Drosophila (Drosophila) montevidensis, Goñi & Vilela, 2016

Goñi, Beatriz & Vilela, Carlos R., 2016, Two new Neotropical species of Drosophilinae (Diptera: Drosophilidae) from Uruguay, Zoologia (e 20160142) 33 (6), pp. 1-13 : 2-9

Drosophila (Drosophila) montevidensis sp. nov.

Figs. 1-8, 17-49, 54-55, 58-63

urn:lsid:zoobank.org:act:DDAFE6AD-5838-4141-84F9-2DB89A1DE856

D. gr. tripunctata (subgroup I) GOñI et al., 1997: 90 (table 1, collected in banana-baited traps).

Unidentified species of the tripunctata group of Drosophila GOñI et al., 1998: 134 (table 2, geographic distribution), 137 (table 3, breeding site), 139 [affiliation = not D. angustibucca Duda sensu Frota-Pessoa (1954)].

Drosophila aff. nappae GOñI et al., 2012: 308 (abstract), 312 (table 2, feeding site), 313 (distribution, level of association), 314 (abundance), 316 (abundance and richness).

Types. Holotype male, labeled “ Uruguay – Montevideo, Montevideo city, Facultad de Agronomía , (34°50’69”S, 56°13’44”W), Beatriz Goñi coll. / net swept over fallen fleshy seeds of Ginkgo biloba 17.IV.2005 /from isofemale line F6/ Drosophila montevidensis ♂ Goñi and Vilela/HOLOTIPO [red label]” ( MZSP) . Paratypes: five males and one female same data as holotype, except isofemale line label (F1-F5), plus two males collected on the same place ( MZSP) . The latter two specimens were collected as follows: one male net swept over fallen, decaying fruits of Syagrus romanzoffiana (Cham.) Glassman ( Arecaceae ), and the other male over fallen, decaying fruits of Psidium cattleianum Afzel. ex. Sabine ( Myrtaceae ) but on 01.IV.2005.

Diagnosis. Scutum subshining tan, darkening gradually from anterior to posterior region, anterior half with two narrow, diffuse and slightly darker stripes between and just adjacent to the dorsocentral rows; scutellum darker, dull; facial carina large and broad, not sulcate; wing brownish, crossveins strongly clouded, C index = 3.6-4.2; three strong black setae in a line at base of metatarsomere I; abdomen shining yellow, tergites 2-6 with posterior dark brown bands medially slightly interrupted, not reaching lateral margins, and a variable (diffuse to well delimited) median, light brownish to dark brown longitudinal stripe; epandrium devoid of upper and lower setae (3-6 upper setae present in Drosophila nappae ), gonopod subdistally microtrichose (without macrotrichia in D. nappae ), aedeagus antero-dorsally bearing a conspicuous pair of slightly membranous, dorsally somewhat sclerotized, finger-shaped processes, 2/3 the length of aedeagus (1/3 the length of aedeagus in D. nappae ), backwards directed and covered with tiny spines, aedeagus distal end medially bearing a V-shaped (U-shaped in D. nappae ) membranous area in dorsal view, ventral rod as long as aedeagus (shorter than aedeagus in D. nappae ), ventral margin of aedeagus and posterior margin of ventral rod abruptly converging, as seen in lateral view (mildly converging in D. nappae ); spermathecal capsule spherical (larger and somewhat elliptical in D. nappae ), devoid of basal furrows (present in D. nappae ).

Description. Male (n = 8). Head. Frons mostly yellowish-brown, dull; frontal length 0.32 (0.29-0.37) mm, frontal index = 0.78 (0.71-0.86), top to bottom width ratio = 1.70 (1.56-1.93). Frontal triangle light brown, not well-defined, about 67-86% of frontal length; ocellar triangle dark brown, about 33- 42% of frontal length, ocelli surrounded by conspicuous black crescents along inward-directed margins. Orbital plates light brown, subshining, about 80-108% of frontal length. Orbital setae black, or2 just outside of or1, shorter and about one-half diameter of larger setae of pedicel, distance of or3 to or1 = 50-80% of or3 to vtm, or1/or3 ratio = 0.73 (0.67-0.82), or 2/or 1 ratio = 0.40 (0.33-0.50), postocellar setae 64-83%, ocellar setae 86-108% of frontal length, vt index 1.17. Postocellar setae cruciate at tip. Face light brown, dull; facial carina slightly darker, broad, divergent downwards, not sulcate; vibrissal index = 0.45 (0.30-0.63). Cheek index = 8.10 (5.20-11.0). Eye red, dorsally remarkable darker. Eye index = 1.28 (1.19-1.39). Antenna brown to light brown; pedicel, dorsally darker, with two larger setae of about same size. First flagellomere short-haired; length to width ratio = 1.69 (1.50-2.00). Arista with 6 upper and 3-4 lower branches, plus terminal fork; 7-10 inner branches. Proboscis brown, palpus light brown with a row of about 5 long setae, decreasing in length from tip to middle area, plus several fine setulae.

Thorax. Length = 1.21 (1.15-1.32) mm. Scutum tan, posteriorly darker, subshining, 5-7 irregular rows of acrostichals. h index = 0.82 (0.67-0.91). Transverse distance of dorsocentral setae 180-243% of longitudinal distance; dc index = 0.82 (0.79-0.85). Prescutellar setae absent. Scutellum dark brown, dull, distance between apical scutellar setae about 73-90% of that between apical and basal one, basal setae divergent, apical setae cruciate at median region; scut index = 1.05 (1.00-1.10). Pleura light brown at anterior lower half, brownish dorsally and posteriorly, shining, sterno index = 0.52 (0.50-0.57); median katepisternal seta 67-100% of anterior one and noticeably thinner than other two, posterior one thicker. Proepisternal seta absent. Halter stalk pale yellow, halter knob proximally brown, yellowish at distal region. Legs uniformly light brown. Three strong black setae in line at base of inner surface of metatarsomere I, which is slightly wider than metatarsomere II, but not twice as wide, as it conspicuously occurs in Drosophila platitarsus Frota-Pessoa, 1954 . One small thick black seta at base of inner surface of mesotarsomere I. Apical setae on protibia and mesotibia, the latter spur-shaped; preapicals on all three.

Wing. Brownish, slightly pointed at tip of R 4+5, crossveins clouded, tips of longitudinal veins slightly darkened; length 2.74 (2.46-2.93) mm, length to width ratio = 2.27 (2.20-2.35). Indices: C = 3.86 (3.63-4.16), ac = 1.74 (1.54-2.11), hb = 0.47 (0.45-0.52), 4C = 0.72 (0.66-0.76), 4v = 1.59 (1.52-1.75), 5x = 0.88 (0.79-1.00), M = 0.40 (0.38-0.43), prox. x = 0.76 (0.69-0.83).

Abdomen. Shining brownish-yellow, tergites 2-6 with a posterior, medially slightly interrupted dark brown band, not reaching lateral margins, and a variable (diffuse to well delimited) median, light brownish to dark brown longitudinal stripe, which may be completely absent in some specimens.

Terminalia ( Figs. 17-24, 26-49). Epandrium almost bare, slightly microtrichose on posterior dorsal area; upper and lower setae absent; ventral lobe roundish, slightly covering surstylus. Cercus slightly microtrichose on dorsal area, linked to epandrium by membranous tissue. Surstylus not microtrichose, with about 7 cone-shaped prensisetae, about 4 long, strong outer setae and about 11 long, thin, mostly inner setae. Decasternum as in Fig. 18. Hypandrium ( Fig. 19) as long as epandrium, anterior margin convex; posterior hypandrial process absent; dorsal arch present, strongly sclerotized; gonopod subdistally microtrichose, fused to paraphysis, bearing one long seta on median inner margin. Aedeagus ( Figs. 20-24, 26-49) lateroventrally strongly sclerotized, anterodorsally bearing a distinctive pair of membranous, dorsally slightly sclerotized, finger-shaped, backwards directed processes, which are shorter than aedeagus (ca. 2/3 its length) and lateroventrally covered with tiny spines. Aedeagus in dorsal view (Fig. 20) bearing a small, slightly sclerotized, crescent-shaped plate at subdistal area which embraces the gonopore of endophallus; distal end medially bearing a V-shaped membranous area, distal margin rounded in dorsal as well as in ventral view ( Figs. 31-35, 41-45, 48, 49) (remarkably angled in Drosophila nappae , Figs. 52 - 53). Aedeagal apodeme rod-shaped, laterally flattened, slightly shorter than aedeagus; anteriorly expanded dorsoventrally in aged males ( Figs. 28, 38). Ventral rod completely fused to aedeagal apodeme, relatively long, remarkably right-angled in relation to ventral margin of the aedeagus as seen in lateral view (in D. nappae it is much shorter than aedeagus and obtuse-angled in relation to ventral margin of the aedeagus).

Female (n = 1). Main differences from male: usually larger; median anteroposterior stripe on tergite 6 seems to be thinner and paler than that of male.

Measurements. Frontal length 0.37 mm; frontal index = 0.79, top to bottom width ratio 1.58. Ocellar triangle 33% of frontal length. Orbital plates 93% of frontal length. Distance of or3 to orb1 = 67% of or3 to vtm, or1/or3 ratio not determined (or3 missing), or2/orb1 ratio = 0.33, postocellar setae = 60%, ocellar setae = 100% of frontal length, vt index = 1.25, vibrissal index = 0.36. Cheek index 7. Eye index 1.4. First flagellomere short-haired; length to width ratio 2.00. Arista with 7 upper and 3 lower branches, plus terminal fork; 8 inner branches. Thorax length 1.34 mm. h index = 0.75. Transverse distance of dorsocentral setae 250% of longitudinal distance; dc index not determined (bristles missing). Distance between apical scutellar setae about 82% of that between apical and basal one; scut index not determined (bristles missing), sterno index = 0.50, median katepisternal seta about 82% of anterior one. Wing length 2.98 mm, length to width ratio not determined (wings posteriorly broken). Indices: C = 3.96, ac = 1.69, hb = 0.41, 4C = 0.67, 4v = 1.52, 5x and M not determined (wings posteriorly broken), prox. x = 0.64.

Female terminalia ( Figs. 25, 54, 55). Valves of oviscapt ( Figs. 25, 54) pointed at tip, ventrally convex, dorsally rounded subdistally (angled in D. nappae , Fig. 56), with ca. 15 marginal and 5 discal peg-like ovisensilla; inner trichoid-like ovisensilla: 3 thin, distally positioned and 1 long, curved, subterminal. Spermathecal capsule ( Fig. 55) spherical (larger and somewhat elliptical in D. nappae , Fig. 57), devoid of basal furrows (present in D. nappae ); spermathecal duct distally dilated, becoming gradually wider apically, sclerotized.

Egg (n = 6). Length ca. 0.50 mm; four slender, divergent filaments; anterior pair slightly shorter than posterior pair.

Puparium (n = 3). Reddish-brown; horn index ca. 3.9; each anterior spiracle with about 14 branches; anterior stalk as long as branches length; tip of stalk of anterior spiracle blackish brown; posterior spiracles relatively long, only slightly shorter than anterior spiracles stalks.

Chromosomes ( Figs. 58-63). Basic diploid chromosome number of 2n = 12, XX in females and XY in males ( Figs. 58 - 61), with the haploid karyotype formula: 5R, 1D. The 4 pairs of autosomes range from medium to small-sized acrocentrics but smaller than any of the sex chromosomes. In early C-banded prometaphase cells, the autosomes show a short heterochromatic arm ( Fig. 59). The X chromosome, the biggest of the complement, has a large block of pericentromeric heterochromatin that covers almost half of its length and a tiny heterochromatic short arm, while the Y is heterochromatic and shorter than the X ( Fig. 60, 61). Dot chromosomes are quite small. Prophase I cells of male meiosis show four bivalents representing the pairs 2, 3, 4, 5, the small dot chromosomes, and the heterologous XY association ( Figs. 62, 63). The autosome bivalents pair along their length excepting the centric and paracentromeric regions. The sex chromosomes pair at a specific site, located at the distal heterochromatic region in the X and the proximal region in the Y chromosome ( Figs. 62, 63).

Distribution. Neotropical: Argentina (Buenos Aires) and Uruguay (Lavalleja, Montevideo, Rocha).

Remarks. This species belongs to the subgroup I (cf. VILELA 1992: 198) of the Drosophila tripunctata species group of the subgenus Drosophila . It shares with D. angustibucca , D. mediocris , D. medioobscurata , D. nappae , D. neoguaramunu , D. platitarsus , D. rostrata, and D. setula , the following remarkable features: aedeagus dorsally with a small, sclerotized, crescent-shaped plate at subdistal area, and anterodorsally bearing a pair of finger-shaped (sometimes diffuse) and backwards directed processes. The processes are small, diffuse and mostly membranous in all species except in D. nappae , where they are only slightly membranous and proportionally longer; and they are even longer in D. montevidensis sp. nov. Additionally, all of them but the latter two, have in common a sclerotized, inverted T-shaped area partially surrounded by the pair of processes in the anterodorsal, mostly membranous surface of aedeagus.

The karyotype of four out of the eight species included in the subgroup I of the Drosophila tripunctata group, namely D. nappae (originally referred to as D. angustibucca ) (see FRANCK et al. 1984 and PIRES 2000 [as Drosophila sp. U3]), D. neoguaramunu (see FRYDENBERG 1956), D. platitarsus (see PIRES 2000) and D. setula (see CLAYTON & WASSERMAN 1957), were reported. Apparently, the observed haploid karyotype of D. montevidensis sp. nov. (n = 6) is indistinguishable from D. nappae , with 5R, 1D (Y chromosome is a rod shorter than X); however, it differs remarkably from the haploid karyotype formula of D. neoguaramunu (n = 3), with 3V (X chromosome considerably shorter than rod-shaped Y chromosome), in samples collected from Peru ( FRYDENBERG 1956). The karyotype of these species differ from that of D. platitarsus (n = 6), being 4R, 1V, 1D (V-shaped X and J-shaped Y), with heterochromatic pericentromeric regions in the rod-shaped pairs, the dots, but differ in the shape of the Y, and the location of the heterochromatin in the X chromosome (interstitially located in one arm, and proximally, at the pericentromeric region, in the other arm), in samples of an isofemale line derived from an individual collected at the Forest Reserve of the IB-USP, located in the Cidade Universitária “Armando de Salles Oliveira”, São Paulo city, state of São Paulo, Brazil ( PIRES 2000). They also differ from that of D. setula (n = 6) with 4R, 1V, 1D in a strain from Santa Martha, Colombia, and (n = 5[?]) with 3R, 1V, 1D (?) in a strain from Barro Colorado Is., Canal Zone, Panama ( CLAYTON & WASSERMAN 1957). There is no description of the sex chromosomes for D. setula in the latter reference. These data reveal that, excepting for D. montevidensis sp. nov. and D. nappae , a high interspecific karyotype variation is found among three species of the subgroup I of D. tripunctata group. The polytene chromosomes map of D. nappae (misidentified as D. angustibucca ) described by FRANCK et al. (1984) allows the opportunity to investigate the genetic divergence between this pair of sibling species by using polytene banding pattern as primary chromosomes markers. The feasibility to maintain laboratory strains of both sibling species let to investigate other biological aspects, such as life cycle, the existence or not of reproductive isolation mechanisms. So far, D. montevidensis sp. nov. has been collected in natural areas of southern Uruguay as well as in urban areas along both margins of Rio de la Plata (Buenos Aires and Montevideo cities), as well as other localities of the province of Buenos Aires and at southern and southeastern Departments of Uruguay (as detailed in material examined). Up to date, it has been absent in drosophilid samples emerged from decaying fruits collected in northern Uruguay, Department of Salto (B. Goñi, unpublished data). However, the apparently allopatric distribution of D. montevidensis sp. nov. and its sibling species, D. nappae , remains to be confirmed.

Laboratory Cultures. It is cultivated at 18 °C with a modified banana-agar culture medium (recipe above).

Etymology. The specific name is an adjective in allusion to the type locality (Montevideo city).

Material examined. Type series (8 males, 1 female, as detailed above) plus 318 non-type specimens (142 males, 103 females, and 73 adults not sexed) which were analyzed for distributional and ecological purposes only, as detailed below. ARGENTINA. Buenos Aires: Azul city (36°46’39”S, 59°51’48”W), 1 female, net swept over fallen, decaying infructescence of Ficus cairica L. ( Moraceae ), 06.IV.2006, B. Goñi leg. (MZSP); Buenos Aires city, Universidad de Buenos Aires, Facultad de Agronomía, Jardín Botánico “Lucien Hauman (34°35’36”S, 58°29’03”W), 2 males (MZSP) and 5 females (FCE-D), net swept over fallen, decaying fruits of Butia capitata (Mart.) Becc. ( Arecaceae ), 2 males, 3 females (MZSP), plus 10 males, 2 females (offspring of isofemale line Q23F2, MZSP), net swept over fallen, decaying fruits of Ocotea acutifolia , Crataegus sp. and Butia yatay (Mart.) Becc. 1916 ( Arecaceae ) (locally known as butiá), 11, 18, 27.IV.2006, B. Goñi leg. URUGUAY. Lavalleja: Sierra de Minas (woodland sierra, riparian forest and pine plantation habitats, between 34°30’59”S, 55°20’07”W and 34°30’54”S, 55°19’53”W), 10 males, 4 females (dung traps), 4 males, 3 females (carrion traps), V.2002 - IV.2003, P. González-Vainer leg. (FCE-D) ( GOñI et al. 2012). Montevideo: Montevideo city, Cerro Montevideo, Parque Vaz Ferreira (near waterpond, 34°53’49”S, 56°15’41”W), 3 males, 1 female in banana-baited traps, I, VI.1994, B. Goñi & M.E. Martinez leg. (FCE-D) ( GOñI et al. 1997); Universidad de la República, Facultad de Agronomía (backyard garden, 34°50’69”S, 56°13’44”W) as follows: 1 female, emerged from fallen, decaying fruit of Butia yatay (Mart.) Becc. 1916 ( Arecaceae ) (locally known as yatay), 1 female in banana-baited trap, IV, V, XII.2000, B. Goñi, P. Fresia, M. Calviño & M.J. Ferreiro leg. (FCE-D); 5 males, 2 females, emerged from fallen, decaying fleshy seeds of Ginkgo biloba (locally known as ginko), V.2005, B. Goñi & M.E. Martinez leg. (FCE-D); 10 males (MZSP), plus 10 males, 3 females (isofemale line Q37F51), 10 males, 5 females (Q37F53), 11 males, 3 females (Q37F54), 9 males, 5 females (Q37F55), 7 males, 2 females (Q37F56), 5 males, 2 females (Q37F57) and 4 males (Q37F58), net swept over fallen, decaying fleshy seeds of Ginkgo biloba , 6, 10, 16.V.2006, Goñi & M.E. Martinez leg. (MZSP); the following 127 specimens were net swept over fallen, decaying fleshy seeds of Ginkgo biloba , detailed as follows: 6 males, 5 females, III-V.2005, B. Goñi & M.E. Martinez leg. (FCE-D); 73 adults not sexed, 6, 10, 16.V.2006, idem leg. (FCE-D), and 14 males and 29 females offspring from eight isofemales (Q49F1 to F3, and Q49F5 to F9), 19.IV-15.V.2007, B. Goñi leg. (FCE-D). Rocha: Boca del Sarandí , on the western shore of the Laguna Negra (34°00’36”S, 53°45’26”W), 1 female, emerged from fallen, decaying cladode of Opuntia arechavaletai Speg. 1905 ( Cactaceae ) (locally known as opuntia), 4.VII.1995, M.E. Martinez leg. (FCE-D) ( GOñI et al. 1998); Laguna Negra, Don Bosco camp gallery forest, (53°45’18”W; 34°05’24”S), 20 males, 25 females, net swept over fallen, decaying fruits of Schinus longifolius (Lindl.) Speg. ( Anacardiaceae ) (locally known as molle), 17-25.V.2003, B. Goñi, M.E. Martinez, I. Machado, M. Gandelman, I. Corvo & M.J. Cabrera leg. (FCE-D).