Cataulacus mckeyi

Cataulacus mckeyi is a plant-ant specifically associated with the patchily distributed understorey tree Leonardoxa africana africana (Cesalpiniaceae) in Cameroonian rainforests. The presence of a colony of C. mckeyi in a tree prevents Petalomyrmex phylax from occupying this tree, and does not provide protection against herbivores. The proportion of trees occupied by C. mckeyi of L. a. africana varies from 0% to 33% (Debout, unpublished data) among populations. In some of the study sites, C. mckeyi expresses polydomous colony structure (i.e. one colony occupies several different trees). (Debout et al. 2002)

Identification
The worker of this species will run in Bolton's (1974) key to Cataulacus pygmaeus and appears to be related to that species. The most obvious differences are the shorter and sparser pilosity, the more coarsely sculptured mesosomal dorsum and much finer piligerous punctures of the first gastric tergum of pygmaeus. The metafemur of pygmaeus has several conspicuous longitudinal rugae on the posterior surface; these usually are entirely lacking in mckeyi. According to Bolton the CI, OI and SI for pygmaeus are 94-97, 41-46 and 49-51, respectively, versus 98-102, 43-47 and 43-46, respectively, for mckeyi. The latter is also a smaller species, with a HW range of 0.87-0.94 versus 0.92-1.06 in pygmaeus.

The females of the two species are very similar, but mckeyi, with a HW range of 0.92-0.96 (1.08 in pygmaeus) is smaller. The CI, OI and SI of pygmaeus. as given by Bolton, are 92-95, 40-46 and 48-50, respectively. These are 98-102, 43-47 and 43-46, respectively, for mckeyi. Presumably there are differences in pilosity much like those between the workers of these species.

Bolton's description of the pygmaeus male does not suggest many differences between it and the male of mckeyi. According to Bolton, the side of the head, behind the eye, is denticulate (simple in mckeyi) and the pronotum is conspicuously rugoreticulate (very sparse rugulae laterad in mckeyi). Bolton does not state that the punctures of the first gastric tergum become conspicuously weaker caudad as they do in mckeyi nor does he mention conspicuously coarse piligerous punctures. Until more males of members of the tenuis group become available, it is impossible to characterize that of mckeyi in a meaningful manner. (Snelling 1979)

Distribution
This taxon was described from Cameroun.

Biology
Cataulacus mckeyi has been the subject of numerous studies (Guame and Mckey 1999, Debout et al. 2002, 2003) in large part to explore it relationship with the only plant it has ever been found to nest within, Leonardoxa africana africana, and its mutualist ant partner Petalomyrmex phylax.

Foraging is diurnal. Workers are not aggressive, passing over many potential prey and not recruiting to larvae that are readily preyed upon by the smaller P. phylax. Unlike the latter, C. mckeyi provides little protection against herbivores for its host and in fact can be viewed as a parasite of the mutualism between phylax and the nectar producing plant.

Genetics
Polymorphic microsatellites have been identified for this species. (Debout et al. 2002)

Nomenclature

 *  mckeyi. Cataulacus mckeyi Snelling, R.R. 1979a: 5, figs. 9-18 (w.q.m.) CAMEROUN. See also: McKey, 1984: 81.

Worker
Holotype worker. TL 3.93; HL 0.91; HW 0.91; CI 100; EL 0.41; OI 45; IOD 0.74; SL 0.42; SI 46; PW 0.74; WL 1.06; MTL 0.44.

Occipital crest absent, vertex rounded into occiput. Occipital corner denticulate and with a small denticle on margin close to corner, denticles small; side of head denticulate behind eyes. Side of pronotum strongly marginate and denticulate. In dorsal view, mesonotum and propodeum abruptly narrower than pronotum, denticulate at sides; propodeum with a pair of broad dorsoventrally flattened spines. Thoracic dorsum without sutures. Subpetiolar process quadrate, with prominent anterior and posterior angles. Subpostpetiolar process short, simple, acute. First gastric tergum not laterally marginate.

Dorsum of head with a very fine, loose rugoreticulum; interspaces moderately shiny, finely, densely and weakly reticulate-punctate, punctures stronger on vertex. Mesosomal dorsum with a rugoreticulum, no coarser than that of head, with transverse meshes obsolescent, so that rugae are largely longitudinal; interspaces slightly shiny, strongly and densely reticulate-punctate. First gastric tergum moderately shiny, densely reticulate-punctate, with fine, irregular longitudinal rugulae resulting from fusion of margins of aligned punctures, without conspicuous longitudinal rugae. Piligerous punctures scattered, coarser than hairs arising from them.

Dorsal surfaces of head, body and appendages with numerous short, flattened (rarely weakly clavate on cephalic dorsum), simple hairs, longest on gaster; hairs of first tergal dorsum separated by less than their length.

Paratype workers. TL 3.58-4.04; HL 0.86-0.94; HW 0.87-0.94; CI 98-102; EL 0.38-0.44; OI 43-47; IOD 0.66-0.73; SL 0.38-0.42; SI 43-46; PW 0.65-0.77; WL 0.96-1.09; MTL 0.40-0.44 (18 measured).

Queen
Paratype females. TL 5.06-5.19; HL 0.95-0.97; HW 0.92-0.96; CI 97-99; EL 0.41-0.44; OI 44-47; IOD 0.73-0.76; SL 0.44-0.45; SI 45-49; PW 0.92-0.96; WL 1.37-1.45; MTL 0.45-0.47 (7 measured).

As workers, with usual modifications of mesosoma for flight. Denticulae of head behind eye and of pronotal margin reduced, sometimes absent. Mesoscutum strongly longitudinally rugate, with few or no cross meshes; rugation of propodeum coarser than that of mesoscutum. Metafemur often with conspicuous longitudinal rugae on posterior face.

Male
Allotype male. TL 4.53; HL 0.81; HW 0.85; CI 105; EL 0.36; OI 42; IOD 0.70; SL 0.32; SI 38; PW 0.83; WL 1.44; MTL 0.55.

Occipital crest absent, occipital corner denticulate, the tooth broad and more or less sharply angulate mesad. Side of head behind eye not denticulate, though margin often irregular. Preocular denticle absent or present but small. Pronotal margin irregular but not denticulate. Anterior arms of notauli well developed and cross-ribbed, posterior arm absent or marked by a very weak depression. Propodeal spines short, stout. Subpetiolar and subpostpetiolar processes simple.

Dorsum of head densely reticulate-punctate with a few fine rugulae and a few weak rugulae close to and behind eyes, the cross-meshes reduced or absent. Pronotum densely reticulate-punctate, with a few irregular rugulae, especially at side. Mesoscutum densely reticulate-punctate, with fine longitudinal rugulae resulting from fusion of margins of aligned punctures. Scutellum similar but less shiny. Propodeal base densely reticulate-punctate and dull, with conspicuous fine longitudinal rugae. Dorsum of petiole densely reticulate-punctate and dull, with a few widely spaced fine rugae; dorsum of postpetiole densely reticulate-punctate and dull, sometimes with a few obscure rugulae at side. First gastric tergum moderately shiny and densely reticulate-punctate on basal one-fourth, punctures becoming increasingly faint caudad; with scattered coarse, setigerous punctures.

Simple, erect hairs present on all dorsal surfaces of head and body, some on head distinctly flattened.

Paratype males. TL 4.39-5.13; HL 0.78-0.86; HW 0.81-0.94; CI 103-109; EL 0.33-0.37; OI 40-43; IOD 0.66-0.77; SL 0.27-0.33; SI 33-37; PW 0.79-0.92; WL 1.44-1.60; MTL 0.47-0.56 (7 measured).

Type Material
Holotype worker and allotype. CAMEROUN: near Lac Tissongo, Douala-Edea Reserve (lat. 3°29' N, long. 9°50' E), about 5 km S of Sanaga River and about 15 km E of Mouanko, 18 July 1976 (D. McKey) in Natural History Museum of Los Angeles County. Paratype females (20), workers (135) and males (7) in BMNH, LACM, MCZ and collection of Mr. McKey.

Etymology
This species is dedicated to its collector, Mr. Doyle McKey.

Additional References

 * Debout, G., A. Dalecky, et al. 2002. Isolation and characterization of polymorphic microsatellites in the tropical plant-ant Cataulacus mckeyi (Formicidae: Myrmicinae). Mol. Ecol. Notes 2: 459-461.


 * Debout, G., E. Provost, M. Renucci, A. Tirard, B. Schatz, and D. McKey. 2003. Colony structure in a plant-ant: behavioural, chemical and genetic study of polydomy in Cataulacus mckeyi (Myrmicinae). Oecologia. 137:195-204.


 * Gaume, L. and D. McKey. 1999. An ant-plant mutualism and its host-specific parasite: activity rhythms, young leaf patrolling, and effects on herbivores of two specialist plant-ant inhabing the same mymecophyte. Oikos. 84:130-144.