The Crematogaster Ʋacca-subgroup

The phylogenetic relationship between the C. Ʋaccasubgroup and their ancestral state reconstruction suggests that their common ancestor occurred in the Sundaic region and its founder dispersed to Sumatra (Fig. 4). During glacial periods, the populations (C. yamanei) retracted into glacial forest refugia. When environmental conditions became favourable for expansion, the populations recolonized, but in the Sundaic region they were restricted to higher elevation areas due to competition with the C. inflata -subgroup and the C. difformis -subgroup, which were already present in this area at lower elevations.

Crematogaster yamanei is endemic to Sumatra, but closely related to C. Ʋacca, which is distributed in the Malay Peninsula and Borneo. Meijaard’s (2004) mammal studies suggested that Sumatra shares elements of its fauna with both the Bornean/Javan and Malayan regions as a result of secondary contact. Those patterns are found in the younger taxon C. yamanei, but not in the older taxon C. mucronata. The restricted distributions of C. mucronata and C. yamanei could have resulted from another speciation event and extirpation of the relatives, respectively.