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|Aulacopone in Ponerinae, Ectatommini: Arnol'di, 1930a PDF: 143; all subsequent authors to the following.|
AulacoponeHNS is the only extant genus of subfamily PonerinaeHNS with known distribution limited to some part of Holarctica. In addition it is one of only two ant genera known exclusively from the Soviet Union, the other being Rossomyrmex ArnoldiHNS (subfamily FormicinaeHNS).
Following a recent visit to Moscow (under the Australia/ U.S.S. R. Science Exchange Agreement) I was permitted by Dr. Arnoldi and Dr. A. A. Zakharov to carry the over-glued Mt. Gugljaband specimen to Australia on loan, there to re-mount, clean and prepare it for examination by scanning electron microscopy. This paper is the result. The general accuracy of Arnoldi's original description is confirmed and some additional features are described, though the risk of damage to the specimen precluded dissection of its mouthparts or sting. The relationship of AulacoponeHNS to Heteroponera MayrHNS, suggested by Brown, is supported. This has interesting evolutionary and biogeographical implications.
* Manuscript received by the editor April 18, 1980
The allocation of AulacoponeHNS to tribe EctatomminiHNS is unquestionable, and is further supported by the absence of arolia from the tarsi of the available specimen. Within subfamily PonerinaeHNS the absence of arolia is apparently unique to species of tribe EctatomminiHNS, except Paraponera clavataHNS (Fabricius) (J. Freeland and R. D. Crozier, pers. comm.).
In order to understand in modern terms Arnoldi's discussion on the possible affinities of AulacoponeHNS, the following synonymies by Brown are relevant: Gnamptogenys RogerHNS = Alfaria Emery = Stictoponera MayrHNS; Proceratium RogerHNS = Sysphincta MayrHNS; EctatomminiHNS = ProceratiiniHNS = Stictoponerini.*
Arnoldi considered AulacoponeHNS close to GnamptogenysHNS, a genus of somewhat diverse content now strongly and disjunctly represented (a) in the Indo-Australian area (from Ceylon and Western China to the Philippines and Fiji, with one New Guinean species on far northern Cape York Peninsula providing the only known Australian records), and (b) in the New World (from Texas south to Tucumán and Buenos Aires, including the Antilles and Peru, but as yet not Chile). The genus is not known from Africa. Brown recognised 26 Indo-Australian species, and more are now known. Sixty-four neotropical species were listed by Kempf (1972). One extinct species, G. europaeum (Mayr), is known from Oligocene Baltic Amber, and according to Brown, Archiponera wheeleri CarpenterHNS, of the North American Oligocene Florissant Shale, seems close to GnamptogenysHNS. Arnoldi indicated specific resemblances between A ulacopone and the palaeogean " StictoponeraHNS " and neogean "Alfaria" species groups of Brown's GnamptogenysHNS classification. He considered these three taxa, comprising his spurious subtribe Stictoponerini, to represent a " grade" standing parallel to ProceratiumHNS in ectatommine evolution, especially to those species then assigned to SysphinctaHNS.
*The name Stictoponerini was proposed by Arnoldi (1930); it seems not to have been used subsequently, or formally synonymized under EctatomminiHNS, where it belongs following Brown's reclassification.
Brown, however, related AulacoponeHNS to HeteroponeraHNS, a genus which has its distribution somewhat more peripheral to the main northern continents than that of GnamptogenysHNS, especially in the Old World. There are two faunistic elements : one in eastern and southwestern mainland Australia, Tasmania and New Zealand; the other in South America, from Panama south to Uruguay and Chile (Kempf and Brown 1968). HeteroponeraHNS is unknown from the Palearctic, Oriental and Ethiopian regions, or from Melanesia. It has no known fossil record. Undescribed species known from Australia could at least treble its continental fauna of three species recognised by Brown, and the name H. imbellisHNS (Emery), as applied by Brown, certainly refers to a partly intractable complex of several Australian species. New Zealand has a single known endemic species. Kempf (1972) listed 13 Neotropical species.
The AulacoponeHNS female (Figs. 1-4) is very like her counterparts in species of the Heteroponera imbellisHNS complex, in size, general habitus, structure of the mesosoma, and colour. AulacoponeHNS and HeteroponeraHNS share several major features distinguishing them from GnamptogenysHNS, including the presence of a median longitudinal costa, distinct from other sculpture, on the head (terminating in front of the anterior ocellus in females), and the absence of a tooth or spine on the upper surface of each posterior coxa (a feature of almost all GnamptogenysHNS species, found nowhere else among the Ectatom-mini). AulacoponeHNS also shares with HeteroponeraHNS those features distinguishing the latter from the neotropical genus AcanthoponeraHNS; these include the absence of long propodeal spines and a strong tooth or spine on the petiolar summit, and the lack of a prominent basal lobe accompanying a distinct submedian tooth on each tarsal claw. Basal lobes are characteristic of AcanthoponeraHNS. Submedian teeth are vestigially represented on the claws of some neotropical HeteroponeraHNS species, though they are lacking from all Australian species, and from AulacoponeHNS. The lack of submedian teeth on the tarsal claws also distinguishes AulacoponeHNS and HeteroponeraHNS from the prominent and diverse Australia-based genus RhytidoponeraHNS, the species of which, in addition, almost all have a strong tooth-like process on each lateral pronotal margin. Such structures are lacking in other ectatommine genera, including AulacoponeHNS, and all Heteroponera species except H. relictaHNS (Wheeler). The latter could stand close to the RhytidoponeraHNS ancestry.
AulacoponeHNS resembles HeteroponeraHNS in all fundamental structural details referred to in Brown's discussion of features diagnosing or characterising ectatommine genera, except those related to cranial and petiolar structure, and other minor features, as detailed below.
In discussing likely relationships among the ectatommine genera Brown considered AcanthoponeraHNS to be "the genus surviving with the greatest number of primitive characters". HeteroponeraHNS was considered "a rather conservative stock" that "can be derived directly from AcanthoponeraHNS ", and RhytidoponeraHNS was represented as a genus "very closely related to HeteroponeraHNS " which "may have originated in the Australian region from some Heteroponera-like stock". According to Brown these genera stand apart as a lineage separate from that of the exclusively neotropical genera Ectatomma Fr. Smith and Paraponera Fr. Smith. GnamptogenysHNS, while difficult to relate precisely to other genera, "seems closer to the AcanthoponeraHNS / HeteroponeraHNS line than to EctatommaHNS ". All the above genera are essentially epigaeic, in contrast to the two further ectatommine genera, Proceratium Roger and Discothyrea RogerHNS, which are cryptobiotic and "seem, on the basis of adult characters, to be closest to HeteroponeraHNS ", while "the Baltic Amber species Bradoponera meieriHNS (Mayr) looks like a reasonable step in this line".
Workers of ProceratiumHNS and DiscothyreaHNS are notable for their possession of cryptobiotic attributes, including medium to small size, with relatively small eyes, reduced sculpture and pilosity, and depigmented coloration. In particular the mesosomal structure is streamlined, through ankylosis of its component sclerites, and the fronto-clypeal structure is highly modified. The antennal sockets are exposed in full-face view, through elevation of the lobes of the frontal carinae, and they have migrated anteromedially, carrying the clypeus and frontal area forwards to form a shelf-like process over the mandibles. This is especially prominent in DiscothyreaHNS, which usually has an erect vertical plate separating the antennal sockets, a structure which in some species is "T" shaped in transverse section and extends back along the head to enclose an antennal scrobe on each side, usually accompanied by a weak parallel longitudinal concavity of the frons. Both ProceratiumHNS and DiscothyreaHNS have their tubulate abdominal segment IV reflexed downwards or forwards under the body, a characteristic shared with various HeteroponeraHNS species and with BradoponeraHNS. In some DiscothyreaHNS species, in particular, the petiole is transverse in dorsal view and only slightly constricted behind, at its articulation with the following (postpetio-lar) abdominal segment. These attributes are doubtless adaptations to life in confined moist and irregular spaces in soil or rotting wood, where effective use of the antennae and sting would otherwise be compromised. The clypeal shelf probably functions wih the mandibles to aid transport of arthropod eggs, upon which several species of both genera (including the remarkable secondarily epigaeic Mauritian Proceratium avium BrownHNS) are known to feed (Brown 1958b, 1974). Females generally resemble workers, though the eyes are usually less reduced, and the mesosoma non-ankylosed, at least in those species with winged gynes.
Figures 1-4. Aulacopone relictaHNS, female, Mt Gugljaband, Azerbaydzhan. Fig. 1, head, full-face view. Fig. 2, Head, oblique frontal view. Fig. 3, mesosoma and petiole, lateral view (position of humeral pits indicated by arrow). Fig. 4, mesosoma and petiole, dorsal view. Scanning electron micrographs; see text for dimensions.
The structural features of AulacoponeHNS are, of course, known only for the female; those of the worker must be surmised. A. relictaHNS nonetheless shows clear cryptobiotic tendencies. The female is of small to medium size for an ectatommine*, with fine sculpture comparable to that of various ProceratiumHNS and DiscothyreaHNS species, and relatively pale yellowish brown colour. The pilosity is dense, though short and not unlike that of some DiscothyreaHNS species, and the eyes are smaller than would be expected in an epigaeic ectatommine. The really distinctive features of the genus have to do with its cephalic structure (Figs. 1, 2), in which the fronto-clypeal part of the head is extended forwards to form a strong triangular process, partly covering the closed mandibles. The antennal fossae are carried forwards on this process almost to the level of the mandibular bases. The resulting structure is, however, very different from that of any ProceratiumHNS or DiscothyreaHNS species, for here the lobes of the frontal carinae are not elevated; they are instead extended laterally and posteriorly to form, on each side, the upper enclosure of a strong, deep scrobe, in which the folded antenna can be stowed. Such strong antennal scrobes are unusual in ectatommine ants, though those of Heteroponera relictaHNS and of some DiscothyreaHNS species (discussed above) are almost as well developed. Each frontal carina is narrowed immediately above the appropriate antennal socket. This might facilitate anterior extension of the scapes, as is so generously accommodated in ProceratiumHNS and DiscothyreaHNS. Immediately behind this section the carina is laterally expanded and partly reflexed, to form an obtuse lobe, which appears to partially lock the scape into position when the antennae are folded (Arnoldi, Fig. 3). These modifications cause the frons and posterior parts of the clypeus to form a regularly convex, more-or-less triangular shield-like face to the cranium, a configuration not unlike that of other small cryptobiotic ants, such as some in the myrmicine tribes DacetiniHNS and BasicerotiniHNS. The fronto-clypeal structure of AulacoponeHNS is unlike that of any other ponerine ant, and thus immediately diagnoses the genus. The extent to which it might be associated with specialised trophic behaviour, like egg-feeding, is quite unknown. In addition the petiolar node (Figs. 3, 4), though relatively broad, is structured similarly to those of some DiscothyreaHNS females, and is quite unlike those of any HeteroponeraHNS species. The structure is somewhat like that typical of the primitive ponerine tribe AmblyoponiniHNS, and might represent a holdover from a remote amblyoponine ancestry. Abdominal segment IV is somewhat reflexed (Arnoldi, Fig. 1), though less strongly so than in Proceratium, BradoponeraHNS or DiscothyreaHNS; or even some HeteroponeraHNS species (notably H. leaeHNS (Wheeler), in which segment IV is more strongly reflexed than in A. relictaHNS and relatively short compared to segment III). Other descriptive details are covered by Arnoldi and illustrated in Figs. 1-4. Several points deserve further discussion. (1) The eyes are notably hairy (Figs. 1,2). This might not be the case in workers. However, the only similar condition I have seen in tribe EctatomminiHNS is that of a worker of an undescribed species of HeteroponeraHNS (aff. H. leaeHNS) from southwestern Western Australia. No other Australian HeteroponeraHNS has hairy eyes. (2) The scanning electron microscope has revealed an unusual structure on each pronotal humerus of the subject specimen, positioned as shown in Fig. 3. One of these structures is illustrated in detail in the stereoscopic pair of micrographs comprising Fig. 5. Each consists of a small shallow depression, without pilosity, enclosing several irregular troughs which each contain a number of minute pores. These are presumably the ducts of some previously unreported prothoracic gland. A detailed survey by steroscopic light microscope has revealed no comparable structure in any other of the several hundred ectatommine species, of all known genera, represented in the Australian National Insect Collection.
* The measurements (mm) of the Mt Gugljaband specimen are: aggregate total length 4.25; maximum head length 1.08; head width across eyes 1.02; chord length of scape 0.59; maximum diameter of eye 0.24; Weber's length of mesosoma 1.36; scutum width 0.82; petiole width 0.52; petiole height 0.58; width of postpetiole (abd. II) 0.96.
AulacoponeHNS thus emerges as a genus close to HeteroponeraHNS which, like ProceratiumHNS and the BradoponeraHNS / DiscothyreaHNS line, shows adaptations to a cryptobiotic lifestyle, though these have probably been separately, and convergently evolved in the three lineages. The full degree of cryptobiotic specialisation cannot be assessed until workers of AulacoponeHNS are collected, and checked for fronto-clypeal structure, palpal formula, mesosomal ankylosis, and relative development of the eyes, pilosity and gastral reflexion. The genus can reasonably be considered an ancient ectatommine relict, very restricted in distribution, and perhaps more readily analagous to the extinct Baltic Amber and Florissant ectatomtnines than to extant species. Incidentally, in addition to Bradoponera meieriHNS and Gnamptogenys europaeaHNS, the Baltic Amber fauna includes Electroponera dubia WheelerHNS, which might link the AcanthoponeraHNS / HeteroponeraHNS and EctatommaHNS / ParaponeraHNS lineages, according to Brown. In addition I have seen, courtesy of Drs. G. D. Dlussky and A. P. Rasnitsyn, an indubitably ectatommine male from the Miocene of Kirgiziya S.S.R., in Soviet Central Asia.
The presence of these extinct or extant palearctic relicts supports Brown's view that ectatommine evolution has occurred mainly on the larger continental land masses of Eurasia, North America, and perhaps Africa; with the various lineages successively retreating, under pressure from more recently evolved groups, into the peripheral southern land areas of Australasia and South America. This model satisfactorily explains the present distribution of GnamptogenysHNS and the less derived and more peripheral HeteroponeraHNS, especially in the Indo-Australian area. The absence today of epigaeic ectatommines in Eurasia, Africa and much of North America is explained as a result of their past retreat under pressure from the rising subfamily Myrmici-lae, which itself seems derived from an ectatommine stock, with the Baltic Amber Agroecomyrmex duisburgi MayrHNS providing a plausible intermediate. ProceratiumHNS and DiscothyreaHNS, unlike the epigaeic ectatommine genera, are both represented in North America, Eurasia (including Japan), and Africa, in addition to the other peripheral southern continents, where DiscothyreaHNS has its richest development. The recluse habits of these ants might explain their survival in areas which now lack, and perhaps have lost, epigaeic ectatommines. These were certainly once present in Eurasia and North America at least, as evidenced by the fossil record.
Despite the circumstances of its original collection, there is little reason to suppose that A. relictaHNS is a social parasite of Lasius emarginatusHNS, although its bionomics might include cleptobiosis or lestobiosis, and the clypeal structure could be related to the latter.
The desirability of collection and study of further material of this exceptional ant provides a great challenge to Soviet myrmecology.