Migration rate, timing of sex, and resident genetic diversity jointly shape effective gene flow during rotifer colonization

Abstract Dispersal is a complex process that affects all living organisms, with the settlement phase being particularly critical. This phase depends on the interaction between the environmental conditions of the new habitat and the biological traits of both resident and immigrant populations. While these factors have been studied individually, their combined effects remain poorly understood. To address this gap, we conducted a controlled laboratory experiment using populations of the facultatively sexual rotifer Brachionus plicatilis assembled from clonal lines originating from two natural populations—one serving as the resident and the other as the immigrant. We examined how the combination of initial immigrant density, resident population genetic diversity, and the timing of sexual reproduction in immigrants influences effective gene flow. Using genome‐wide single nucleotide polymorphism (SNP) tracking, we quantified the contribution of immigrants to the diapausing‐egg bank. Our results indicate that all three factors—both individually and interactively—significantly affect settlement success. Specifically, higher immigrant density, lower genetic diversity in the resident population, and earlier sexual reproduction in immigrants were all associated with greater effective gene flow. Notably, these factors interacted: high initial density had the strongest impact when combined with early sexual reproduction in immigrants, while low genetic diversity in the resident population facilitated the settlement of immigrants with delayed sexual reproduction. Overall, our results highlight that multiple interacting factors jointly shape colonization outcomes and provide mechanistic insight into how dispersal and reproduction jointly drive gene flow in metapopulations.