Myrmecia pilosula

Myrmecia pilosula is considered by Taylor (2015) to comprise two geographical races. M. pilosula (Western Race) includes all Jack-jumper specimens known from western Victoria, southeast mainland South Australia and Kangaroo Island. It occurs widely in Tasmania (from where M. pilosula was originally described) and is found there sympatric with Myrmecia haskinsorum at higher elevations. It is common in Tasmania from sea level to at least 1,000 meters.

The Eastern Race of Myrmecia pilosula is abundant at moderate to high elevations in components of the Great Dividing Range in eastern Victoria, eastern New South Wales and the ACT. Its most northern records are in the high ranges east of the New England Tableland in northern central-eastern New South Wales, including mile-high Point Lookout and nearby Cathedral Rock National Park. It has not been collected at lower elevations westward on the Tableland proper towards Armidale, where Myrmecia croslandi and Myrmecia impaternata are sympatrically common. In the southwest of its range M. pilosula (Eastern Race) is found in the vicinity of Melbourne, west to Ballarat across central Victoria and southeast to Mornington Peninsula, where its distributional range encounters that of the putatively conspecific Western Race.

Distribution
Taylor (2015) - M. pilosula (Eastern Race) is known to range southwards in NSW from the mountains east of the New England Tableland, along the Great Dividing Range and its flanks, including the Snowy Mountains, the Blue Mountains, and the Brindabella Ranges in the ACT, to the Victorian Alps and their slopes and the Gippsland coast in eastern Victoria. The known Victorian distribution carries westwards at least as far as Ballarat in the elevated country which extends the Great Dividing Range westwards across central Victoria north of Melbourne. This distribution evidently fails to carry approximately 120 km further west to the Grampians Range, SA, which is generally considered the western terminus of the East Australian Cordillera, because there the western putative race, M. pilosula (W), is exceptionally common at Halls Gap, its surrounds and elsewhere (as also southwards in the Hamilton district), and the Eastern Race of M. pilosula is unreported. Two damaged specimens from Ararat, Victoria (MVMA), not far northeast of The Grampians, are identified as M. pilosula (Eastern Race). There are records of the Eastern Race from the SE corner of Victoria near Mallacoota, westwards to the Mornington Peninsula.

Colonies of the two races of M. pilosula appear to intersperse in Victoria SE of Melbourne, on or immediately east of the Mornington Peninsula, which they enter from the east and west respectively.

The Western Race of M. pilosula is the only Jack-jumper taxon known from southern Victoria west of Port Philip Bay and contiguously from southeast SA east of Spencer Gulf, including Kangaroo Island. It is very common in the central and southwest districts of Victoria; spectacularly so in and around Halls Gap in the Grampians. Elsewhere in Victoria it is known from the Mornington Peninsula and in west Gippsland, where its range contacts or intersects the putatively conspecific Eastern Race. It is the only Jack-jumper species known from South Australia. Myrmecia pilosula (Western Race) is widespread in Tasmania, including King, Flinders and Bruny Islands. It appears to be absent from well surveyed Maria Island (testé B.B. Lowery).

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Biology
Taylor (2015) - Research prospects. Prospective research topics involving the Eastern and Western Races of M. pilosula include (1) genetical investigation of both races, to challenge the Tasmanian inrogression hypothesis discussed above, and to clarify whether these taxa are genuinely parapatric in distribution in Victoria; (2) investigation of the several implied Victorian areas of geographical range contact or intersection, with search for possible genetical introgression between the two taxa, notably in West Gippsland and areas between Ballarat and the Grampians, possibly also at other localities on the eastern flanks of Melbourne; (3) investigation of comparative bionomics of both taxa in contact versus non-contact zones; and (4) locating the distributions of these two races and other Jack-jumper species in the Melbourne area and greater Victoria, and of the Eastern Race in the ACT and surrounding NSW.

Karyology
Taylor (2015) - Chromosome numbers determined by Imai for M. pilosula (Western Race) (cited as “M. pilosula s. str.”) are given in Imai, Taylor et al., 1994, appendix, and illustrated in their fig. 7 (p. 149). The overall range is 2N=21 to 2N=30, with known haploid numbers N=10 to N=15. Both ranges have all intermediate values represented. Note that N=10 presumably indicates a likely minimum of at least 2N=20. Myrmecia pilosula (Western Race) exhibits less-prominent C banding than described above for M. pilosula (Eastern Race). It is also characterized by centric fission polymorphism (fission burst), versus fusion burst in the Eastern Race (Imai, pers comm. and in Imai, Taylor et al., 1994). This distinction is considered by Imai (pers comm.) and the author to provide adequate evidence that the two taxa could be separate biological (and thus nomenclatural) species. That conclusion was also supported by Crozier (pes comm).

Chromosome numbers determined for M. pilosula (Eastern Race) by Imai are given in Imai, Taylor et al., 1994, appendix. The overall range is slightly greater than in M. pilosula (Western Race), with 2N=18 to 2N=32 (with all intermediate values represented except 2N=27 and 2N=31), and with a single recorded haploid count of N=15. Karyologically M. pilosula (Eastern Race) is distinguished from M. pilosula (Western Race) by remarkably elongated C-band polymorphisms and chromosome arrangements involving centric fusion (fusion burst) (Imai, Taylor et al., 1994, fig. 11). Alternatively, “Fission burst’ characterizes the karyology of M. pilosula (Western Race).

Nomenclature

 *  pilosula. Myrmecia pilosula Smith, F. 1858b: 146 (w.q.m.) AUSTRALIA. Wheeler, G.C. & Wheeler, J. 1971d: 252 (l.); Imai, Crozier & Taylor, 1977: 345 (k.). Combination in M. (Halmamyrmecia): Wheeler, W.M. 1922b: 195; in M. (Promyrmecia): Wheeler, W.M. 1933i: 56; in Promyrmecia: Clark, 1943: 109; in Myrmecia: Brown, 1953j: 6. Senior synonym of ruginoda: Brown, 1953j: 6. See also: Crawley, 1926: 383; Clark, 1951: 202; Crosland, Crozier & Imai, 1988: 13; Ogata, 1991a: 361.
 * ruginoda. Ponera ruginoda Smith, F. 1858b: 93 (m.) AUSTRALIA. Crozier, 1970: 123 (k.). Combination in Ectatomma: Roger, 1861b: 168; in Rhytidoponera: Emery, 1911d: 38; in Myrmecia: Brown, 1953j: 6. Junior synonym of pilosula: Brown, 1953j: 6.

Description
Taylor (2015)

Worker
Eastern Race - General features as illustrated and in key couplets 1, 2, 5 & 6. Distinguished morphologically from the Western Race of M. pilosula largely by leg coloration (see key). Expression of this character-set in pilosula (Eastern Race) is generally similar to that of M. pilosula (Western Race) (see below), but the tibiae and tarsi are dull medium brown in color, lighter than the proximal leg segments, where those of M. pilosula (Western Race) are brightly reddish-brown, much like the fore-tarsi. The color difference between these forms is clearly distinguishable even in old, dry cabinet specimens. They correlate exactly with the karyological differences distinguishing the two taxa.

Sculpturation of large individuals is more intensely developed than in small specimens, with gradation in intermediate series. Large workers can be similar to those of Myrmecia croslandi (including details of leg coloration) and readily misidentified (see couplet 6 in the key to species above). Such specimens can most confidently be identified if associated with smaller nest mates or field associates. Single, unassociated large workers can be problematic.

(Holotype, smallest paratype, largest paratype (mm): TL = 1 27, 10.27, 12.26; HW = 2.28, 2.04, 2.37; HL = 2.07, 1.81, 2.14; CI = 110, 112, 111; EL = 0.86, 0.79, 0.92; OI = 38, 39, 38; SL = 1.91, 1.65, 1.93; SI = 84, 81, 81; PW = 1.42, 1.18, 1.53; WL = 3.28, 3.02, 3.47; PetW = 0.86, 0.68, 0.87; PpetW = 1.38, 1.10, 1.38.

Western Race - General features as illustrated and in key couplet 1, 2 & 5. Morphologically distinguished from the Eastern Race of M. pilosula largely by leg coloration, and otherwise by convincing karyological differences. Here all coxae and trochanters are typically dark brown, slightly paler but almost matching the body tagmata. The femoral apices are briefly flushed reddish-orange, slightly more so on the forelegs, and all tibiae and tarsi are similarly colored reddish-orange. That color is brightly clear in life, and usually somewhat faded in cabinet specimens. The recognition of faded museum specimens like the M. pilosula lectotype (see above) versus those of M. pilosula (Eastern Race), which has brown tibiae and tarsi, is however not usually compromised.

Sculpturation is more intense in large individuals than in small specimens, with intermediate gradation. In this regard large workers can resemble those of M. croslandi. The leg coloration in croslandi however resembles that of the Eastern Race of M. pilosula (with brown hind tibiae – see above) enabling distinction of pilosula. Specimens of large workers of both races of M. pilosula can most confidently be discriminated from M. croslandi if accompanied by smaller nest mates or conspecific field associates. Single large workers can be problematic.

Dimensions of the smallest and largest available Tasmanian workers are (mm: TL = 10.31, 13.97; HW = 2.04, 2.63; HL = 1.81, 2.36; CI = 89, 90; EL =0.80, 0.97; OI = 39, 37; SL = 1.65, 2.12; SI = 81, 81; PW = 1.22, 1.70; WL = 3.06, 3.99; PetW = 0.69, 1.04; PpetW = 1.11, 1.55. These dimensional ranges also apply to mainland specimens examined.