RESEARCH ARTICLE High occurrence of colony fusion in a European population of the American termite Reticulitermes flavipes E. Perdereau • A.-G. Bagne `res • S. Dupont • F. Dedeine Received: 16 February 2010 / Revised: 26 March 2010 / Accepted: 30 March 2010 / Published online: 27 April 2010 Ó International Union for the Study of Social Insects (IUSSI) 2010 Abstract The coexistence of multiple unrelated repro- ductives within social insect colonies decreases the related- ness among colony members and therefore challenges kin selection theory. This study investigated the colony genetic structure of a French introduced population of the American subterranean termite Reticulitermes flavipes by analyzing genotypes at eight microsatellite loci and at one mtDNA region. Results revealed that all colonies contained numerous related secondary reproductives, and that 31% of colonies possessed more than two unrelated reproductives. The presence of several unrelated reproductives within colonies of this species is commonly assumed to result from colony fusion. Although such a high occurrence of colony fusion is the highest ever observed in a termite population, it is probable that the available methodology underestimated the detection of colony fusion in French populations. Overall, these results suggest that French colonies might differ strongly from the great majority of American colonies in their capacity to produce sec- ondary reproductives as well as in their ability to merge. The nature and evolutionary origin of these population dif- ferences are discussed. Keywords Termites Á Colony fusion Á Social organization Á Breeding system Á Biological invasion Á Reticulitermes Introduction Social organization—the number and relatedness of repro- ductives within social groups—of animal societies has well been characterized, especially in social insects. However, little is known about the ecological and genetic factors causing its evolution (Bourke and Franks, 1995; Wilson and Ho ¨lldobler, 2005; Johns et al., 2009). The presence of mul- tiple queens and/or kings within social insect colonies is problematic when invoking kin selection as an explanation for the maintenance of eusociality, because the potential for inclusive fitness benefits appears to be lower in these colo- nies in comparison with those headed by a single pair of reproductives (Bourke and Franks, 1995). The coexistence of multiple unrelated reproductives within colonies has long been viewed as an evolutionary paradox (Keller, 1993). This paradox is particularly evident in unicolonial ants, which are characterized by the absence of colony boundaries between interconnected nests that contain many queens and exchange workers, brood and fertile queens (Helantera ¨ et al., 2009). Until now, colony genetic structure in social insects has mostly been studied in ants where almost half of all species may have colonies with several reproducing queens (Heinze and Foitzik, 2009). However, a detailed knowledge of the colony genetic structure of other social insect groups might bring decisive information for understanding the mecha- nisms by which colonies with multiple unrelated reproduc- tives evolve and are maintained within populations. Termites (Isoptera) may provide an appropriate critical comparative system for studying social evolution within complex insect societies, because their eusociality has evolved independently from the Hymenoptera, without haplo- diploid sex determination and with a hemimetabolous devel- opment (Korb, 2008). However, there is still little infor- mation on the ecology and evolution of termites. Typical E. Perdereau Á A.-G. Bagne `res Á S. Dupont Á F. Dedeine (&) Institut de Recherche sur la Biologie de l’Insecte, UMR-CNRS 6035, Faculte ´ des Sciences, Universite ´ de Tours, Parc de Grandmont, 37 200 Tours, France e-mail: franck.dedeine@univ-tours.fr Insect. Soc. (2010) 57:393–402 DOI 10.1007/s00040-010-0096-z Insectes Sociaux