Myrmecia pilosula species complex

BAsed on: Taylor, R.W. 2015. Ants with Attitude: Australian Jack-jumpers of the Myrmecia pilosula species complex, with descriptions of four new species (Hymenoptera: Formicidae: Myrmeciinae). Zootaxa. 3911:493–520. doi:10.11646/zootaxa.3911.4.2


 * Myrmecia banksi
 * Myrmecia croslandi
 * Myrmecia haskinsorum
 * Myrmecia imaii
 * Myrmecia impaternata
 * Myrmecia pilosula

Key to Myrmecia pilosula complex species

The Myrmecia pilosula complex was defined by Ogata and Taylor (1991) as a section of the species group of M. pilosula Fr. Smith 1858. There are six component species, four of which are described here as new. In addition, M. pilosula comprises two newly recognized geographical races. These sometimes common ants are known to Australians variously as “Jack-jumpers, “Jackie-Jumpers, “Jumping Jacks, “Jumper Ants", “Black Jumpers" or “Hopper Ants. Myrmecia imaii is apparently endemic to southwest Western Australia (WA) and the other species are collectively distributed in a zone extending from extreme SE Queensland (QLD), south along the Great Dividing Range and its flanks in eastern New South Wales (NSW), the Australian Capital Territory (ACT), Victoria (VIC) and Tasmania (TAS), ranging from sea level to the high slopes of Mt Kosciuszko (2, 228m) and the Tasmanian mountains; thence from SE Victoria westwards to SE South Australia (SA) and Kangaroo Island. The nearest records of an eastern species to the distributional range of M. imaii are those for M. pilosula in SA east of Spencer Gulf, an overland distance of over 2, 000km.

Because of close interspecific similarity relevant museum specimens were previously often labeled or placed in collections as “Myrmecia pilosula”, as if representing a single biological species. Various authors (e.g. Wheeler, 1933; Clark, 1943, 1951; Haskins & Haskins, 1951; W. L. Brown, 1953; Taylor & D. R. Brown, 1985, Browning, 1987; Heterick, 2009) followed this portmanteau nomenclature, though sometimes aware that the action was not well supported (e.g. Browning, 1987). During this project specimens of all six species recognized here were found identified as M. pilosula in Australian public collections. Material in the Australian National Insect Collection (ANIC), Museum of Victoria (MVMA) and Queensland Museum (QMBA) labeled by Clark when compiling his revisions of Myrmecia and its erstwhile subgenus Promyrmecia (Clark, 1943, 1951), indicate that he identified as M. pilosula specimens assigned here to M. haskinsorum, M. imaii and both races of M. pilosula.

The view that “M. pilosula” was composite was eventually confirmed by the author’s discovery of two distinct sympatric species widely present in urban and suburban Canberra, including the CSIRO/ANIC Black Mountain site and the adjacent National Botanic Gardens, and a third species at higher elevations in the nearby Brindabella Ranges (taxa now recognized as M. croslandi, M. impaternata and the eastern race of M. pilosula), and by cytotaxonomic demonstration that there was diversity in “pilosula” chromosome numbers consistent with species differentiation: most notably that one species (M. croslandi) frequently possesses only a single pair of chromosomes (Imai, Crozier et al., 1977; Crosland and Crozier, 1986; Crosland et al., 1988; Taylor, 1991). In his unpublished PhD dissertation Browning (1987) separately concluded that “M. pilosula sens.lat. is a complex of sibling species with indistinguishable (sic!) workers”, basing this opinion on “the variety of nest structures”, his own cytotaxonomic studies, and the karyological work of Imai, Crozier et al. (1977) and Crosland and Crozier (1986).

Previous karyological and cytotaxonomic research has importantly illuminated this study (references below). Myrmecia, which comprises about 100 estimated species, is one of the most karyologically diverse of all investigated non-polyploid animal genera, with chromosome numbers ranging from 2n=2 in M. croslandi to 2n=84 in M. brevinoda Forel (Crosland and Crozier, 1986; Imai and Taylor, 1989)—a 42-fold difference, second only to the maximum known animal range of 48-fold in the scale insect genus Apiomorpha (Hemiptera: Coccoidea: Eriococcidae), which has 2n=4 to about 192 (Cook, 2000). 2n=2 is the lowest possible eukaryote value and in animals is unique to Myrmecia croslandi and the nematode Diploscapter coronata (Cobb), which also has 2n=2 (Hechler, 1968). Myrmecia covers much of the chromosome number range known for the order Hymenoptera, which has 2n=2 (Myrmecia croslandi) to 2n=94 (in the related monotypic Australian myrmeciine ant Nothomyrmecia macrops Clark), and a large part of the range for class Insecta (polyploids excepted), which comprises the known range for all arthropods (Imai, Taylor et al., 1990).

Some complexes of closely similar Myrmecia species are chromosomally very diverse. Four similar species of the M. piliventris F. Smith complex cover almost two thirds of the known hymenopteran chromosome number range, with 2n=4, 6, 34, 64 (Imai and Taylor, 1986). It seems likely that most of the other putative Myrmecia “species” considered to be morphologically variable will be found actually to comprise sets of “good” biological species, as in the pilosula complex.

Australian ants, especially species of Myrmecia, have from 1976 until recently been subject to karyological research by Japanese and Australian myrmecologists and geneticists working in association with Dr Hirotami T. Imai, formerly of the Japanese National Institute of Genetics, Mishima, the late Professor Ross H. Crozier (University of New South Wales: later at La Trobe University, Melbourne and James Cook University, Townsville) and the author (initially at CSIRO Division of Entomology, Canberra). This program is informally designated the “Japan/Australia Cooperative Ant Karyology Program” (JACP). Attention focused increasingly on the M. pilosula complex. Relevant papers include: Imai, Crozier et al., 1977; Imai, Taylor, Crosland et al., 1988; Imai, Taylor, Crozier et al., 1988; Crosland et al., 1988, Imai, Taylor et al., 1992, and others referred to below. The project continued with research on molecular genetics in which base sequences in Myrmecia ribosomal and mitochondrial DNA were compared (Hirai et al., 1994; Crozier et al., 1995), on the analysis of telomere sequences (Meyne et al., 1995) and on molecular phylogenetic analysis (Hasegawa & Crozier, 2006).

The purpose of this study is to provide a new species-level revision of the M. pilosula species complex, and to integrate these results with existing karyological knowledge.

The Myrmecia pilosula species complex
Diagnosis. Workers of the M. pilosula complex are easily recognized within Myrmecia (Ogata and Taylor, 1991). Relatively small species: total length, including mandibles, ranging overall from about 10 to 14 mm; mean size only slightly different in the separate species. Body color essentially uniformly dark blackish brown to black; mandibles, antennae, and frequently tarsi and/or tibiae reddish-orange; clypeus pale yellowish to light brown. Tip of apical antennomere flushed dark brown. Foreleg tarsi and tibiae in all known species prominently reddish-orange; coxae, trochanters and femora always darkly colored, approximately matching body color; no transverse dorsal preoccipital carina; a ventral secondary tooth present near mandibular apex; mandibular dentition complete along length of jaw, all teeth essentially symmetrically erect, none inclined asymmetrically towards the mandibular base.

General morphology General habitus as in the accompanying figures. Sculpturation generally similar among the species: mandibles smooth and shining, each dorsally with a few effaced apical longitudinal rugae. Head with longitudinal spaced striae separated by fine puncturation and effaced on the sides behind the eyes. Pronotum more strongly longitudinally striate than head, the nucal collar smooth to very finely transversely striate. Mesonotum similarly or more finely longitudinally striate than pronotum, varying to almost smooth, with a “leathery” appearance in several species due to superficial sculpturing, notably in both races of M. pilosula. Propodeal dorsum generally with a short anterior section bearing essentially longitudinal, often posteriorly divergent striate rugosity; the remainder transversely more strongly striate rugose. Petiolar dorsum ranging from almost smooth to quite strongly rugose, the intensity of sculpturation varying, but in most specimens approximately matching that of the mesonotum. In both races of M. pilosula the sculptural intensity in these areas varies allometrically and in concert. Postpetiole and gaster very finely and densely micropunctate, only moderately shining. The exposed anterior sections of the second and third gastral tergites (true abdominal segments 5 and 6), which each insert beneath the preceding tergite, minutely transversely striate and reflective.

Pilosity generally abundant on body and appendages, with the notable exception of M. haskinsorum (see key couplet 1 below); the hairs generally short and erect to suberect, longer and more flexuous on the underside and apex of the gaster, beneath the postpetiole and on the propleurae.

Pubescence generally very fine, often dense, varying in density and color interspecifically (generally either silvery grey or yellowish gold) as specified below in the species descriptions.

Human exposure
Urban Jack-jumpers are common in Hobart (M. pilosula (Western Race)), Canberra (M. croslandi, M. impaternata) and Adelaide (M. pilosula (Western Race)). They are less commonly represented in collections from Melbourne, with records of both races of M. pilosula and of M. croslandi, and poorly represented from Sydney, where there is only a single current record of M. banksi from Leumeah in the southeast of the city. There have been relatively few reports of Jack-jumper sting allergy from Sydney (B. Baldo, pers comm.) unlike Melbourne and especially Hobart, Adelaide and Canberra, so Jack-jumpers might not be well represented there. This was also the view of long-time Sydney resident Rev B.B. Lowery (pers comm.), who collected many Jack-jumper samples elsewhere (including all species recognized here). I have located few Melbourne urban records, but this is a possible artifact of inadequate collecting. Brisbane and Perth are, as far as known, outside the range of any species, though M. imaii is likely present in Perth.

In recreational bushland areas “Western” M. pilosula is common in the Adelaide Hills, the Grampians (VIC) and widely in Tasmania. The eastern race of M. pilosula is widespread in the NSW Snowy Mountains and associated ranges including the Victorian Alps, the Brindabella Ranges (ACT) and in the Blue Mountains west of Sydney.

Taxonomy of the primary JACP report and other papers
Imai, Taylor et al. (1994) and Crozier et al. (1995) recognized the species M. banksi, M. croslandi, M. haskinsorum and M. imaii precisely as defined here. The “scientific” names of these taxa, apart from M. croslandi, were then used prematurely (and with explanation) without the sanction of formal taxonomic publication. Nomenclature of these neglected species is rectified here, and this is their place of formal taxonomic publication. The name “M. pilosula s. str.” of the JACP publications was applied to the Western Race of that species as defined here. Other entities deemed speculatively in 1994 to represent hybrids between M. banksi (B) and M. pilosula (P) are assigned here to the Eastern Race of M. pilosula. These and the other “PB hybrids” of the above papers are allocated below as follows: (1) The Tasmanian P/PB–1 Mix and P/PB–2 Mix entities are assigned to the Western Race of M. pilosula; (2) PBF1–1 and PBF1–2 are “synonymous” with M. impaternata; and (3) PB–1 and PB–2 are identified as the Eastern Race of M. pilosula. Details are discussed in the following section and under the relevant species headings.