Stigmatomma luyiae

Stigmatomma luyiae
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Hymenoptera
Family:	Formicidae
Subfamily:	Amblyoponinae
Tribe:	Amblyoponini
Genus:	Stigmatomma
Species:	S. luyiae
Binomial name
Stigmatomma luyiae Hsu, F., Esteves, Chou & Lin, 2017

The types were collected from the soil of a subtropical evergreen broad-leaved forest in Taiwan.

Identification

Hsu et al. (2017) - Workers of Stigmatomma luyiae can be distinguished from those of other Stigmatomma species by the combination of the following characters (asterisks flag putative unique characters within Stigmatomma):

1. Eleven antennomeres.
2. Mandibles as long as the head (MI: 100).
3. Mandibles’ baso-masticatory margin with a single row of teeth.
4. Mandibles with longer, jigsaw-tab-shaped median teeth.
5. *Anterior clypeal margin flat; modified setae or tubercular cuticular projections absent.
6. Anterior portion of the median area of the clypeus with seven stout, acuminate flattened-apex setae arranged in a single transversal row.
7. Frontal lobes closely approximated; median area of the clypeus extending posteriorly as a narrow longitudinal strip between the antennal sockets.
8. Antennal scrobe absent.
9. Genal teeth present, but minute.
10. Dorsal face of the head densely costate-foveolate, slightly catenated.
11. Head quadrate (CI: 100).
12. Mesepisternum divided into anepisternum and katepisternum.
13. Lamella absent on the ventral margin of the calcar of strigil.
14. *Anterior face of mesobasitarsus with round sulcus filled with microvilli-like projections.
15. One metatibial spur.
16. Sulcus absent on the anterior face of the metabasitarsus.
17. Fenestra absent on the subpetiolar process.
18. Stout spiniform setae absent on the hypopygium.

Stigmatomma luyiae is easily distinguished from most of its congeners in Asia due to its mandibles, which present only a single row of teeth instead of two rows. The only Stigmatomma species in that region sharing this character with the new species are those formerly classified as Bannapone (Eguchi et al., 2015): Stigmatomma caliginosum, Stigmatomma crypticum, Stigmatomma fulvidum, Stigmatomma mulanae, Stigmatomma pertinax, and Stigmatomma scrobiceps. Within this group, S. fulvidum possesses antennae with twelve antennomeres (Terayama 1987), while the antennae of the other species, including S. luyiae, have eleven antennomeres. Only S. luyiae and S. mulanae possess the median mandibular teeth in a jigsaw tab-shaped arrangement.

The diagnostic characters for setting apart Stigmatomma luyiae from S. mulanae are the presence/absence of cuticular projections and modified setae on the anterior margin of the clypeus, head shape, and relative size of the mandibles. In S. luyiae, the anterior clypeal margin is flat and bears neither tubercular projections nor stout setae. Instead, stout, acuminate flattened-apex setae rise from the anterior portion of the median area of the clypeus. Also, the head is quadrate (CI: 100), and the mandibles are as long as the head (MI: 100). In S. mulanae, the anterior margin of the clypeus presents tubercle-like cuticular projections, and each of which bears a stout, conic seta; the head is rectangular (CI: 84; Xu 2000); and the mandibles are shorter than the head (ML: 0.30, HL: 0.38; Xu 2000).

Sahanashree et al. (2023) - Stigmatomma luyiae is unique in the following combination of characters:

1. antennae with 11 segments
2. baso-masticatory margin of mandible with undivided teeth arranged in a single row
3. frontal carinae short, not surpassing mid-length of the head
4. antennal scrobe absent
5. median mandibular teeth jigsaw-tab-shaped
6. anterior clypeal margin flat, clypeal setae rise from the anterior portion of the median area of the clypeus (Hsu et al., 2017).

Stigmatomma luyiae is similar to its Chinese congeneric Stigmatomma mulanae in general appearance including the presence of 11 segmented antennae, jigsaw tab-shaped arrangement of the median mandibular teeth. However, S. luyiae is easily distinguished from S. mulanae based on the combination of following characters:

1. anterior clypeal margin flat, clypeal setae arise from the anterior portion of the median area of the clypeus in S. luyiae (clypeal setae arise from small tubercular projections of the anterior clypeal margin in S. mulanae)
2. head approximately square in S. luyiae (head distinctly rectangular in S. mulanae)
3. mandibles as long as head in S. luyiae (mandibles shorter than head in S. mulanae) (Hsu et al., 2017).

Variation: S. luyiae worker specimen from India has prominent body hairs and striations and slight differences in the body measurements in comparison to holotype.

Keys including this Species

• Key to Asian Stigmatomma with 11 antennomeres
• Key to the Stigmatomma species of Hong Kong SAR, China

Distribution

Within India, Stigmatomma luyiae has only been reported from the Eastern Himalayas (Sahanashree et al., 2023).

Distribution based on Regional Taxon Lists

Oriental Region: India, Taiwan (type locality).
Palaearctic Region: China.

• 

  Hamer et al. (2023), Fig. 2. Distribution map of Amblyoponinae species in Hong Kong (SAR), iNat = iNaturalist. A) Prionopelta kraepelini; B) Stigmatomma amblyops, S. crypticum, S. draconis; C) Stigmatomma luyiae, S. pagei, S. zwaluwenburgi; D) Stigmatomma nr. quadratum. Dark green zones indicate greater tree cover.

Distribution based on AntMaps

Distribution based on AntWeb specimens

Check data from AntWeb

Countries Occupied

Number of countries occupied by this species based on AntWiki Regional Taxon Lists. In general, fewer countries occupied indicates a narrower range, while more countries indicates a more widespread species.

Estimated Abundance

Relative abundance based on number of AntMaps records per species (this species within the purple bar). Fewer records (to the left) indicates a less abundant/encountered species while more records (to the right) indicates more abundant/encountered species.

Biology

Hamer et al. (2023) - Previously only known from Taiwan, this is the first record for mainland China, and the endemic status to Taiwan is therefore considered obsolete. This species in Hong Kong is known from a single individual.

Although not continuous, the nearly 30 years of ant research in Hong Kong has included thousands of Winkler extractors and pitfall traps across hundreds of sites and yet this species was has only been collected once and with a single worker. This suggests that this species is potentially very rare and may possess very small colony size. Alternatively, we cannot exclude the possibility of a completely subterranean lifestyle to explain its scarcity in sampling records. Such a hypothesis is supported by the very pale colouration of the specimen, the absence of eyes characteristic of subterranean habits (Wong & Guénard 2017) and last but not least the collection of type specimens in Taiwan from sifted soil (Hsu et al. 2017). Further research focusing on soil samples may thus provide useful insights about the ecology and distribution of this species.

Fig. 5, Hsu et al. 2017, subtropical evergreen broad-leaved forest in the Lienhuachih Forest Dynamics Plot, Nantou Country, Taiwan.

Castes

• 

  Hamer et al. (2023), Fig. 8. Stigmatomma luyiae A) profile view B) head view C) closeup of mandibles.

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Nomenclature

The following information is derived from Barry Bolton's Online Catalogue of the Ants of the World.

• luyiae. Stigmatomma luyiae Hsu, F. et al. 2017: 83, figs. 1-4, 8B (w.) TAIWAN.
  • Type-material: holotype worker, 1 paratype worker.
  • Type-locality: holotype Taiwan: Nantou County, LFDP (Lienhuachih Forest Dynamics Plot), 10.i.2015, Winkler sample (sifted soil) (F.C. Hsu); paratype with same data.
  • Type-depositories: NMNS (holotype); TARI (paratype).
  • Distribution: Taiwan.

Unless otherwise noted the text for the remainder of this section is reported from the publication that includes the original description.

Description

Worker

Holotype: TL: 2.45 mm, HL: 0.5 mm, HW: 0.5 mm, HW2: 0.47 mm; SL: 0.3 mm, ML: 0.5 mm, WL: 0.6 mm, PPW: 0.24 mm, PnW: 0.31 mm, PtW: 0.24 mm, PtL: 0.16 mm, CI: 100, MI: 100, and SI: 60. Paratype: TL: 2.43 mm, HL: 0.48 mm, HW: 0.48 mm, HW2: 0.45 mm, SL: 0.29 mm, ML: 0.48 mm, WL: 0.6 mm, PPW: 0.22 mm, PnW: 0.32 mm, PtW: 0.24 mm, PtL: 0.16 mm, CI: 100, MI: 100, and SI: 60.

Head. Dorsal face of the head quadrate (CI: 100), bearing longer erect to suberect hairs, and numerous shorter suberect to subdecumbent pilosity; sculpture densely costate-foveolate, slightly catenated. Posterior margin of the head slightly concave in full-face view. Antenna with eleven antennomeres, bearing abundant erect to subdecumbent pilosity. Frontal lobes closely approximated: median area of the clypeus extending posteriorly as a narrow longitudinal strip between the antennal sockets. Antenna with eleven antennomeres. Antennal scrobes absent. Compound eyes absent Genal teeth present, but minute. Anterior clypeal margin flat; modified setae or tubercular cuticular projections absent. Anterior portion of the median area of the clypeus with seven stout, acuminate flattened-apex setae arranged in a single transversal row; longer median seta; each seta rises from a minute tubercle-like cuticular projection. Mandibles elongated, falciform; baso-masticatory margin with a single row of five teeth. Mandibular teeth arrangement, from base to apex: smaller blunt tooth; two longer jigsaw-tab-shaped teeth; long diastema; indistinct, acute pre-apical tooth, immediately followed by an acute apical tooth. Dorsal face of the mandibles costate. Mandibles with erect to subdecumbent pilosity. Mandibles as long as the head (MI: 100).

Mesosoma. Mesepisternum divided into anepisternum and katepisternum. Metanotal suture present. In profile, lateral margins of propodeal declivitous face are not continuous: ventral portion is raised. In the dorsal view, pronotum, mesonotum, and propodeum strigate-rugulose; declivitous face of the propodeum weakly strigate-rugulose. Posterolateral portion of the pronotum, mesepisternum, and posterolateral face of propodeum areolate; remainder of the lateral face of the propodeum strigate-rugulose-somewhat areolate; metapleuron imbricate. Mesosoma covered with erect to subdecumbent pilosity.

Legs. Lamella absent on the ventral margin of the calcar of strigil. Anterior face of calcar of strigil with squamiform microtrichia; posterior face with lanceolate microtrichia. Multiple spatulate, carinate setae on the anterior face of protibial apex, next to calcar of strigil. Multiple spatulate, carinate setae on the anterior face of probasitarsus. Mesotibial spur absent. Anterior face of mesobasitarsus with round sulcus filled with microvilli-like projections. One metatibial spur; pectinate; anterior and posterior faces glabrous. Sulcus absent on the anterior face of the metabasitarsus. Arolium present on pro-, meso-, and metapretarsus.

Metasoma. Subpetiolar process well developed and lobe-shaped; fenestra absent. Prora present. Stout spiniform setae absent on hypopygium. Petiolar tergite, laterotergite, and poststernite areolate/imbricate. Gaster imbricate; mostly covered with suberect pilosity.

Color. Head color orange-brown; body yellow-brown; apex of gaster and appendages yellowish.

Type Material

Holotype: worker, pinned. Original label: “TAIWAN: Nantou County, LFDP, 10.i.2015, F. C. Hsu col. CASENT0922349” Deposited at NMNS (National Museum of Natural Science). Paratype: worker, pinned. Original label: “TAIWAN: Nantou County, LFDP, 10.i.2015, F. C. Hsu col. ANTWEB1032000” Deposited at Taiwan Agricultural Research Institute. Type locality. Lienhuachih Forest Dynamics Plot (LFDP), 23°55’01”N / 120°52’58”E, 770m, Nantou County, Taiwan, 10.i.2015, F. C. Hsu col., Winkler sample (sifted soil).

Etymology

The name luyiae is homage to Miss Lu-Yi Wang. The fieldwork that yielded specimens for this study could not have been completed without her participation.

References

• Billen, J., Khalife, A., Ito, F., Anh, N.D., Esteves, F.A. 2021. The basitarsal sulcus gland, a novel exocrine structure in ants. Arthropod Structure, Development 61, 101041 (doi:10.1016/j.asd.2021.101041).
• Cantone S. 2018. Winged Ants, The queen. Dichotomous key to genera of winged female ants in the World. The Wings of Ants: morphological and systematic relationships (self-published).
• Hamer, M.T., Pierce, M.P., Guénard, B. 2023. The Amblyoponinae (Formicidae) of Hong Kong. Asian Myrmecology 16, e016005 (doi:10.20362/am.016005).
• Hamer, M.T., Weemaels, A.I., Fu, Y., Xuan, L., Tse, C.Y.L., Tang, K.L., Guenard, B. 2024. New insights into the diversity and distribution of Leptanillinae (Formicidae) within China. Zootaxa 54711, 99–112 (doi:10.11646/zootaxa.5471.1.6).
• Hsu, F.-C., Esteves, F.A., Chou, L.-S., Lin, C.-C. 2017. A new species of Stigmatomma from Taiwan (Hymenoptera, Formicidae, Amblyoponinae). ZooKeys 705: 81–94 (DOI 10.3897/zookeys.705.10296).

• Sahanashree, R., Aswaj, P., Aniruddha, M., Priyadarsanan, D.R. 2023. Two new reports of Stigmatomma Roger, 1859 (Hymenoptera, Formicidae, Amblyoponinae) species from the Indian Subcontinent. Sociobiology 70(4): e9315 (doi:10.13102/sociobiology.v70i4.9315).