Data from: Dispersal and selection mediate hybridization between a native and invasive species

Hybridization between native and non-native species has serious biological consequences, but our understanding of how dispersal and selection interact to influence invasive hybridization is limited. Here, we document the spread of genetic introgression between a native (Oncorhynchus clarkii) and invasive (Oncorhynchus mykiss) trout, and identify the mechanisms influencing genetic admixture. In two populations inhabiting contrasting environments, non-native admixture increased rapidly from 1984 to 2007 and was driven by surprisingly consistent processes. Individual admixture was related to two phenotypic traits associated with fitness: size at spawning and age of juvenile emigration. Fish with higher non-native admixture were larger and tended to emigrate at a younger age―relationships that are expected to confer fitness advantages to hybrid individuals. However, strong selection against non-native admixture was evident across streams and cohorts (mean selection coefficient against genotypes with non-native alleles (s) = 0.60; s.e. = 0.10). Nevertheless, hybridization was promoted in both streams by the continuous immigration of individuals with high levels of non-native admixture from other hybrid source populations. Thus, antagonistic relationships between dispersal and selection are mediating invasive hybridization between these fish, emphasizing that data on dispersal and natural selection are needed to fully understand the dynamics of introgression between native and non-native species.

本土物种与外来物种间的杂交可引发严重的生物学后果，但目前学界对扩散与选择如何协同作用影响入侵性杂交的认知仍较为有限。本研究记录了本土鱼类克拉克大麻哈鱼（*Oncorhynchus clarkii*）与入侵性虹鳟（*Oncorhynchus mykiss*）间遗传渐渗（genetic introgression）的扩散过程，并解析了影响遗传混合的潜在机制。在两个栖息于迥异生境的种群中，外来遗传组分占比自1984年至2007年快速上升，且其背后的驱动过程出人意料地一致。个体的遗传混合程度与两个关联适合度的表型性状相关：产卵体型与幼鱼迁出年龄。外来遗传组分占比更高的个体体型更大，且倾向于更早迁出——这类关联被认为可赋予杂交个体适合度优势。然而，在两条溪流及不同同龄群中均观察到了针对外来遗传组分的强烈选择：携带外来等位基因的基因型的平均选择系数（s）为0.60，标准误（s.e.）为0.10。尽管如此，来自其他杂交源种群的高外来遗传组分个体持续迁入，推动了两条溪流中的杂交过程。综上，扩散与选择间的拮抗作用介导了该类鱼类的入侵性杂交过程，这凸显出唯有获取扩散与自然选择的相关数据，方能全面解析本土与外来物种间的渐渗动态。