Discothyrea oculata Emery, 1901

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 : 24-28

Discothyrea oculata Emery, 1901

( Figs. 4B , 6B , 7B , 8B , 9B , 10B , 11B , 12B , 14B , 16A , 20 , 21 , 22 ; Supp Video S2 [online only])

Discothyrea oculata Emery, 1901: 52 .

Discothyrea oculata var. sculptior Santschi, 1913: 302 , by monotypy. [Raised to species by Brown, 1958a] Syn. n.

Type Material

Of D. oculata : LECTOTYPE, by present designation, pinned worker, CAMEROON, 1895 (L. Conradt) ( MSNG: CASENT0903856) [examined]. PARALECTOTYPES [designated here], five pinned workers with same data as lectotype ( MHNG: CASENT0247011; CASENT0247012; NHMB: CASENT0915307, CASENT0915307; NHMW: CASENT0915934) [examined].

Of D. sculptior : HOLOTYPE, CONGO, Brazzaville (A. Weiss) ( NHMB: CASENT0915308 ) [examined].

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 (CASENT0195471) 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 2).

Nontype Material

CAMEROON: 7 km E. Batchenga, [4.289, 11.586], 480 m, 6.X.1966 (E.S. Ross); Nkoemvon, [2.7517, 11.0814], ca. 630 m, 1980 (D. Jackson); Pan Pan, 28.XII.1990 (A. Dejean); Ottotomo, [3.65, 11.3167], ca. 700 m, 2.IV.1989 (A. Dejean) ; DEMOCRATIC REPUBLIC OF CONGO: Kongo Central, Matadi, [−5.83636, 13.43014], 1937 (Dartevelle); Leopoldville , [−4.4578, 15.2716], 360 m, 3.IV.1948 (A.E. Emerson); 24 mi. S. of Mambasa, [1.13, 29.05], 950 m, 1.X.1957 (E.S. Ross & R.E. Leech) ; GHANA: Eastern, Bunso, near Tafo , [6.28761, −0.46948], ca. 250 m, secondary forest, 17.IV.1992 (R. Belshaw); Legon, A.D., [5.65, −0.18333], ca. 100 m, 15.X.1970 (D. Leston); Tafo, [6.216, −0.373], ca. 200 m, 6.X.1966 (D. Leston); Tafo, [6.216, −0.373], ca. 200 m, 3.X.1970 (B. Bolton) ; GUINEA: Kamsar , [10.655, −14.585], ca. 2 m, 9.X.1972 (D.H. Kistner) ; IVORY COAST: Lamto , [6.217, −5.033], ca. 70 m (Toumodi) ; KENYA: Coastal Province, Arabuko Sokoke Forest , −3.32111, 39.92944, 50 m, coastal dry forest, VI.2009 (F.Hita Garcia & G. Fischer) ; MOZAMBIQUE: Sofala, Gorongosa National Park, Portao 1, 18.99944, 34.20083, 172 m, miombo Forest, 7.VI.2012 (G.D. Alpert) ; NIGERIA: Oyo, Ibadan , IITA, 7.494, 3.887, ca. 220 m, forest, 7.VIII.1981 (A. Russel-Smith) ; TANZANIA: Lindi, Lindi, Ndimba Forest Reserve, −9.62695, 39.62964, 138 m, primary forest, 25.–28.II.2008 (P. Hawkes, Y. Mlacha & F. Ninga); Mkomazi Game Reserve, gorge 1 km NW of Ibaya, 3.9667, 37.7833, 791 m, 30.I.1996 (A. Russel-Smith); Mkomazi Game Reserve , Umba River camp site, 4.50222, 38.54056, 1317 m, open woodland, 3.XII.1995 (H.G. Robertson) ; ZIMBABWE: Victoria Falls , [-17.93, 25.85], ca. 1003 m, 5.XII.1914 (G. Arnold) .

Diagnosis

Distinguished from D. mixta by the following combination of characters: larger species (WL 0.75–0.90); narrower head (CI 84–87); larger eyes (OI 14–16); propodeum without strong angles, denticles, or margination; declivitous face of propodeum deeply costate to rugose; longer legs (HFI 73–79); AT4 smooth and unsculptured; scrobal area striate to strigulate, without punctate or alveolate sculpture.

Worker Measurements and Indices (n = 10)

EL 0.12–0.15; HL 0.83–0.93; HW 0.70–0.78; SL 0.58–0.70; PH 0.44–0.51; PW 0.55–0.65; DML 0.51–0.63; PrH 0.53–0.59; WL 0.75–0.90; HFL 0.58–0.69; PeL 0.15–0.21; PeW 0.36–0.45; PeH 0.37–0.41; LT3 0.71–0.81; LT4 0.38–0.48; OI 14–16; CI 84–87; SI 69–76; LMI 54–58; DMI 66–78; DMI2 102–108; ASI 53–60; HFI 73–79; DPeI 201–275; LPeI 195–258.

Worker Description

Head broader than long (CI 84–87), posterior head margin strongly convex, evenly curving into sides, such that posterodorsal corners of head indistinct; sides of head in frontal view converging anteriorly; eyes large and well developed, setose (OI 14–16), comprising around 30 ommatidia; ommatidia globose, silvery, eyes protruding from head, visible in frontal view; eyes situated anterolaterally 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 Model 1. 3D surface model of D. mixta Brown, 1958 (CASENT0285473). An interactive version of this model is available in the HTML version of this article online and at https://sketchfab.com/3d-models/26d1d008e1ac4f1489a 87245ef274a76.

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 reduced to thin, translucent septum between antennal sockets; posterolateral portion of torulus flangelike, reduced posteromedially, thus confluent with deep, exposed antennal acetabulum; scrobe strigulate to laterally striate; medial clypeus rectangular, strongly projecting, anterior margin transverse, bearing very dense layer of appressed to decumbent white pilosity, sides of medial clypeus subparallel laterad antennal sockets. Antenna with long scape (SI 69–76), scape somewhat expanded apically, slightly bent; pedicel a short cylinder, broader than long; true antennomere count nine; apparent antennomere count nine to twelve; flagellomeres basad apical club highly compressed, taken together approximately as long as apical club. Ventral head surface with two low but prominent rounded tumuli situated laterally, slightly posterad midline (in profile); postoccipital ridge with small anteromedian carina, extending less than one-fourth of the way between occipital foramen and posteromedial extent of hypostoma; medial region of hypostoma triangular, hypostomal arms slightly narrowed, similar in width throughout their length; palpal formula 6,4 ( Keller 2011). 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 slightly less than halfway along masticatory margin, leaving short comma-shaped to triangular, depressed, unsculptured medial region on masticatory margin.

Mesosoma robust, evenly convex, pronotum scarcely higher than propodeum; in dorsal view, mesosoma broad and stout (DMI 66–78; DMI2 102–108) and distinctly narrowed posteriorly, pronotum distinctly wider than propodeum; pronotal humeri obliquely rounded; posterior propodeal margin straight; posterodorsal corners of propodeum rounded, lacking denticles; declivitous face of Model 2. 3D surface model of D. oculata Emery, 1901 (CASENT0285471). An interactive version of this model is available in the HTML version of this article online and at https://sketchfab.com/3d-models/f49c344f0f6a4e88a857 f5c6141d38f6.

propodeum slightly concave in profile and oblique posterior view; propodeal spiracle small but distinct, offset by unsculptured annulus around spiracular opening, directed posterolatearally; propodeal lobes rather short and rounded.

Legs quite long (HFI 73–79) and robust; mesotibia with short but distinct apicoventral spur.

Petiolar node thickly disciform, not attenuated dorsally, about 2.0 to 2.6 times higher than broad (LPeI 195–258); 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 2.0 to 2.75 times broader than long (DPeI 201– 275); in anterior view, petiolar outline subcircular; in oblique anterodorsal view anterior face convex; in ventral view, broad and roughly campaniform, sides weakly curved; 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 moderatlely concave anteromedial region of reduced sculpture bordered anteriorly by strongly carinate, laterally broad prora; AT3 approximately twice as long as AT4 (ASI 53–60); AT4 hemidemipsherical 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 deeper on head and/or weaker on mesosoma; ventral head surface posteromedially with significantly reduced sculpture, only a few scattered foveae present; scape sparsely foveate; declivitous face of propodeum deeply costate to rugose; AT4 and succesive abdominal segments very smooth (unsculptured except for inconspicuous, microscopic piligerous punctulae, appearing polished relative to rest of body); mandible with numerous piligerous punctae.

Setation fairly consistent on dorsal surfaces of head, mesosoma, and petiole, a dense layer of appressed to decumbent white setae; gena and lateral mesosoma sometimes with sparser setation; density 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, but fine appressed pubescence; successive abdominal segments with dense, flocculent, erect yellowish setae; ectal face of mandible with fine, curved, appressed to decumbent setae; masticatory margin with row of stout, spatulate setae on mesal face; legs with fairly dense but relatively fine and entirely appressed white pubescence.

Color iron-red, testaceous- to luteous-orange; legs and abdominal segments four through seven orange to yellowish, lighter than remainder of body.

Distribution and Biology

Discothyrea oculata appears to have a broad range throughout most of the Afrotropical region ( Fig. 4B ), even though it is represented by fairly sparse records. Preferred habitats are drier, more open, and usually at lower elevations than in D. mixta , including open patches of forest, dry coastal forest, and even grassland, while it is less often found in dense rainforests. The apparent rarity from museum collections is at odds with the results of Dejean and Dejean (1998) who studied this species extensively in the field and laboratory, suggesting that D. oculata may be rather common but difficult to collect with standard sampling methodology. Nearly 200 colonies in southern Cameroon were observed within oothecae of segestriid spiders of the genus Ariadna , while laboratory colonies provided with oothecae manipulated the silk to line and operculate their test-tube nests. Successful foundresses did not produce a generation of nanitics, leading the authors to term this highly derived form of colony foundation ‘claustral lestobiotic colony founding’. Similar to D. mixta , D. oculata only accepted spiderlings and eggs in foraging experiments, while ignoring all other potential prey items ( Dejean and Dejean 1998).

Comments

On the basis of detailed examination of the type material of both, D. oculata ( Fig. 20 ) and D. sculptior ( Fig. 21 ), we propose to treat the latter as junior synonym of the first. The original description of D. sculptior states details of sculpturation, body color, and proportions of the antennal club and frontal carinae as diagnostic ( Santschi 1913), which, on examining the type and various collections of D. oculata , fall within reasonable limits of intraspecific variation. Why Brown (1958a) raised the variety to species status is rather puzzling, as he noted he did not examine the types of either D. oculata nor D. sculptior , and went so far as to say ‘Santschi’s sculptior , described as a variety of oculata , may in fact be no more than a variant of that species’. Based on our data, morphological evidence agrees with Brown’s sentiment rather than his taxonomic decision.

The differentiation of D. oculata from D. mixta is straightforward, as can be seen in the identification key. As noted for D. mixta , considering the unusually wide distribution and even more specialized lifestyle, we cannot rule out cryptic species within the material of D. oculata . However, currently, our data do not permit any conclusions supporting any existence of cryptic species.

Variation

Discothyrea oculata varies slightly in overall size (WL 0.75–0.90), which is neither surprising nor unusual considering its wide distribution range. There is also some moderate diversity in coarseness of sculpture and number of ommatidia, as well as in the length and abundance of pilosity. Again, as in D. mixta , this is considered as regular intraspecific geographical variation over a wide distribution range. The color ranges trivially from luteous-orange to ferrous red.

Figures

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

Fig. 6. Diagnostic plate showing still images from surface volume renderings of the head in full-face view (the remainder of the body virtually removed). All Afrotropical species are shown, species names are embedded in each particular image for better comparison and orientation.Specimen codes are given inTable 1.

Fig. 7. Diagnostic plate showing still images from surface volume renderings of the head in profile (the remainder of the body virtually removed).All Afrotropical species are shown, species names are embedded in each particular image for better comparison and orientation. Specimen codes are given inTable 1.

Fig. 8. Diagnostic plate showing still images from surface volume renderings of the right mandible in dorsal view (the remainder of the body virtually removed).All Afrotropical species are shown,species names are embedded in each particular image for better comparison and orientation.Specimen codes are given inTable 1.

Fig. 9. Diagnostic plate showing still images from surface volume renderings of the mesosoma in profile (the remainder of the body virtually removed). All Afrotropical species are shown, species names are embedded in each particular image for better comparison and orientation.Specimen codes are given inTable 1.

Fig. 10. Diagnostic plate showing still images from surface volume renderings of the body in dorsal view with focus on mesosoma.All Afrotropical species are shown, species names are embedded in each particular image for better comparison and orientation. Specimen codes are given inTable 1.

Fig. 11. Diagnostic plate showing still images from surface volume renderings of the posterior propodeum in posterior view (the remainder of the body virtually removed). All Afrotropical species are shown, species names are embedded in each particular image for better comparison and orientation. Specimen codes are given inTable 1.

Fig. 12. Diagnostic plate showing still images from surface volume renderings of the petiole and gaster in profile (the remainder of the body virtually removed).All Afrotropical species are shown, species names are embedded in each particular image for better comparison and orientation.Specimen codes are given inTable 1.

Fig. 14. Diagnostic plate showing differences in body pilosity. (A) D. mixta (CASENT0235473),(B) D. oculata (CASENT0235467),(C) D. aisnetu (CASENT0235475), (D) D.athene (CASENT0235476),(E) D.chimera (CASENT0235471),(F) D.damato (CASENT0247362),(G) D.dryad (CASENT0247371),(H) D.gaia (CASENT0247040), (I) D. gryphon (CASENT0247367), (J) D. hawkesi (CASENT0235470), (K) D. kalypso (CASENT0235468), (L) D. maia (CASENT0790541), (M) D. michelae (CASENT0235469), (N) D. patrizii (CASENT0235472), (O) D. penthos (CASENT0247383), (P) D. poweri (SAM-ENT-0011509), (Q) D. schulzei (CASENT0247370), (R) D. traegaordhi (CASENT0790122), (S) D. venus (CASENT0247017), (T) D. wakanda (CASENT0790326).With the exception of F, L, R,T, all other images are from https://www.antweb.org—photographers Michele Esposito and Will Ericson.

Fig. 16. Shaded surface display of transparent volume renderings showing internal and external flagellar subsegmentation. (A) Discothyrea oculata (CASENT0195471), (B) Proceratium deelemani Perrault, 1981 (CASENT0790842), (C) Brachyponera sennaarensis (Mayr, 1862) (CASENT0790837), (D) Solenopsis invicta Buren, 1972 (OKENT0011209).

Fig. 20. Stacked digital color images of D. oculata Emery, 1901 paralectotype (CASENT0903856 - from https://www.antweb.org, photographer Michele Esposito).(A) body in profile,(B) body in dorsal view,(C) head in full-face view.

Fig. 21. Stacked digital color images of D. sculptior Santschi, 1913 holotype = D. oculata (CASENT0915308 - from https://www.antweb.org, photographer Zach Lieberman). (A) body in profile, (B) body in dorsal view, (C) head in full-face view.

Fig. 22. Still images from shaded surface display volume renderings of D. oculata Emery, 1901 (CASENT0195471) showing virtually segmented body parts. (A) Body in dorsal view, (B) body in profile, (C) head in full-face view, (D) head in dorsal view, (E) head in anterodorsal view, (F) head in anterior view, (G) head in profile, (H) head in ventral view, (I) posterior propodeum in posterior view, (J) petiole in profile, (K) petiole and gaster in profile, (L) petiole in dorsal view, (M) petiole in anterior view, (N) petiole oblique anterior view, (O) gaster in dorsal view, (P) petiole in ventral view, (Q) abdominal sternite 3 in ventral view, (R) mesotibia and mesotarsus in anterior view.