Offspring's early-life performance varies with father's sperm quality in a genetically monogamous seabird

Although the effect of sperm quality is well studied in the context of sperm competition, its effect on offspring performance, especially after the embryo stages, has been less investigated. Here, we investigated whether the proportion of spermatozoa with normal morphology was associated with offspring performance during chick development in the black-legged kittiwake, a behaviorally and genetically monogamous seabird in which sperm competition is absent. First, we found that, at hatching, the difference in body condition between the first- and second-hatched siblings was higher when the father had a lower proportion of normal spermatozoa. We discuss this result in light of maternal allocation strategy to manipulate sibling competition. Second, we showed that, in first-hatched chicks, body mass growth between hatching and the age of 10 days, body condition at the age of 10 days and maximum body mass reached before fledging were positively related to the proportion of normal spermatozoa in the father's sperm. Overall, our results support the role of sperm quality on offspring performance in the black-legged kittiwake and call for further studies investigating the importance of sperm quality in genetically monogamous species. The importance of sperm quality has been poorly studied in other contexts than sperm competition. We show that, in a genetically monogamous seabird, the mass growth and condition of first-hatched chicks increase with the proportion of normal spermatozoa in the father's sperm. Unexpectedly, our results further suggest that females might differentially invest into eggs according to traits correlated with the quality of their partner's sperm.