Polyrhachis lama

Polyrhachis lama is an inquiline within the nests of sp.

Identification
A member of the P. veihmeyeri group.

The undeniable similarity between P. lama and the viehmeyeri-group prototype shows that both probably derived from the same ancestral stock. As noted earlier (Kohout, 1990:506), most of this group exhibit variability in the length of pronotal spines even within the same population. Their complete absence and replacement by forward produced carinae, as seen in lama, demonstrates their variability to the extreme and can be interpreted as a product of an independent development of the species in isolation (Kohout, 1994)

Distribution
The known distribution of the viehmeyeri-group is from the Moluccas through Papua New Guinea to the Solomon Islands and northern Australia (Kohout, 1990) but this could be underestimated. With the description of P. lama it appears that the group was in the past more widely distributed and, perhaps, lama is an isolated relic (Kohout, 1994).

Distribution based on Regional Taxon Lists
Indo-Australian Region: Indonesia, Philippines. Oriental Region: Tibet. Palaearctic Region: China.

Biology
The formicine ant Polyrhachis lama is a social parasite, exploiting its ponerine host ant species Diacamma sp. In most social parasitic associations, the parasitic species are closely related to their host species group, evolving directly from independent ancestors of the host species. However, in the Polyrhachis lama - Diacamma sp. association, the associated species belong to different ant subfamilies. Based on preliminary field surveys, the authors (Maschwitz et al. 2000) had presumed that P. lama might have given up its reproductive division of labour, i.e. workers would be able to produce males as well as workers and females parthenogenetically. In Maschwitz et al. 2004, this hypothesis was disproved: Polyrhachis lama workers cannot be fertilized and are only able to produce males. In the host-parasite association originating from nests possessing a P. lama queen, workers penetrate surrounding Diacamma sp. nests, carrying eggs or small larvae for rearing them within these satellite nests. The Polyrhachis-workers participate in prey items brought into the nest by the host workers. In this peculiar way, a single P. lama colony is able to exploit several Diacamma sp. colonies simultaneously. The strategy of P. lama reminds that of slave-making ants, though the latter have slave workers stolen as pupae from several neighbouring host colonies, whereas P. lama workers rear their queen‘s brood within neighbouring nests of the Diacamma host species.

The formicine ant Polyrhachis lama parasitises a phylogenetically distant host species, Diacamma sp. of the subfamily Ponerinae, but lives spatially mixed with the host colonies. Studies on integration and communication have indicated that P. lama shows a high degree of host integration. Witte et al. (2009) have studied the allocation of brood care behaviour, a central aspect of parasite integration, in mixed colonies of P. lama and Diacamma sp. Here, the parasite brood has a high degree of spatial integration, although it remains functionally separated regarding nutritive brood care. The observed spatial confinement of parasite brood is most likely due to an unusual method of chemical host integration. The parasite brood remains accepted in the Diacamma colonies only under the presence of adult parasites (P. lama workers). This suggests an active mechanism of chemical integration based on the acceptance allomones originating from P. lama workers.

Nomenclature

 *  lama. Polyrhachis lama Kohout, 1994b: 137, fig. 1 (w.) TIBET. See also: Maschwitz, Dorow, Buschinger & Kalytta, 2000: 27.

Worker
(holotype cited first): TL c. 8.11, 8.32-8.72; HL 1.93, 1.87-2.03; HW 1.50, 1.47-1.56; CI 78, 75-79; SL 2.31, 2.21-2.40; SI 153, 150-155; PW 1.03, 0.97-1.06; MTL 2.97, 2.87-3.07 (5 measured).

Clypeus with deeply impressed basal margin; median longitudinal carina distinct anteriorly, indistinct posteriorly; median portion of anterior margin dentate laterally. Median ocellus rudimentary, lateral ocelli lacking. Pronotum unarmed; humeri produced into distinct, forward converging dorso-lateral carinae almost reaching the anterior pronotal margin. Promesonotal suture well impressed, metanotal groove rather ill defined. Propodeal spines well elevated, only slightly divergent. Dorsum of petiole convex, anterior and posterior margins obsolete; spines well elevated, divergent.

Clypeus, frontal and lateral areas of head, lateral branches of mesosoma and petiole moderately rugose; rugosity increasing dorsally and posteriorly with dorsa of head and mesosoma fairly coarsely vermiculate-rugose. Gastral dorsum opaque, striate-rugose, with sculpture progressively less distinct posteriorly.

Moderately long, yellowish and reddish bristlelike hairs fairly dense on all body surfaces, including appendages. Silvery pubescence, of distinctly shaggy appearance, rather dense, except on promesonotal dorsum where it is somewhat less abundant.

Generally dark reddish brown with head, mesosoma and petiole on dorsal aspect piceous. Mandibles, appendages and gaster a shade lighter.

Queen
TL c. 9.07; HL 1.96; 1.53; CI 78; SL 2.28; SI 149; PW 1.71; MTL 2.97 (1 measured).

Besides the usual characters identifying full sexuality, the general appearance of the available single female resembles the worker very closely. Pronotal humeri with short, ill-defined carinae. Propodeal and petiolar spines shorter, the former slightly, the latter rather more divergent. Sculpturation similar to that of worker, with density increasing from moderately rugose to fairly coarsely vermiculate-rugose, namely on the head and mesoscutum, contrasting sharply with that on mesoscutellum where it is distinctly less coarse with somewhat granular appearance. Bristle-like pilosity is definitely more dense than in the worker and abundant shaggy pubescence almost obscures the underlying sculpturation.