Temnothorax brunneus, found in only one very small site in the Great Atlas of Morocco, represents a workerless parasitic species which is derived from actively dulotic congeners ("degenerate slavemaker"). The host species is Leptothorax cf. marocanus. The C. brunneus queen apparently eliminates the host colony queen by stinging her. She also stings to death a considerable part of the host colony workers, but, different from the dulotic congeners, the T. brunneus queen then is accepted by the remaining adult host workers. The sexual production is queen-biased (sex ratio 0.43 male/female); mating presumably takes place close to the nest. We found no evidence for a female sexual pheromone, but the T. brunneus males react on the pheromone from poison glands of other Temnothorax species. The life history of T. brunneus parallels that of other "degenerate slave-makers" in the genus Epimyrma. (Buschinger et al. 1989)
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As reported by Buschinger et al. 1989:
Our field and laboratory data clearly reveal that Chalepoxenus brunneus is a workerless parasitic ant, in contrast to the other species of this genus. Except for Temnothorax spinosus, of which only alate sexuals are known (Buschinger 1987), all other species have a worker caste, and Temnothorax muellerianus as well as Temnothorax kutteri have been shown to conduct slave raids. For Temnothorax tramieri (Cagniant 1983) dulotic life habits are also assumed. C. brunneus thus represents a "degenerate slavemaker" like several species in the genus Epimyrma (= Myrmoxenus), which are parasites of Leptothorax (= Temnothorax) species (s.g. Myrafant and Temnothorax) as is Chalepoxenus (Buschinger and Winter 1985, Buschinger et al. 1987, Buschinger in press).
As in the workerless Epimyrma corsica (= Temnothorax corsicus) and Epimyrma adlerzi (= Temnothorax adlerzi), the C. brunneus females apparently are able to eliminate the host colony queens during parasitic colony founding, using the genus-specific technique of stinging them, while Epimyrma females throttle the host queens to death. Different from the dulotic Chalepoxenus species, however, where the host queen soon dies when stung, the L. marocanus queens are only paralyzed by the C. brunneus female, and may even recover, as was shown in one experiment, or die only after several days. Another difference refers to the behavior towards the host colony workers: In C. muellerianus and C. kutteri the parasitic queen stings most of the workers to death (some workers and the queen often escape), and takes over only their broods. C. brunneus, on the other hand, stings only part of the host workers, which also do not die immediately (only after several days), and she is accepted by the remainder of the adult host colony workers. This parallels our observations in Epimyrma, again, in that during colony foundation the Epimyrma queens also sting a small number of host workers (Buschinger and Winter 1985, Buschinger et al. 1987, Douwes et al. 1988), and are accepted by the others. Adoption of the parasitic queen by adult host workers, however, occurs in all Epimyrma (= Myrmoxenus) species, not only in the degenerate slave-makers. This acceptance in Epimyrma thus is a preadaptive feature already present in the slave-making species; it is certainly favorable for a degenerate slave-maker who, when workerless, cannot replenish its slave stock through raiding. In Chalepoxenus brunneus, on the contrary, the queens had to evolve de novo the capability of being accepted by adult host workers.
It remains an open question of whether or not C. brunneus is on the way to an even more specialized type of coexistence with the host queens, a true inquilinism. Some of our experiments seemingly support such an assumption. However, the observed instances of coexistence between the C. brunneus and the host queens might well be artifacts due to inappropriate laboratory conditions. In the field such a coexistence has not been observed. And also in C. muellerianus and C. kutteri, in a total of now close to 500 field colonies checked, a coexistence of host and parasite queens has never been found. In laboratory colony founding experiments, however, it has been recorded in a couple of instances, also in these species (Ehrhardt unpubl.).
As was demonstrated in our laboratory cultures of C. brunneus, the production of sexuals is markedly queen-biased, with a numerical sex-ratio close to 0.43 (male/female). This might indicate a certain degree of inbreeding, with sexuals mating close to the maternal nests; in fact we saw mating behavior within our narrow formicaries. The apparent absence of a female sexual pheromone would fit to this assumption. Queen bias is usually found in such parasitic (and also free-living) species, where inbreeding occurs, most evidently in Epimyrma species with mating inside their nests (Buschinger and Winter 1985, Douwes et al. 1988). For a discussion of this feature see Buschinger (in press).
The C. brunneus population of Tizi-n’-Test, according to our observations, is very small, covering an area of not more than 50 X 100 m, and is certainly isolated. The species has not been found in close vicinity nor in farther distant sites of similar elevation, exposition, etc., despite our spending several days in search of additional localities. With an estimated population of less then 100 nests at any time a high degree of inbreeding is inevitable, even if sexuals do not mate exclusively with those of the same, or closely neighboring, nests.
In conclusion, we may state that C. brunneus is a workerless species, derived from actively dulotic congeners. The queens have evolved the capability to coexist with adult host workers of the colonies, which they invade for colony foundation. The higher initial number of host workers makes slave-raiding less necessary. The C. brunneus queens have retained (always?) the feature of killing the host colony queens through stinging, as their dulotic congeners. Due to overgrazing and deforestation of the Great Atlas, as in other parts of Morocco, suitable habitats of C. brunneus have been largely destroyed. The population we studied is certainly but a tiny relic of a once much more widespread species, and it appears close to extinction. We do not know whether or not such relics exist elsewhere. It remains also questionable how much of the peculiar features of C. brunneus is due to the secondarily very small population size and isolation, and what was characteristic of the species as a whole.
The following information is derived from Barry Bolton's New General Catalogue, a catalogue of the world's ants.
- brunneus. Chalepoxenus brunneus Cagniant, 1985a: 141, figs. 1-5 (q.m.) MOROCCO. Combination in Temnothorax: Ward et al., 2014: 15. See also: Buschinger, Cagniant, Erhardt & Heinze, 1989: 253.
- Buschinger, A., Cagniant, H., Erhardt, W., & Heinze, J. 1989. Chalepoxenus brunneus, a workerless "degenerate slave-maker" ant. Psyche 95 (1988): 253-264. [13.vi.1989.] PDF
- Buschinger, A. (2009) Social parasitism among ants: a review. (Hymenoptera: Formicidae). Myrmecological News 12: 219-235.
- Cagniant, H. 1985a. Contribution à la connaissance des fourmis marocaines: Chalepoxenus brunneus n. sp. (Hymenoptera, Myrmicidae). Nouv. Rev. Entomol. (n.s.) 2: 141-146 PDF (page 141, figs. 1-5 queen, male described)
- Ward, P.S., Brady, S.G., Fisher, B.L. & Schultz, T.R. 2014. The evolution of myrmicine ants: phylogeny and biogeography of a hyperdiverse ant clade (Hymenoptera: Formicidae). Systematic Entomology, DOI: 10.1111/syen.12090.