ORIGINAL ARTICLE Seasonal nestmate recognition in the ant Formica exsecta Andreas Katzerke & Peter Neumann & Christian W. W. Pirk & Peter Bliss & Robin F. A. Moritz Received: 10 March 2006 / Revised: 21 June 2006 / Accepted: 21 June 2006 / Published online: 4 August 2006 # Springer-Verlag 2006 Abstract Under favorable conditions, the mound-building ant Formica exsecta may form polydomous colonies and can establish large nest aggregations. The lack of worker aggression towards nonnestmate conspecifics is a typical behavioral feature in such social organization, allowing for a free flux of individuals among nests. However, this mutual worker toleration may vary over the seasons and on spatial scales. We studied spatio-temporal variation of worker–worker aggression within and among nests of a polydomous F. exsecta population. In addition, we deter- mined inter- and intracolony genetic relatedness by micro- satellite DNA genotyping and assessed its effect on nestmate recognition. We found significant differences in the frequency of worker exchange among nests between spring, summer, and autumn. Moreover, we found signif- icant seasonal variation in the level of aggression among workers of different nests. Aggression levels significantly correlated with spatial distance between nests in spring, but neither in summer nor in autumn. Multiple regression analysis revealed a stronger effect of spatial distances rather than genetic relatedness on aggressive behavior. Because nestmate discrimination disappeared over the season, the higher aggression in spring is most plausibly explained by cue intermixing during hibernation. Keywords Ants . Intraspecific aggression . Nestmate recognition . Polydomy . Seasonal variation Introduction Social insects are well-known for their ability to distinguish nestmates from nonnestmates (Jaisson 1991), which is fundamental for colony integrity (Crozier and Pamilo 1996). If individuals recognize nestmates by comparing an innate or learnt template with innate or acquired labels or colony odors (Lacy and Sherman 1983), individuals should show a differentiated behavior towards nonnestmates correlating with the nest affiliation (Gamboa et al. 1986). The recognition cues can be of genetic and/or environmen- tal origin in various species (Jutsum et al. 1979; Stuart 1987; Crozier 1988; Crozier and Pamilo 1996). Environ- mental cues, such as food and nesting material (Heinze et al. 1996; Liang and Silverman 2000), may override genetically based ones (Gamboa et al. 1986; Bennett 1989; Beye et al. 1997, 1998). Behav Ecol Sociobiol (2006) 61:143–150 DOI 10.1007/s00265-006-0245-6 Communicated by J. Heinze A. Katzerke (*) : P. Bliss : R. F. A. Moritz Institut für Zoologie, Martin-Luther-Universität Halle-Wittenberg, Hoher Weg 4, 06099 Halle (Saale), Germany e-mail: andreas.katzerke@zoologie.uni-halle.de P. Neumann Swiss Bee Research Centre, Agroscope Liebefeld-Posieux, Swiss Federal Research Station for Animal Production and Dairy Products, Schwarzenburgstrasse 161, 3003 Bern, Switzerland P. Neumann Department of Zoology and Entomology, Rhodes University, Grahamstown 6140, South Africa P. Neumann Eastern Bee Research Institute, Yunnan Agricultural University, Heilongtan, 650201 Kunming, People’s Republic of China C. W. W. Pirk Department of Zoology and Entomology, University of Pretoria, Pretoria 0002, South Africa