Gesomyrmex

Gesomyrmex Temporal range: 48.6–0 Ma K Pa Eo Ol Mi Pl Eocene – Recent
Gesomyrmex chaperi
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Hymenoptera
Family:	Formicidae
Subfamily:	Formicinae
Tribe:	Gesomyrmecini
Genus:	Gesomyrmex Mayr, 1868
Type species
Gesomyrmex hoernesi
Diversity
7 species 11 fossil species (Species Checklist, Species by Country) Gesomyrmex chaperi Specimen Label
Synonyms
Dimorphomyrmex André, 1892 Gaesomyrmex Dalla Torre, 1893

Evolutionary Relationships

Formicinae Myrmelachistini   (2 genera) Lasiini   (10 genera) Melophorini   (9 genera) Formicini   (8 genera) Gesomyrmex   (7 species) Oecophylla   (15 species) Plagiolepidini   (9 genera) Gigantiops, Myrmoteras, Santschiella Camponotini   (8 genera)

Based on Ward et al. 2016.

A poorly known resident of tree canopies in Oriental tropics, showing a striking diversity of caste morphologies. Queens and supersoldiers share an elongate head with powerful mandibles, an adaptation to chew an entrance tunnel to the innermost pith of living branches (Peeters et al. 2017).

Photo Gallery

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  Gesomyrmex chaperi worker from Vietnam
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  Supersoldier, soldier, workers and brood of Gesomyrmex sp. From Danum, Sabah. Photo © Christopher Wilson.
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  Two size classes of Gesomyrmex sp. soldiers (above), and workers (Sabah colony). Pupae are naked (Wheeler 1923a), thus cocoons have been lost as in Oecophylla. Photo by Christopher Wilson.
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  Gesomyrmex sp. from Baltic amber. Photo by Levon Biss.
• 

  A Baltic amber fossil.

Identification

Workers of the genus are easily recognised by the following features: elongated compound eyes; antennal scape passing below the eye; masticatory margin of mandible with more than four teeth (Bolton, 1994). The workers have 8-jointed antennae and soldiers of Gesomyrmex chaperi have 9-jointed antennae (Wheeler, 1916), whereas females have 10-jointed antennae Dubovikov (2004).

Gary Alpert is of the opinion that all described species belong to Gesomyrmex chaperi (the name with priority). Caste polymorphism has led to great taxonomic confusion, both in extant and fossil species. Marked colour variations further complicate alpha taxonomy. Wheeler (1929) already suggested that extant species may correspond to “sub-species or varieties”.

The genus is similar to Santschiella: two very large eyes, widely separated antennal insertions, and scapes that pass below the eyes.

See images of species within this genus

 

Distribution

Fossils

Fossils are known from: Baltic amber (Bartonian, Middle to Late Eocene), Bitterfeld amber (Bartonian, Middle to Late Eocene), Bol’shaya Svetlovodnaya, Sikhote-Alin, Russia (Priabonian, Late Eocene), Danish-Scandinavian amber (Bartonian, Middle to Late Eocene), Eckfeld, Germany (Lutetian, Middle Eocene), Messel, Germany (Lutetian, Middle Eocene), Oise amber, France (Ypresian, Early Eocene), Radoboj, Croatia (Burdigalian, Early Miocene), Rovno amber (Priabonian, Late Eocene).

Biology

From Peeters et al. (2017) Gesomyrmex chaperi presents an intriguing division of labour: workers are the active hunters, with very distinct mandibles. Queens (as well as two kinds of soldiers) have different mandibles, indicating that they do not hunt during colony foundation. However, a foundress needs to chew an entrance tunnel through living wood, and then block this nest entrance for many months until the colony is strong enough to produce the first soldiers. Supersoldiers are presumably reared even later in colony ontogeny, because they are more costly. Relatively few supersoldiers are present and they show two queen-like behaviours: they stay inside nest chambers and block the entrances, and they chew entrance holes when starting other nests belonging to the same colony. Supersoldiers also store nutrients (trophic eggs) in their gaster.

Gesomyrmex nest entrance. Photo by Decha Wiwatwitaya

Gesomyrmex nest in the very center of the heartwood in living branches of small diameter. Photo by Decha Wiwatwitaya

To access this secure innermost pith, the founding queen needs to chew an entrance tunnel. Photo by Decha Wiwatwitaya

Supersoldier head blocking the entrance. Photo by Decha Wiwatwitaya

Dubovikov (2004) - Members of this genus are very rare and ancient forms. The population of their nests are small and they live in small branches of trees (Cole, 1949b). Identification key to five living Gesomyrmex species was published by Cole (1949a).

Castes

In addition to winged queens, three sterile castes can be distinguished using discrete morphological traits, morphometry and total body size (Peeters et al. 2017). Observations of behaviour are challenging in tree canopies, and functional morphology can be used to predict the specialised functions of different castes.

Heads of all four castes of Gesomyrmex sp. shown at different scales (A: worker, B: soldier, C: supersoldier (all from Sabah colony); D: queen from Ulu Gombak). Note differences in ocelli, clypeus, mandibles and frontal lobes (covering the antennal sockets). Photo by Mônica Antunes Ulysséa

Morphology

Worker Morphology

• Antennal segment count: 8 in worker, 10 in queen
• Antennal club: gradual
• Palp formula: 6,4
• Total dental count: 6-10
• Spur formula: 1 simple, 1 simple; 0, 0
• Eyes: present
• Scrobes: absent
• Caste: polymorphic
• Sting: absent

Male Morphology

 • Antennal segment count 11 • Antennal club 0 • Palp formula 6,4 • Total dental count 1 • Notes: from literature

Nomenclature

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

• GESOMYRMEX [Formicinae: Gesomyrmecini]
  • Gesomyrmex Mayr, 1868c: 50. Type-species: †Gesomyrmex hoernesi, by monotypy.
  • Gesomyrmex senior synonym of Gaesomyrmex: Forel, 1893a: 167.
  • Gesomyrmex senior synonym of Dimorphomyrmex: Wheeler, W.M. 1929a: 1.
• DIMORPHOMYRMEX [junior synonym of Gesomyrmex]
  • Dimorphomyrmex André, 1892b: 49. Type-species: Dimorphomyrmex janeti (junior synonym of Gesomyrmex chaperi), by monotypy.
  • Dimorphomyrmex junior synonym of Gesomyrmex: Wheeler, W.M. 1929a: 1.
• GAESOMYRMEX [junior synonym of Gesomyrmex]
  • Gaesomyrmex Dalla Torre, 1893: 175, unjustified emendation of Gesomyrmex.
  • Gaesomyrmex junior synonym of Gesomyrmex: Forel, 1893a: 167.

Dubovikov (2004) - The genus Gesomyrmex was established by G. Mayr (1868) for a single species from Baltic amber (Lower Oligocene). The four extant species (Gesomyrmex chaperi, Gesomyrmex howardi, Gesomyrmex kalshoveni and Gesomyrmex spatulatus) are known only from workers. Gesomyrmex luzonensis and Gesomyrmex tobiasi were described from lone queens.

Ward et al. (2016) - The tribe Gesomyrmecini is here restricted to Gesomyrmex and two similar fossil taxa (Wheeler 1915). Bolton (2003) also placed Santschiella in Gesomyrmecini, but the molecular results do not support a close relationship between Gesomyrmex and Santschiella (Blaimer et al. 2015). The similarities between the two—very large eyes, widely separated antennal insertions, and scapes that pass below the eyes (Bolton 2003)-must be interpreted as due to convergence.

References

• Agosti, D. 1991. Revision of the oriental ant genus Cladomyrma, with an outline of the higher classification of the Formicinae (Hymenoptera: Formicidae). Syst. Entomol. 16: 293-310. (page 295, Gesomyrmex in Formicinae, Formica genus group)
• Ashmead, W. H. 1905c. A skeleton of a new arrangement of the families, subfamilies, tribes and genera of the ants, or the superfamily Formicoidea. Can. Entomol. 37: 381-384 (page 384, Gesomyrmex in Gesomyrmicinae, Gesomyrmicini)
• Bolton, B. 1994. Identification guide to the ant genera of the world. Cambridge, Mass.: Harvard University Press, 222 pp. (page 50, Gesomyrmex in Formicinae, Gesomyrmecini)
• Bolton, B. 2003. Synopsis and Classification of Formicidae. Mem. Am. Entomol. Inst. 71: 370pp (page 108, Gesomyrmex in Formicinae, Gesomyrmecini)
• Cole, A. C., Jr. 1949a. A study of the genus Gesomyrmex Mayr, and a description of a species new to the genus (Hymenoptera: Formicidae). Ann. Entomol. Soc. Am. 42: 71-76. (page 71, Revision of genus)
• Dalla Torre, K. W. von. 1893. Catalogus Hymenopterorum hucusque descriptorum systematicus et synonymicus. Vol. 7. Formicidae (Heterogyna). Leipzig: W. Engelmann, 289 pp. (page 175, Gesomyrmex in Camponotinae)
• Dubovikoff, D.A. 2004a. A new species of the genus Gesomyrmex Mayr, 1868 (Hymenoptera: Formicidae) from Vietnam. Trudy Russkogo Entomologicheskogo Obshchestva. 75(1):219-221. (page 220, queen described) PDF
• Donisthorpe, H. 1943g. A list of the type-species of the genera and subgenera of the Formicidae. [part]. Ann. Mag. Nat. Hist. 11(10): 617-688 (page 647, Gesomyrmex in Formicinae, Dimorphomyrmecini)
• Dlussky, G. M., T. Wappler and S. Wedmann. 2009. Fossil ants of the genus Gesomyrmex Mayr (Hymenoptera, Formicidae) from the Eocene of Europe and remarks on the evolution of arboreal ant communities. Zootaxa 2031: 1-20.
• Emery, C. 1895l. Die Gattung Dorylus Fab. und die systematische Eintheilung der Formiciden. Zool. Jahrb. Abt. Syst. Geogr. Biol. Tiere 8: 685-778 (page 772, Gesomyrmex in Camponotinae, Oecophyllini)
• Emery, C. 1925b. Revision des espèces paléarctiques du genre Tapinoma. Rev. Suisse Zool. 32: 45-64 (page 47, Gesomyrmex senior synonym of Gaesomyrmex; Gesomyrmex in Formicinae, Dimorphomyrmecini)
• Forel, A. 1878c. Études myrmécologiques en 1878 (première partie) avec l'anatomie du gésier des fourmis. Bull. Soc. Vaudoise Sci. Nat. 15: 337-392 (page 367, Gesomyrmex in Camponotinae [Camponotidae])
• Forel, A. 1893b. Sur la classification de la famille des Formicides, avec remarques synonymiques. Ann. Soc. Entomol. Belg. 37: 161-167 (page 167, Gesomyrmex senior synonym of Gaesomyrmex; page 165, Gesomyrmex in Camponotinae, Camponotini)
• Forel, A. 1912j. Formicides néotropiques. Part VI. 5me sous-famille Camponotinae Forel. Mém. Soc. Entomol. Belg. 20: 59-92 (page 89, Gesomyrmex in Camponotinae, Gesomyrmecini)
• Forel, A. 1917. Cadre synoptique actuel de la faune universelle des fourmis. Bull. Soc. Vaudoise Sci. Nat. 51: 229-253 (page 249, Gesomyrmex in Camponotinae, Gesomyrmecini)
• Mayr, G. 1868c. Die Ameisen des baltischen Bernsteins. Beitr. Naturkd. Preuss. 1: 1-102 (page 50, Gesomyrmex in Formicinae [Formicidae])
• Peeters C, Ito F, Wiwatwitaya D, Keller R, Hashim R & Molet M. 2017. Striking polymorphism among infertile helpers in the arboreal ant Gesomyrmex. Asian Myrmecology 9: e009015 (1-15) PDF
• Vankerkhoven, F., Hendrickx, H. & Dekoninck, W. 2008. A well preserved fossil in Baltic amber of the enigmatic genus Gesomyrmex Mayr, 1868 (Hymenoptera: Formicidae). Bulletin de la Société Royale Belge d'Entomologie 145:87-90.
• Ward, P.S., Blaimer, B.B., Fisher, B.L. 2016. A revised phylogenetic classification of the ant subfamily Formicinae (Hymenoptera: Formicidae), with resurrection of the genera Colobopsis and Dinomyrmex. Zootaxa. 4072(3):343–357. (doi:10.11646/zootaxa.4072.3.4).
• Wheeler, W. M. 1910b. Ants: their structure, development and behavior. New York: Columbia University Press, xxv + 663 pp. (page 143, Gesomyrmex in Camponotinae, Oecophyllini)
• Wheeler, W. M. 1915i [1914]. The ants of the Baltic Amber. Schr. Phys.-Ökon. Ges. Königsb. 55: 1-142 (page 107, Gesomyrmex in Camponotinae, Gesomyrmecini)
• Wheeler, W. M. 1922i. Ants of the American Museum Congo expedition. A contribution to the myrmecology of Africa. VII. Keys to the genera and subgenera of ants. Bull. Am. Mus. Nat. Hist. 45: 631-710 (page 697, Gesomyrmex in Formicinae, Gesomyrmecini)
• Wheeler, W. M. 1929a. The identity of the ant genera Gesomyrmex Mayr and Dimorphomyrmex Ernest André. Psyche (Camb.) 36: 1-12 (page 1, Gesomyrmex senior synonym of Dimorphomyrmex; page 12, Gesomyrmex in Formicinae, Gesomyrmecini)
• Wheeler WM, 1929b. Note on Gesomyrmex. Psyche (Camb.) 36: 91 – 92.
• Wheeler WM, 1930. A second note on Gesomyrmex. Psyche (Camb.) 37: 35 – 40.