Data from: Mixed-source reintroductions lead to outbreeding depression in second-generation descendents of a native North American fish

Reintroductions are commonly employed to preserve intraspecific biodiversity in fragmented landscapes. However, reintroduced populations are frequently smaller and more geographically isolated than native populations. Mixing genetically divergent sources is often proposed to attenuate potentially low genetic diversity in reintroduced populations that may result from small effective population sizes. However, a possible negative tradeoff for mixing sources is outbreeding depression in hybrid offspring. We examined the consequences of mixed-source reintroductions on several fitness surrogates at nine slimy sculpin (Cottus cognatus) reintroduction sites in southeast Minnesota. We inferred the relative fitness of each crosstype in the reintroduced populations by comparing their growth rate, length, weight, body condition, and persistence in reintroduced populations. Pure strain descendents from a single source population persisted in a greater proportion than expected in the reintroduced populations, whereas all other crosstypes occurred in a lesser proportion. Length, weight, and growth rate were lower for second-generation intra-population hybrid descendents than for pure strain and first generation hybrids. In the predominant pure strain, young-of the-year size was significantly greater than any other crosstype. Our results suggested that differences in fitness surrogates among crosstypes were consistent with disrupted co-adapted gene complexes associated with beneficial adaptations in these reintroduced populations. Future reintroductions may be improved by evaluating the potential for local adaptation in source populations or by avoiding the use of mixed sources by default when information on local adaptations or other genetic characteristics is lacking.

重新引入通常被用于保护破碎化景观中的种内生物多样性。然而，相较于原生种群，重新引入的种群往往规模更小、地理隔离程度更高。学界常提出通过混合遗传分化的来源种群，以缓解因有效种群规模较小而可能导致的重新引入种群遗传多样性偏低问题。但混合来源种群存在一项潜在的负面权衡：杂交后代会出现远交衰退（outbreeding depression）。我们于明尼苏达州东南部的9个黏糊杜父鱼（*Cottus cognatus*）重新引入点位开展研究，探究了混合来源种群重新引入对多项适合度替代指标的影响。我们通过比较各杂交类型（crosstype）的生长速率、体长、体重、身体状况以及在重新引入种群中的存续情况，推断了其在引入种群中的相对适合度。来自单一来源种群的纯系后代在重新引入种群中的存续比例高于预期，而其余所有杂交类型的存续比例则低于预期。相较于纯系后代与第一代杂交后代，种群内杂交产生的第二代后代的体长、体重与生长速率均更低。在占优势的纯系种群中，当年幼鱼的体型显著大于其他所有杂交类型的个体。我们的研究结果表明，不同杂交类型间的适合度替代指标差异，与这些重新引入种群中与有益适应性相关的共适应基因复合体被破坏的情况相符。未来的重新引入工作可通过两种方式得到优化：一是评估来源种群的本地适应潜力，二是在缺乏本地适应或其他遗传特征相关信息时，默认避免使用混合来源种群。