The aggression test as a taxonomic tool: Evaluation in sympatric and allopatric populations of wood-ant species

Abstract

Ant-workers of Formica lugubris and F. rufa from colonies living sympatrically (from the same area) and allopatrically (from different areas) were tested in pairs using a laboratory aggression test. The aim was to verify whether sharing the same area of origin influences the relationships among heteroeolonials between and within these species which belong to the F. rufa group. The results suggest that a similar degree of agonistic behaviour (ritualised aggression) was shown in sympatric and allopatric conspecific dyads of both species studied. The interactions between F. lugubris and F. rufa were characterised by a low level of overt aggression both in sympatric and allopatric pairs, confirming the interspecific tolerance observed in our previous studies on these wood-ant species. This reduced aggressiveness between workers of F. lugubris and F. rufa coming from the same or a different area can be interpreted on the basis of their sharing common signals, such as odours and patterns of behaviour. Therefore, their mutual tolerance and acceptance can be indicative of a phylogenetic closeness between such species. We propose that an aggression test can be a valid tool for elucidating systematic problems in this taxonomically difficult group of ants. © 1993 Wiley-Liss, Inc.