Carebara species groups

The page below outlines one recent perspective on Carebara species groups. There is clearly a need for much more taxonomic work within this species rich genus that also exhibits a wide range of morphological diversity.

The following is based on Fischer et al. (2014) The establishment of the Carebara polita species group highlights the need to revise all Carebara species to better delimit species group boundaries in the genus and to rearrange the groups suggested by Fernández (2004, 2010) and later adapted to include the Indian Carebara fauna treated by Bharti and Kumar (2013). The establishment of new species groups will likely be necessary with ongoing taxonomic research and will help unravel the evolutionary history of this genus. Especially the Afrotopical region holds a large number of unrevised and new species, many of which are located in the BMNH collection in London.

The former Pheidologeton species could in future revisions be split into two species groups, one that shares characters with C. aberrans and C. affinis, where the minor and large major workers are connected through a continuous series of intermediate subcastes, and another group that shares characters with C. pygmaea and C. alperti, that are dimorphic and morphologically similar to some species of the former genus Oligomyrmex. In this publication we are establishing and focusing on the polita species group, which is mostly characterized by their minor workers’ morphology, i.e. head and mesosoma shape, medially smooth and shiny frons, present propodeal spines, and, most importantly, an elongate postpetiole in minor workers. The diagnosis for minor and major workers (where known) of the polita group is summarized below.

polita species group
Key to Carebara polita species group

Diagnostic characters of the polita species group

1. Antennae with usually eleven, but one species with nine segments; scapes, when laid back, never reaching or surpassing posterior head margin.

2. Eyes of minor workers small, in most specimens consisting of only one ommatidium, in major workers absent to multi-facetted, in all subcastes situated anterior to cephalic midlength and relatively close to anterior head margin.

3. Mandibles with four to six teeth, number in minor workers often one less than in major workers.

4. Posterior margin of head concave to weakly concave medially, or nearly straight.

5. Frons in minor workers medially smooth and shiny.

6. Minor workers with short to comparatively long propodeal spines present, in major workers sometimes reduced to a blunted angle (C. urichi).

7. Minor and/or major workers often with petiolar ventral process present as anteriorly directed small tooth, which is sometimes reduced or inconspicuous.

8. Petiole node in minor workers usually subangulate to rounded in profile, dorsally smooth and shiny, in major workers very well-developed and high, the dorsum rounded to angulate-subangulate and anterodorsally compressed.

9. Minor worker postpetiole relatively elongate, distincly longer than high (LPpI 131–173) and lower than petiole, major worker postpetiole compact, dorsally rounded, and in profile about as high as long (LPpI 83–107).

Comments on diagnosis of polita group worker caste

Range in head shape and sculpture, the number of distinctly expressed mesosomal sclerites in major workers, and the propodeum varying from having spines or not in this group is relatively large and comparable to the range found in former Pheidologeton species. Interestingly the major worker caste has shown itself completely elusive in two of the polita group species. Despite a multitude of collections from several localities C. brevipilosa and C. villiersi are known only from the minor workers so far. But C. polita has been collected without any major workers for almost a century, and C. nicotianae for more than 50 years. The minor workers of C. polita were described by F. Santschi in 1914 and majors have not been collected until 2001 by the late R. R. Snelling, but remained unidentified at first. If not for another collection of major workers together with queens and minor workers in 2008 by the first author, the fact that these two different worker subcastes belong to the same species, and one important link between Carebara and the former Pheidologeton, might have remained unnoticed.

Biogeographic notes on the polita species group

Six species occur in the Afrotropical region, two of them are widely distributed throughout sub-Saharan Africa: C. perpusilla in Kenya, Rwanda, South Africa, Tanzania, Uganda, Zambia, and Zimbabwe and C. silvestrii in Cameroon, Central African Republic, Equatorial Guinea, Gabon, Ghana, Ivory Coast, Kenya, Uganda, and Zimbabwe. Two species are widely distributed from Western to Eastern Africa: C. polita in Cameroon, Central African Republic, Gabon, Kenya, Tanzania, and Uganda and Carebara madibai sp. n. is known from the Central African Republic, Dem. Rep. Congo, Gabon, and Uganda. Carebara villiersi occurs throughout Western Africa and was found in Cameroon, Central African Republic, Gabon, Ghana, Guinea, and Ivory Coast. Carebara nicotianae seems restricted to Zambia and Zimbabwe in Southern Africa. Two of the species included in this group are present and widespread in the Neotropical Region: C. brevipilosa is reported from Brazil, Colombia, Costa Rica, and Panama, while C. urichi was found only in Belize, Brazil, Colombia, Costa Rica, Mexico, Panama, Peru, Suriname, and Trinidad.