Abstract: Ant societies exhibit striking diversity in their social systems, including variation in the number of queens and mating partners. Knowledge on the number of breeders in a colony is crucial for a better understanding of the evolution of social insect life history traits such as reproductive skew or worker reproduction. Little is known about the breeding system of the formicine ant Lasius fuliginosus (latreille, 1798), even though it is widely distributed in the Palearctic and able to compete ecologically with dominant genera like Formica. Moreover, L. fuliginosus has a particularly interesting life history in that it is a temporary social parasite of several Lasius species, which themselves are tem porary social parasites. We determined the number of (reproductive) queens and mating partners of L. fuliginosus colonies and queens, respectively, from a population in Münster, Germany. Workers from 33 colonies and males from 12 of these colonies were genotyped for four polymorphic microsatellite markers. Our results show that 29 of these colonies were monogynous and monandrous and that two colonies were monogynous and polyandrous. Workers of the remaining two colonies were derived from multiple queens, possibly due to adoption of unrelated queens after the original queen’s death. Furthermore, genotyping of male offspring provided evidence for worker reproduction in three colonies, potentially also in response to queen orphanage in two of these. We estimated the mutation rate at one microsatellite locus in L. fuliginosus to be 1.46 × 10-3 mutations per generation, which is similar to what has been observed in Apis mellifera linnaeus, 1758 and Drosophila melanogaster meiGen, 1830. To our knowledge, this is the first study to provide molecular insights into the breeding system of L. fuliginosus, which appears to be characterized by facultative polyandry and monogyny. In addition, L. fuliginosus now represents the second species in the genus Lasius for which worker reproduction has been documented.

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