Discothyrea traegaordhi Santschi, 1914

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 : 72-75

Discothyrea traegaordhi Santschi, 1914

( Figs. 4R , 6R , 7R , 8R , 9R , 10R , 11R , 12R , 13C , 14R ,

15B, 15E , 54 , 55 ; Supp Video S18 [online only]) Discothyrea traegaordhi Santschi, 1914: 3 , by monotypy Discothyrea hewitti Arnold, 1916: 160 . Syn. n.

Type Material

Of D. traegaordhi : HOLOTYPE, pinned worker, SOUTH AFRICA Natal , Pietermaritzburg, 21.III.1905 (I. Trägårdh) (not in NHMB, apparently lost; see below).

NEOTYPE, by present designation, pinned worker, SOUTH AFRICA, KwaZulu-Natal, Town Bush, near Pietermaritzburg [−29.5616, 30.323], 900 m, native forest, 20.I.1977 (W.L. & D.E. Brown) ( BMNH: CASENT0790122 )

Of D. hewitti : SYNTYPES, two pinned queens, SOUTH AFRICA, Grahamstown [−33.3, 26.53333], ca. 533 m, IV.1915 (Hewitt) ( AMGS; SAMC: SAM-ENT-11508) [ SAMC type 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 the neotype (CASENT0790122) 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 18).

Nontype Material

SOUTH AFRICA: Eastern Cape, Mountain Zebra National Park , −32.23333, 25.46667, 1200 m, 27.X.1985 (H.G. Robertson) ; Eastern Cape, Riet River near Port Alfred , −33.566, 27.0166, ca. 4 m, 5.IV.1986 (H.G. Robertson) ; Eastern Cape, Silaka, near Port St Johns , −31.65, 29.5, ca. 80 m, indigenous wet forest along stream, 24.XI.1987 (S. Endrody-Younga) ; KwaZulu-Natal, Dukuduku Forest Reserve, 12–15 km E. Mtubatuba , [-28.365, 32.336], ca. 30 m, coast vine forest on sand, 26.I.1977 (W.L. & D.E. Brown) ; KwaZulu-Natal, St. Lucia Estuary , [-28.382, 32.41], ca. 25 m, 23.IX.1977 (D.J. Brothers) .

Diagnosis

The following character combination distinguishes D. traegaordhi from the remainder of the species complex: smaller species (WL 0.51–0.57); shorter antennal scapes (SI 50–55); apicoventral mesotibial spur present; relatively shorter legs (HFI 54–58); petiole relatively thinner (DPeI 235–289; LPeI 236–313); gastral terga without erect setae, only with appressed pubescence.

Worker Measurements and Indices (n = 10)

EL 0.03–0.05; HL 0.47–0.52; HW 0.39–0.43; SL 0.24–0.28; PH 0.25–0.28; PW 0.24–0.31; DML 0.33–0.39; PrH 0.29–0.33; WL 0.51–0.57; HFL 0.28–0.32; PeL 0.07–0.09; PeW 0.19–0.23; LT3 0.28–0.35; LT4 0.34–0.43; OI 7–10; CI 82–84; SI 50–55; LMI 47–52; DMI 48–55; DMI2 67–76; ASI 113–124; HFI 54–58; DPeI 235–289; LPeI 236–313.

Worker Description

Head somewhat longer than broad (CI 82–84), posterior head margin straight to weakly convex, posterodorsal corners of head broadly rounded; sides of head in frontal view convex; eyes present, relatively large (OI 7–10), round, usually comprising five to eight ommatidia, placed about a third of the way between anterolateral corner of gena and posterior head margin; eyes visible in frontal view; frontal lamella fairly short and roughly triangular in profile, apex rounded to acute; lamella not translucent across its disc, lacking a distinct fenestra; medial clypeus convex, lateral clypeus curving shallowly between antennal sockets and anterolateral corners of head, bearing short, curved setae. Antenna with short to moderately long scape (SI 50–55), scape slightly expanded apically, gently bent; pedicel subglobose, approximately as long as broad to slightly broader than long; apparent antennomere count seven to nine, but eight in most cases, flagellomeres basad apical club highly compressed, taken together shorter than apical club. Ventral head with low, V-shaped preoccipital ridge with short, triangular anteromedial projection; median area of hypostoma broadly triangular, arms narrowed, similar in width across their length; palpal formula not examined. Mandible edentate except for long, square to crenulate prebasal angle; basal angle rounded to squared; ectal face with carina originating at basal angle, becoming confluent with masticatory margin at around apical one-third, leaving narrow depressed region including prebasal angle.

Mesosoma weakly convex, pronotum either slightly higher than propodeum or at about same height; in dorsal view, mesosoma conspicuously slender and elongate (DMI 48–55; DMI2 73–83), moderately narrowed posteriorly, pronotum somewhat wider than propodeum; pronotal humeri rounded; posterior propodeal margin straight to very slightly concave; posterodorsal corners of propodeum rounded, without denticles or strong angles; declivitous face of propodeum slightly concave in profile and oblique posterior view; propodeal spiracle distinct, directed posterolaterally; propodeal lobes short, rounded.

Legs short (HFI 54–58); mesotibia with distinct apicoventral spur; mesobasitarsus relatively short, subequal in length to tarsomeres II–IV taken together.

Petiolar node weakly attenuated dorsally, about 2.4 to 3.1 times higher than long (LPeI 236–313) in profile anterior face of node straight to weakly convex, apex peaked, petiolar dorsum straight or sloping down anteriorly, posterior face subvertical; in dorsal view, node approximately rectangular, about 2.3 to 2.9 times broader than long (DPeI 235–289), sides divergent posteriorly; in anterior view, petiolar outline broadly pentagonal to round, angles rounded; in oblique anterior view; anterior face flat; subpetiolar process variable in shape, moderately long, broadly lobate, subrectangular to rectangular.

Abdominal segment 3 campaniform, widest just anterad end of segment; tergite slightly anteriorly prolonged over petiole; sternite evenly curved to posteriorly bulging in profile; AS 3 without median ridge, posterior lobe broad and indistinct; prora carinate, concave in ventral view; AT4 around 1.1 to 1.2 times longer than AT3 (ASI 105–124); AT4 evenly rounded hemidemispherical; AS 4 with anterior lip overlapping about median two-third the width of AS 3, anterior face convex in ventral view; successive abdominal segments short, telescopic, often concealed.

Sculpture of head, mesosoma, petiole, and abdominal segment 3 shallowly punctate-reticulate; mandibles moderately shining with piligerous punctulae; punctae on lateral mesosoma somewhat larger but sparser; absent or nearly so on declivitous face of propodeum, the disc of which more strongly shining than remainder of mesosoma; fine rugulae present on ventrolateral and declivitous surfaces of propodeum; AT4 with minute but distinct, very densely arranged piligerous punctae, clearly shinier than AT3.

Setation mostly consisting of appressed white pubescence, more or less evenly distributed over entire body, sometimes more diluted on head; abdominal segments five through seven with long, flexuous standing setae; appendages with well-developed, evenly distributed appressed pubescence; ectal face of mandible with abundant, curved, appressed to decumbent setae; with row of straight, stout setae on masticatory margin.

Color unicolorous luteous to matte orange brown to darker chestnut brown with lighter appendages.

Model 19. 3D surface model of D. venus Santschi, 1914 holotype (CASENT0790116). An interactive version of this model is available in the HTML version of this article online and at https://sketchfab.com/3d-models/ e0479eb664da4ecdb93ad9091e 120281.

Distribution and Biology

At present, D. traegaordhi is only known from South Africa ( Fig. 4R ). It seems to be moderately distributed from the Eastern Cape to Kwa- Zulu Natal. Based on the limited data available, D. traegaordhi prefers forested habitats at low to medium elevations.

Comments

The original holotype with the data SOUTH AFRICA, Natal, Pietermaritzburg, 21.III.1905 (Tragaordh) (NHMB: CASENT0915310) is presumably lost. The pin with the original label located in the collection of NHMB lacks a specimen. This was confirmed by us, as well as by the curatorial staff of NHMB. Since the original description does not provide sufficient diagnostic information to properly delineate this species and no type material exists, we consider it necessary to designate a neotype in order to clarify and stabilize the taxonomic and nomenclatorial status of D. traegaordhi . The chosen neotype is from the same area around Pietermaritzburg in Kwa-Zulu Natal as the original holotype representing a very close geographical approximation to the type location from the original publication.

In the original description of D. hewitti Arnold (1916) already suggested that both taxa could represent the same species, but due to the lack of workers of D. hewitti and queens of D. traegaordhi he hesitated to unite them under one name. Later, Brown (1958a) opined that the only dissimilarities between the two taxa are typical caste-specific differences. Based on the comparison of one syntype queen of D. hewitti with two queens associated with D. traegaordhi , we are able to solve this problem. Since the material of both does not show any significant morphological differences, it is apparent that both species are conspecific. Consequently, we propose D. hewitti as junior synonym of D. traegaordhi .

As noted above, D. traegaordhi can be grouped with D. gaia and D. poweri since they all possess a conspicuously large apicoventral spur on the mesotibia and relatively large eyes (OI 7–10). Nevertheless, the separation of these three species is straightforward. Discothyrea traegaordhi has a considerably thinner petiole (DPeI 235–289; LPeI 236–313) and shorter antennal scapes (SI 50–55) than D. poweri (DPeI 135–173; LPeI 152–194; SI 61–68). In addition, the latter species is also much larger (WL 0.67–0.84 vs. WL 0.51–0.57) and has longer legs (HFI 61–69 vs. HFI 54–58). Discothyrea gaia possesses numerous erect setae, especially on AT3, and a generally thicker petiole (DPeI 192–255; LPeI 194–264), both distinguishing it clearly from D. traegaordhi . Otherwise, these two species are morphologically very close and could be sister species.

Variation

There is some slight variation in the thickness of the petiole and the coarseness of the sculpture, but all well within species-specific boundaries.

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. 13. Diagnostic plate showing still images from surface volume renderings of mesotibiae and mesotarsi with mesotibial apicoventral spur, if present, colorized in green. (A) D. gaia, (B) D. poweri, (C) D. traegaordhi, (D) D. dryad, (E) D. maia, (F) D. wakanda.

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. 15. Antennal anatomy showing flagellar fusion in Discothyrea. (A) D. mixta (CASENT0285473)—light microscopy, (B) D. traegaordhi (CASENT0790122) —light microscopy, (C) D. traegaordhi (CASENT0790122)—equivalent view to 15B but performed with surface volume rendering, (D) Zasphinctus sarowiwai Hita Garcia, 2017 (CASENT0764654)—sagittal section of surface volume rendering, (E) D. traegaordhi (CASENT0790122)—sagittal section of surface volume rendering, (F) D. mixta (CASENT0790542)—surface volume rendering showing each antennomere in different color, (G) D. mixta (CASENT0790542)—equivalent view to 15F but sagittal section, (H) D. dryad (CASENT0247374)—sagittal section of surface volume rendering showing each antennomere in different color, (I) D. gryphon (CASENT0790103),sagittal section of surface volume rendering showing each antennomere in different color.

Fig. 54. Stacked digital color images of D. traegaordhi Santschi,1914 neotype (CASENT0790122). (A) body in profile, (B) body in dorsal view, (C) head in full-face view.

Fig. 55. Still images from shaded surface display volume renderings of D. traegaordhi Santschi, 1914 neotype (CASENT0790122) 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.