This continues to illustrate how important multidisciplinary studies are for the sound understanding of a biological system.

In his first paper, Doyle McKey, relates the beginnings of his study of an "ant-plant", which he names as Leonardoxa africana. This tree (then known as Schotia africana) was mentioned by J. Bequaert as having swollen internodes and often being inhabited by ants but he found no evidence of it being a true myrmecophyte (Bequaert, 1922).

The tree species

Geographical range of the tree subspecies

L. africana africana (ssp L4 or T4 in earlier papers) appears to be restricted to a limited area of coastal rain forest in Cameroun (approximately that shown as the "area of 2001 collections" in Map 7) - from ca 4°28'N to 2°34'N, and no further than 10°25'E. McKey, 2000).

L. africana letouzeyi McKey (2000) (ssp L3 or T3 in earlier papers) of L. africana is described as occurring in the wettest forests of Africa, the lowland forests near the Bight of Biafra, running east from Uwet Division in Calabar Province, Nigeria, across the border into western Cameroun, essentially in the dark understorey of wet, cloudy forest.

The Ants

Aphomomyrmex afer and Petalomyrmex phylax. Both are Formicines and are the only African members of the Tribe BRACHYMYRMECINI. Both ants are inhabitants of subspecies of the forest understorey tree Leonardoxa africana.

In Cameroun, Aphomomyrmex afer primarily occupies the L. africana letouzeyi , but it also has been found, albeit much more rarely, in hollow twigs of another myrmecophyte Vitex grandifolia. In L. africana letouzeyi, A. afer tends homopterans inside the domatia (specialised "ant cavities"). The homopterans have been identified as a coccid, Houardia abdita, and/or a pseudococcid, Paraputo anomla.

Petalomyrmex phylax is found solely as an occupant of domatia of the L. africana subspecies africana , which is as very specialised myrmecophyte apparently with an obligate mutualistic relationship with this sole species of ant. Some 75% of all the trees are occupied by P. phylax but the remainder are occupied by completely unrelated small myrmicine ant, Cataulacus mckeyi.

Cataulacus mckeyi - whereas P. phylax actively patrols all immature leaves, removing or dislodging potential small insect herbivores, Cat. mckeyi has smaller and much less active colonies doing little or nothing to protect the young leaves. Both ant species, however, get most of their sustenance from extra-floral nectaries on mature leaves. Thus, as Cat. mckeyi appears to convey no real benefit on the host tree, it is regarded as a parasite of the Leonardoxa-Petalomyrmex relationship. Gaume & McKey (1999) knew of no other plant-ant to be an obligate non-protective parasite of its sole host-plant species.

Other ants in "McKey group" papers

McKey (1984, p83) mentions Technomyrmex laurenti (as Engramma laurentii) as sometimes cutting an entrance hole into an internode of L. africana africana (in the 1984 paper simply as "L. africana").

In the same paper (p85), McKey also mentions a "very small, unidentified grayish ant species" as being found to occupy internodes of a few moribund saplings, which lacked healthy colonies of P. phylax and C. mckeyi.

Gaume et al. (2000, p88) mention that on rare occasions the ants Axinidris bidens and a Crematogaster sp. had been collected from domatia in juvenile L. africana letouzeyi (as T3) tending the pseudococcid Paraputo anomala. They added that A. bidens is usually associated with a Planococcus sp (but without giving any details or source of the information).

Species identified by me from 2001 collections

Found in or on L. africana africana plants (single collections unless indicated).

In domatia -

• Axinidris bidens, four separate collections (note unbeknown to me this species was referred to by Gaume et al., 2000);
• Crematogaster (Decacrema) petiolidens
• Monomorium dolatu, five collections; note the diagnosis is questionable and this may be a new species
• Tapinoma debouti (Cameroon 60, three collections)
• Tapinoma arnoldi (two collections);
• Tetramorium peutli

Otherwise found on L. africana africana -

• Monomorium draxocum (only in a dead domatia);
• Pyramica (Serrastruma) mckeyi (Cameroon 113);
• Tetraponera unidens (Cameroon 20);
• Tetraponera ophthalmica (Cameroon 17).

Other ants found in plant domatia or at extra-floral nectaries

• Crematogaster (Atopogyne) depressa (2 small specimens) at nectaries of Alchorea floribunda.
• Crematogaster (Sphaerocrema) striatula at nectaries of Alchorea floribunda.
• Crematogaster (Sphaerocrema) gabonensis on an extrafloral nectary-bearing plant (Macaranga sp. or Bridelia sp.).
• Crematogaster (Oxygyne) margaritae on a domatia-bearing and lianescent Rubiaceae.
• Myrmicaria exigua at extrafloral nectaries of a shrub in a treefall gap.
• Pheidole megacephala in leaf-pouch domatia of Delpydora sp.
• Technomyrmex kohli in leaf-pouch domatia of Delpydora sp. (Cameroon 21)
• Technomyrmex laurenti in pouch-like stipules of Diospyros conocarpa (Cameroon 18).
• Tetraponera aethiops in domatia of Barteria fistulosa.

References (in chronological order)

McKey group

McKey, D. (1984)

Interaction of the Ant-Plant Leonardoxa africana (Caesalpinaceae) with its obligate inhabitants in a rainforest in Cameroon. Biotropica, 16, 81-99.

Gaume, L., Matile-Ferrero & McKey, D. (2000)

Colony foundation and acquisition of coccoid trophobionts by Aphomomyrmex afer (Formicinae): co-dispersal of queens and phoretic mealybugs in an ant-plant-homopteran mutualism? Insectes Sociaux, 47, 84-91.