Myrmecia imaii Taylor, 2015, sp.n.

Myrmecia imaii sp.n.

(Figs 19–21)

Myrmecia imaii is known only from extreme southwest WA: south and SE of Perth, east to Esperance, seldom more than a few km from the coast.

Type locality. North of Denmark, Western Australia (-34 8, 117 21).

Type deposition. Holotype and paratypes in ANIC, paratypes or type-compared vouchers in AMSA, MVMA, QMBA, SAMA, WAMA, TMHA) and in BMNH, CASC, MCZC, MHNG.

Material examined, distribution. Known only from extreme southwest WESTERN AUSTRALIA: Albany (- 34.59.290, 117.42.246) SB, Oct 2006; TG, 7/ii/1947; Denmark (-34.50.032, 117.24.430) SB, Oct 2006; TG, 7/xi/ 1947; N. Solomon, 23/i/1935 (MVMA); 11 mi. N of Denmark [-34 50, 117 24±11km], 24/x/1969, RWT; N of Denmark (Type Locality) HI89–005 –007, HI89–009, HI91–001–003, 0 0 5, 008; W of Denmark HI91–008; Esperance (-33.51.540 121.51.025) SB, Oct 2006; Esperance Airport, near Gibson [-33 39, 121 49], HTI&RWT; Jakkawilla (-34.38.256 118.2243), SB Oct 2006; Keynton, near Mount Mehniup [-34 58, 117 1], 28/ix/1969, RWT; 10mi. E of Nornalup, (-34 59, 116 49), 17/ii/1958, EFR; Porongurup National Park (-34.40.32, 117.52.164) 24/x/ 1969, 60m, RWT (accs 69/403, 407, 408); Porongurup Range [-34 41, 117 53], HI91–005; Telegraph Hill/ Dempster Head [-33 53, 121 54], HTI&RWT; N of Walpole [-34 59, 116 44], 350m, 25/x/1969, RWT. JACP records may be identified above by their HI codes.

This is the species recorded as Promyrmecia pilosula by Clark (1951) from Albany (confirmed by MVMA voucher specimens), Denmark and Mundaring [-31 54, 116 10], the last locality extends the range indicated by the above records, and was a prime collecting site to Clark (who collected ants widely in the south-west, where he resided for many years). He commented that this species “is quite common in Albany and surrounding district, but it is rare further north” (1951: 204).

Worker diagnosis. General features as illustrated and in key couplets 1–4 above. The brassy cephalic pubescence is more diffuse and less evident than in M. banksi, and the middle and hind tibiae are consistently medium to dark brown, with the tarsi a shade lighter. Local identification remains straightforward as long as M. imaii remains the only species of the M. pilosula complex found in WA.

Dimensions. (Holotype, smallest paratype, largest paratype (mm): TL = ca 13.40, 12.00, 14.46; HW = 2.68, 2.32, 2.79; HL = 2.49, 2.16, 2.59; CI = 107, 107, 107; EL = 0.99, 0.88, 1.01; OI = 37, 38, 36; SL = 2.15, 1.93, 2.17; SI = 80, 83, 77; PW = 1.63, 1.43, 1.70; WL = 3.90, 3.33, 4.06; PetW = 1.07, 0.85, 1.08; PpetW = 1.64, 1.27, 1.65.

Etymology. Named for Hirotami T. Imai celebrating long friendship; to commend his leadership of the JACP project, his distinguished research on the karyology of Myrmecia species and other ants, his important “Minimum Interaction Hypothesis” for the evolution of chromosome numbers in animals and his productive stewardship of the Japanese Ant Database Group (2003).

Karyology. The basic karyotype, 2K=6A +2A m(2n=8) differs strongly from those of other species reviewed above. Two independent AM inversions on chromosomes 1 and 2 were described in detail by Imai, Taylor et al. (1994: 146, Fig 5 c–g). Complicated chromosome polymorphisms accompanying chromosome number reduction (2n=8>7> 6) by AM inversion, centric fission and centric fusion were also observed between chromosomes 1L and 4 and between chromosomes IS and 3. Despite this complexity the authors considered all examined specimens to be conspecific.

Discussion. All records of M. imaii are from the “High Rainfall” and “SE Coastal Provinces” of the “South Western Australian Floristic Region” defined by Hopper and Gioia (2004) and Hopper et al. (1996). Heterick (2009) reported the species from the recognized Botanical Districts of Esperance Plains, Jarrah Forest, Mallee and Warren. The fact that its relatives at species-complex level are of eastern Australian provenance implies that Jackjumpers must previously have ranged or dispersed across southern Australia. The M. imaii progenitors were likely first geographically isolated in the west by incursion of inhospitable arid habitat across the early Nullarbor Plain, which is variously estimated to have occurred between 50 and 30 million years ago (Frakes, 1999; Nelson, 1996). The M. pilosula clade must therefore have originated no later than early Oligocene. This argument precludes the (unlikely?) possibility that Jack-jumper stock reached Southwest WA from the east since Oligocene times by a later dispersal event across increasingly-extending unsupportive Nullarbor habitat, and fully accords with well-accepted current hypotheses regarding the origins and isolation of the exceptional, highly endemic southwestern WA flora (see Hopper and Gioia, 2004; Hopper et al. 1996). The closest contemporary geographical records of a related eastern species are those of M. pilosula in South Australia east of Spencer Gulf.

Research prospects. Sociobiological and genetical investigation of this long-time geographically-isolated species, versus its eastern relatives, is desirable.