Ms Quek Swee Peck is currently a PhD candidate at the Harvard University. Studying the evolution of host affiliation in Crematogaster (Formicidae) associates of Macaranga (Euphorbiaceae), she is reconstructing the evolutionary relationships of the ants using molecular characters from a ca. 600 base-pair segment of DNA from Cytochrome Oxidase I, a mitochondrial gene. See her webpage for more details.

Despite attempts to test hypotheses of cospeciation between obligately associated ant and plant mutualists, the dominant route to the species diversity of ant - plant mutualisms worldwide appears to have involved ecological fitting between pre-adapted partners having no history of co-adaptation.

In western Malesia, a speciose group of 26 closely-related myrmecophytes in the genus Macaranga is inhabited and defended almost solely by Crematogaster ants that are in turn hosted exclusively by Macaranga in hollow stems (domatia). The vast majority of these ants are members of a species-complex in the subgenus Decacrema. The high degree of mutual specificity between Macaranga and Decacrema as a whole suggests a possible history of cospeciation.

In the light of phylogenetic relationships of 204 Crematogaster ants (based on the mitochondrial gene Cytochrome Oxidase I [COI]) and the Macaranga phylogeny, we examine the phylogenesis of host use.

The colonization of Macaranga appears to have evolved independently in three lineages of Crematogaster. Additionally, Asian and Madagascan Decacrema appear to form a monophyletic group. Although Decacrema and Macaranga are mutually specific as a group, associations between lineages of Decacrema and species of Macaranga do not show strict pairwise specificity, and their phylogenies are not congruent. However, host association patterns show some degree of specificity and conservatism and suggest that Decacrema and Macaranga likely diversified contemporaneously (codiversified) rather than undergoing speciation in parallel.

The phylogenesis of host use also suggests that ecological fitting has contributed to the species diversity of the mutualists. Based on biogeographical history of Southeast Asia and rates of COI evolution, the association between Macaranga and Decacrema is inferred to have originated in the mid-Miocene about 11.33 my ago.