Article révisé par les pairs
Résumé : There is an evolutionary trade-off between the resources that a species invests in dispersal versus those invested inreproduction. For many insects, reproductive success in patchily-distributed species can be improved by sibling-mating. Inmany cases, such strategies correspond to sexual dimorphism, with males–whose reproductive activities can take place withoutdispersal–investing less energy in development of dispersive resources such as large body size and wings. This dimorphism isparticularly likely when males have little or no chance of mating outside their place of birth, such as when sperm competitionprecludes successful fertilisation in females that have already mated. The economically important bark beetle pest speciesDendroctonus micans (Coleoptera: Curculionidae, Scolytinae) has been considered to be exclusively sibling-mating, with 90% offemales having already mated with their brothers by emergence. The species does not, however, show strong sexualdimorphism; males closely resemble females, and have been observed flying through forests. We hypothesised that this lack ofsexual dimorphism indicates that male D. micans are able to mate with unrelated females, and to sire some or all of theiroffspring, permitting extrafamilial reproduction. Using novel microsatellite markers, we carried out cross-breeding laboratoryexperiments and conducted paternity analyses of resulting offspring. Our results demonstrate that a second mating with a lessrelatedmale can indeed lead to some offspring being sired by the latecomer, but that most are sired by the first, sibling male.We discuss these findings in the context of sperm competition versus possible outbreeding depression.

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