Pseudomyrmecine ants associated with specialized ant-plants

Introduction

Phylogenetic analysis of representative groups of ants in the subfamily Pseudomyrmecinae indicates that specialized relationships with domatia-bearing plants have evolved independently at least 12 times within the subfamily (Ward, 1991). The plants involved in such associations include swollen-thorn acacias in Mexico and Central America; Neotropical trees in the genera Cordia, Myrcia, Tachigali and Triplaris; African species of Acacia, Barteria and Vitex; a Malagasy species of Mimosa; and an Australian tree in the genus Cupaniopsis. In most instances the plant provides some kind of intrinsically hollow, or easily excavated, cavity (domatium) in which the ants keep brood and scale insects (Coccoidea). The ants, in turn, protect the host plant from herbivores and (sometimes) from other competing plants. In the case of the interaction between Pseudomyrmex ants and swollen-thorn acacias, scale insects are absent from the domatia, but the ants receive nutritional rewards from extrafloral nectaries on the leaf petiole and from lipid-rich food bodies (Beltian bodies) produced at the leaf tips.

Pseudomyrmex ferrugineus workers on swollen-thorn Acacia	Area at base of a swollen-thorn Acacia cleared free of competing plants by its resident ants

Table 1. The obligate plant-ants in the subfamily Pseudomyrmecinae (from Ward, 1991, 1993, 1999b). These are species which, as far as known, nest only in live plant domatia. Taxa identified only by a code number (e.g., Pseudomyrmex sp. PSW-35) represent undescribed species whose descriptions and new names will be found in Ward (1999b).

Genus/species group	Species	Distribution	Plant(s)	Notes
Ps. ferrugineus group	ferrugineus	Mexico to El Salvador and Honduras	Acacia spp. (9 species)	See Ward (1993) for full list of Acacia species
Ps. ferrugineus group	flavicornis	Guatemala to Costa Rica	Acacia collinsii, A. cornigera, A. hindsii
Ps. ferrugineus group	janzeni	Mexico	Acacia hindsii
Ps. ferrugineus group	mixtecus	Mexico	Acacia collinsii, A. hindsii
Ps. ferrugineus group	nigrocinctus	Guatemala to Costa Rica	Acacia collinsii, A. cornigera, A. hindsii
Ps. ferrugineus group	particeps	Costa Rica	Acacia allenii
Ps. ferrugineus group	peperi	Mexico to Nicaragua	Acacia spp. (6 species)	See Ward (1993) for full list of Acacia species
Ps. ferrugineus group	satanicus	Panama	Acacia melanoceras
Ps. ferrugineus group	spinicola	Honduras to Colombia	Acacia allenii, A. collinsii, A. cornigera
Ps. ferrugineus group	veneficus	Mexico	Acacia collinsii, A. hindsii
Ps. gracilis group	hospitalis	Peru	Tachigali
Ps. gracilis group	nigropilosus	Mexico to Costa Rica	Acacia collinsii, A. cornigera, A. hindsii	Non-protective "parasite"
Ps. gracilis group	reconditus	Nicaragua	Acacia collinsii
Ps. gracilis group	simulans	Panama	Acacia collinsii
Ps. sericeus group	cordiae	Panama to Bolivia	Cordia
Ps. sericeus group	crudelis	Peru	Tachigali
Ps. sericeus group	deminutus	Brazil	Tachigali
Ps. sericeus group	eculeus	Ecuador, Peru	Tachigali
Ps. sericeus group	ferox	Colombia, Peru, Brazil	Tachigali
Ps. sericeus group	fortis	Mexico to Colombia, Venezuela	Triplaris (part)	See discussion in Ward (1999b)
Ps. sericeus group	longior	Colombia to Brazil, Bolivia	?Platymiscium
Ps. sericeus group	pictus	Colombia, Peru, Brazil, Bolivia	Tachigali, ?Platymiscium
Ps. sericeus group	rubiginosus	Colombia, Peru, Brazil	Gustavia, Ocotea, Pleurothyrium, Tachigali, Triplaris,
Ps. sericeus group	vinneni	Colombia, Peru Venezuela, Brazil	Tachigali
Ps. subtilissimus group	subtilissimus	Nicaragua, Costa Rica	swollen-thorn Acacia
Ps. viduus group	concolor	Venezuela, Guyana, Brazil	Tachigali
Ps. viduus group	dendroicus	Colombia to Brazil, Bolivia	Triplaris
Ps. viduus group	insuavis	Colombia	Tachigali
Ps. viduus group	malignus	Venezuela, Guianas, Brazil	Tachigali
Ps. viduus group	mordax	Panama, Colombia, Venezuela,	Triplaris
Ps. viduus group	penetrator	Venezuela, Guianas, Brazil	Tachigali
Ps. viduus group	tachigaliae	western Brazil, Peru	Tachigali
Ps. viduus group	triplaridis	Colombia to Brazil	Triplaris
Ps. viduus group	triplarinus	Colombia to Brazil, Bolivia	Triplaris
Ps. viduus group	ultrix	Ecuador	Triplaris
Ps. viduus group	viduus	Mexico to Brazil, Bolivia	Cordia, Coussapoa, Macrolobium, Ocotea, Pseudobombax, Pterocarpus, Sapium, Triplaris	See discussion in Ward (1999b)
Pseudomyrmex	perboscii	Mexico to Brazil, Bolivia	Albizia saman, Cordia, Pseudobombax
Myrcidris	epicharis	Brazil	Myrcia sp.
Tetraponera	aethiops	west Africa	Barteria
Tetraponera	latifrons	west Africa	Barteria
Tetraponera	nigra (part)	India	Acacia horrida, Stereospermum personatum	Possibly an obligate plant-ant at the population (not species) level
Tetraponera	penzigi	east Africa	Acacia, Stereospermum
Tetraponera	tessmanni	west Africa	Vitex
Tetraponera	tucurua	Australia	Cupaniopsis	Additional details in Ward (2001)
Tetraponera	binghami	Malaysia	Gigantochloa
Tetraponera	sp. PSW-87	Madagascar	Mimosa

For general reviews on the interactions between ants and domatia-bearing plants see Beattie (1985), Benson (1985), Davidson & McKey (1993), and Wheeler (1942).

Identification of pseudomyrmecine plant-ants

Identification keys are available for the Pseudomyrmex species inhabiting swollen-thorn acacias (Ward, 1993) and Triplaris and Tachigali plants (Ward, 1999b). Problematic specimens of Pseudomyrmex may be sent for identification to: Philip S. Ward, Department of Entomology, University of California, One Shields Ave., Davis, CA 95616, USA.

Literature Cited

• Beattie, A. J. 1985. The evolutionary ecology of ant-plant mutualisms. New York: Cambridge University Press, 182 pp.
• Benson, W. W. 1985. Amazon ant-plants. Pp. 239-266 in: Prance, G. T., Lovejoy, T. E. (eds.) Key environments. Amazonia. Oxford: Pergamon Press, xiv + 442 pp.
• Davidson, D. W., McKey, D. 1993. The evolutionary ecology of symbiotic ant-plant relationships. J. Hym. Res. 2:13-83.
• Ward, P. S. 1991. Phylogenetic analysis of pseudomyrmecine ants associated with domatia-bearing plants. Pp. 335-352 in: Huxley, C. R., Cutler, D. F. (eds.) Ant-plant interactions. Oxford: Oxford University Press, xviii + 601 pp.
• Ward, P. S. 1993. Systematic studies on Pseudomyrmex acacia-ants (Hymenoptera: Formicidae: Pseudomyrmecinae). J. Hym. Res. 2:117-168.
• Ward, P. S. 1999b. Systematics, biogeography and host plant associations of the Pseudomyrmex viduus group (Hymenoptera: Formicidae), Triplaris- and Tachigali-inhabiting ants. Zool. J. Linn. Soc. 126:451-540.
• Ward, P. S.  2001. Taxonomy, phylogeny and biogeography of the ant genus Tetraponera (Hymenoptera: Formicidae) in the Oriental and Australian regions. Invert. Taxon. 15:589-665.
• Wheeler, W. M. 1942. Studies of Neotropical ant-plants and their ants. Bull. Mus. Comp. Zool. 90:1-262.

Philip S. Ward Department of Entomology and Center for Population Biology University of California at Davis Davis, CA 95616, USA email: psward@ucdavis.edu

http://entomology.ucdavis.edu/faculty/ward/antplant.html last modified 22 October 2002