Protanilla lini Terayama, 2009

Hsu, Po-Wei, Hsu, Feng-Chuan, Hsiao, Yun & Lin, Chung-Chi, 2017, Taxonomic notes on the genus Protanilla (Hymenoptera: Formicidae: Leptanillinae) from Taiwan, Zootaxa 4268 (1), pp. 117-130 : 123-129

Protanilla lini Terayama, 2009

Figs. 5–6 .

Material examined. 2 ♀ (worker): TAIWAN, Nantou, Lienhuachih Forest Dynamics Plot, by hand-collecting, 07.XII.2015, Po-Cheng Hsu leg. ( NCUE) ; 1 ♀ (queen): same data as workers. ( NCUE) .

Measurements. Worker: see Terayama, 2009: 126; female (queen): HL 0.63, HW 0.54, CI 86, SL 0.52, SI 96, ML 0.31, PW 0.42, WL 1.03, PNL 0.24, PNH 0.41, PNW 0.28, PPNL 0.22, PPNH 0.43, PPNW 0.32.

Supplementary description. Worker: see Terayama, 2009: 126. Furthermore, a longitudinal inconspicuous groove running along dorsolateral margin of mandible, traversing the width to inner margin at approximately half the length. A series of long stout hairs on masticatory ventral apex of mandible. Presclerites of abdominal segment IV constricted to articulation with postpetiole; pretergite thin; presternite bulging and coarsely sculptured.

Female (queen): Body yellowish-brown, similar to worker. In full-face view, head somewhat round, as broad as long; sides convex; posterior margin straight to slightly concave. Compound eyes large, located slightly above the middle of sides of head. Ocelli present. Clypeus same shape as in workers. Mandibles long and triangular, with a longitudinal groove running dorsolaterally, traversing the width to inner margin at 1/3 the length to apex; masticatory margin slightly crenulate with approximately 15 peg-like teeth; apical 1/3 denticulate and without peglike teeth. A series of long stout hairs on masticatory ventral margin of mandibular apex, with the foremost one stoutest. In lateral view, mandibles down-curved apically. Antennae 12-segmented; scape long, reaching posterior margin of head; segments 2–11 as long as wide; terminal segment approximately 1.5 times as long as wide. Mesosoma well developed, in lateral view with a flat to slightly convex dorsal outline. Pronotum in dorsal view approximately as long as scutum, with convex sides, in lateral view with a convex dorsal outline. Scutum in dorsal view triangular, in lateral view with a flat dorsal outline. Scutellum in dorsal view small, half the length of scutum, in lateral view with a flat dorsal outline. Propodeum in dorsal view trapezoidal, with straight posterior face and round corners, in lateral view with round dorsal outline. Propodeal spiracle large, above bulla of metapleural gland.

Petiole and postpetiole same shape as that of workers in both dorsal and profile view, but in lateral view petiole and postpetiole thinner than those of workers.

Remarks. Records have revealed that P. lini is distributed across the north and central parts of Taiwan, primarily in natural or seminatural areas above an altitude of 600 m. Protanilla lini workers seem to be spotted more easily on rainy days, possibly because of migrations caused by floods.

Biological notes on Protanilla in Taiwan. The P. lini colony was collected from the Lienhuachih Forest Dynamics Plot at an altitude of 760 m . The area is a Machilus-Castanopsis forest zone that is mainly composed of Lauraceae and Fagaceae trees. The colony was found nesting in some cavities and tunnels within a fallen dead branch. The P. jongi colony was collected from the Fenghuang Education Area at an altitude of 840 m. The area is a tea garden with several types of vegetation, mainly Cunninghamia lanceolata , Schima superb , bamboo, and various ferns. It is near secondary forest which mainly consists of Acacia confuse . The colony was found nesting in a built chamber at a depth of approximately 20 cm in soil, covered by a stone.

The P. lini and P. jongi colonies were observed in our laboratory for the duration of 6 and 2 months, respectively. All of the members demonstrated the behavior noted by Wilson and Hölldobler (1990), which is consistent with those of typical trap-jaw ants (e.g. Odontomachus and Anochetus ). Although mandibles of Protanilla workers are not linear in shape, they are able to open to 180 degrees and strike during predatory interactions. This behavior was also recorded in " P. wallacei " a few times in the laboratory (F. Ito, personal communication). Furthermore, we observed that Protanilla workers locked their mandibles in the striking position when guarding their nest entrances in the laboratory. The guarding behavior was also recorded in L. japonica by Masuko (1990), who noted that most of the workers stood near the brood pile facing outward, with the anterior half of the body raised, the forelegs suspended in the air, and the mandibles open. However, whether Leptanilla could quickly snap their mandibles as those of Protanilla and other trap-jaw ants was not mentioned in the previous articles.

In our laboratory observations, we provided various types of prey (centipedes, cockroaches, meal worms, termites, springtails, and woodlice). Only certain types of centipedes were accepted; specifically, both species appeared to prefer geophilomorph centipedes that were approximately 3–4 cm in length. Smaller and larger geophilomorph centipedes were also acceptable, but the members were unable to finish those exceeding 4 cm. We removed them to avoid a sanitation problem in the nest. Moreover, as P. jongi is larger than P. lini , P. jongi seemed to prefer larger prey compared with P. lini . This observation is similar to the ecological notes in Ogata et al. (1995), which reported that L. taiwanensis larvae were found in the field feeding on a geophilomorph centipede approximately 4 cm in length; Masuko (1990) also demonstrated this phenomenon, indicating that L. japonica exclusively fed on geophilomorph centipedes ranging from 1–2 cm in the laboratory (but whether centipedes larger than 2 cm were provided is unclear). However, " P. wallacei " was observed to feed on Occasjapyx diplurans (Billen et al. 2013). Further field and laboratory observations are required to determine the degree to which Protanilla and other Leptanillinae specialize on centipedes.

In our captive colonies, when a live centipede was encountered by Protanilla , the workers grabbed the appendages of the centipede by quickly snapping their mandibles and stinging the victim. The centipede was paralyzed within a few minutes and transported back to the nest, where it was consumed by numerous larvae that were carried and attached to the prey by the workers. We did not observe the situation discussed in Masuko (1990), where L. japonica workers carried the larvae toward the paralyzed prey rather than bringing the prey back to the nest.

However, whether the synchronized larval development and larval hemolymph feeding behaviors in L. japonica also appear in Protanilla species remains unclear. In our observations, we did not record the gynes of either species feeding on larvae. Nevertheless, during the 6-month observation of the P. lini colony, we did note the larvae of different instars present in the colony at the same time. More living material of Protanilla species is needed for the further examination of larval biology.

In addition, strong and distinct odors spread when the two Protanilla colonies were excavated and even when undisturbed in the laboratory. However, it remains unclear whether the odor was produced by adults or larvae.

Furcotanilla as a synonym of Protanilla . According to Xu (2012), the monotypic genus Furcotanilla is morphologically close to Protanilla , but is distinguishable by the combination of the following characteristics:

1) Massive mandibles armed with a long tooth and a short tooth on the lateroventral margin; 2) Postpetiole broadly attached to the anterior face of gaster;

3) Ventral outline of postpetiolar sternite in lateral view deeply concave; and

4) Anterior margin of the abdominal segment IV deeply concave in order to accept the postpetiole.

However, we found that the characters of P. jongi are intermediate between those of Protanilla and Furcotanilla, raising doubts about the validity of Furcotanilla. First, P. jongi has a single, inconspicuous, and small tooth at the ventral margin of its long and thin mandibles. The tooth seems to be equivalent to the two rather developed teeth seen in Furcotanilla; that is to say that the shape of the mandibular blade of P. jongi is intermediate between Furcotanilla and typical Protanilla spp., though overall more similar to those of Protanilla . Specialized shapes of mandibular blades are also found in P. izanagi and Anomalomyrma taylori , which have a high, convex lamella projecting vertically from the dorsal surface of each mandible. Thus, the shape of the mandibular blade seems to be inadequate for distinguishing genera of Leptanillinae because modifications of the character have probably occurred frequently in the tribe Anomalomyrmini (see also Borowiec et al. 2011). Furthermore, Furcotanilla and Protanilla species (including P. jongi ) exhibit similarities in the arrangement of teeth and setae/ hairs of the mandibles, including peg-like teeth on the masticatory margins, which were considered a synapomorphy of Protanilla (Borowiec et al. 2011) , denticles at the down-curved mandibular apex, and a long stout hair in the anteroventral part.

In addition to the mandible features, P. jongi shows an intermediate or mosaic condition between Furcotanilla and typical Protanilla regarding the shape of the postpetiole and the structure of the articulation between the postpetiole and abdominal segment IV. The postpetiole of P. jongi is trapezoidal in dorsal view, and broadly attached to abdominal segment IV; these characteristics are identical to those of Furcotanilla. In P. jongi , however, the anterior margin of abdominal segment IV is just slightly concave in dorsal view, and the side of abdominal segment IV lacks any deep and narrow notch between the tergite and sternite at the anterior margin; these characteristics are similar to those of Protanilla . Furthermore, the postpetiolar sternite and presternite of the abdominal segment IV in P. jongi , when the articulation is outstretched, form a continuous ventral outline that is nearly straight at the postpetiolar sternite and prominent at the presternite of abdominal segment IV. By contrast, the ventral outline of the postpetiolar sternite in Furcotanilla is deeply concave according to Xu (2012). Overall, the characteristics observed in P. jongi are more typical of Protanilla species, in which the postpetiolar sternite is not concave, and the presternite of abdominal segment IV is coarsely sculptured and bulging, which can be seen in other species to varying degrees.

Current taxonomy strives to make all higher taxa monophyletic. Rates of evolution vary among characters, and creating a new higher taxon based on only a few traits may result in paraphyly. This may be misleading for studies of behavior and biology. Some major ant genera, which consist of hundreds of species, contain subgroups with highly divergent morphology. We should avoid creating new genera based only on morphological gaps, and instead place highly divergent species into informal “species-groups.” We should avoid the description of new genera until we have a clear understanding of their evolutionary history. In this case, we can easily speculate that Furcotanilla is actually well-embedded within the Protanilla clade, with highly-derived mandibles and some other notable characters. In fact, the only species of Furcotanilla, F. furcomandibula , was initially described as Protanilla furcomandibula in Xu, 2002 . The intermediate status of P. jongi helps further bridge the gap between these two genera. In conclusion, we synonymize Furcotanilla with Protanilla , and transfer “ F. furcomandibula ” back to Protanilla as Protanilla furcomandibula rev. comb.

Figures

FIGURE 5. Protanilla lini Terayama, 2009 worker. A. Full-face view. B. Body in dorsal view. C. Body in profile view. Scale bars: A, 0.5 mm; B and C, 1 mm.

FIGURE 6. Protanilla lini Terayama, 2009 queen. A. Full-face view. B. Body in dorsal view. C. Body in profile view. Scale bars: A, 0.5 mm; B and C, 1 mm.