Mystrium voeltzkowi Forel, 1897

Yoshimura, Masashi & Fisher, Brian L., 2014, A revision of the ant genus Mystrium in the Malagasy region with description of six new species and remarks on Amblyopone and Stigmatomma (Hymenoptera, Formicidae, Amblyoponinae), ZooKeys 394, pp. 1-99 : 72-76

Mystrium voeltzkowi Forel, 1897 Figs 1B, 4B, 5A, 11B, 13B, 13D, 15, 16B, 19B, 20B, 20D, 20F, 24A, 27A, 27C, 37H, 38H, 39H, 40H, 41H, 50F, 51F, 52F, 53F, 54F, 55F, 56F

Mystrium voeltzkowi Forel, 1897. MADAGASCAR. Syntypes: four workers were confirmed, one male [lectotype is designated below].

Mystrium fallax Forel, 1897. syn n. [lectotype is designated below].

Mystrium fallax : Brown 1960; Menozzi 1929.

Mystrium voeltzkowi fallax : Emery 1911.

Lectotype of Mystrium voeltzkowi

[here designated]. Worker: CASENT0101952 (the specimen on the bottom side with open mandible out of the two workers on the same pin), MADAGASCAR, Nossi-Bé (Nosy Be), Voeltzkow [MHNG: examined].

Lectotype of Mystrium fallax

[here designated]. Ergatoid queen: CASENT0101995, MADAGASCAR, Nossi-Bé (Nosy Be), Voeltzkow [MHNG: same data with lectotype of Mystrium voeltzkowi , examined].

Worker.

Description. Measurements: lectotype. HL 2.08, HW 2.12, SL 1.63, ML 2.67, HD 1.35, WL 2.58, PnW 1.17, PpW 1.00, PtW 0.97, PtL 0.66, CI 102.0, SI 76.9, MI 125.8, PpI 84.9, PtI 147.6.

HL 1.45-2.15, HW 1.41-2.26, SL 1.05-1.65, ML 1.47-2.72, HD 0.96-1.46, WL 1.72-2.68, PnW 0.80-1.20, PpW 0.69-1.09, PtW 0.70-1.03, PtL 0.46-0.67, CI 96.6-104.7, SI 71.7-80.1, MI 104.0-125.7, PpI 86.2-91.0, PtI 141.7-164.6 (9 specimens measured).

Posterolateral corner of head strongly expanding posteriorly. Posterior face of vertex forming blunt angle with dorsal face on median line of the head, so that declivity of vertex on lateral part distinctly steeper than on median part. Ventral half of vertex sculptured. Eye moderately small. Anterior margin of clypeus straight to weakly convex with moderately long conical setae. Genal tooth of head moderately developed, reaching about half of lateral lobe of clypeus. Masticatory surface of mandible in full-face view visible on basal half and invisible on distal half, width of dorsal surface of mandible almost identical from mandibular shaft to distal portion. Second maxillary palpomere longer than third. First flagellomere (third antennal segment) about 1.0 –1.3× length of pedicel (second antennal segment). Pronotal dorsum covered with strong to weak longitudinal striae often waved and irregular, but median stria always deeply, straightly and clearly impressed. Shallow, fine longitudinal striae irregularly impressed on lateral surface of pronotum. Mesonotum not differentiated from propodeum in dorsal view in small individuals but differentiated in large individuals, its length shorter than that of propodeum. Metanotal groove indistinct in small individuals and shallowly and gently impressed in large individuals; mesonotum higher than pronotum in lateral view. Metapleural gland bulla strongly developed, so that propodeal declivity in lateral view convex posteriorly on ventral side. Petiole widened on posterior 1/4-1/2, gently narrowed anteriorly in dorsal view, anterior margin straight to gently rounded and not edged by striae.

Body color reddish brown to black. Four distal segments of antennal club brighter.

Ergatoid queen.

Description. Measurements: HL 1.18-1.59, HW 1.12-1.63, SL 0.88-1.35, ML 1.13-1.64, HD 0.82-1.13, WL 1.56-2.34, PnW 0.70-0.99, PpW 0.70-1.14, PtW 0.68-0.95, PtL 0.38-0.57, CI 95.2-106.4, SI 76.1-85.7, MI 93.1-108.7, PpI 97.1-115.9, PtI 161.8-186.9 (10 specimens measured).

Wings absent or vestigial and reduced to quite small appendages. Wing sclerites undeveloped. Posterolateral corner of head gently expanding posteriorly, expansion distinctly weaker than that in workers. Vertex usually thin, forming blunt angle between dorsal and posterior faces on median line of head, so that declivity of vertex on lateral part distinctly steeper than median part. Ventral half of vertex sculptured, not differentiated from dorsal region. Eye small but distinct. Ocelli absent. Anterior margin of clypeus straight to weakly convex with short conical setae. Genal tooth of head absent, usually even not angular, but angular in smallest individuals. Masticatory margin of mandible almost invisible in full-face view, dorsal surface on distal portion as wide as that on mandibular shaft. Spatulate seta present on basal side of each basal denticle on masticatory margin of mandible. First flagellomere (third antennal segment) moderately long, about 1.1 –1.2× length of pedicel (second antennal segment). Setae on pronotum almost simple, narrowing distally with strongly sharpened apex. Metapleural gland bulla extremely developed and expanding dorsally to propodeal spiracle, so that propodeal declivity in lateral view strongly convex posteriorly on ventral 2/3. Petiole relatively long in dorsal view, about 0.5 –0.8× length of abdominal segment III.

Body color brown to reddish brown.

Male.

Description. Measurements: HL 1.27, HW 1.87, SL 0.42, EL 0.91, WL 2.97, MnW 1.72, CI 146.9, SI 22.2, EI 71.4, MnI 92.0 (1 specimen from original type series measured).

Eye quite large, occupying about 0.75 × head length. Ocelli protruding from dorsal margin of head in full-face view. Dorsal margin of head in full-face view rounded. Both anterior and lateral ocelli large. Distance between lateral ocellus and eye equal to or shorter than diameter of lateral ocellus. Posterior half of vertex clearly differentiated from dorsal half, dorsal face distinctly shorter than posterior face. Palpal formula 4,3. First maxillary palpomere flattened and distinctly wider than second segment. Second maxillary palpomere longer than third. Notauli shallowly and weakly impressed on mesoscutum, but often unclear. Petiole in dorsal view thin, length 0.55 × that of abdominal tergite III. Petiolar dorsum covered with shallow, irregular punctures. Abdominal tergum VIII without deep punctures, almost smooth.

Distal portion of abdominal sternum IX smooth and not punctured. Basal ring moderately long, gently expanding basally. Telomere distinctly extending distally farther than digitus. Basoventral expansion of aedeagus well developed basoventrally, distinctly longer than dorsal extension. Ventral margin of the aedeagus gently curved ventrally in lateral view. Aedeagus distinctly narrowing distally on distal half and apex rounded.

On forewing, cu-a located far basal from junction of Media (M) and Cubitus (Cu).

Body color yellowish to reddish brown.

Distribution.

MADAGASCAR and MAYOTTE: as in Figure 56F.

Additional material examined.

In addition to the type material, specimens from the following localities were examined in this study: MADAGASCAR. Antsiranana. Réserve Spéciale d’Ambre, 3.5 km 235° SW Sakaramy (-12.46889°, 49.24217°), tropical dry forest, 325 m alt.; Parc National Montagne d’Ambre, 3.6 km 235° SW Joffreville (-12.53444°, 49.1795°), montane rainforest, 925 m alt.; Réserve Spéciale de l’Ankarana, 13.6 km 192° SSW Anivorano Nord (-12.86361°, 49.22583°), tropical dry forest, 210 m alt.; 22.9 km 224° SW Anivorano Nord (-12.90889°, 49.10983°), tropical dry forest, 80 m alt.; Forêt d’Ampondrabe, 26.3 km 10° NNE Daraina (-12.97°, 49.7°), tropical dry forest, 175 m alt.; Forêt d’Analabe, 30.0 km 72° ENE Daraina (-13.08333°, 49.90833°), littoral rainforest, 30 m alt.; Forêt d’ Andavakoera, 21.4 km 75° ENE Ambilobe; 4.6 km 356° N Betsiaka (-13.11833°, 49.23°), rainforest, 425 m alt.; Forêt de Bekaraoka, 6.8 km 60° ENE Daraina (-13.16667°, 49.71°), tropical dry forest, 150 m alt.; Forêt d’ Antsahabe, 11.4 km 275° W Daraina (-13.21167°, 49.55667°), tropical dry forest, 550 m alt.; Nosy Be, Réserve Naturelle Intégrale de Lokobe, 6.3 km 112° ESE Hellville (-13.41933°, 48.33117°), rainforest, 30 m alt.; Forêt d’Anabohazo, 21.6 km 247° WSW Maromandia (-14.30889°, 47.91433°), tropical dry forest, 120 m alt.

MAYOTTE. Mt. Combani (-12.8°, 45.13333°), forest litter, 420 m alt.; (-12.80486°, 45.15266°), rainforest, 460 m alt.; (-12.80632°, 45.15314°), rainforest, 370 m alt.; Dapani (-12.96279°, 45.15037°), rainforest, 135 m alt.

Remarks.

The worker of Mystrium voeltzkowi is distinguished from other Mystrium workers by the combination of the following characters: the vertex forming a blunt angle between posterior and dorsal faces on the median line of the head (Fig. 16B), small compound eye (Fig. 20D), the genal tooth of the head reaching to half of the lateral lobe of the clypeus (Fig. 20B), and a medial pair of conical setae on the clypeus that is smaller than adjacent pair (Fig. 19B). In addition, the characters of a central longitudinal furrow on the pronotal dorsum (Fig. 13B) but without deep, stout striae impressed on dorsal and lateral surface of pronotum, and the posterior declivity of the propodeum convex posteriorly on the ventral half (Fig. 20F), so that the margin is somewhat rounded in lateral view, are also useful. The workers of Mystrium mirror and Mystrium shadow are quite similar to those of Mystrium voeltzkowi , and the differences among the three species in workers are even slighter in small-sized individuals. When the comparison is made in workers within the same body size range, Mystrium voeltzkowi can be distinguished from Mystrium shadow by the small central clypeal conical setae (Fig. 19B), and from Mystrium mirror by either a rounded declivity of the propodeum (Fig. 20F) or smaller compound eye (Fig. 20D). The queen of Mystrium voeltzkowi is easily distinguished from the other Mystrium queens by the mesosoma without developed wing sclerites (ergatoid: as in Fig. 25C), the developed metanotal gland bulla expanding dorsally to the propodeal spiracle (Fig. 24A), and the brighter body color. Among males, only genital characters distinguish Mystrium voeltzkowi from Mystrium mirror (Fig. 27).

The male of Mystrium voeltzkowi was described with conspecific workers from the same colony in the original description ( Forel 1897). We confirmed one male in the Forel collection in MHNG; its pin has the same collection label as the other syntypes. This is the only reliable male description in all previous male descriptions of the genus Mystrium .

Mystrium fallax Forel, 1897 is synonymized with Mystrium voeltzkowi in this study. Mystrium fallax was apparently described by a simple mistake. According to the original description of Mystrium voeltzkowi by Forel (1897), he received a vial containing workers, two other reddish individuals, and males which were collected in Nossi-Bé by Dr. Voeltzkow. When Forel (1897) described the worker and male as Mystrium voeltzkowi , he tentatively regarded the two reddish individuals in the same vial as a different species due to the distinct differences in their appearance (as Figs 50F vs. 53F), and named these specimens Mystrium fallax . Forel doubted that the two small reddish individuals belonged to the same colony as Mystrium voeltzkowi ; and later Menozzi (1929) even determined these to be a species distinct from Mystrium voeltzkowi . However, the type specimens of Mystrium fallax were probably from the same colony of types of Mystrium voeltzkowi . The mistake was due to the remarkable polymorphism in this species. Once the original descriptions of Mystrium fallax and Mystrium voeltzkowi were published, the association between the large black worker (Fig. 50F) and the small reddish individuals (Fig. 53F) was not clarified for more than 110 years. Now accumulated material clearly shows the small reddish individuals are conspecific with the black large worker, and an ecological study ( Molet et al. 2007a) revealed these small reddish individuals are ergatoid queens of this strange species (Fig. 1B).

The distribution of Mystrium voeltzkowi is limited to Mayotte and the northern part of Madagascar (Fig. 56F). The collection localities of Mystrium mirror are in tropical dry forest, gallery forest, and spiny forest (Fig. 56C), while those of Mystrium voeltzkowi are in tropical dry forest, montane rainforest, littoral rainforest, and rainforest (Fig. 56F). The distinct development of the metapleural grand bulla observed in Mystrium voeltzkowi (Figs 20F, 24A) may be related to its nesting environment, which has higher moisture levels and requires stricter control of fungi.

The reference to Mystrium voeltzkowi in recent molecular phylogenetic studies ( Brady et al. 2006; Kück et al. 2011; Moreau and Bell 2013; Ouellette et al. 2006; Saux et al. 2004) and ecological studies ( Molet et al. 2009; Molet et al. 2007a) need to be reassessed. Material identified as Mystrium voeltzkowi in Saux et al. (2004) are confirmed here. Mystrium mysticum material in Brady et al. (2006), Ouellette et al. (2006), Kück et al. (2011), and Moreau and Bell (2013) is actually Mystrium voeltzkowi . This complicated species also has been represented by species codes as Mystrium ‘red’ in Molet et al. (2009), Molet et al. (2007a), and Molet et al. (2012), as Mystrium sp.2 in Saux et al. (2004), and as Mystrium mysticum2 in Ouellette et al. (2006). These complications represent the typical difficulty of species-level identification in Mystrium .