Data for: Multi-generational fitness effects of natural immigration indicate strong heterosis and epistatic breakdown in a wild bird population

<b>Abstract</b><br/><p><span lang="en-US">The fitness of immigrants and their descendants produced within recipient populations fundamentally underpins the genetic </span><span lang="en-US">and population dynamic</span><span lang="en-US"> consequences of immigration. </span><span lang="en-US">I</span><span lang="en-US">mmigrants can </span><span lang="en-US">in principle </span><span lang="en-US">induce contrasting genetic effects on fitness across generations, reflecting multi-faceted additive, dominance, and epistatic effects. Y</span><span lang="en-US">et, full multi-generational and sex-specific fitness effects of regular immigration have not been quantified within naturally structured systems, precluding inference on underlying genetic architectures </span><span lang="en-US">and population outcomes</span><span lang="en-US">. We used four decades of song sparrow </span><span lang="en-US">(<em>Melospiza melodia</em>)</span> <span lang="en-US">life-history and pedigree data to quantify fitness of natural immigrants, natives, and their F1, F2, and backcross descendants, and test for evidence of non-additive genetic effects. Values of key fitness components (including adult lifetime reproductive success and zygote survival) of F1 offspring of immigrant-native matings substantially exceeded their parent mean, indicating strong heterosis. Meanwhile, F2 offspring of F1-F1 matings had notably low values, indicating surprisingly strong epistatic breakdown. Further, magnitudes of effects varied among fitness components, and</span> <span lang="en-US">differed between female</span><span lang="en-US">s</span><span lang="en-US"> and male</span><span lang="en-US">s</span><span lang="en-US"> descendants. These results demonstrate that strong non-additive genetic effects on fitness can arise within </span><span lang="en-US">weakly </span><span lang="en-US">structured </span><span lang="en-US">and fragmented </span><span lang="en-US">populations </span><span lang="en-US">experiencing </span><span lang="en-US">frequent </span><span lang="en-US">natural </span><span lang="en-US">immigration. </span><span lang="en-US">Such effects will substantially affect the net </span><span lang="en-US">degree of effective gene flow and resulting local genetic introgression and adaptation.</span></p>