Résumé
Ixodes uriae is a common ectoparasite of colonial seabirds in thecircumpolar areas of both hemispheres. Despite its potentialeffects on host population dynamics and its role as a vector ofpathogens, little is known about the reproductive strategies ofthis tick under natural conditions. Multiple mating of engorgedfemales has been recorded in several instances, but the resultingpaternity of offspring and its potential evolutionary significancehave never been evaluated. Here, the paternity of offspringproduced by females collected in the field was determined by using5 polymorphic microsatellite markers. The results indicate thatmultiple mating in I. uriae can lead to multiple paternity inbroods and, given the life history of this parasite, may berelated to the adaptive benefits of producing genetically diverseoffspring. Copulations took place both before and after thefemale's blood meal, but most successful fertilizations seemed tooccur before engorgement. This suggests that the mating strategiesof this tick may have evolved in response to local environmentalconstraints and, in particular, to the availability of conspecificticks.