Myrmecia croslandi

Individuals may have a single pair of chromosomes. Myrmecia croslandi (along with the locally less frequent M. impaternata) is common in Canberra parks, gardens, suburban grass lawn roadside “nature strips” and in grassy bushland. Nests of the two species are sometimes found only meters apart. Croslandi was found similarly common at localities near Armidale, NSW in Dec/Jan. 1995–96 and Nov. 1999 by JACP collectors. It is also sympatric there with M. impaternata. Several records confirm the presence of this species in SE Queensland.

Distribution
Myrmecia croslandi was described initially from the ACT, nearby NSW and Warrandyte South, VIC. It is now known also from the New England Tablelands in northeastern NSW and upland localities on the Darling Downs of SE QLD, from Glen Innes in northeastern NSW, and from near Cobangra, VIC.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Biology
Sympatric variously with Myrmecia impaternata and Eastern Myrmecia pilosula, and with Myrmecia haskinsorum (and Eastern pilosula) at Corang River Bridge (-35 12, 150 03). Most known records of M. impaternata were taken in sympatry with M. croslandi.

Morphology
Myrmecia use their large eyes to locate prey and to find their way back to the nest from their foraging forays. Ogawa et al. (2015) wanted to know how complex the color reception in ants may be and they felt M. croslandi was a good candidate for exploring this question. They provided evidence about photoreceptors in M. croslandi and Myrmecia vindex that show ants can have sophisticated trichromatic color reception. Their abstract (Ogawa et al. 2015): Ants are thought to be special among Hymenopterans in having only dichromatic colour vision based on two spectrally distinct photoreceptors. Many ants are highly visual animals, however, and use vision extensively for navigation. We show here that two congeneric day- and night-active Australian ants have three spectrally distinct photoreceptor types, potentially supporting trichromatic colour vision. Electroretinogram recordings show the presence of three spectral sensitivities with peaks (lmax) at 370, 450 and 550 nm in the night-active Myrmecia vindex and peaks at 370, 470 and 510 nm in the day-active Myrmecia croslandi. Intracellular electrophysiology on individual photoreceptors confirmed that the night-active M. vindex has three spectral sensitivities with peaks (lmax) at 370, 430 and 550 nm. A large number of the intracellular recordings in the night-active M. vindex show unusually broad-band spectral sensitivities, suggesting that photoreceptors may be coupled. Spectral measurements at different temporal frequencies revealed that the ultraviolet receptors are comparatively slow. We discuss the adaptive significance and the probability of trichromacy in Myrmecia ants in the context of dim light vision and visual navigation.

Karyology
Taylor (2015) - Workers and queens in some colonies have the minimum possible eukaryote chromosome count of 2N=2. Myrmecia croslandi is widely celebrated as the only animal other than the nematode Diploscapter coronata known to possess a single pair of chromosomes. Imai & Taylor (1989) reported that its chromosome numbers in fact vary, ranging 2n=2, 3 or 4, and that croslandi demonstrates highly complicated chromosome polymorphisms, including telomere fusion, shift of centromeric activity by centromeric inactivation, salutatory growth of constitutive heterochromatin (C+), and AM inversion. Typical croslandi karyotypes with 2n=2 (2K=2Mci), and 2n=3 (2K=lAc+1M+1Mci) were illustrated by Imai, Taylor et al. (1994, figs 5a, 5b), and karyological details discussed by Imai, Hirae et al. (1992).

Determination Clarifications
It was discussed as “M. pilosula” by Crosland and Crozier (1986), and as “M. (pilosula) n=1” by Imai & Taylor (1989).

Nomenclature

 *  croslandi. Myrmecia croslandi Taylor, 1991c: 288 (w.k.) AUSTRALIA. Imai, Taylor & Crozier, 1994: 145 (k.).

Worker
Taylor (2015) - General features as illustrated and in key couplets 1, 2, 5 & 6. Distinguished from other pilosula-complex species by its robust form, more massive petiolar node, especially versus representatives of the two races of Myrmecia pilosula (compare Figures) and other details, as specified in the key. Middle and hind tibiae medium brown, matching the femora, the tibial apices minutely lightly infuscated at the bases of the reddish-orange spurs. Larger workers of both races of M. pilosula often closely resemble those of Myrmecia croslandi. Western M. pilosula is then distinguishable by its reddish-orange hind tibiae (see below under that species), but Eastern M. pilosula and M. croslandi are essentially identical in leg coloration (see key couplet 6 for their discrimination).

The holotype and smallest and largest available specimens have the following dimensions (mm): TL = 13.54, 12.46, 13.53; HW = 2.63, 2.54, 2.79; HL = 2.35, 2.37, 2.51; CI = 112, 107, 111; EL =1.02, 1.02, 1.08; OI = 39, 40, 39; SL = 2.02, 1.99, 2.06; SI = 77, 78, 74; PW = 1.70, 1.60, 1.81; WL = 3.88, 3.73, 4.06; PetW = 1.06, 0.93, 1.14; PpetW = 1.59, 1.43, 1.69.

Etymology
Named for Michael W. J. Crosland, who as a student of R. H. Crozier at the University of New South Wales, Sydney, discovered the 2n=2 chromosome count while experimenting with the Crozier/Imai air-drying technique of chromosome preparation for microscopy (to great initial consternation that the technique had failed, but later celebration). Crosland had collected the subject specimens shortly before at Tidbinbilla Nature Reserve near Canberra.