Ectatomma parasiticum

A social parasite that preys on Ectatomma tuberculatum

Identification
Feitosa et al. (2008) - Size relatively small (WL approximately 3.80 mm); clypeus and frontal area without sculpture; antennal scapes longer than the maximum head width (SI > 108); petiole relatively thick in lateral view.

Gynes of the socially parasitic Ectatomma parasiticum can be distinguished from the gynes of its host species, Ectatomma tuberculatum, by the following features: sparser sculpture on the body; smaller size (Fig. 2), with WL approximately 3.80 mm (around 5.40 mm in E. tuberculatum); clypeus and frontal area devoid of any sculpture (usually longitudinally striate in E. tuberculatum); antennal scapes longer than the maximum head width, with SI > 108 (< 99 in E. tuberculatum); propodeal spines reduced to minute teeth; and petiole thicker in lateral view (flattened anteroposteriorly in E. tuberculatum). The reduced size and widener petiole of E. parasiticum are also characteristic of the inquiline syndrome in other ant species (Wilson 1984; Radchenko & Elmes 2003).

Distribution
Up to now, the occurrence of this species is restricted to Apazapan, state of Veracruz, Mexico. However, its host, E. tuberculatum, is widely distributed in the Neotropics, from Mexico to northern Argentina. We expect that the excavation and detailed examination of E. tuberculatum colonies in different localities could reveal new populations of E. parasiticum. (Fetosa et al. 2008)

Distribution based on Regional Taxon Lists
Neotropical Region: Mexico.

Biology
Fetosa et al. (2008) - Males produced by parasitized colonies were of a uniform morphology and indistinguishable from males of Ectatomma tuberculatum. Thus it remains unknown if males of E. parasiticum are lacking, present but not yet observed, or observed but indistinguishable from E. tuberculatum. According to Hora et al. (2005), one of the 10 colonies of E. parasiticum reared in laboratory produced four small “workers.” However, these workers presented a developed spermatheca and six to 10 ovarioles, in contrast to typical workers of E. tuberculatum which lack the spermatheca and possess only one to four ovarioles (Fénerón & Billen 1996; Hora et al. 2001). The presence of developed reproductive structures in these specimens suggests that they are possibly intermediate (intercaste?) reproductive forms of E. parasiticum and not true workers.

A detailed behavioral and genetic study on the interaction between E. tuberculatum and E. parasiticum (so far undescribed and treated as “microgynes”) was conducted by Hora et al. (2005). Gynes and workers of E. tuberculatum and gynes of E. parasiticum were sequenced for the cyt b region and the results showed two haplotypes. The haplotypes differed in seven variable sites, with a nucleotide sequence difference of 0.93%. They clearly discriminate E. parasiticum from the group composed of workers and gynes of E. tuberculatum. According to the findings of Hora et al. (op. cit.), E. parasiticum is a genetically distinct social parasite producing of almost exclusively sexual offspring. The co-occurrence of E. parasiticum and E. tuberculatum in the field (nine mixed colonies found) suggests that the parasite usurps established colonies of the host, but does not kill the resident gynes. Agonistic interactions were also observed, exclusively from workers and gynes of E. tuberculatum against the parasites.

Microgynes are also found in Ectatomma ruidum; however, this is a truly gyne-polymorphic species, and the offspring of both microgynes and normal gynes consist of workers, males, and both microgynes and normal gynes. It was therefore suggested that the two gyne morphs in E. ruidum represent alternative phenotypes adapted to different ways of dispersal and colony founding. Ectatomma ruidum microgynes are thought to disperse and to found new colonies solitarily, while the macrogynes are a stationary morph (Lachaud et al. 1999).

The study of Hora et al. (2005) and the present paper raise the possibility of the occurrence of similar undescribed social parasites within other basal ant lineages.

Nomenclature

 *  parasiticum. Ectatomma parasiticum Feitosa & Fresnau, in Feitosa, Hora, et al. 2008: 49, figs. 1, 2 (q.) MEXICO.

Queen
Holotype (paratypes): HL 2.10 (2.06–2.16); HW 1.85 (1.73–1.88); SL 2.04 (1.92–2.06); EL 0.51 (0.50–0.58); PW 1.69 (1.62–1.77); WL 3.88 (3.65–4.04); PTL 0.79 (0.78–0.88); PTW 0.92 (0.92–1.07); CI 88.07 (84.11–88.89); SI 110.42 (108.57–113.04); OI 27.50 (27.50–31.25); PTI 85 (82.14–85.71). Color yellowish brown to dark reddish brown, including appendages. Mandibles finely and densely striate, with sparse piligerous punctures; clypeus, genae, and frontal area predominantly smooth, but opaque; dorsal surface of head densely and coarsely reticulated, except for the areas of antennal articulations, which are finely punctate; ventral surface of head with sparse longitudinal striae; antennal scapes finely and longitudinally striate. Mesosoma with variously oriented costulae, from sparse and transverse on dorsum of pronotum and propodeum to dense and subconcentric on the dorsum of scutum and scutellum; forecoxae with dense, fine, regular transverse striation; legs mostly smooth and shining. Lateral and posterior faces of petiolar node with sparse, short, longitudinal costulae; sculpture of gaster consisting of arched, transverse costulae, becoming gradually finer from first to terminal segment.

Pilosity cream-colored. Body covered by relatively sparse, long, suberect hairs; antennal scapes and legs with short, suberect hairs; antennal funiculi and tarsi covered by fine apressed pubescence.

Head subrectangular, with weakly convex lateral borders and vertexal margin straight; masticatory margins of mandibles multidenticulate and with a large apical tooth; clypeus strongly convex anteriorly; frontal lobes reduced; scapes in repose fairly surpassing the posterolateral margins of vertex; funicular segments gradually thickened distally; compound eyes placed near the posterolateral portions of head; ocelli present and reduced in size.

Pronotum with a distinct median eminence directed forward and a conspicuous pair of dorsolateral (humeral) projections; scutum large and rounded; notauli almost indistinct among sculpturation; parapsidial lines feebly visible and subparallel; scutoscutellar sulcus deeply impressed; scutellum relatively narrow and strongly convex, in lateral view; dorsal face of propodeum meeting the declivous face in a pair of reduced, blunt teeth; propodeal spiracle elliptical. Wing venation fully developed. Forewing with a weakly colored stigma; longitudinal veins Sc+R, SR, M, Cu, and A present; SR extending distally beyond stigma, forming 1R and 2R cells; cross vein 1r vestigial, not forming the 2R cell; M and Cu also extend distally as tubular veins for most of their length; A not extending beyond the junction with Cu; C, R, Cu, 1M, 1Cu, and SR cells closed. Hind wing with Sc+R extending beyond point where they connect to M, which continues as a tubular vein as much as Sc+R and then extends as spectral vein to wing distal border; basally M+Cu extending as a tubular vein beyond junction with Anal vein, which continues shortly beyond this point; seven submedian hamuli present.

Petiole ventrally carinate; in lateral view, petiolar node thick and subtriangular; anterior slope nearly concave and posterior slope slightly convex. Sternite of first gastral segment with a distinct anterior projection.

Type Material
Holotype gyne. MEXICO: Apazapan, Veracruz, 19º19’38”N 96º43’21”W, ix.1999, D. Fresneau col. INEC.

Paratypes. same data as holotype (1 gyne) ; (1 gyne) UNCB; (1 gyne) [INEC]; vii.2000, D. Fresneau & R. Hora cols. (1 gyne) ; (2 gynes) ; (1 gyne).

Etymology
The specific epithet is a reference to the parasitic nature of this species.