tint, subcostal cell darker brown (fig. 2D). Eyes reddish.

Head: Occiput moderately concave, head partially “cupped” onto anterior face of thorax; head inserted low on thorax, frons in line with curvature of thoracic dorsum (fig. 2A). Proboscis relatively short, when retracted slightly exposed ventrally; labellum laterally flattened when closed, lateral surface of lobe lightly sclerotized; each lobe with ~15 pseudotracheae; anterior margin of lobe with row ~20 short, stiff, spinule-like setulae (figs. 1C, 2B). Palp clavate, with 7–8 setae; prementum short, overlapping cibarium; lacinia with short dorsal arm. Cibarium relatively simple: almost rectangular, hypopharynx very lightly sclerotized, no other sclerotization; pair of campaniform sensilla at distal end, 10–12 smaller campaniform sensilla scattered over and near hypopharynx; no sensilla trichodea or combs of sensilla; proximal end without bend, bulb, or sclerotization (fig. 1B). Clypeus deep, laterally narrow, inserted into oral cavity, small anterior portion exposed (fig. 2B). Oral margin of face with shallow cleft in middle. One large pair of vibrissae, smaller second pair ~0.5x the thickness and length. Face very narrow, width ~0.50–0.68x the depth, flat to slightly concave, carina entirely absent; sides of face parallel (fig. 1A).

Antenna: Entire pedicel and portion of scape recessed into ptilinum; pedicel with 5–6 fine setulae (dorsal one largest); basal flagellomere short, apex distant from oral margin, with very short microtrichia (no long, fine ones); arista with 2 dorsal, 1 ventral branch, plus terminal fork, ventral branch midway between second dorsal one and terminal fork. Eyes large, virtually no cheeks; almost bare, with very few, very fine ommatrichia (fig. 1A).

Frons: Lateral margins significantly diverge dorsad. Most of frons matte except frontal-orbital plates, which are slightly shiny; plates narrow, end slightly anterior to proclinate. Frontal vittae slightly velvety. Frontal-orbital setae: proclinate slightly longer to slightly shorter than anterior reclinate; anterior reclinate closer to proclinate than to posterior reclinate; posterior reclinate longest orbital, midway between anterior reclinate and inner vertical; ipsilateral orbitals in line with inner vertical; verticals close, inners convergent, outers divergent. Postocellars small, usually convergent; ocellar setae lateral to anterior ocellus ( Fig. 1A ).

Thorax: Dorsum moderately arched. Acrostichals relatively long, in 6–8 irregular rows between levels of dorsocentrals, prescutellar acrostichals slightly thicker and longer. Posterior dorsocentrals relatively close to scutellar margin; anterior dorsocentrals small, slightly longer and thicker than acrostichals. Postpronotal lobe with 2 long setae, 2 smaller ones dorsally. Anterior spiracle deeply recessed, covered by posterior margin of eye, open to surface through short, broad, pollinose channel (fig. 2C). Notopleural setae: 1 dorsal, 2 ventral pre-suturals; 1 dorsal, 2 ventral post-suturals; 2 ventral ones on low tubercles. One long supra-alar seta, 1 short postalar seta. Scutellum relatively long, apex narrowed; 2 pairs scutellar setae, posterior ones slightly longer. Subscutellum slightly swollen, postnotum large. Katepisternum with 2 setae: anterior one 0.45–0.70x size of posterior one. Pleuron bare of setulae.

Legs: Very light, covered with very light setulae. Coxae relatively short. Femora: profemur very short and stout, 0.65–0.85X length of mid femur, hind femur largest (fig. 3). Protibia with 5–6 oblique, transverse rows fine, comb-like setulae; hind tibia with fine, preapical dorsal seta. Protarsus with basal segment very short, shorter than tarsomere 2. Tarsomeres 1 and 2 with large, black, heavily sclerotized, spine-like on ventral surface: 3–4 on tarsomere 1, 4–5 spines on tarsomere 2, as numbered in fig. 5). Spines alternating in size: #6> 3> 1 = 8> 2, 4, 5, 7, except in nigrospinipes n. sp., where most spines are of equivalent sizes, as are ones on tarsomere 2 of jambiya n. sp. Spines usually fang-shaped, except for ones on tarsomere 2 in jambiya ; the larger spines with a longitudinal furrow on broad surface (fig. 2E, F). No sexual dimorphism in spines. Mid and hind tarsus with length of tarsomere 1 approximately equal to combined lengths of tarsomeres 2–5. Tarsomere 5 with dorso-apical ring of 7 long setulae. Pretarsal claws large, black, heavily sclerotized; pulvilli large, feathery; empodium slightly feathered.

Wing (fig. 2D): Sc ending halfway to C, apically evanescent; C with fine, longer spinules proximal to Sc break; dense, short, thick spinules ending slightly past R 2+3; C thick, well developed to apex of M 1. R 2+3 long, R 4+5 ending at apex of wing. Cell bm absent (bm-m absent); cell cua present but small. CuA+CuP largely absent, a small spur; A 1 absent; anal lobe highly reduced; alula and calypter each with marginal fringe of long, fine setae.

Abdomen (fig. 4): Relatively short, length approximately equal to that of thorax. Anterior end broad, abdomen laterally tapered to narrow posterior end in both sexes. Tergites evenly covered with short setae; longer ones on posterior margins and lateral surfaces, especially segments 4 and 5.

Male Terminalia (figs. 8–12): Epandrium: approximately as broad as deep, U-shaped, dorsal arch with microtrichia and ~10 setae; ventral lobe slender, tapered to an apical point, reaching to approximately ventral level of surstylus, setose but lacking microtrichia, apex with one to three spine-like setae (not black). Cerci: relatively flat, with microtrichia and setae, not connected laterally to epandrium; without ventral lobes. Surstylus: relatively long, narrowed ventrad, pair attached dorsally to subepandrial sclerite; each surstylus with dorsoventral row of 10–20 black, sclerotized, spine-like prensisetae, no pegs; several fine setulae on inner margin of surstylus. Subepandrial sclerite large, variable though roughly H-shaped, broader than deep. Hypandrium: Approximately same length as phallus + aedeagal apodeme; apical-lateral lobes turned inward; one short pair of postgonites (paraphyses) present, at base of phallus, lightly to moderately sclerotized, each lobe with a fine setula. Aedeagal apodeme apically broadened, length approximately equal to that of phallus. Phallus (aedeagus): bilaterally divided into pair of valves, with coarse or fine teeth/serrations, fine spicules, sometimes with fine scales medially, or bare; apical margins finely serrate, papillate, or smooth.

Female Terminalia (figs. 6, 7): Tergite 7 very short dorsally (barely visible dorsally), ventrally long, triangular in lateral view. Tergite 8 (“tergite 7” in David et al., [2011]) dorsally long and narrow, with microtrichia; with long, narrow, lateral lobes whose apices become faintly sclerotized and spectral, lateral lobes without microtrichia. Small hypoproct and epiproct present; no cerci. Sternite 8 (oviscapt) with pair of laterally flattened valves joined by nar- row bridge at anterior end; each valve with 10–15 pegs, depending on species; largest pegs always 5 apical-most ones. Oviscapt with following structures, from dorsally to ventrally (fig. 7K): always with group of 3 large, apical-dorsal pegs (“dorsal triad”), below them the “apical notch”, then another two large pegs (the “ventral pair”), a subapical setula (apical sensilla trichodea absent) and finally a ventral row of 5–10 small pegs (the “ventral series”). Oviprovector membrane well developed, but lacking scales, fine or coarse. Spermathecae not observed in this study (contra Burla [1954], David et al. [2011]), either lost or highly vestigial; ventral receptacle well developed but membranous, with 4–5 folds and having a narrow blind end, lying approximately in segment 4 when oviscapt retracted (fig. 6).

Egg (fig. 6E): Very large, width approximately 0.5x the length; lacking any anterior filaments (even minute ones), micropyle well developed; chorionic pattern of follicle-cell imprints very faint. One or two large eggs matured at one time. Of 8 dissected females from throughout the range, three had one egg, one had two. No eggs contained an unhatched larva.

Included species: Drosophila spinipes Lamb , D. suma Burla, D. cameroonensis n. sp., D. freidbergi n. sp., D. hypandrilata n. sp., D. jambiya n. sp., D. malagasy n. sp., D. nigrospinipes n. sp., D. phalloserra , n. sp.

Relationships: Flies in the spinipes group superficially resemble ones in the Zygothrica genus group based on coloration and a few aspects of the arista and terminalia. A thorax with a dark, moderately arched notum, contrasting with light pleura and sterna is found in many species of Hirtodrosophila , most Mycodrosophil a, all Paraliodrosophila , and some Zygothrica . One ventral, terminal branch of the arista is common to all species of the Zygothrica group, but unlike the spinipes group they have 4 or more dorsal, longer branches. Bare eyes are found in Mycodrosophila and Zygothrica . A pendulous, setose ventral lobe of the epandrium occurs in Paramycodrosophila , many Hirtodrosophila , and some Zygothrica , but which lack the apical, spine-like setae. An oviscapt with large apical pegs and a gap between them occurs in Paramycodrosophila and many Hirtodrosophila , but in the latter the distalmost ventral pegs are extended into an apical lobe. A female tergite 8 that is elongate and sloped, with long lateral extensions, is also found in some Zygothrica , but appears to be a feature associated with anthophily (found as well in some Drosophila , in Laccodrosophila and Zapriothrica ). The relatively simple male terminalia, lacking a second pair of postgonites, occurs throughout Drosophila (except Sophophora ), the Zygothrica group, and some other genera of Drosophilinae ( Grimaldi, 1990). The prensisetae in spinipes -group flies are not pegs, but spine-like, as occur in a few Hirtodrosophila and Zygothrica . But, in almost all Zygothrica -group species some are peg prensisetae as well, even if just a short dorsal row. The condition of prensisetae in spinipes -group flies is more similar to what occurs in many Scaptomyza Hardy and Diathoneura Duda.

Plesiomorphic features of the spinipes group, which exclude them from the Zygothrica genus group include the following: face flat, without any carina; flagellomere 1 short, apex not near the oral margin; anterior reclinate orbital seta large, approximately equal in size to proclinate (vs. a fraction the size, often minute); cibarium lacking a large, sclerotized proximal bulb, and with only scattered, trich-less sensilla ( Grimaldi, 1990); in males the ejaculatory bulb lacks a pair of diverticula (cf. Throckmorton, 1966), in females scales are lacking on the eversible membrane between the oviscapt valves, the oviprovector (vs. heavily scaled); in males none of the prensisetae (on the surstylus) are peg-like.

Autapomorphic features of the spinipes group are many and include the following: the distinctive protarsal spines found in both sexes; profemur and protarsomere 1 very short; very narrow face; eyes large, with very shallow cheek; ocellar setae lying outside the triangle; dorsal arm of lacinia short; spinule-like microsetae on the labellum; notopleural area with two low, setigerous tubercles; thick costal spinules ending slightly after apex of R 2+3 (normally these end midway between R 2+3 and R 4+5); anal lobe and vein CuA+CuP highly reduced; anterior dorsocentral setae small, barely larger than acrostichals; anterior spiracle deeply recessed; 1–2 large eggs lacking apical filaments (vs. generally 4 filaments in the Zygothrica group); spermathecae lost or highly vestigial. Burla (1954) and David et al. (2011) mentioned the presence of minute, unsclerotized spermathecae, though we did not find evidence of these at even 400X (this may be due to our use of specimens that were macerated rather than fresh or fixed). We also found, like these authors, a large but membranous ventral receptacle.

The large 1– 2 eggs without filaments, the loss/great reduction of spermathecae, and large apical pegs on the oviscapt are features correlated with anthophily ( Brncic, 1983). The foretarsal spines and shortened profemur and protarsomere 1 are related to the manner of adult feeding, as possibly are the spinule-like labellar spinules (for rasping surfaces).

In summary, various plesiomorphic features of the spinipes group exclude them from the Zygothrica genus group, which agrees with a comment by David et al. (2011), about unpublished data from 28S rRNA sequences. Similarities between the two groups appear to be either superficial or due to convergence. Loss of the second pair of postgonites indicates that the spinipes group is more derived than the genera/subgenera Scaptodrosophila , Lordiphosa and Sophophora , Chymomyza , Neotanygastrella and some other Drosophilinae ( Grimaldi, 1990). Spinipes - group flies are less derived than Drosophila by the lack of a facial carina, the plesiomorphic cibarial structure ( Grimaldi, 1990), and having prensisetae that are not peg-like.

Cariou et al. (2009) may be correct that a separate genus should accommodate spinipes -group species, but we would rather wait for additional genetic analyses (genes and taxa) before erecting a new genus. The group has a perplexing combination of very primitive features and derived genitalic ones. We agree with David et al. (2011) that male genitalia (and other morphology, including oviscapt and tarsal spine structure) of spinipes -group flies show no relationship to other anthophilous drosophilids with tarsal spines, specifically the Asian genus Colocasiomyia de Meijere and the Neotropical genus Laccodrosophila Duda (cf. Grimaldi, 1990). Impatiophila Fu and Gao from Southeast Asia, which is also anthophilous, has small, paired spines on the hind tarsomeres, leading us to think that convergent origins of tarsal spines is perhaps functionally related to anthophily.

For now, it seems adequate to retain the spinipes group in the genus Drosophila , unplaced to a subgenus.

Figures

FIGURE 1. A. Head, frontal view. B. Cibarium and prementum, ventral view. C. Mouthparts, lateral view. B and C to the same scale. All are specimen HS-30 (female from Perinet, Madagascar, TAU).