Myrmecina gopa

Myrmecina gopa is uniconial, an unusual trait for a tropical, forest dwelling ant species. It is also polygynous, and only ergatogyne queens have been found. It is unusual for there to be only wingless reproductives in a unicolonial species. Typically there are wingless and winged queens. The latter allows for independent colony founding beyond the unicolonial nesting site.

Identification
Okido, Ogata, and Hosoishi (2020) - Myrmecina gopa does not belong to any species complex. But M. gopa is similar to Myrmecina dolichothrix on the basis of some characters (see the remarks of M. dolichothrix). Among those species, M. gopa can be distinguished from the remains by having the short pilosity and the anterior clypeal margin with three processes.

Distribution based on Regional Taxon Lists
Indo-Australian Region: Indonesia.

Biology
Okido, Ogata, and Hosoishi (2020) - Colonies of this species are unicolonial. Their nests are contiguously rather than uniformly distributed, and conspecific nonnestmates are easily incorporated into alien nests (Tsuji et al., 2001). Ito (1996) reported that this species, which has a specialized myrmecophilous oribatid mite Aribates javensis Aoki, Takaku & Ito (Ito & Takaku, 1994; Aoki et al., 1994), has no queen, but an ergatogyne as a reproductive caste. Ergatogynes distinguish from workers only in width and length of their first gastral tergum. Colonies of this species are polygynous, having 8 ergatogynes on average per colony, and all mated ergatogynes reproduce without aggressive interactions.

Ito and Takaku (1994) - The authors found an obligate myrmechophilous oribatid mite in nests of the myrmicine ant Myrmecina sp. in the Oriental tropics, in which (1) the oribatid mite was found only in ant nests and reproduced there, (2) ants frequently took care of live mites of all stages who could not survive without ant attendance, (3) under normal conditions, ants rarely ate living mites but dead mites were immediately consumed by adults and larvae, (4) and during severe food shortages, living mites were frequently eaten by ants.

We investigated this novel relationship in Bogor, West Java, Indonesia, during the rainy seasons, January to February, of 1992 and 1993. Colonies of Myrrnecina sp. nested under stones or dead branches on the floor of a small artificial forest. The average colony was composed of 10 ergatoid queens and 80 workers [6]. Of the 30 nests examined, all contained a number of eggs, nymphs, and adults of an oribatid mite species. The mean number of adult mites was 24.7 + SD 23 (range 1 to 89) per nest. The relative number of adult mites to ant workers was 1 to 75 % (mean 24.9 _+ SD 19.3%). The mites were considerably numerous, as compared to hitherto known myrmecophilous Acarina, which usually account for less than 0.1% of the number of adult ants in the nests [2]. The oribatid mites were not found in the sample of soil arthropods collected by hand sorting and Tullgren methods from soil near the ant nests, and they were also never found in nests of sympatric ants such as Tetrarnorium spp., Pheidole sp., Anochetus graeffei, and Oligomyrmex sp., suggesting that the oribatid mite is a specialized myrmecophile in Myrmecina nests.

To observe the behavior of the ants and the oribatid mites, we kept some colonies in artificial nests in the laboratory, and behavioral interactions were investigated under a microscope. The mites were remarkably inactive: although their legs were well developed, they never walked alone on the nest floor. They were also immobile when removed from the nest. In the nest, the mites were usually deposited on the nest floor within a brood cluster of ants, but some mites were attached to decomposed leaves in ant nests. Feeding habits of the oribatid mites are still uncertain. Regurgitation from ant workers was not observed, and we believe they may feed on some form of bacteria or fungi. The ants sometimes transported nymphs and adult mites in the nest chamber. Mites were often groomed by ant workers in the nests. In the typical sequence, the worker picked up a mite by grasping it with her mandibles and licked the dorsal surface, then the ventral surface. Finally, she licked the legs and deposited the mite on the nest floor. Adult mites underwent this routine from ant workers zero to four times every 30 min (1.42 + SD 1.47, N = 15). The average duration of the routine for one mite was 43.1 s (N = 22).

When the nests were artificially disturbed, the ant workers grasped the mites and transported them to the new nest site prior to transporting their own brood. Oviposition by the mites was observed ten times. Mite eggs, differing in shape and size from ant eggs, were picked up by the ant worker and deposited on an egg cluster of ants. The mite eggs were also licked by the ant workers along with ant eggs. These observations indicate that the myrmecophilous oribatid mites in Myrmecina nests owe their entire lives to the host ants.

Ito (1996) - Colony composition of Myrmecina sp. A, which has a specialized myrmecophilous oribatid mite Aribates javensis Aoki, Takaku, & Ito, was studied in Bogor, West Java, Indonesia. The colonies had no alate or dealate queens. Alternatively, an average of 8 ergatoid queens, who were easily distinguished from workers in width and length of the 4th abdominal tergaite, mated and laid eggs. Males were frequently produced in many, but, production of ergatoid queens was observed in only 2 of 24 colonies in the field. Expulsion of some old ergatoid queens by workers was observed after emergence of new ergatoid queens in one colony. Experimental evidence confirmed the presence of queens had the negative effect on production of new ergatoid queens.

Colonies contained 8 (±SD8.4) ergatoid queens and 66 (±SD 24) workers (means, n=41). All but 4 colonies had multiple ergatoid queens, with up to 45 found in a single colony. In 12 polygynous colonies, dissected ergatoid queens (n = 150) showed almost all (142) were inseminated. Queens had from 1-9 developed oocytes with yellow bodies, indicating functional polygyny. Workers had only 1 oocyte and no spermatheca. Virgin queens had no developed oocytes and were easily distinguished from inseminated queens by the color of the abdomen; tergites of virgins were darker than those of inseminated queens.

Most colonies collected in the field during the rainy season produced alate males. ergatoid queens were only produced in 2 colonies, one queenright and the other queenless. Morphological specialization of ergatoid queens in Myrmecina sp. A is not well developed. The structure of the head and thorax is almost identical to that of workers, there are no ocelli present, thoracic structure was similar to workers and not very enlarged, and the number of ovarioles was not very great relative to conspecific workers. In sum, the workers and queens were not clearly distinguished from one another anterior to their gasters. The 4th abdominal tergite of ergatoid queens was distinctive, and was noticeably wider and longer relative to workers.

Aoki and Ito (1997) - The oribatid mite, Aribates javensis, exhibits novel behavioral characteristics. The mites always live in nests of the ant, do not walk by themselves, are cared for by ants in their nests, cannot survive without ant attendance, and the oribatid mites are fed on by the ants after the mites die. Their morphological characteristics of Aribates javensis are unique in lacking sesilli as well as in the variable number of anogenital setae.

Tsuji, Ohkawara, and Ito (2001) - We studied the nest distribution pattern, the inter-nest relationship, and egg-laying ability of workers in the Indonesian myrmicine ant Myrmecina sp. A. This rare species has recently attracted biologists attention by their peculiar symbiosis with a mite. The ant was locally quite dominant and occupied about 80% of the ant nests within a 10 × 10m-study plot on the floor of the secondary forest in the Botanical Garden of Bogor. We conclude that the local population of M. sp. A consisted of an unicolonial colony, because of the following three reasons: (1) they were usually tolerant to conspecific non-nestmates while showing strong aggression to the different species Tetramorium sp., (2) nests were contiguously rather than uniformly distributed, and (3) a mark-recapture experiment revealed that conspecific non-nestmates were easily incorporated into alien nests. This study reports the first discovery of unicoloniality in an ant species whose female reproductives are obligatory wingless ergatoid queens. Also, unicoloniality in a forest dwelling ant in the tropics is unique. Workers can lay male destined eggs but they seem to lay only trophic eggs in the presence of the queen. We presented a hypothesis on the evolution of unicoloniality in this and other ant species with regard to the possible effects of genetic, ecological and historical factors. A population bottleneck following the introduction to a new habitat, policing and domination in the local habitat seem responsible for the evolution and maintenance of the unicoloniality.

Nomenclature

 * . Myrmecina gopa Okido, Ogata & Hosoishsi, 2020: 42, fig. 17 (w.) INDONESIA.

Worker
Holotype. TL 2.61, HL 0.61, HW 0.58, CI 95, SL 0.53, SI 92, PW 0.41, ML 0.67. Paratype. TL 2.54-2.90, HL 0.57-0.65, HW 0.54-0.62, CI 91-97, SL 0.50-0.56, SI 88-96, PW 0.37-0.44, ML 0.64-0.75 (25 measured).

Head subrectangular, slightly longer than broad in full-face view; median portion of occipital margin slightly concave; occipital corners rounded, not projected posteriorly. Masticatory margin of mandible bent at midlength (third small tooth or sixth tooth); apical tooth strong, third tooth robust, followed by 4-5 small teeth and a small basal tooth; small teeth frequently unclear. Dorsal surface of clypeus slightly concave; median portion of anterior margin projected with three processes; lateral portion simple, lacking sharp ridge in front of antennal insertions. Anterior dorsal surface of labrum with paired denticles very small. Frontal carinae virtually absent, indistinguishable from rugae on dorsum of head. Eyes large and moderately convex, varying in size with maximum diameter 0.08-0.11 mm and 5-6 ommatidia; malar space twice as long as diameter of eye or shorter in profile; distance between occipital margin and posterior margin of eye three times as long as diameter of eye. Antennal scape long, extending beyond posterolateral corner of head; antennal flange developed.

Dorsal outline of mesosoma convex in profile. Pronotum without denticles; anterior portion usually marginate; anterior ventrolateral portion not angulate. Furrow between pronotum and mesoepisternal projection more or less broad. Eumetanotal spine absent. Propodeal spine elongate, 1.5 times as long as broad at base, extending over vertical posteriormost limit of propodeum in profile. Propodeal lobe low. Propodeal spiracle large, situated near posterior margin of propodeum, distance between posterior margin of spiracle and posterior margin of propodeum shorter than diameter of spiracle. Petiole short, as long as or slightly longer than high in profile, and longer than broad in dorsal view; dorsal crest located at midlength in profile; subpetiolar process present at anterior portion, usually bearing acute anterior apex, but varied in shape, sometimes triangular or lobed with a hole. Postpetiole broader than petiole in dorsal view; lateral margin usually straight; anterior portion sharply raised; ventral outline projected with two acute points.

Anterior margin of gaster not concave in dorsal view; first gastral sternum simple without median longitudinal ridge.

Head with straight rugae distinctly; ventrolateral portion usually smooth and shining. Clypeus smooth and shining. Mesosoma with straight rugae distinctly. Forecoxa smooth and shining. Petiole and postpetiole with a few rugae. First gastral segment smooth and shining. Head with relatively dense and long pilosity on dorsum. Mesosoma with dense and long pilosity on dorsum, hairs of pronotum slightly shorter than propodeal spine. Dorsal pilosity of petiole slightly longer than that of mesosoma. Petiole without hairs on ventral surface. Postpetiole usually without hairs on ventral surface. Head and mesosoma black, petiole, postpetiole and gaster reddish brown, mandibles, antennae and legs yellowish brown.

Type Material
Holotype worker, INDONESIA: Kebun Raya, Bogor, W. Java, 11. ix. 1996, FI96-375 (F. Ito). Paratypes. numerous workers, ergatogynes and males with same data as holotype; numerous workers, ergatogynes and males with same data as holotype but 17-20. ii. 1993, FI93-157; numerous workers and ergatogynes, and 1 male with same data as holotype but 17-20. ii. 1993, FI93-159; numerous workers, ergatogynes and males with same data as holotype but 17-20. ii. 1993, FI93-162; numerous workers, ergatogynes and males with same data as holotype but 17-20. ii. 1993, FI93-163 (BZM,, ).

Determination Clarifications
This species corresponds to Myrmecina sp. A of Ito (1996), Aoki & Ito (1997), Ito et al. (2001) and Tsuji et al. (2001).