Aphaenogaster gamagumayaa

Aphaenogaster gamagumayaa is one of only two troglobiotic (true cave-dwelling) ant species, the other being Leptogenys khammouanensis from Laos. The type series of Aphaenogaster gamagumayaa is based on workers probably from a single nest, collected in a limestone cave on the island of Okinawa, Ryukyu Archipelago, Japan. All specimens were found in a guano hall, an area of approximately 25 m2 (2–3m in height), approximately 20m from the cave entrance. This species has only been found in a cave area with heavy guano deposits, and some worker ants were observed carrying guano.

Identification
Naka & Maruyama (2018) - Distinguished from the other East Asian species by having the most elongate body, the longest antennae and legs, and the most reduced eyes. Among the Japanese species, it is most similar to Aphaenogaster irrigua from the Ryukyu Archipelago. It differs from A. irrigua in lighter color, smaller eyes (EL 0.19 x TmL vs. 0.38 x TmL), basal margin of mandible with weaker serration, and scapes more elongate and slim (SL 2.28 x HW vs. 1.53 x HW).

Distribution based on Regional Taxon Lists
Palaearctic Region: Japan.

Biology
The type series of Aphaenogaster gamagumayaa is based on workers probably from a single nest, collected in a limestone cave on the island of Okinawa. All specimens were found in a guano hall (Fig. 5), an area of approximately 25 m (2–3 m in height), approximately 20 m from the cave entrance. The hall is completely dark, and during the study period (August to October 2017), it was consistently cooler (< 25°C during the day) than the exterior of the cave (28–32°C). The cave contains no pools or streams but is generally wet, and the substrate is clay soil.

The ants were moving around an approximately 4-m2 area in which there were many small holes (Fig. 6) and cracks in the cave floor. Ants were observed entering these holes. Although one of the authors, TN, did not dig into the holes, they were surmised to be associated with a core part of the nest. TN observed a maximum of 12 individual workers, most likely nest mates; no aggression was seen between them. Most of them were solitary foragers and observed on the cave floor or on the lower part of the cave wall. However, on one occasion two ants were observed walking together (Fig. 7) for some time. On two occasions ants were seen carrying balls of guano into a hole (Fig. 8). Another individual was observed carrying a small white object that did not appear to be guano. Upon perceiving human movement, the ants stopped moving and hid. While motionless, they waved their antennae, most likely to assess the situation. Gaster bending behavior, which is often observed in other Aphaenogaster species (Terayama et al. 2014), has not been observed in A. gamagumayaa.

There are four pieces of morphological and circumstantial evidence to support our view that Aphaenogaster gamagumayaa is a troglobiotic species: 1) this species has only been found inside a cave; 2) it has several characteristics that are unique to cave insects; 3) ants were concentrated in an area of the cave with a high abundance of guano; 4) this cave is located on Okinawa, which harbors many endemic troglobiotic species.

1) The first specimens of A. gamagumayaa were found in a cave situated in a small evergreen forest in Okinawa. TN performed six searches of the area outside the cave (three during the day and three at night; 24 h in total). These searches were focused especially on the forest floor, crevices in and under rocks, and an old cemetery, all of which are generally suitable habitats for Aphaenogaster species. Also several other Okinawa forests were surveyed on multiple occasions to confirm the presence/absence of A. gamagumayaa. However, no A. gamagumayaa specimens were found in any of these searches. The ant fauna of Japan, including Okinawa, has been well investigated (e.g., Japanese Ant Database Group 2008), and A. gamagumayaa is a large and conspicuous species. It seems likely that if its habitat is not restricted to cave interiors, it would have been discovered prior to this study.

2) In general, Aphaenogaster ants are slender, with elongated bodies, antennae and legs. The body of A. gamagumayaa is especially slender and is characterized by extremely elongated antennae and legs. It also has reduced eyes, and a less pigmented body than other Aphaenogaster species. Loss of wings, reduction of eyes, elongation of antennae and legs, and loss of pigmentation are commonly observed in troglobiotic arthropods (Vandel 1964, Christiansen 1965, Culver 1982, Marques & Gnaspini 2001; Juan et al 2010). It is unclear whether A. gamagumayaa displays any wing loss/reduction in the queen and male, as during the course of the study only workers were found. However, its other characteristics are typical of troglobiotic arthropods. The only previously known troglobiotic ant, L. khammouanensis, shares similar characteristics (Roncin & Deharveng 2003).

3) Cave environments are generally nutritionally poor. The unique morphologies and life histories of many troglobiotic arthropods can be explained as adaptations to this oligotrophic habitat (Deharveng & Bedos 2000). Leptogenys khammouanensis is regarded as a troglobiotic species because of its habitat in the deep parts of caves, and of the typical morphology of troglobiotic arthropods. However, as Wilson (1962) stated, caves do not usually provide suitable habitats for ants because of the difficulty of sustaining a colony in such an oligotrophic environment. This difficulty has led to a paucity of troglobiotic species among ants. Although caves are generally characterized by an oligotrophic environment, areas with high densities of guano deposits (so-called guano halls) are an important exception. Guano deposits represent an important source of nutrients derived from the outside environment and are carried into the cave by cave-dwelling bats. Aphaenogaster gamagumayaa was found only in a part of a cave where guano is deposited by two bat species (Rhinolophus pumilus Andersen, 1905 and Miniopterus fuscus Bonhote, 1902). TN observed workers entering and leaving small holes or crevices in rocks on the cave wall and floor; some of them were carrying small balls of guano. They apparently nested under the cave floor and may have adapted to feed on guano (Leptogenys khammouanensis), which was not found in guano halls, may possess different adaptations to cave habitats).

4) Okinawa, the type locality of A. gamagumayaa, is located in a subtropical region of the Ryukyu Archipelago. Much of the land on Okinawa and its neighboring islands is formed from uplifted coral reef (Machida et al 2001), and limestone caves are common in the region. These caves harbor many endemic Okinawan troglobiotic or troglophilous animals (Machida et al 2001), such as the bat R. perditus Andersen, 1918, the shrimp Macrobrachium miyakoense Komai & Fujita, 2005, the crab Orcovita miruku Naruse & Tamura, 2006 and the millipede Epanerchodus subterraneus Verhoeff, 1938. The cave-dwelling spider Coelotes troglocaecus Shimojana & Nishihira, 2000 and several species of assimineid snails are found only on Okinawa (Maeda et al. 2017). Okinawa may harbor many more troglobiotic species that have yet to be identified. Fifteen species of Aphaenogaster ants have been identified in the Ryukyu Archipelago (Terayama et al. 2014). Many of these are endemic to one or a few islands and have obviously speciated by island or small island chain. This suggests that Aphaenogaster ants may have a low migratory ability and are relatively prone to allopatric speciation. Some Aphaenogaster species (for example A. irrigua) prefer dark, wet habitats such as the area around mountain streams. Aphaenogaster gamagumayaa evolved as a troglobiotic ant on Okinawa (and possibly its adjacent islands) as a result of various factors, namely the geologic features of the region, traits of the taxon, basic habitat features of Aphaenogaster ants and presence of guano in the cave.

Nomenclature

 *  gamagumayaa. Aphaenogaster gamagumayaa Naka & Maruyama, 2018: 136, figs. 1-4 (w.) JAPAN.

Worker
(n = 6). HL, 1.499 ± 0.047 (1.439–1.566); HW, 1.118 ± 0.030 (1.073–1.152); TmL, 0.790±0.038 (0.743–0.843); GL, 0.808±0.027 (0.778–0.856); SL, 2.429±0.053 (2.350–2.509); EL, 0.143±0.006 (0.134–0.149); EW, 0.119±0.005 (0.114–0.128); ML, 2.563±0.074 (2.463–2.659); PSL, 0.363±0.017 (0.348–0.388); SDL, 0.252±0.010 (0.242–0.270); HTL, 2.121±0.047 (2.046–2.176); PL, 0.753±0.026 (0.702–0.769); PPL, 0.480±0.017 (0.465–0.513); PH, 0.389±0.008 (0.380–0.399); PPH, 0.356±0.034 (0.330–0.423); PNW, 0.748±0.022 (0.713-0.775) ; PW, 0.271±0.009 (0.260–0.283); PPW, 0.327±0.007 (0.317–0.338).

Body almost entirely yellowish. Head and mesosoma yellow, but mandibles and antennae darker, and base of head and anterior area of prothorax brown; legs light yellow but bases of femora, tibiae and tarsi darker. Gaster light yellow, but basal constriction brown, and posterior 1/2 slightly darker.

Head oval, without basal constriction or neck. Anterior margin of clypeus with weak transverse wrinkles and shallowly concave. Eyes very small, 0.19 times as long as length of tempora. Scapes elongate and slim, 2.28 times as long as width of head, at base 1.7 times as wide as at apex, gradually widened, straight, only apex slightly bent down with slight preapical constriction. Surface of scape shiny, uniformly covered with short and sparse adherent setae. Scape straight, only apex slightly bent down with shallow preapical constriction. Funicle elongate and thin, 1.38 times as long as scape, first funicular segment elongate, 3.17 times as long as wide at apex, 1.74 times as long as second segment, relative lengths of segments, 100:57:68:75:76:76:92:150:145:143:213, apical segment 3.1 times as wide as first segment. Pronotum elongate, 1.37 times as long as wide, regularly convex in profile. Propodeum almost as long as wide, propodeal spines short, needle-like, obliquely directed upwards. Petiole elongate with long peduncle, its anterior face deeply concave, node globular and strongly convex. Ventral margin of petiole with low, short carina around middle. In dorsal view, petiole gently widened postriorly before petiolar node. Postpetiole short, 0.68 times as long as petiole, in profile regularly rounded, its node slightly lower than petiole. In dorsal view postpetiole 1.5 times as long as wide with regularly rounded sides.

Mandible elongate, with outer edge straight, dorsal surface with distinct striation, inner margin with 7 or 8 small teeth. Lateral portion of clypeus with 2–3 thin oblique rugae, central part without sculpture, shiny. Frontal carinae short, not extending to line connecting anterior margin of eyes, subparallel; interantennal area deeply impressed, smooth and shiny, frontal triangle shiny, with a few, shallow longitudinal wrinkles. Anterior portion of frons with thin longitudinal rugae, mesal area between eyes glabrous and shiny, posterior portion around vertex without rugae but with distinct microreticulation. Pronotum with microreticulation, but with smooth areas postero-laterally, with 8 short setae. Top of mesonotum covered with strong longitudinal rugae; mesopleuron with distinct granulate sculpture, matte. Propodeum with slightly granulate sculpture, below spiracles with two short, thin, longitudinal rugae with distinct transverse wrinkles, and dorsal surface of both mesonotum and propodeum appears slightly matte. Entire petiole and postpetiole covered with fine microreticulation, without rugae. appearing slightly matte, covered with several sparse setae. Gaster smooth, shiny, without microreticulation except in basal area, tergites with sparse, suberect setae much shorter than propodeal spines. Legs very long, hind femora 1.13 times as long as mesosoma, hind tibiae 0.77 times as long as hind femora, hind tarsi 1.19 times as long as hind femora. Surface of legs shiny, fore tarsi only on ventral surface covered with very short, appressed pubescence; femora and mid- and hind tibiae completely without pubescence.

Type Material
Holotype, worker, Nakagusuku-son, Okinawa-jima, Japan, 10 IX 2017, T. Naka (The Institute of Tropical Agriculture, Kyushu University = KUM, no MMANT001). Paratypes, 7 workers, the same locality, collected between 31 VIII - 10 IX 2017 (5 in KUM, nos. MMANT002-006; 2 in, nos. MMANT007,008).

Etymology
The specific epithet is a Ryukyuan dialect “gamagumayaa” (= cave-dwelling hermit), referring to the habitat of the new species.