Discothyrea mixta Brown, 1958

Hita-Garcia, Francisco, Lieberman, Ziv, Audisio, Tracy L., Liu, Cong & Economo, Evan P., 2019, Revision of the Highly Specialized Ant Genus Discothyrea (Hymenoptera: Formicidae) in the Afrotropics with X-Ray Microtomography and 3 D Cybertaxonomy, Insect Systematics and Diversity 5, pp. 1-84 : 18-22

Discothyrea mixta Brown, 1958

( Figs. 2A , 4A , 5 A–D, 6A, 7A, 8A, 9A, 10A, 11A, 12A,

14A, 15A, 15F, 15G, 17B, 17D, 17G, 18, 19; Supp

Video S1 [online only])

Discothyrea mixta Brown, 1958a: 343 .

Type Material

HOLOTYPE, pinned worker, LIBERIA, Bolahun (L. Bequaert) ( MCZ: MCZ_ Holotype _29872) [examined] . PARATYPES, three pinned workers with same data as holotype ( MCZ: MCZ_ Paratype _29872; MHNG: CASENT0911150 ; USNM) [examined except USNM]

Virtual dataset. Volumetric raw data (in DICOM format), 3D rotation video, still images of surface volume rendering, and 3D surface (in PLY format) of a nontype specimen (CASENT0285473) in addition to stacked digital color images illustrating head in full-face view, profile and dorsal views of the body. The data are deposited at Dryad (Hita Garcia et al. 2019, http://doi. org/10.5061/dryad.3qm4183) and can be freely accessed as virtual representation of the species. In addition to the data at Dryad, we also provide a freely accessible 3D surface model at Sketchfab (Model 1).

Nontype Material

ANGOLA: Dundo, R. Mussungue, [−7.3697, 20.813], ca. 630 m, gallery forest, 18.XII.1963 (Luna-Carvalho); Dundo, R. Kahingo, [−7.39, 20.51], ca. 650 m, gallery forest, 20.VI.1964 (Mwaoka); Route Dundo-Saurimo km 39, 23.XI.1963 (Luna-Carvalho); Salazar, [−9.3, 14.916667], ca. 700 m, forest, 9.III.1972 (P.M. Hammond) ; CAMEROON: Abona Mbana, 28.XI.1988 (A. Dejean); Ebodjie, [2.63, 9.88], ca. 70 m, 28.X.1991 (A. Dejean); Nkoemvon , [2.7517, 11.0814], ca. 630 m, 28.IX.1980 (D. Jackson); Mbalmayo, [3.4597, 11.4714], ca. 600 m, XI.1993 (N. Stork); South, Pan Pan, 1.IV.1990 (A. Dejean); Ottotomo, [3.65, 11.3167], ca. 750 m, 12.IX.1988 (A. Dejean) ; DEMOCRATIC REPUBLIC OF CONGO: Epulu , −1.38333, 28.58333, 750 m, 1.XI.1995 (S.D. Torti) ; North Kivu, Kivu, Lubero Territory, Rte. Kimbulu, ruis. Kitagoha , [-0.05311, 29.22183], 1760 m, tamisage de terreau, IV.1954 (R.P.M.J. Celis) ; North Kivu, Massif Ruwenzori, Mt. Ngulingo, prés Nyamgaleke , [0.498, 29.883], 2500 m, ex P. N.A., 13.I.1954 (H. Synave) ; GHANA: Ashanti, Ofinso, [6.93, −1.65], ca. 230 m, cocoa plantation, 2.XI.1992 (R. Belshaw); Aiyaola River Forest Reserve, [6.1510, −0.945], ca. 210 m, primary forest, 1.X.1992 (R. Belshaw); Atewa Forest Reserve , near Kibi, [6.1747, −0.5861], ca. 400 m, primary forest, 26.II.1992 (R. Belshaw); Kibi, 23.III.1970 (D. Leston); Sui River Forest Reserve , [6.129, −2.731], ca. 220 m, primary forest, 6.X.1992 (R. Belshaw) ; IVORY COAST: Abidjan, Banco Forest , [5.38694, −4.05275], ca. 20 m, I.1963 (W.L. Brown) ; Abidjan, Banco National Park, [5.38694, −4.05275], ca. 20 m, primary forest, 3.III.1977 (I. Löbl); Tai Forest, [5.75, −7.12], ca. 250 m, 14.V.1976 (T. Diomande); Anyama, Teke Forest , [5.55194, −4.01111], ca. 80 m, 15.II.1974 (T. Diomande) ; KENYA: Western Province , Kakamega Forest, Buyangu Nature Reserve, Buyangu Hill , 1570 m, 0.343, 34.863, 14.III.2002 (R.R. Snelling); Western Province , Kakamega Forest, Buyangu Nature Reserve near Salazar Circuit , secondary rainforest, 0.33, 34.87, 1500 m, 21.IV.2001 (R.R. Snelling & A. Espira); Western Province , Kakamega Forest, Mukangu Trail, 0.35328, 34.85886, 1623 m, primary rainforest, VII.2007 (F. Hita Garcia); Western Province , Kakamega Forest, Salazar , 0.32667, 34.87083, 1650 m, primary rainforest, 21.VI.2007 (M. Peters) ; MOZAMBIQUE: Sofala, Gorongosa National Park, Camp #1, −18.61865, 34.80866, 216 m, small forest, 18.IV.2013 (L.E. Alonso) ; RWANDA: Kayove, -[1.876, 29.357], 2100 m, 12.VIII.1973 (P. Werner); Rangiro , [2.39361, 29.18278], 1800 m, IX.1976 (P. Werner) ; SOUTH AFRICA: KwaZulu-Natal, Ukilinga Research Farm , 10 km SE of Pietermaritzburg, −29.6666, 30.4, 840 m, grassland, 31.XII.1991 (B. Chambers) ; TANZANIA: Iringa, Kilolo, Ndundulu Forest Reserve , −7.78912, 36.48539, 1567 m primary forest, 23.–26.X.2007 (P. Hawkes, M. Bhoke & U. Richard) ; Lindi, Lindi, Ndimba Forest Reserve, −9.62695, 39.62964, 138 m, 25.–28.II.2008 (P. Hawkes, Y. Mlacha & F. Ninga); Mkomazi Game Reserve, Kinondo Forest , −3.91667, 37.76667, 1270 m, montane forest, 9.V.1996 (H.G. Robertson) ; Pwani, Mafia, Mlola Forest, Mafia Island , −7.89576, 39.82842, 20 m, primary forest, 9.–13.III.2008 (P. Hawkes, Y. Mlacha & F. Ninga); South Pare Forest , −4.13056, 37.88389, 1650 m, montane forest, 29.XI.1995 (H.G. Robertson) ; Tanga, Kilindi, Kilindi Forest Reserve , −5.57934, 37.57971, 1000 m, primary forest, 27.–30.VIII.2005 (P. Hawkes, J. Makwati & R. Mtana) ; UGANDA: Kabarole, Kanyawara , Kibale National Park , 0.56427, 30.35876, 1510 m, montane wet forest, ex sifted leaf litter, collection code JTL7864-s, 8.VIII.2012 (J. Longino) ; Kabarole, Kanyawara , Kibale National Park , 0.55906, 30.35954, 1510 m, montane wet forest, nocturnal foragers, 11.VIII.2012 (J. Longino) ; Kabarole, Kanyawara , Kibale National Park , 0.55878, 30.35998, 1520 m, montane wet forest, nest in dead wood, collection code JTL7912, 13.VIII.2012 (J. Longino) ; Kibale National Park, Kanyawara Biological Station , 0.56437, 0.56437, 1510 m, rainforest, 16.VIII.2012 (G. Fischer) .

Diagnosis

Discothyrea mixta differs from D. oculata by the following combination of characters: smaller species (WL 0.59–0.72); broader head (CI 88–94); smaller eyes (OI 5–9); propodeum strongly angulate to denticulate; declivitious face of propodeum without costae or rugae; propodeum dorsally and laterally finely marginate; shorter legs (HFI 62–68); AT4 roughly sculptured, striate to punctate; scrobal area alveolate to punctate posterolaterally, becoming striulate to strigulate medially.

Worker Measurements and Indices (n = 10)

EL 0.04–0.07; HL 0.63–0.75; HW 0.57–0.68; SL 0.40–0.50; PH 0.31–0.40; PW 0.43–0.53; DML 0.35–0.50; PrH 0.39–0.50; WL 0.59–0.72; HFL 0.38–0.49; PeL 0.10–0.13; PeW 0.30–0.33; PeH 0.28–0.35; LT3 0.54–0.79; LT4 0.27–0.41; OI 5–9; CI 88–94; SI 64–69; LMI 51–56; DMI 68–75; DMI2 107–121; ASI 46–58; HFI 62–68; DPeI 250–313; LPeI 240–313.

Worker Description

Head very broad (CI 88–94), posterior head margin strongly convex, evenly curving into sides, posterodorsal corners of head indistinct; in frontal view sides of head convex, slightly concave between eye and anterolateral corner of gena; eyes small but well developed, setose (OI 5–9), comprising around ten small ommatidia; ommatidia globose, silvery, eyes protruding from head; eyes situated laterally on gena, slightly anterad halfway between anterolateral corner of gena and posterior head margin; frontal carinae produced as broad, elevated plate; rhomboid in frontal view, extending to around posterior third of head, widest point at around anterior eye margin, broad at posterior attachment to head, pointed anteriorly; in profile rooflike, forming broad, deeply depressed scrobal area extending to just anterad eye; anteromedially fused and reduced to thin, translucent septum between antennal sockets; posterolateral portion of torulus flangelike; torulus reduced posteromedially, thus confluent with deep, exposed antennal acetabulum; scrobe mostly strigulate, becoming punctate closer to eyes, merging with alveolate sculpture of head at scrobal margin; medial clypeus rectangular, short, anterior margin transverse, bearing very dense layer of appressed to decumbent white pilosity; sides of medial clypeus subparallel laterad antennal sockets. Antenna with moderately long scape (64–69), scape somewhat expanded apically, slightly bent; pedicel a short cylinder, broader than long; true antennomere count eleven; apparent antennomere count nine to eleven; flagellomeres basad apical club highly compressed, taken together approximately as long as apical club. Ventral head surface with two low, somewhat indistinct rounded tumuli situated laterally, slightly posterad midline (in profile); postoccipital ridge with well-developed anteromedial carina, extending about a onethird of the way between occipital foramen and posteromedial extent of hypostoma; medial region of hypostoma semicircular to a low triangle, apex somewhat rounded, hypostomal arms somewhat narrowed, arms expanded slightly apicolaterally; palpal formula not examined. Mandible edentate; basal angle rounded; with blunt prebasal angle; ectal face with longitudinal carina extending from prebasal angle to apex, carina becoming confluent with masticatory margin apically, leaving long comma-shaped, depressed, smooth medial region on masticatory margin.

Mesosoma robust, evenly convex, pronotum scarcely higher than propodeum; in dorsal view mesosoma relatively broad and stout (DMI 68–75; DMI2 107–121) and distinctly narrowed posteriorly, pronotum distinctly wider than propodeum; pronotal humeri obliquely rounded; posterior propodeal margin straight; posterodorsal corners of propodeum strongly angulate to denticulate, angles subtended and medially joined by narrow carinulae, thus propodeum laterally and dorsally marginate; in posterior view, carinulae forming two arches, shaped like an inverted lowercase omega, medially joining as unpaired carina traversing declivitous face; declivitous face of propodeum distinctly concave in profile and oblique posterior view; propodeal spiracle small and indistinct, directed posterolaterally; propodeal lobes very short and blunt.

Legs quite long (HFI 62–68) and robust; mesotibia with short but distinct apicoventral spur.

Petiolar node thickly disciform, not attenuated dorsally, about 2.4 to 3.2 times higher than broad (LPeI 240–313); in profile anterior face of node distinctly convex, curving smoothly over dorsum, without distinct apex; posterior face of node vertical; in dorsal view, node roughly a rounded trapezoid, sides strongly diverging posteriorly, anterior margin convex, posterior margin concave, about 2.2 to 3.2 times broader than long (DPeI 215–313); in anterior view, petiolar outline subcircular; in oblique anterodorsal view with weak median concavity; in ventral view, a narrow trapezoid, sides diverging strongly posteriorly; subpetiolar process short, lobate to subquadrate.

Abdominal segment 3 asymmetrically campaniform, tergite evenly convex, widest posteriorly; AS 3 somewhat flat to bulging posteriorly, deepest posteriorly, with concave, mostly unsculptured anteromedial region bordered anteriorly by sharply carinate, laterally narrow prora; AT3 approximately 1.9 to 2.2 times longer than AT4 (ASI 46–58); AT4 hemidemispherical to semicylindrical, gently recurved, spiracle sometimes exposed, small but prominent; successive abdominal segments short, telescopic, often concealed.

Sculpture on head, mesosoma, petiole, and abdominal segment 3 alveolate, alveoli giving rise to one or several setae; coarseness of sculpture somewhat variable, equivalently developed on all tagma, or often weakest on lateral mesosoma; ventral head surface posteromedially unsculptured; scape densely punctate; declivitous face of propodeum smooth except for fine medial carina; AT4 densely punctate, punctae usually more distinct posterolaterally; mandibles with numerous piligerous punctae.

Setation fairly consistent on dorsal surfaces of head, mesosoma, and petiole, a dense layer of appressed to erect white setae; gena and lateral mesosoma sometimes with sparser setation; density and length of setae somewhat variable between individuals; scrobal area glabrous and shining; AT3 evenly setose over its dorsal and lateral surfaces, setation shorter and less dense than on mesosoma, not forming distinct dorsal layer; AT4 with long, abundant, fine appressed pubescence and dense dorsal layer of decumbent to erect pilosity; successive abdominal segments with dense, flocculent, erect yellowish setae; ectal face of mandible with fine, curved, appressed to decumbent setae; with row of stout, spatulate setae on mesal face of masticatory margin; legs with fairly dense but relatively fine and entirely appressed white pubescence.

Color testaceous- to luteous-orange; legs and abdominal segments III–VII often bright orange to yellowish, lighter than rest of body.

Distribution and Biology

Discothyrea mixta is better represented in collections than D. oculata and most species of the traegaordhi complex, which may suggest lifestyle differences, making them more amenable to discovery, or be indicative of truly greater abundance. The species is known from a variety of forest habitats at different elevations throughout most of the Afrotropical region ( Fig. 4A ).

In foraging experiments, Dejean et al. (1999) found that D. mixta only accepted spiderlings and spider eggs as prey items. They rapidly consumed the spiderlings while often storing the eggs as a long-term resource. These findings are supported by unpublished observations made on a nest collection in Kibale Forest, Uganda, which revealed a large number of unidentified, rounded eggs, presumably of spiders.

Comments

The separation of D. mixta from D. oculata is very easy and both are difficult to mistake for each other. They differ in body size, eye size, and location on the head, as well as the shape of the propodeum and the sculpture on the propodeal declivity.

Something that we cannot rule out, despite considering it not very likely, is that the material here considered as D. mixta might represent a complex of cryptic species. The observed variety (see below) is not very pronounced but the highly specialized lifestyle might constrain morphological diversity, which would hinder species recognition purely based on morphology. Future studies including molecular data from most populations of D. mixta should revisit this question. However, on the basis of our study there is no evidence for cryptic species.

Variation

Discothyrea mixta varies slightly in overall size (WL 0.59–0.72), number of ommatidia, and coarseness of sculpture. Frequently, the sculpture of the lateral mesosoma is somewhat reduced, and the propodeal carinulae can vary slightly in shape and distinctness. The length, abundance, and stature of pilosity are somewhat variable, forming a more or less distinct dorsal layer on the mesosoma and abdominal terga. Nevertheless, considering the extremely wide distribution of D. mixta , this observed intraspecific variation is not surprising and even lower than one might expect.

Figures

Fig. 2. Still images generated from surface display volume renderings of petiole and gaster showing different proportions of abdominal segments III (in orange) and IV (in blue). (A) D. mixta, (B) D. kalypso, (C) D. venus.

Fig. 4. Maps showing the known distribution ranges of Afrotropical Discothyrea species.

Fig. 5. Still images from surface display volume renderings displaying the general morphology of both species complexes. Discothyrea oculata complex, D. mixta (CASENT0285473): (A) head in full-face view, (B) head in profile, (C) head in ventral view, (D) body in profile. Discothyrea traegaordhi complex, D. wakanda (CASENT0790326): (E) head in full-face view, (F) head in profile, (G) head in ventral view, (H) body in profile.