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.

物种再引入（reintroductions）通常被用于维持破碎化景观中的种内生物多样性。然而，再引入种群往往比原生种群规模更小、地理隔离程度更高。混合遗传分化的源种群常被提议用于缓解由有效种群规模偏小导致的再引入种群遗传多样性偏低问题，但混合源种群可能存在一项潜在的负面权衡：杂交后代出现远交衰退（outbreeding depression）。我们以明尼苏达州东南部9处黏滑杜父鱼（Cottus cognatus）再引入点位为研究对象，分析了混合源种群再引入对多项适合度替代指标（fitness surrogates）的影响。我们通过比较各杂交组合类型（crosstypes）个体的生长速率、体长、体重、躯体状况以及在再引入种群中的存续率，推断了其相对适合度。单一源种群的纯系后代在再引入种群中的存续比例高于预期，而其余所有杂交组合类型的个体占比均低于预期。第二代种群内杂交后代的体长、体重及生长速率均低于纯系个体与第一代杂交个体。在占绝对优势的纯系种群中，当年幼鱼的体长显著高于其他所有杂交组合类型。本研究结果表明，不同杂交组合类型间的适合度替代指标差异，与这些再引入种群中与有益适应相关的共适应基因复合体（co-adapted gene complexes）被破坏的情形相符。未来的物种再引入工作可通过评估源种群的本地适应（local adaptation）潜力，或是在缺乏本地适应或其他遗传特征相关信息时，默认避免使用混合源种群，以实现优化。