Metapone jacobsoni Crawley, 1924

Taylor, Robert W. & Alpert, Gary D., 2016, The myrmicine ant genus Metapone Forel (Hymenoptera: Formicidae): a global taxonomic review with descriptions of twelve new species, Zootaxa 4105 (6), pp. 501-545 : 518-520

9. Metapone jacobsoni Crawley, 1924

( Figs 42–46 )

Metapone jacobsoni Crawley, 1924: 389 —Gyne; Type locality: Fort de Kok (now Bukittingii— 0°18′20″S, 100°22′9″E), Sumatra, Indonesia.

= Metapone nicobarensis Tiwari and Jonathan, 1986:150, Fig.1 —Worker, Gyne; Type locality: Rajendra Nagar, Nicobar Is [07°N, 93°E], India (NEW SYNONYMY).

Distribution, material examined. M. jacobsoni is represented here by its holotype and a single paratype, both alate gynes (BMNH). Labels: Holotype: (1) red, printed “ Type ”; (2) white handwritten “No 153”; (3) white, printed “Fort de Kok (Sumatra), 920m, October 1922, leg. E. Jacobson”; (4) white handwritten “ Metapone jacobsoni Cr. , Type ”. Paratype: (1) white handwritten “12/13”; (2) blue printed “Cotype”; (3) white handwritten “E. Jacobson, Fort de Kok, (Gad Boven I), Sumatra, iv 1914; (4) white handwritten “ Metapone jacobsoni Crawley Cotype ”. Comparison confirms their conspecificity.

Worker diagnosis. General features as in original description ( Crawley, 1924), the key above to Asian Metapone species and the relevant Figures. Posterior face of subpetiolar process in oblique view relatively large, triangular; subpetiolar angle in side view approximately a right angle, not spinose; subpetiolar lamella opaque, approximately equilaterally triangular (note that the petiole could not be viewed unobstructed in true profile for illustration; its somewhat obscure outline is highlighted in Fig 45 ). Other features are adequately illustrated here.

Dimensions (holotype, paratype): TL: 8.5, 8.75; HL: 1.48, 1.44; HW (across eyes): 1.00, 1.04; Maximum eye length: 0.42, 0.38; CI: 68, 72; MSL: 2.26, 2.30; PMW: 0.92, 0.94; PDW: 0.70, 0.72; PetL: 0.56, 0.60; PetW: 0.44, 0.46; PetH: 0.72, -; PpetL: 0.44, -; PpetW: 0.58, 0.58.

The junior synonymy of Metapone nicobarensis: The M. nicobarensis types were said at description to have been deposited in the entomological collection of the Zoological Survey of India, Calcutta. Curator Dr S. Sheena, searching on our behalf, has however been unable to locate them.

Dimensions of the worker holotype cited (inter alia) in the original description are: TL (as Body Length): 6.1; HL: 1.4; HW: 1.05; CI: 75; PMW (as Pronotum Width): 0.59; PetL (as Petiolar Node Length): 0.5; PetW (as Dorsal Petiolar Width): 0.56; PetH (as Petiole Height): 0.84; PpetL (as Postpetiolar Node length): 0.42; PpetW (as Dorsal Postpetiolar Width): 0.59; PpetH (as Postpetiole Height): 0.63. Those for the paratype gyne are: TL (as Body Length): 8.6; HL: 1.26; HW: 0.91; CI: 72; PMW (as Pronotum Width): 0.7; PetL (as Petiolar Node Length): 0.56; PetW (as Dorsal Petiolar Width): 0.49; PetH (as Petiole Height): 0.56; PpetL (as Postpetiolar Node length): 0.49; PpetW (as Dorsal Postpetiolar Width): 0.59; PpetH (as Postpetiole Height): 0.56.

M. nicobarensis was originally described and illustrated as having a “weak anterior (clypeal) lobe” (our italics), and thus to lack a rostrate median anterior clypeal projection of the type seen in workers and gynes of several other known Asian Metapone species. This character immediately distinguishes it from the Sri Lankan, M. greeni (compare Tiwari and Jonathan’s figs 1a and 1c with Figs 16–20 here). Other Asian taxa lacking strong clypeal projections include the very differently sculptured Philippines taxa M. gracilis and M. bakeri .

Consideration of the jacobsoni and nicobarensis descriptions and the jacobsoni type specimens suggests these taxa to be essentially identical. We are unable on available evidence to differentiate them, and therefore consider M. nicobarensis probably to be a junior synonym of M. jacobsoni . The discrepancy in promesonotal width measurements between their gyne types cited above are probably due to differences in the parameters used for measurement.

If this assessment is correct, M. jacobsoni seems more likely to be introduced than native on Great Nicobar Island, and Sumatra is the most likely ancestral source for the island population. The two lands are separated by less than 200km of open ocean, across which there must have been much past human passage in small boats, perhaps often carrying unmilled (fire)wood, possibly facilitating introduction. The new synonymy is thus considered biogeographically plausible.

Figures

FIGURES 42 – 46. Metapone jacobsoni, holotype gyne, see text for dimensions.

FIGURES 1 – 4. Metapone madagascarica, holotype worker, see text for dimensions.

FIGURES 16 – 20. Metapone greeni, syntype worker, HW 1.01, PMW 0.82, MSL 1.56; FIGURES 21 – 23 gyne (M. johni syntype), HW 1.74, PMW 1.02, MSL 2.90.