Cardiocondyla latifrons

Cardiocondyla latifrons is one of the most abundant species of the C. argentea group and often found in disturbed areas, in ecotones such as wood margins but also in primary and secondary forest. Nests have been discovered in rock crevices, under stones or the bark of fallen trees. It is polygynous and shows intranidal mating, development of only wingless ergatoid males with sickle-shaped mandibles which fight to monopolize mating (Yamauchi et al., 2007). In small colonies without a mature queen, Heinze & Weber (2011) observed that virgin gynes violently fought for inheritance of the nest site and its workers and about 50% of the young queens were killed by queen aggression and subsequent attacks by workers. This represents a novel case of direct killing of unmated sisters or half sisters in ants. (Seifert, 2022)

Identification
Worker (Figure 13, images of paratype specimen CASENT0103274 in www.antweb.org, Table 2): Very small, CS 410 µm. Head short (CL/CW 1.102), with notably concave occipital margin. Postocular distance relatively small, PoOc/CL 0.414. Scape short SL/CS 0.822. Eye rather small, EYE/CS 0.230. In position with CL in visual plane, anterior clypeal margin between the level of frontal carinae strongly concave and not forming a sharp edge; instead this concavity appears in frontal view as a small area, the lower margin of which is marked by the three clypeal macrosetae. In dorsal view, the lower margin is usually concealed under the upper margin that is the anterior reference point to measure CL. Frontal carinae very widely separated (FRS/CS 0.337) and almost parallel immediately posterior of the FRS level. Dorsal mesosomal profile strongly convexly vaulted but with a contrasting small plateau on anterior pronotal dorsum. Pronotal corners in dorsal view weak. Spines very long (SP/CS 0.400, in dorsal view slightly diverging, in lateral view very feebly downcurved and their axis deviating by 25° from longitudinal axis of mesosoma. Petiole in lateral view very high (PeH/CS 0.363), with a short peduncle and a long, convex dorsal node profile that steeply slopes down to the caudal cylinder; petiole in dorsal view rather wide (PeW/CS0.319), the node slightly longer than wide, narrowing frontad. Postpetiole in dorsal view moderately wide (PpW/CS 0.460), and with a concave anterior margin; in lateral view comparatively high (PeH/CS 0.363), its sternite with pronounced anterolateral corners that are formed by bilateral lobes which strongly protrude compared to anteromedian level. Whole surface of head and mesosoma densely foveolate, thus appearing at lower magnifications perfectly matt. Vertex with deep, bicoronate foveolae of 15–20 µm diameter which usually show an inner structure reminiscent of a three- or four-leafed cloverleaf (Figure 13D); such foveolae are on mesosoma restricted to pronotum and dorsal mesonotum, the foveolae on remaining mesosoma and waist are smaller and usually without cloverleaf-structure. First gaster tergite smooth and shiny and with a delicate microreticulum. Pubescence on 1st gaster tergite short and dilute (PLG/CS 4.56%, sqPDG 5.17), in anterior part directed caudad and longer than on central surface where the shorter hairs continuously change direction to caudomediad or mediad. Rather concolorous dirty to blackish brown.

Cardiocondyla latifrons and Cardiocondyla micropila are hypothesized here as different, but closely related species. This stands in contrast to the view of Yamauchi et al. (2007) who considered them as intraspecific color morphs because of fertile hybridization under laboratory conditions and only weak fitness reduction in crosses of F1 hybrid gynes with F1 hybrid males. Yet, fertile hybridization under arranged, artificial conditions is no ultimate indication for conspecificity. Using this criterion, many well-recognized species of different eumethazoan groups would have to be synonymized (Seifert, 2020). Deciding is what happens in the natural context. There are four arguments to treat them as different species.
 * 1) The separation of the two taxa based on the 5 morphometric characters CS, sqPDG, PLG/CS, EYE/CS and SPBA/CS is very strong. The exploratory data analyses NC-Ward, NC-part.hclust, NC-part.kmeans and NC-NMDS.kmeans as well as the PCA separated the 65 nest samples of the two taxa with an error of 0% (Figure 30). Furthermore, the classification of the 131 worker individuals using the same character set was confirmed by both a LDA and LOOCV-LDA with 99.2%.
 * 2) This separation by five morphometric characters is strongly supported by clear differences in pigmentation of the 61 and 70 worker individuals of C. latifrons and C. micropila (Figure 31). If considering the two taxa as intraspecific color morphs with dominant–recessive inheritance, we have to demand that genes directing coloration form a linkage group with genes directing body shape and pubescence characters. This appears unlikely at the first hand but is not impossible and should be checked by whole genome analyses.
 * 3) Syntopic occurrence of both taxa with nesting at the same spot a few hand spans apart has been repeatedly observed by several observers. Performing a very thorough sampling, Sabine Frohschammer collected 19 samples of C. latifrons and 57 of C. micropila in six localities and reported the workers within the nest populations to be either “all blackish” or “all yellow” (data file provided by Frohschammer in 2008).
 * 4) Both species are polygynous and mate exclusively intranidally. The number of queens in four localities collected by S. Frohschammer was 3.06 ± 4.41 [0, 27] n = 64 in C. latifrons and 6.95 ± 7.40 [0, 34] n = 61 in C. micropila. If really belonging to the same species, there would be a high probability in a polygynous species to accept mated gynes of both color morphs, to develop nests with mixed populations of yellow and blackish ants and then to produce hybrids by intranidal mating. Whereas F1 hybrids in Yamuchi’s crossbreeding experiments were in fact mainly yellowish (indicating dominant inheritance of yellow over black), there were many specimens among the F2 hybrids with mixed coloration—i.e., head and mesosoma yellowish but gaster blackish. However, there were no mixed nest populations or distinctly bicolored individuals observed in more than 150 nest samples collected by six different collectors throughout the Indo-Malayan region.

In conclusion, both taxa behave like good species which should rarely or never hybridize when embedded in a natural context. Acceptance of mated C. micropila or C. latifrons gynes in nests of the other species is apparently inhibited—probably because the recognition cues (cuticular hydrocarbons) are mutually exclusive and the invading heterospecific gynes cannot overcome the defense mechanisms of the worker force. The case appears to be a good example that strong prezygotic isolation may impair the development of postzygotic isolation. The ant genus Myrmoxenus is another example with strong prezygotic isolation in nature and at least partially successful hybridization in captivity [37,38]. An extreme situation is found in the bird family Anatidae in which highly discriminative mate recognition by optical and behavioral signals and a long period of pair formation before the onset of oviposition result in a strong prezygotic isolation in nature whereas fertile interspecific crossings are easily achieved in captivity even across genus borders (Buschinger, 2001; Jessen & Klinkicht, 1990).

Distribution based on Regional Taxon Lists
Indo-Australian Region: Indonesia, Malaysia, Philippines, Singapore. Oriental Region: Thailand.

Nomenclature

 * . Cardiocondyla latifrons Seifert, 2022: 41, fig. 13 (w.) MALAYSIA.

Type Material
Holotype worker and 2 worker paratypes labelled “MALAYSIA Neg.Sembilan Pasoh For.Res. xi.1994\M.Brendell K.Jackson S.Lewis”, SMN Görlitz. 3 worker paratypes labelled “MALAYSIA: Ulu Gombak 2000.06.02-M3 coll. Yamauchi”, BMNH London; 2 paratypes with same labelling in SMN Görlitz. 6 worker, 3 gyne, 2 ergatoid male paratypes labelled “MALAYSIA: Ulu Gombak 2000.06.03-1 K.Yamauchi” and “MALAYSIA: Ulu Gombak 2000.06.03-2 K.Yamauchi”, SMN Görlitz. 4 workers and 1 gyne paratypes labelled “Tacloban, Leyte, P.I. XII-10-44 E.S. Ross”, CAS San Francisco.