Drosophila rarotongae, Mcevey & Polak, 2021

Mcevey, Shane F. & Polak, Michal, 2021, Drosophilidae (Diptera) of the Cook Islands, Records of the Australian Museum (Rec. Aust. Mus.) 73 (5), pp. 153-170 : 161-164

Drosophila rarotongae sp. nov.

urn:lsid:zoobank.org:act:B7F9A72F-0A18-47A6-B88C-B867AF9416B5

Figs 13–20

Holotype ♂ “ COOK IS, Rarotonga | –21.2347° –159.7893° | 1.ii.2017 banana bait | Michal Polak”, Australian Museum K. 385599 . Paratypes 19 wild-caught males as follows: 7♂♂ same data as holotype, preserved in 80% alcohol, AM K.385598, AM K.385665–70; 6♂♂, dehydrated from OH and card-mounted: “ COOK IS, Rarotonga | –21.2382° –159.7880° | 1.ii.2017 papaya bait | c.1060’ Michal Polak”, AM K.385659–64; 1♂, terminalia dissected, “ COOK IS, Rarotonga | –21.2347° –159.7893° | 28.i.2017 sweep | Michal Polak”, AM K.385592; 1♂ “ COOK IS, Rarotonga | –21.2325° –159.7901° | 30.i.2017 flowers | Michal Polak”, AM K.385602; 4♂♂, ibid. but “ 30.i.2017 swept”, AM K.385603, K.385656–58.

Additional specimens (males and females collected with, and probably conspecific with, the above males), from the same three localities and the same three dates, all in AM as follows: K.385584– 85 ♂♂, K.385594– 97 ♂♂, K.385600–01 ♀ and ♂, K.385643– 47 ♀♀, K.385648 ♂, K.385671– 73 ♀♀, and nine unregistered in 80% alcohol; K.471879– 80 ♂♂, K.471924– 25 ♂♂, K.471926 ♀, K.471933– 34 ♀♀, K.471935 ♂, K.471944 ♀, all field-pinned by MP .

Distinguishing features

This species is distinguished from all others in the D. ananassae subgroup by reference primarily to the extraordinarily large, pointed, black, and prominent pregonites arising adjacent to the aedeagus ( Figs 16–17 , 26 ). This species can also be distinguished from many others in the subgroup by reference to the heavily pigmented and blackened tergites IV and V ( Fig. 13 ).

Description (male)

Body length 2.5–2.7 mm.

Head. Arista ( Fig. 14 ) with 5 rays above, 3 below, plus a terminal fork (10–11 free ends). Front and face pale brown. Fronto-orbital setae in the ratio proc orb: a. r.orb : p. r.orb = 6: 3: 7. Facial carina prominent. Head morphometrics: hw/fw(ov) = 1.8–2.1; hw/fw(iv) = 1.8–2.1; hw/fw(vt) = 1.7–2.0; hw/fw(a.oc) = 1.8–2.1; hw/fw(a. r.orb ) = 1.9–2.3; hw/fw(x. r.orb ) = 1.9–2.2; hw/fw(ptl) = 2.3–2.7; fw(ov)/ fl = 1.4; fw(iv)/fl = 1.4; fw(vt)/fl = 1.4–1.5; fw(a.oc)/fl = 1.4–1.5; fw(a. r.orb )/fl = 1.2–1.4; fw(vt)/fw(ptl) = 1.3–1.4; orbito-index = 0.7–0.8; oc-gap/pv-gap = 0.4–0.5; fl/fw(ptl) = 0.9–1.0; fw(a.oc)/hw = 0.5–0.6); measurements from males: AM K.385592, K.385599, K.385602, K.385603.

Thorax ( Fig. 13 ). Brown sensu Bock & Wheeler (1972). Acrostichal hairs in 8 rows in front of dorsocentral setae and 6 rows between. Ratio anterior:posterior dorsocentrals 0.55. Sterno-index 0.6–0.7. Preapical bristles on all tibiae; apicals on first and second tibiae. Sex comb of male ( Fig. 20 ) in transverse rows of stout black bristles; 3 metatarsal rows of (from above down) 2, 3, and 4 teeth; 3 rows on the second tarsomere of (from above down) 2, 3, and 2 teeth; and a further tooth distally on the third tarsomere.

Wing ( Fig. 15 ) of AM K.385592: hyaline; C-index = 1.41, 4v-index = 2.46, 4c-index = 1.75, 5x-index = 2.74, M-index = 0.92, ac-index = 3.62, C3 fringe = 0.59, hb = 0.62, prox.x = 0.64. Wing lengths, from humeral crossvein to apex (sensu Okada, Bächli, WL) = 1.58 mm, from basal medial bifurcation to apex (sensu Grimaldi, Toda, L 1) = 1.51 mm; or from axis to apex (sensu Bock, Wheeler, Lax) = 1.86 mm.

Abdomen ( Fig. 13 ). Brown, tending to blackish brown on tergites 3–6.

Male terminalia. Epandrium ( Fig. 18 ) closely resembles D. pandora McEvey & Schiffer, 2015 (see McEvey & Schiffer, 2015, figs 38–53), D. schugi McEvey & Schiffer, 2015 , D. ananassae and other species of the D. ananassae complex and is, consequently, diagnostically less useful than the hypandrium. The surstylus is large with an inner or median row of about 5 strong, well-spaced setae that merge into a cluster of an additional 7–8 setae (one or two longer than the rest) and two series of short, blunt, thick prensisetae laterally to these (prens, Fig. 18 ). The upper series has 2 prensisetae, the lower series about 5 of similar form. The cercal ventral lobe (secondary clasper) is very small with a very large curved, black, medial tooth, and several small setae basally.

Hypandrium ( Figs 16–17 , 26 ). Aedeagus is pale brown, slightly expanded in apical half, hirsute (longer hairs in mid region). Laterally and adjacent to the aedeagus are a pair of very prominent, large, black, pregonites, two thirds the length of the aedeagus, and tapered caudally to an acute apex; the ventral side is smoothly curved, but the dorsal side is notched (pregt proc, Fig. 16 ). There are three sensilla detectable under high power, one arises on the dorsal notch or process, the remaining two lie halfway between it and the base (pregt sens, Fig. 16 ). The gonocoxite (goncx, Fig. 17 ) is hirsute submedially, the pair of submedian spines or gonopodal setae (gon s, Fig. 16 ) are very large and widely spaced (obscured in dorsal view, Fig. 17 ). Phallapodeme is narrow but provides a wide base for the aedeagus.

Female. Resembles male, also with abdomen tending to blackish-brown apically.

Female terminalia ( Fig. 19 ). Oviscapt short, rounded apically, with short marginal spines.

Distribution. Known only from the island of Rarotonga ( Cook Islands Southern Group, Tropical South Pacific) above 135 m altitude ( Figs 2 , 21 ; Table 3).

Etymology. The name “ rarotongae ” is proposed as a noun in the genitive case.

Remarks. Drosophila rarotongae sp. nov. is a member of the

Drosophila melanogaster species group, the D. ananassae Table 5. Number of teeth in each row of the sex comb on the subgroup, and the D. ananassae complex. It resembles male fore-tarsi of Drosophila rarotongae sp. nov., D. schugi Drosophila schugi ( Fig. 25 ) from Samoa and D. phaeopleura McEvey & Schiffer ( Samoa) and D. phaeopleura Bock & ( Fig. 27 ) from Fiji. All three species are restricted to Wheeler ( Fiji) showing total (median) number of teeth per localities at altitude ( Table 1) on islands of the Tropical leg; numbering of rows begins at proximal end of tarsomere. South Pacific and are generally darker than lowland species of the region like D. pandora , D. anomalata , D. pallida , and D. ochrogaster ( Fig. 21 ). Consistent differences exist, however, between D. rarotongae sp. nov., D. phaeopleura and D. schugi in the arrangement and number of sex combs. Sex combs are pictured in Fig. 20 in the present work (see also D. phaeopleura Bock & Wheeler, 1972 : fig. 60 and D. schugi McEvey & Schiffer, 2015 : figs 66–71). Observed differences are quantified, results are presented in Table 5. Drosophila schugi has c. 63 teeth in the male sex combs of one foreleg, D. phaeopleura has c. 34, while D. rarotongae sp nov. has about 17.

The Drosophila ananassae species complex now has 13 species ( Fig. 21 ):

Drosophila ananassae Doleschall, 1859:128

Drosophila anomalata McEvey & Schiffer, 2015:142

Drosophila atripex Bock & Wheeler, 1972:42

Drosophila lachaisei Tsacas, 1984:428

Drosophila monieri McEvey & Tsacas, McEvey et al., 1987:378

Drosophila nesoetes Bock & Wheeler, 1972:41

Drosophila ochrogaster Chassagnard , in Chassagnard & Groseille,

1992:63

Drosophila pallidosa Bock & Wheeler, 1972:38

Drosophila pandora McEvey & Schiffer, 2015:138

Drosophila parapallidosa Tobari , in Matsuda & Tobari, 2009:135

Drosophila phaeopleura Bock & Wheeler, 1972:40

Drosophila rarotongae sp. nov.

Drosophila schugi McEvey & Schiffer, 2015:143 Drosophila rarotongae sp. nov. differs from all members of the ananassae complex by reference to the male genitalia, specifically the very prominent pair of black pregonites adjacent to the aedeagus. Bock & Wheeler (1972: 40) describe the homologous structure in D. phaeopleura as “anterior parameres very large, crescentic, articulated to aedeagus, laterally with 4 well-spaced minute sensilla”; and McEvey & Schiffer (2015: 146) describe the homologous structure in D. schugi as “large, scimitar-shaped or with ragged lateral edge, articulated to aedeagus, and laterally with no [but see below] minute sensilla”. Sensilla have been observed on the lateral face of the D. rarotongae pregonite (pregt sens in Fig. 16 ).

In earlier works (McEvey & Polak, 2005; Schiffer & McEvey, 2006; McEvey & Schiffer, 2015) terms introduced by Bock, Wheeler, and Okada (Bock & Wheeler, 1972; Okada, 1954) were used when describing male terminalia, specifically anterior and posterior parameres for the appendages arising from the gonocoxite or near the base of the aedeagus. More recently arguments presented by Wood, Sinclair, and Cumming (Cumming, Sinclair, & Wood, 1995; Sinclair, 2000; Cumming & Wood, 2017) have compelled us to reconsider this practice and to adopt terms more widely accepted by dipterists. Motivation to adopt new terms comes also from the work of Grimaldi (1990) and recent involvement in the Manual of Afrotropical Diptera (McEvey & Grimaldi, 2021 in press), together with efforts among Drosophila melanogaster researchers to achieve consensus in terminology (Rice et al., 2019). The newly adopted terms pregonite and postgonite replace anterior and posterior paramere respectively; we now use gonocoxite for novasternum, and phallapodeme for apodeme. Pregonites are connected to the gonocoxite, postgonites are dorsal to them and connected to the phallus. Pregonites have sensilla (of variable size and often apically), postgonites do not; McEvey & Schiffer (2015: 146) stated that the D. schugi pregonite has “no minute sensilla”, sensilla have in fact been detected in subsequent examinations using better microscopy. A pregonite may have a process extending from its base that curves caudally—the basal extension (“basal process” of some authors) ( Fig. 28 ). The basal extension is a striking feature of the D. ananassae and D. pandora terminalia ( McEvey & Schiffer, 2015); it is entirely bare. In D. rarotongae the pregonite itself is enlarged, a basal extension is entirely absent, several small sensilla are present, one arises on the small pregonite process (pregt proc, Fig. 16 ).

The base of each pregonite arises adjacent to and separate from the aedeagus and phallapodeme. Being so positioned, they possibly serve to anchor the male genitalia during copulation by moving into an outward pointing orientation (abduction) when the phallapodeme and aedeagus thrust forward.

Figures

Figure 2. Montane forest terrain of Rarotonga showing the relationship between the three “high elevation” collecting sites in the upper Avatiu valley (circles, details in Table 2), close to the more inaccessible higher mountain peaks which could not be reached during the present survey—Te Manga, Te Atkura, Te Kou, and Maungatea. (Colour photo by Marcus Gleinig, terrain image [Te Kou to Te Manga profile distortion due to steepness of gradient] from Google Earth, June 2019).

Figure 21. Distribution map of 12 species of the Drosophila ananassae complex. This map was first published by McEvey & Schiffer (2015) and then updated by them (2018). The discovery of the new species D. rarotongae sp. nov. from the southern group of Cook Islands is indicated on this map. Drosophila ananassae s.str. has pantropical distribution indicated within the pale blue lines, the Ambon type locality is shown. Three or more additional but undescribed species occur in New Guinea (and perhaps also in northern Australia), these are not shown (see McEvey & Schiffer, 2015, for further details).

Figures 13–20. Drosophila rarotongae sp. nov. (13) male habitus; (14) arista of AM K.385602; (15) wing of AM K.385592; (16, 17) ventrolateral and dorsal views respectively, of hypandrium of AM K.385594 and K.385584—aed, aedeagus; gon s, gonopodal seta (one of a pair); goncx, gonocoxite; pgt, postgonite; phapod, phallapodeme; pregt, pregonite; pregt proc pregonite process; pregt sens, pregonite sensilla (three sensilla detected on this structure under high power); prens, prensisetae (lower of two series, upper series with two prensisetae); trn bd, transverse band; (18) epandrium of AM K.385594; (19) oviscapt of female AM K.385600; and (20) sex combs on foretarsi of male AM K.385592.

Figures 22–30. Hypandria of Drosophila rarotongae sp. nov. and related species: (22) D. atripex, Bali, McE32697; (23) D. monieri, Moorea, AM K.380298; (24) D. ochrogaster, New Caledonia, K.282803; (25) D. schugi, Samoa, K.356978; (26) D. rarotongae, Rarotonga, K.385584; (27) D. phaeopleura, Fiji, K.282923; (28) D. pandora, Lake Placid (near Cairns), ex iso-female strain CAQ425; (29) D. ananassae, Marquesas, K.380299; (30) D.anomalata, Townsville, ex type strain CHC221.Abbreviations, see Figs 13–20 caption.