Overbeckia subclavata Viehmeyer, 1916

Klimeš, Petr, Drescher, Jochen, Buchori, Damayanti, Hidayat, Purnama, Nazarreta, Rizky, Potocký, Pavel, Rimandai, Maling, Scheu, Stefan & Matos-Maraví, Pável, 2022, Uncovering cryptic diversity in the enigmatic ant genus Overbeckia and insights into the phylogeny of Camponotini (Hymenoptera: Formicidae: Formicinae), Invertebrate Systematics 36 (6), pp. 277-288 : 565-569

Overbeckia subclavata Viehmeyer

( Fig. 1 , 2 )

Etymology

Viehmeyer (1916) does not explain the reasoning for the species name, but this likely refers to the club-shaped anterior part of antennae, mentioned in the original description (‘Geissel gegen Ende verdickt’: funinculus enlarged towards the tip) ( Fig. 2 h ).

Material examined

Syntypes. All examined from photos (AntWeb codes): CASENT0101191 , CASENT0101192 , workers ( NHMB; F. Santschi collection); focol0130 , worker ( DEIC, marked as ‘ Syntypus’); focol2566 , alate queen (marked as ‘ Typus’), focol2567 and focol2568 , workers, focol2564 and focol2565 , males ( ZMHB, all marked as ‘ Typus’); CASENT0178502 , worker ( MCZC, marked as ‘ Paratype 30741’) ; CASENT0905180 , male ( MSGN)/coll. H. Overbeck, <1915/ Singapore / Nests in dry/narrow, hollow bamboo, colony in the hollow branch of a mango tree / 1°17′35.0″N, 103°51′21.0″E /det. Viehmeyer (1916).

Additional material examined

Indonesia: 5 workers and 1 queen; all leg. J. Drescher, canopy fogging (det. R. Nazarreta & P. Klimes): Worker ( ZMHB): HJ3.1/ 5.xi. 2013 /Harapan Rainforest/jungle rubber/dry season/ 01°50′57.7″S, 103°17′59.7″E. Worker ( MZB): BJ6.2/ 1.xii.2013 /Bukit Duabelas National Park/jungle rubber/rainy season/ 02°01′48.4″S, 102°46′14.9″E. Worker ( IECA): BF3.1/ 5.x.2013 /Bukit Duabelas National Park/jungle rubber/rainy season/ 01°56′34.1″S, 102°34′51.5″E. Worker ( MZB): BF1.1/ 8.x.2013 /Bukit Duabelas National Park/forest/dry season/ 01°59′41.4″S, 102°45′08.5″E. Worker ( CASC): CASENT0872838 (AntWeb)/HymFrm285 1.xii.2013 /Bukit Duabelas National Park/jungle rubber/rainy season/ 02°00′56.2″S, 102°45′11.5″E. Queen without wings ( IECA): HF4.1/ 12.ix.2013 /Harapan Rainforest/forest/dry season/ 02°11′15.4″S, 103°20′34.7″E. Philippines (photos): Acc. No. 3576 ( MCZC)/Lot Bu.of Sci., P.I./coll. M. Ramos (further details in General and Alpert 2012).

Diagnosis

Compared to the other two Overbeckia species described here, Overbeckia papuana sp. nov. and O. jambiensis sp. nov., workers and queens in O. subclavata are less hairy, with a lack of long erect hairs on dorsum of petiole, on thorax and on scape except the apical margin; head integument with fine dense punctation; no erect hairs extending past head margins in frontal view; frontal carinae approaching one another less anteriorly compared to those in O. papuana sp. nov. (FCDI <166; Fig. 1 b , 2 h ). Longer erect hairs present only on clypeus and ventral abdomen. Fine straight lineation on lateral sides of thorax limited to the basal region below metanotal groove ( Fig. 1 a ).

Description of worker

Morphometrics. Non type ‘HJ.3.1’ (six syntypes and further five non-types workers, N.A. = measure not available hereafter; total measured N = 11, min.– max): HL 1.08 (0.87–1.25), HW 1.14 (0.88–1.24), IOD 0.87 (0.67–0.92), CL 0.16 (0.15–0.19), CW 0.49 (0.34–0.54), ML 0.45 (0.33–0.47), EL 0.31 (0.25–0.36), EW 0.22 (0.16–0.26), FCDp 0.38 (0.29–0.44), FCDa 0.28 (0.21–0.29), SL 0.99 (0.70–1.08), SWmax 0.13 (0.11–0.17), SWmin 0.06 (0.05–0.09), WL 1.62 (1.24–1.76), PW 0.79 (0.61–0.88), HFL 1.03 (0.92–1.08), HFT 0.24 (0.20–0.25), HTL N.A. (0.82–1.07), PetW 0.40 (0.32–0.47), PetL 0.22 (0.15–0.24), FCDI 134 (126–165), CI 105 (98–105), SI 87 (80–93), MI 41 (32–42).

Head. General morphology as for the genus (see above). Frontal carinae approaching one another less anteriorly (FCDI = 134) and with relatively straight curvature, slightly concave near antennal sockets ( Fig. 1 d ).

Mesosoma and metasoma. As for the genus (see above).

Pilosity. Numerous tiny appressed hairs (approximately twice the length of 1 ommatidium or shorter) over scape, head and most of the thorax and abdomen; relatively long erect hairs (length ≥ SW) present only on clypeus, head and ventral abdomen and one pair of hairs present on frons in the middle above the eyes ( Fig. 1 a ); these longer hairs missing on genae and the occipital corners of the head including region above the eyes (in frontal view none of the longer hairs surpass the head margin); scape also without erect hairs except a tuft of ~8 setae growing from the apical tip ( Fig. 1 b ). No long erect hairs at the apex of petiole.

Sculpture. Fine punctation on dorsal surface of the head, in particular in the area between frontal carinae and above the clypeus ( Fig. 1 b, d ) and on mesosoma dorsum and lateral sites of thorax above metathoracic spiracle and dorsolaterally on propodeum ( Fig. 1 a ); this punctuation changes to the sculpturing rather forming a cell structure than individual pits posteriorly towards the occipital region; soft lineation on lateral sites of mesosoma, below the metathoracic spiracle and on propodeum between propodeal spiracle and hind coxae; same cuticular lineation also present on frontal coxae, petiole and anteriorly on the head near clypeus, but here much softer than on thorax ( Fig. 1 b, c ).

Colouration. Black head, thorax and petiole; dark brown scape except at the apex where light brown; brown abdomen and femurs; tarsi, funiculus and palps light brown to yellow; femurs brown in the middle but lighter near the joints ( Fig. 1 a, c ).

Description of queen

Morphometrics. Syntype ‘focol2566’: HL 1.43, HW 1.45, IOD 1.08, CL 0.30, CW 0.60, ML 0.67, EL 0.53, EW 0.35, FCDp 0.47, FCDa 0.33, SL 1.17, SWmax 0.16, SWmin 0.08, WL 2.56, PW 1.14, HFL 1.08, HFT 0.36, HTL 1.34, PetW 0.58, PetL 0.28, FCDI 142, CI 101, SI 81, MI 47.

Head ( Fig. 2 e ). Eyes almost twice as large as in worker. Frontal carinae approaching each other anteriorly above the posterior margin of clypeus relatively less when compared to queen of O. papuana (FCDI <160). Mandibles with four teeth; apical and subapical teeth approximately twice as long as and sharper than the other three teeth. Three ocelli well developed.

Mesosoma ( Fig. 2 a, c ). In lateral view, thorax dorsum flat at mesothorax, otherwise evenly rounded with convex prothoracic and propodeal angle. Overall morphology of thoracic segments and wings as in Camponotus queens, except apical part of the forewing being relatively broader with evenly convex margins laterally towards the tip.

Metasoma. Petiole similar to worker but relatively thicker and with less sharp apex. Abdomen as in workers but larger.

Pilosity. Numerous tiny appressed (≥1/2 length of ocellus) hairs over scape; erect relatively long hairs (length>1 ocellus) present only on clypeus, ventral head, near ocelli, on mesothorax dorsum and on 3rd to 5th abdominal tergites ( Fig. 2 a ); these longer hairs missing on genae and the occipital corners of the head including region above the eyes (in frontal view no longer hairs surpass the head margins); scape also lacks erect hairs except five to six setae at the apical tip ( Fig. 2 e ). No long erect hairs on apex of petiole.

Sculpture. Fine punctation on the dorsal surface of the head, and on mesosoma dorsum and propodeum; soft lineation on lateral sites of mesosoma, similar to workers.

Colouration. Brown head, thorax, scape (except the tip that is lighter) and petiole; light brown abdomen; legs and funiculus yellow ( Fig. 2 a, c ).

Notes

The generally lighter colouring may also reflect either the old age of the museum specimen (>100 years) or a relatively young queen collected from inside nest (alate).

Description of male

Morphometrics. Syntype ‘CASENT0905180’: HL 0.90, HW 1.08, IOD 0.69, CL 0.17, CW 0.40, ML 0.34, EL 0.46, EW 0.32, FCDp 0.32, FCDa 0.14, SL 0.80, SWmax 0.09, SWmin 0.07, WL 1.95, PW 1.08, HFL 1.31, HFT 0.18, HTL 1.30, PetW N.A., PetL N.A., FCDI 229, CI 120, SI 74, MI 38.

Head ( Fig. 2 f ). Eyes largely surpass the head margins in frontal view, with EL ~1/2 of HL, placed at ~1/2 of HL posteriorly. Frontal carinae approaching relatively less one another anteriorly above the posterior margin of clypeus compared to those in male of O. papuana (FCDI = 229), although this variance is not as distinct as among workers and among queens of the two species. Mandibles blunt without teeth. Three ocelli well developed and relatively larger than in queens (diameter as SWmax). Antennae with 13 segments not broadened towards the tip of funiculus like in the workers and queen (see frontal image of another male from the type series ‘focol2564’ with intact antennae) (AntWeb, see https://www.antweb.org). Scape long, at half of the length passing the head margin in frontal view.

Mesosoma. Thorax dorsum flat at mesoscutum, otherwise evenly rounded in lateral view with convex prothoracic and propodeal angle, except the mesoscutellar disc that is placed higher and of more convex shape than the other thoracic parts in lateral view ( Fig. 2 b ). Suture between pronotum and mesoscutum not visible in dorsal view due to highly convex and enlarged mesoscutum compared to pronotum ( Fig. 2 d ).

Metasoma. Petiole triangular but relatively thicker and blunter at the apex.

Pilosity. Tiny appressed hairs present on scape and thorax but less numerous over the head compared to queen and workers; long erect hairs (length = SWmax) present only on clypeus, genae, ventral head, near ocelli (one long seta et each) and on 3rd to 5th abdominal tergites ( Fig. 2 b ); these longer hairs missing completely on scape, petiole and at the occipital corners of the head including region above the eyes (in frontal view, no long hairs surpass the head margin).

Sculpture. Fine punctation on dorsal surface of the head, and on mesosoma dorsum and propodeum.

Colouration. Light brown to yellowish body, except brown head, thorax dorsum and antennae. Mandibles and appendages pale.

Remarks

The specimens of O. subclavata from Indonesia that were examined have the posterior parts of the frontal carinae bent slightly inwards and therefore have slightly smaller FCDI (mean 133) than the type specimens from Singapore (mean 155) ( Fig. 1 d , 2 h ). However, the difference is small and this could possibly be due to measurement error from photographs. All other morphological parameters and the general appearance of the specimens are consistent between the two regions, therefore we regard this to be only a variation within the species.

The specimen from the Philippines has a damaged left upper side of the head and a whitish dirt attached to the carinae. Therefore, we did not consider this for morphological measurements. However, absence of the longer hairs on the scape and the thorax, and the finely punctate head with numerous minute recumbent hairs, clearly fit the general appearance of O. subclavata .

Viehmeyer (1916) reported that O. subclavata nested in a hollow bamboo stem and in a hollow branch of a mango tree, therefore there is uncertainty whether the syntype series of the species (six workers, three males and one queen, available from AntWeb) belongs to a single nest. Five vials (samples?) collected in 1913 and two collected in 1914 were reported, therefore several colonies from one or more sites in Singapore might have been pooled for the syntype series (most likely two colonies from two stems, a mango and a bamboo). There is also uncertainty as to whether all specimens collected in 1913–1914 are documented online at AntWeb, therefore more material might be scattered in museums worldwide. Nevertheless, all specimens collected by H. Overbeck illustrated in the AntWeb match O. subclavata . The arboricolous nesting in hollow plant structures of (probably) dead tissues suggests that the species nests in tree canopies, but is rather a generalist; that is, not using living tissues or myrmecophytic plants, as do more specialised arboreal species ( Klimes and McArthur 2014). Specimens of O. subclavata were probably collected by H. Overbeck in a human-managed area but collections from Sumatra suggest that the species utilises a variety of habitats (see Distribution and Discussion for further information).

Figures

Fig. 1. Overbeckia subclavata, non-type. Worker from Indonesia (specimen HJ.3.1) displaying the lateral (a), frontal (b) and dorsal (c) views. Detail of head sculpture and shape of frontal carinae (d). Note hind leg tibia and tarsi are missing (damaged).

Fig. 2. Overbeckia subclavata syntypes. Alate queen (FOCOL2566; photographer: Ch. Klingenberg): lateral (a), dorsal (c) and frontal (e) views; male (CASENT0905180; photographer: W. Ericson): lateral (b), dorsal (d) and frontal (f) views; worker (CASENT0101191; photographer A. Nobile): lateral (g) and frontal (h) views. Photos retrieved from AntWeb.org.