Immigration into small recipient populations is expected to alleviate inbreeding and increase genetic variation, and hence facilitate population persistence through genetic and/or evolutionary rescue. Such expectations depend on three standard assumptions: that immigrants are outbred, unrelated to existing natives at arrival, and unrelated to each other. These assumptions are rarely explicitly verified, including in key field systems in evolutionary ecology. Yet, they could be violated due to non-random or repeated immigration from adjacent small populations. We combined molecular genetic marker data for 150–160 microsatellite loci with comprehensive pedigree data to test the three assumptions for a song sparrow (Melospiza melodia) population that is a model system for quantifying effects of inbreeding and immigration in the wild. Immigrants were less homozygous than existing natives on average, with mean homozygosity that closely resembled outbred natives. Immigrants can therefore be considered outbred on the focal population scale. Comparisons of homozygosity of real or hypothetical offspring of immigrant-native, native-native and immigrant-immigrant pairings implied that immigrants were typically unrelated to existing natives and to each other. Indeed, immigrants’ offspring would be even less homozygous than outbred individuals on the focal population scale. The three standard assumptions of population genetic and evolutionary theory were consequently largely validated. Yet, our analyses revealed some deviations that should be accounted for in future analyses of heterosis and inbreeding depression, implying that the three assumptions should be verified in other systems to probe patterns of non-random or repeated dispersal and facilitate precise and unbiased estimation of key evolutionary parameters.

中文翻译：

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移民是远交和无关的吗？在野生元种群中测试标准假设

预计移民到小接受者种群将减轻近亲繁殖并增加遗传变异，从而通过遗传和/或进化拯救促进种群持久性。这种期望取决于三个标准假设：移民是远交的，与到达时的现有本地人无关，并且彼此无关。这些假设很少得到明确验证，包括在进化生态学的关键领域系统中。然而，由于邻近小群体的非随机或重复移民，它们可能会受到侵犯。我们将 150-160 个微卫星基因座的分子遗传标记数据与全面的谱系数据相结合，以检验歌麻雀 ( Melospiza melodia)的三个假设种群是量化近亲繁殖和野外移民影响的模型系统。平均而言，移民的纯合度低于现有的本地人，平均纯合度与远交本地人非常相似。因此，在焦点人口规模上，移民可以被视为远交。移民-本地人、本地人-本地人和移民-移民配对的真实或假设后代的纯合性比较表明移民通常与现有的本地人和彼此无关。事实上，移民的后代在焦点种群规模上的纯合性甚至低于远交个体。因此，种群遗传和进化理论的三个标准假设在很大程度上得到了验证。然而，