Drosophila butantan, Ratcov & Vilela & Goñi, 2017

Ratcov, Vilma, Vilela, Carlos R. & Goñi, Beatriz, 2017, A new species of Neotropical Drosophila (Diptera, Drosophilidae) belonging to the guarani group, Revista Brasileira de Entomologia 61 (3), pp. 232-238 : 234-238

Drosophila butantan sp. nov.

( Figs. 1–28)

Drosophila sp. W3, Vaz et al., 2014: 608 + Supp. Key S1.

Material examined ( 6 males, 10 females, deposited in MZUSP) . Holotype male [first-generation offspring of an isofemale line, coded I48F71, emerged 10-22.X.1996, dissected] labeled: “ Brasil – SP, São Paulo, Reserva Florestal [forest reserve] do IB-USP [ Instituto de Biociências – Universidade de São Paulo], Cidade Universitária, 28-30.VIII.1996, Ratcov & Vilela coll. / Drosophila butantan [male symbol] Ratcov & Vilela/terminália ilustrada [illustrated terminalia]/ HOLOTYPE /[glass microvial with terminalia in glycerin]” . Paratypes = one male and one female (photomicrographed) from an undetermined generation of the cited isofemale line, one wild-caught female [mother of the cited isofemale line] plus its first-generation offspring but the holotype: 4 males [one dissected] and 8 females [two dissected]: same data as holotype .

Type locality. Forest Reserve of IB-USP, Cidade Universitária “Armando de Salles Oliveira”, district of Butantã, São Paulo city, state of São Paulo, Brazil .

Diagnosis. Small coffee-brown fly; eye wine-red; head, legs, scutum and scutellum coffee-brown, dull; pleura blackish brown, semi-dull; abdomen conspicuously shiny, tergites 1–4 anteriorly light brown, with broad, well delimited, blackish brown distal bands, tergites 5–7 usually entirely blackish brown; halter, cercus, epiproct and hypoproct light brown; anterior scutellars divergent; wing light brown, crossvein dM-Cu and apices of R 2+3, R 4+5 and M veins slightly clouded, tip of M vein slightly turned posterad, C index 2.84–3.29; valve of oviscapt apically somewhat pointed but not sharply.

Description. Male ( n = 6) ( Figs. 1 and 2). Head brown. Frontal length 0.28 (0.27–0.29) mm, frontal index = 0.89 (0.85–0.92), top to bottom width ratio = 1.72 (1.64–1.77). Frontal triangle subshining, about 83–100% of frontal length; ocellar triangle dark brown, about 33–36% of frontal length. Orbital plates subshining, narrower adjacent to or2, anteriorly diverging from eye margin, about 92–100% of frontal length. Orbital setae black, or2 outside or1 and or3; distance of or3 to or1 = 80% of or3 to vtm, or1/or3 ratio = 0.67, or2/or1 ratio = 0.33, postocellar setae = 63 (58–73)%, ocellar setae = 82 (75–83)% of frontal length; vt index 1.00 (0.90–1.11); vibrissal index 0.75 (0.67–0.71). Face and cheek shiny light brown. Carina light brown, prominent, straight, not sulcate. Cheek index about 7–10. Eye wine-red; eye index = 1.17 (1.11–1.25). Scape light brown, pedicel mostly dark brown, apically lighter, first flagellomere brown; length to width ratio 1.8. Arista with 5 dorsal, 2 ventral long branches, and about 7 inner branches relatively long, plus terminal fork. Proboscis and palpus brown.

Thorax mostly dark brown; length ca. 1.00 mm. Scutum pollinose, anteriorly light brown, laterally and posteriorly dark brown; 6 rows of acrostichals. Setae and setulae dark brown with golden sheen. Transverse distance of dorsocentral setae 200% of longitudinal distance; dc index 0.70. Scutellum pollinose dark brown, apically blunt; distance between apical scutellar setae equidistant to that between apical and basal one; basal setae strongly divergent, apical ones cruciate; scut index = 1.04. Pleura shiny brown, sterno index = 0.54, median katepisternal seta about 50–63% of anterior one. Halter light brown basally, dark brown distally. Legs uniformly light brown; apical seta on protibia and mesotibia; preapical seta on all tibiae.

Wing ( Fig. 7) light brown hyaline, crossveins R-M and dM-Cu, and apices of veins R 2+3, R 4+5 and M slightly clouded, tip of vein R 4+5 slightly curved posterad; length 1.90 (1.80–1.93) mm, length to width ratio = 2.02 (1.95–2.08). Indices: C = 3.06 (2.84–3.29), ac = 2.15 (2.00–2.38), hb = 0.49 (0.44–0.50), 4C = 0.79 (0.75–0.86), 4v = 1.67 (1.62–1.73), 5x = 1.14 (1.11–1.22), M = 0.45 (0.42–0.46), prox. X = 0.55 (0.50–0.59).

Abdomen ( Fig. 2) shiny, brownish black; tergites 1–4 light brown with a characteristic distal dark brown band, well delimited, medially interrupted and laterally broadened, reaching anterior margin of tergite; tergite 5 entirely shiny brownish black, except for a thin median longitudinal light brown stripe in some specimens, and tergite 6 entirely shiny dark brown.

Male terminalia ( Figs. 8–18). Epandrium ( Figs. 8, 9 and 16) almost bare, slightly microtrichose on posterior dorsal area; upper setae absent; ca. 8 lower setae; ventral lobe mostly membranous ( Figs. 8 and 16), not covering surstylus. Cercus slightly microtrichose on dorsocentral area, linked to epandrium by membranous tissue ( Fig. 8). Surstylus not microtrichose, with about 7–8 coneshaped prensisetae, about 10 long, strong outer setae and about 2 short, thin, mostly inner setae ( Figs. 8, 9 and 16). Decasternum as in Figs. 8 and 9. Hypandrium ( Figs. 10 and 17) as long as epandrium, anterior margin convex; posterior hypandrial process absent; dorsal arch medially pointed posterad, strongly sclerotized; gonopod not microtrichose, fused to paraphysis, bearing one long seta on median inner margin. Aedeagus ( Figs. 11–15 and 18) distally bifid (in dorsal and ventral views, Figs. 11 and 15), blunt and slightly expanded dorsoventrally (in lateral view, Figs. 13 and 18); subapically bearing a dorsoventral membranous area covered with tiny spines; dorsal cleft ca. 1/3 length of aedeagus ( Fig. 12); paraphysis not microtrichose, fused to gonopod, submedially bearing two setulae adjacent to proximal margin ( Figs. 10 and 17). Aedeagal apodeme as long as aedeagus and fused to it, rod-shaped, dorsodistally bifid ( Figs. 11–15 and 18). Ventral rod triangle-shaped, completely fused to aedeagal apodeme ( Figs. 12–15, 18).

Female ( n = 10) ( Figs. 3 and 4). Color difference from male: in some specimens, color pattern of tergite 5 is similar to that of male tergite 4 (compare Figs. 2 and 4) with dark brown distal band interrupted by a large light brown triangle-shaped longitudinal stripe running from tergite 4 to 5, and color pattern of tergite 6 of some specimens not being entirely dark brown but bearing a thin median light brown longitudinal stripe.

Measurements: Frontal length 0.30 mm; frontal index = 0.87, top to bottom width ratio = 0.61. Frontal triangle about 75–92% of frontal length. Ocellar triangle about 33–42% of frontal length. Orbital plates about 92–100% of frontal length. Distance of or3 to or1 = 67–125% of or3 to vtm, or1/or3 ratio = 0.65 (0.60–0.70), postocellar setae = 67 (54–75)%, ocellar setae = 91 (85–100)% of frontal length; vt index = 1.04 (1.00–1.10); vibrissal index = 0.61

Decasternum

(0.44–0.75). Cheek index about 7.43 (6.67–10.50). Eye index = 1.16 (1.10–1.24). Thorax length 1.12 (1.10–1.17) mm. h index = 1.00 (0.90–1.14). Transverse distance of dorsocentral setae 229–267% of longitudinal distance; dc index = 0.63 (0.53–0.72). Distance between apical scutellar setae about 88–114% of that between apical and basal one; scut index = 1.01 (0.94–1.12), sterno index = 0.54 (0.44–0.62), median katepisternal seta about 44–67% of anterior one. Wing length 2.18 (1.95–2.46) mm, length to width ratio = 2.13 (1.95–2.28). Indices: C = 3.21 (3.05–3.44), ac = 2.26 (2.00–2.57), hb = 0.47 (0.42–0.50), 4C = 0.78 (0.74–0.83), 4v = 1.70 (1.60–1.96), 5x = 1.26 (1.10–1.44), M = 0.49 (0.42–0.54), prox. X = 0.56 (0.48–0.71).

Terminalia ( Figs. 19 –22). Oviscapt valve double-walled, apically roundish, submedially slightly expanded dorsad, ventrally slightly undulate, with ca. 16 discal and about 6 marginal, peglike, mostly roundish-tipped (neither sharply pointed nor bearing a mediodorsal, pointed triangle-shaped process, as it occurs in D. nigrifemur ), outer ovisensilla; trichoid-like inner ovisensilla: 3 thin distally positioned, and 1 long, slightly curved, subterminal; inner wall ( Fig. 21, dashed line) proximally narrow, distally as wide as outer wall. Spermathecal inner capsule elongate, light bulbshaped, sclerotized, distally not flatten (somewhat flatten in D. nigrifemur ), slightly waisted subbasally, furrowed at basal 1/7; basal introvert deeply invaginated (but neither reaching the tip nor distally expanded, as it occurs in D. nigrifemur ) and subproximally dilated.

Egg ( n = 1). Whitish, length ca. 0.51 mm, bearing 4 thin filaments of equal length ( 0.43 mm), slightly shorter than egg.

Puparium ( n = 1) ( Figs. 5 and 6). Reddish dark brown; horn index about 2.8, with ca. 18 light brown tracheal branches per stalk; stalks of anterior and posterior spiracles light brown.

Distribution. This species is known only from the type locality (city of São Paulo, state of São Paulo, Brazil).

Etymology. The epithet butantan [alternative spelling of Butantã] is a noun in apposition and an allusion to the district where the type locality is located.

Ecology. Only 9 males (0.07%) of Drosophila butantan sp. nov. were identified among 13.057 males of species belonging to the genus Drosophila sampled in two years (1996–1997) by Ratcov (unpublished thesis) and Vilela from fermenting banana-yeast baited traps set in the type locality. It was comparatively more abundant in four non-consecutive days of collection conducted in December 2006, in the same forest reserve, by aspirating flies from inflorescences of Goeppertia monophylla , where four males of Drosophila butantan , sp. nov. (1.29%), in addition to six females, were collected among 309 males of species of Drosophila sampled. However, none of the 137 drosophilids that emerged from 20 inflorescences of Goeppertia monophylla collected in the same date and site belonged to Drosophila butantan sp. nov. Thus, the larval breeding sites of this species remain unknown.

Chromosomes ( Figs. 23–28). Drosophila butantan sp. nov. has a karyotype of 2 n = 10 (2 R, 2 V, 1D), comprising two pairs of rod-shaped telocentric chromosomes of decreasing size, two pairs of large V-shaped metacentrics, and one pair of barely recognizable dot (D) microchromosomes. The V’s are of two kinds, one is approximately equal-armed with both euchromatic arms being observed in pairs in mitotic cells of both sexes, and corresponding to an autosome, while the other, the largest V’s with unequal arms, being the shortest arm totally heterochromatic and representing the X chromosome. The sex chromosomes are definitely heteromorphic, while the X is a large V, the Y is a telocentric (rod-shaped) chromosome, shorter than the X chromosome, totally heterochromatic and often curved rather than bent, bearing a small satellite at the proximal region ( Figs. 26–28).

Relationship. It belongs to the Drosophila guarani species group and is apparently closely related to Drosophila nigrifemur from Bolivia (Department of La Paz: Mapiri and San Carlos), redescribed and illustrated by Vilela and Bächli (1990: 116, 293C, 323E). Drosophila butantan sp. nov. also shares some similarities with D. alexandrei and D. guaraja regarding the shape and structure of the inner spermathecal capsules. The karyotype of D. butantan sp. nov. shown here ( Figs. 23–28) differs from the karyotype of D. alexandrei from Porto Alegre, Brazil, with 2 n = 8 (3 R, 1 V) reported by Cordeiro (1951), and also from D. guaraja from Campos de Jordão, SP, and Rio de Janeiro, Brazil, with 2 n = 10 (3 R, 1 V, 1D) (X = R, Y = R) described by King (1947). The mitotic plates of D. guaraja from Ubatuba shown in Figs. 29–34 agree, in general, with the chromosome description reported by King (1947) in quotation marks below. This species “shows five pairs of chromosomes, one pair of large equal-armed V’s, 3 pairs of rods of different lengths, and one pair of small dots. The two pairs of longer rods often show satellites and appear to have subterminal centromeres”. The author pointed out that “The sex chromosomes are evidently the smallest rods”, however, our data support that the X clearly corresponds to the largest rod chromosome, as it is shown in Figs. 29–34.

Seven species of the guarani group show a diploid number of 12 chromosomes: D. araucana (see Brncic, 1957), D. griseolineata (see Dobzhansky and Pavan, 1943; King, 1947), D. guaru (see Dobzhansky and Pavan, 1943), D. limbinervis (see Clayton and Wasserman, 1957), D. maculifrons (reported as D. guaramunu according to Vilela and Bächli, 1990, in Dobzhansky and Pavan, 1943, King, 1947), D. ornatifrons (reported as D. guarani according to Vilela and Bächli, 1990, in Dobzhansky and Pavan, 1943, King, 1947), and D. subbadia (see King, 1947). The karyotypes of D. butantan sp. nov. and D. guaraja differ from those of all other species of the group in showing five rather than six pairs of chromosomes (or four pairs of chromosomes, as in D. alexandrei ). King (1947) proposed an explanation for the reduced chromosome number in D. guaraja , and relevant to the hitherto undescribed species shown here. He argues that two autosomal rods have become fused by translocation with resulting loss of one of the centromeres. The sex chromosomes in D. butantan sp. nov. are, like those reported for D. subbadia by King (1947), definitely heteromorphic (X = V, Y = R). At present, the cytological observations shown here support the morphological distinctiveness among D. butantan sp. nov. and some species of its group. For the time being, Drosophila butantan sp. nov. remains unassigned to any of the two subgroups currently recognized within the guarani group.