Urbanization influences the trophic position, morphology, and colony structure of invasive African big-headed ants (Hymenoptera: Formicidae) in Taiwan

Ants are among the most prolific invaders especially of urban environments. It has been hypothesized that ants can undergo changes in their behavior, genetics, and phenotype to survive in novel urban habitats. We compared the biology of African big-headed ants (Pheidole megacephala) between urban and periurban forest environments in Taiwan. Specifically, we investigated differences in colony structure and morphology between urban and periurban ants in relation to their diet. We further assessed genetic structure of urban and forest P. megacephala populations to elucidate the possible role of genetic variation to colony structure and morphology. Urban P. megacephala populations exhibited elevated nitrogen stable isotope (815N) values, suggesting a higher trophic position relative to periurban forest habitats; these differences may result from the intake of animal-based resources in urban habitats. Colonies had lower queen number and higher worker relatedness in urban habitats compared with periurban forest habitats. Urban colonies also had larger workers than colonies from periurban populations. Gene flow was not restricted between colonies from urban and periurban environments suggesting that these differences were not strongly influenced by genetic variation among populations.