Data from: Do pathogens reduce genetic diversity of their hosts? Variable effects of sylvatic plague in black-tailed prairie dogs

Introduced diseases can cause dramatic declines in—and even the loss of—natural populations. Extirpations may be followed by low recolonization rates, leading to inbreeding and a loss of genetic variation, with consequences on population viability. Conversely, extirpations may create vacant habitat patches that individuals from multiple source populations can colonize, potentially leading to an influx of variation. We tested these alternative hypotheses by sampling 15 colonies in a prairie dog metapopulation during 7 years that encompassed an outbreak of sylvatic plague, providing the opportunity to monitor genetic diversity before, during and after the outbreak. Analysis of nine microsatellite loci revealed that within the metapopulation, there was no change in diversity. However, within extirpated colonies, patterns varied: In half of the colonies, allelic richness after recovery was less than the preplague conditions, and in the other half, richness was greater than the preplague conditions. Finally, analysis of variation within individuals revealed that prairie dogs present in recolonized colonies had higher heterozygosity than those present before plague. We confirmed plague survivorship in six founders; these individuals had significantly higher heterozygosity than expected by chance. Collectively, our results suggest that high immigration rates can maintain genetic variation at a regional scale despite simultaneous extirpations in spatially proximate populations. Thus, virulent diseases may increase genetic diversity of host populations by creating vacant habitats that allow an influx of genetic diversity. Furthermore, even highly virulent diseases may not eliminate individuals randomly; rather, they may selectively remove the most inbred individuals.外来传入的疫病可导致自然种群出现剧烈衰退，甚至彻底消亡。种群局部灭绝后，再定殖率往往偏低，进而引发近交并造成遗传变异流失，对种群存续能力产生负面影响。反之，局部灭绝可形成空置的生境斑块，可供多个源种群的个体进行定殖，有可能带来遗传变异的大量流入。我们针对上述两种对立假说开展了实证检验：在7年时间内对一个草原犬鼠（prairie dog）集合种群（metapopulation）中的15个群落进行采样，采样周期覆盖了一次野生鼠疫（sylvatic plague）的暴发过程，从而得以对疫病暴发前、暴发期间及暴发后的遗传多样性进行动态监测。对9个微卫星位点（microsatellite loci）的分析结果显示，整个集合种群的遗传多样性并未发生显著改变。但在发生局部灭绝的群落中，遗传模式存在分化：其中一半群落的恢复后等位基因丰富度（allelic richness）低于鼠疫暴发前的水平，而另一半群落的等位基因丰富度则高于暴发前。此外，对个体内部遗传变异的分析显示，在重新定殖的群落中出现的草原犬鼠，其杂合度（heterozygosity）高于鼠疫暴发前存活的个体。我们在6个奠基者个体（founders）中证实了鼠疫存活现象，这些个体的杂合度显著高于随机预期值。综合来看，我们的研究结果表明，尽管空间邻近的种群同时发生局部灭绝，高迁入率仍可在区域尺度维持遗传变异水平。因此，强毒性病原体可通过形成空置生境、促进遗传变异流入的方式，提升宿主种群的遗传多样性。此外，即便是高毒性的疫病，也并非随机清除宿主个体；相反，它们可能选择性地移除近交程度最高的个体。