Robustagramma, 2005

Marshall, Stephen A. & Cui, Yongsheng, 2005, Systematics of Robustagramma, a new genus of New World Sphaeroceridae (Diptera), Zootaxa 1026 (1), pp. 1-122 : 6-12

ROBUSTAGRAMMA MARSHALL AND CUI , NEW GENUS

Type species: Leptocera (Scotophilella) robusta Spuler 1925: p.81

Diagnosis: Stout Limosininae . Wing broad (half as broad as long), with second costal sector much shorter than third costal sector. Head distinctly higher than long, with two pairs of orbital bristles (rarely one pair). Arista with long pubescence. Palpus with 2 large preapical bristles. Mid tibia with one (rarely two) proximal dorsal or posterodorsal bristle(s), usually one anterodorsal bristle near middle, and three (anterodorsal, dorsal and posterodorsal) distal bristles. Mid tibia of male with several short, stout distal ventral bristles; mid femur with a corresponding group of ventral proximal bristles. Distiphallus broad, complex; a pair of long, conspicuous, flagellum­like or whip­like sclerites arising dorsobasally. Female abdomen short, broad, not telescoping.

Generic description: Length 1.0– 2.2 mm. General body color brown to dark brown, pollinose but rarely with conspicuous pigmentation. Head much wider than long. Ocellar triangle, interfrontal strips and orbital strips silvery. Interfrontal bristles in 3–5 pairs (rarely 1 or 2 pairs), an additional small pair of interfrontal setulae just above ptilinal suture. One or 2 pairs of very small setulae between interfrontal strips and orbital strips above ptilinal suture. Two (rarely one) exclinate orbital bristles on each side, anterior orbital bristle much shorter than posterior. Posterior orbital setula almost always present between orbital bristles; anterior orbital setulae smaller. Ocellar, inner vertical, and outer vertical bristles well developed; inner and outer occipital bristles developed, but distinctly shorter than inner and outer vertical bristles or ocellar bristles. Postvertical bristles usually smaller than inner occipitals. Postocellar bristles small or absent. Face with a broad central ridge, slightly depressed at middle. Eye height usually 2–3 times genal height. Anterior genal bristle always well developed, larger than subvibrissa. Arista dorsolateral, preapical, usually slightly longer than head height (much shorter in brevicilium group); aristal pubescence long, 2–3 times basal width of arista. Palpus with two preapical bristles, usually longer than maximum palpal width.

Prosternum narrow, usually bare (setulose in crassipalpus ­group). Dorsocentral bristles usually in 2 pairs; if 3 pairs then anterior pair inconspicuous; prescutellar dorsocentral bristles much larger than other pair(s). Acrostichal setulae usually in 6–8 rows between anterior postsutural dorsocentral bristles. Apical scutellar bristles 1.5–2.0 times length of scutellum; basal scutellar bristles similar in length to scutellum. Two katepisternal bristles; anterodorsal katepisternal bristle very small, posterodorsal katepisternal bristle more than half as long as distance between its base and wing base. Halter knob pale to dark brown, stem pale brown to white. Wing clear or variously pigmented.

Costa and R 4+5 usually ending together before wing apex. Second costal sector approximately half as long as third costal sector. Discal cell with or without a short stump vein CuA 1. Longitudinal wing fold always present, passing through middle of discal cell. Tarsi and fore tibia usually yellow, legs otherwise pale to dark brown. Tarsomere one of fore leg about twice as long as tarsomere 2. Mid tibia with one (rarely two) dorsal or posterodorsal proximal bristle(s), one anterodorsal bristle near middle (reduced or lost in some crassipalpus ­group species), and one anterodorsal, one dorsal and one posterodorsal bristle distally (distal dorsal bristle relatively small). Mid tibia of male with one apicoventral bristle and a row of short, stout ventral bristles on distal 1/4–3/4; mid femur with one or two corresponding rows of ventral proximal bristles. Mid tibia of female with only a long apical bristle on ventral surface. Hind tibia with a short, stout apicoventral bristle. Both tarsomeres one and two of hind leg swollen, markedly so in some males.

Male abdomen: Sternite 5 usually more than 1.5 times as long as sternite 4, occasionally unmodified but often with a pale posteromedial area (sometimes a distinct borderline between pale posteromedial area and dark anterior area), and with a few distinctive bristles or dense flattened setulae on posteromedial margin. Sternite 6 thin and unmodified, fused with sternite 7, which is narrowly fused with sternite 8. Epandrium asymmetrical, with a finger­like, anteroventral process extending into notch in right side of anterior half of hypandrium ( Fig. 1 ). Subanal plate complete, with a pair of bristles and usually distinctly separate from cerci; cerci elongate and prominent (except in R. brevicauda ), usually setulose and with a few small bristles basally, tapered and usually with only a few small bristles distally. Surstylus always symmetrical and relatively simple, without stout bristles, but differing between species in shape, setulosity, and size. Hypandrium with anterior apodeme well­developed; right side indented by anteroventral process of epandrium (there is no process on the left side of the epandrium); posterior part of hypandrium with two pairs of arms or processes as follows: lateral arms forming separate sclerites articulating with sides of hypandrium and with margins of epandrium; posterior arms elongate and extending to postgonite ( Fig. 1 ). Subepandrial sclerite simple, transverse. Pregonite small, suspended between posterior hypandrial arm and anterobasal surface of postgonite ( Fig.1 ). Basiphallus very small, frame­like. Distiphallus broad, complex, with a pair of thin, whiplike, dorsal sclerites arising dorsobasally, and usually with a short brush­tipped process mediodorsally (“dorsal” refers to the dorsal position of the aedeagus in repose, as illustrated). Ejaculatory apodeme small to large. Aedeagal apodeme usually a simple, laterally flattened rod as in most Limosininae .

Female abdomen: Usually short and broad; not telescoping. Tergite 8 divided into two broad lateral sclerites; tergite 10 with two (rarely more, as noted) small bristles and usually a posteromedial patch of small setulae (sometimes entirely bare or entirely setulose, as noted). Cerci short, setose, with long apical and preapical bristles. Sternite 8 usually reduced to small sclerites, or absent, sometimes entire. Three spermathecae, single and paired, varying in shape among species groups.

Phylogeny: Robustagramma belongs in a well­supported clade including the primarily neotropical genera Pterogramma , Rudolfina , Bromeloecia , and Archiceroptera , but its sister group within this clade is unknown. The rest of the clade was therefore used as a generalised outgroup in developing a matrix of 38 morphological characters (table 1). The Robustagramma robustum group (including R. robustum (Spuler) , R. aequale , R. angustistylum , R. biangulatum , R. crassisaccus , R. gigantisclerosum , R. grenadens e, R. kittsense , R. luciense , R. mayense , R. oculiculus , R. ovipennis (Duda) , R. sinuosum , R. spinatimargo and R. vulgare ) and the Robustagramma altifrons group ( R. altifrons , R. arizonense , R. hebes , R. incurvum , R. minutiseta and R. obscurifrons ) are each well supported by unique synapomorphies (see group descriptions) and are extremely uniform. Including all component species of these indubitably monophyletic species groups would have made the matrix unnecessarily large. These two well­defined species groups were therefore each coded as single taxa (operational taxonomic units) in the matrix. When analysed using the parsimony program PAUP version 4.0 10 ( Swofford, 2003) the matrix yielded 144 trees of equal length (consistency index = 0.42, retention index = 0.75). All species groups except the binitidum group were supported as monophyletic on 100% of the trees; the binitidum group was monophyletic on 67% of the trees but its species and the altifrons group form an unresolved polytomy on the strict consensus tree ( Fig. 379 ). Characters were optimized on one of the equal length trees ( Fig.380 ) using Winclada ( Nixon, 2002). The following six species groups, in addition to the altifrons and robustum groups, are recognized.

The R. brevicilium group, characterized by two or fewer pairs of interfrontal bristles and an arista that is much shorter than head height, includes R. setilamella , R. brevicilium , R. atratum , R. longiseta , R. paralongiseta , R. uniseta , R. lingulatum and R. parauniseta .

The R. robustinervus group, a small South American group characterized by a male wing with a thickened first costal sector (between humeral and subcostal breaks), includes R. robustivervus , R. dilatatum and R. setosum .

The R. binitidum group is primarily characterized by a great reduction (or absence) of female sternite 8. Although the four species ( R. binitidum , R. obscuratum , R. macrosternum and R. rarum ) in this species group form part of a polytomy with the altifrons group on the strict consensus tree, they form a recognizable group that comes out as monophyletic on most of the equal length trees generated from the character matrix ( Table 1).

The R. crassipalpus group is strongly supported by several characters, especially character 11 (setulose prosternum). This apparently uncommon Central and South American group includes R. longistylum , R. latistylum , R. nigrivittatum , R. crassipalpus , R. bolivarense and R. brasilense .

00000 00001 11111 11112 22222 22223 33333 333

12345 67890 12345 67890 12345 67890 12345 678

ancestor 00000 00000 00000 00000 00000 00000 00000 000 R. robustum­group 00000 00010 00100 20001 00011 01000 00011 120 R. altifrons­group 00100 01110 01100 20000 00011 00010 10010 110 R. mirabile 00000 00000 00100 20001 00011 00010 10110 120 R. triangulatum 00000 00010 00200 20001 00011 10010 10010 020 R. multiseta 00000 00110 01200 20001 00011 10000 10010 020 R. binitidum 00000 00111 00100 00000 00011 00010 10020 020 R. obscuratum 00000 00111 00100 00000 00011 00010 10020 020 R. rarum 000? 0 00111 00100 00000 00011 00010 100 ?? ??0 R. disjunctum 00000 00000 00200 20001 01011 01000 11010 010 R. macrosternum 00000 00210 00000 00000 00011 10011 10020 011 R. setilamella 01010 10110 00100 00001 01011 10011 001?? ??0 R. crassipalpus 00000 00201 10100 00000 10011 00100 00010 120 R. bolivarense 00000 00201 10100 00000 10011 0?100 00010 120 R. brasilense 00000 00201 10100 00000 10011 0?100 00010 120 R. longistylum 00000 00202 10100 00000 10011 00100 11010 120 R. latistylum 00000 00201 10100 00000 00011 00100 000?? ??0 R. nigrivittatum 00000 00201 10100 00000 00011 00100 00010 120 R. flavistylum 00000 00010 00200 11001 00111 00010 10010 100 R. angusticauda 00000 00010 0020? 11001 00111 00011 100?? ??0 R. cultriforme 00000 00010 00200 11001 00111 00010 10010 100 R. setituberosum 00000 00010 00200 11001 00111 00010 100?? ??0 R. pallidistylum 00000 00110 00200 11001 00111 00010 10010 100 R. brevicauda 00000 00010 00100 11001 00111 10011 10010 100 R. setosum 00000 00111 00101 10001 00011 00001 001?? ??1 R. robustinervus 00000 00112 00101 00001 00011 00001 00100 111 R. acutistylum 00000 00110 00110 20001 00011 00001 00110 100 R. dilatatum 00000 00110 00101 20001 00011 00000 00100 111 R. orthogonium 00000 00211 00100 00001 00011 00000 10010 111 R. brevicilium 02011 00110 00200 01001 00111 00000 001?? ??0 R. lingulatum 02011 00010 00200 11111 01011 00010 100?? ??0 R. parauniseta 1201 ? 00010 00200 01111 01011 0000? 101?? ??0 R. uniseta 12011 00010 00200 11111 01111 0000? 001?? ??0 R. atratum 02011 00010 00200 01011 01011 00010 00100 110 R. longiseta 02011 00110 00200 01011 01011 00010 00100 100 R. paralongiseta 02011 00110 00200 01111 01011 00000 001???00

Character list for table 1 (plesiomorphic states characters with only two states are given in brack­

ets, otherwise character polarity is indicated by sequential numbering from zero to two)

1. Head with one pair of orbital bristles (head with two pairs of orbital bristles)

2. Head with one pair of interfrontal bristles (in addition to the pair of setulae, or small bristles, just above ptilinal suture) (2), head with two pairs of interfrontal bristles (1); head with three or more pairs of interfrontal bristles (0).

3. In profile, frontal vitta between interfrontal plates distinctly convex (frontal vitta between interfrontal plates indistinctly convex)

4. Arista much shorter than head height (arista at least subequal to head height)

5. Postvertical bristles as long as inner occipital bristles (postvertical bristles distinctly shorter than inner occipital bristles)

6. Head without a setula between two orbital bristles (head with a setula between two orbital bristles)

7. Facial ridge between antennae distinctly narrower than diameter of scape (facial ridge between antennae subequal to or wider than diameter of scape)

8. Greatest diameter of palpus subequal to or longer than 1/3 of its length (2); greatest palpal diameter distinctly longer than 1/5 and shorter than 1/3 of palpal length (1); greatest palpal diameter equal to or shorter than 1/5 of its length (0)

9. Two preapical palpal bristles similar in length (bristle nearest apex much longer)

10. Palpal bristles distinctly shorter than greatest palpal diameter (2); subequal to greatest palpal diameter 1); longer than greatest palpal diameter (0)

11. Prosternum with setulae (prosternum bare)

12. Scutum with weak longitudinal stripes (scutum without longitudinal stripes)

13. Scutum with three pairs of dorsocentral bristles (2); scutum with two pairs of dorsocentral bristles (1); scutum with one pair of dorsocentral bristles (0)

14. Anterodorsal katepisternal bristle absent (anterodorsal katepisternal bristle present)

15. First costal sector (between humeral and subcostal breaks) thicker than second costal sector (first costal sector subequal to or thinner than second sector)

16. Wing distinctly pigmented, with clear transverse bands beyond intersection of R 2+3 and costa (2); wing pigmented, but without clear bands (1); wing clear, or indistinctly pigmented(0).

17. Distal portion of R 2+3 conspicuously curved forward (distal portion of R 2+3 slightly curved forward, or almost straight)

18. R 2+3 with stump vein (R 2+3 without stump vein)

19. Costa extending past R 4+5 by more than one vein width (costa extends past R 4+5 by less than one vein width)

20. Mid tibia with a posterodorsal proximal bristle (mid tibia with a dorsal proximal bristle)

21. Mid tibia without a distinct middle anterodorsal bristle (mid tibia with a distinct middle anterodorsal bristle)

22. Mid femur of male with a row of posteroventral bristles (mid femur of male with one or more rows of ventral or anterioventral bristles)

23. Mid tibia with an additional, distinct, distal anterodorsal bristle before distal dorsal bristle (mid tibia without an additional, distinct, anterodorsal bristle)

24. Distal third of mid tibia with a dorsal bristle (distal third of mid tibia without a dorsal bristle)

25. Distiphallus with a pair of thin, basally fused, whip­like dorsal sclerites (distiphallus without a pair of thin, basally fused, whip­like dorsal sclerites)

26. Whip­like sclerites of distiphallus with node­like structures (whip­like sclerites of distiphallus without node­like structures)

27. Ejaculatory apodeme at least 1/4 as long as aedeagal apodeme (ejaculatory apodeme shorter than 1/4 of aedeagal apodeme)

28. Distiphallus with some small spicules on inner surface (distiphallus without small spicules on inner surface)

29. Sternite 5 of male with a distinct borderline between dark anterior and pale posterior area (sternite 5 of male without a distinct borderline between dark anterior and pale posterior area)

30. Sternite 5 of male over twice as long as sternite 4 (sternite 5 of male shorter than twice of length of sternite 4)

31. Sternite 5 of male with many tiny flattened setulae on posteromedial margin (sternite 5 of male without tiny, flattened setulae on posteromedial margin)

32. Distal halves of male cerci far away from each other (distal halves of male cerci close to each other)

33. Surstylus bifurcate (surstylus not bifurcate)

34. Sternite 8 of female greatly reduced or absent (2); sternite 8 of female split (1); sternite 8 of female entire (0).

35. Single spermatheca different in shape from paired spermathecae (single spermatheca similar in shape to paired spermathecae)

36. Single spermatheca distinctly smaller than paired spermathecae (single spermatheca similar in size to paired spermathecae)

37. Ducts of paired spermathecae twice, or more, as long as spermatheca (2) ducts of paired spermathecae shorter than double length of spermatheca, but longer than spermatheca (1); ducts at most as long as spermatheca (0)

38. Distiphallus with a pair of exceptionally large ventral sclerites, over 2/3 as long as distiphallus (distiphallus without large ventral sclerites)

The R. triangulatum group, including a Dominican species, R. multiseta , and a Cuban species, R. triangulatum , is characterized by a distiphallus with a saccate structure on the whip­like sclerite. This structure is unique, and obviously different in shape and size from the apparently homologous node­like structure of the distiphallus in some other species. Robustagramma disjunctum , ranging from Mexico to Panama, shares character 13 (three pairs of dorsocentral bristles) with the R. triangulatum group, but other characters (especially the spermathecae) suggest that the change from two to three dorsocentral bristles took place independently in this species and the R. triangulatum group.

The monophyly of the R. flavistylum group (including R. pallidistylum , R. flavistylum , R. cultriforme , R. setituberosum , R. angusticauda and R. brevicauda ) is weakly supported by four homoplasious characters (characters 17, 23, 29 and 31).

The R. altifrons group is strongly supported by two unique synapomorphies (a narrow facial ridge and a convex frontal vitta). This group of six species is mainly Nearctic, although R. obscurifrons occurs in Honduras and Mexico.

The R. robustum group (including 15 closely related species), the largest species group in Robustagramma , is characterized by the unpaired spermatheca (of 3) which is different in shape from the paired spermathecae. Robustagramma vulgare is an extremely common fly in much of the southern United States, and is also found in northern Mexico and (rarely) southern Canada. Other members of this species group are found in Central and South America and the Caribbean.

Figures

FIGURE 1. Male terminalia of Robustagramma gigantisclerosum sp. nov. (anteroventral view, with distiphallus removed).

FIGURE 379. A strict consensus tree for Robustagramma species­groups and species.

FIGURE 380. Phylogeny of Robustagramma species­groups and species. Character numbers above boxes refer to the characters in Table 1; numbers below the boxes refer to transformation series states. Autapomorphies are not shown. Tree selected from 144 equal­length trees (CI.43, RI 74).