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.

外来传入的疫病可引发自然种群数量急剧下降，甚至导致种群完全消亡。局部灭绝发生后，种群再定殖率往往偏低，进而引发近交衰退与遗传变异丢失，对种群存续能力造成负面影响。反之，局部灭绝亦可形成空置的生境斑块，可供多个源种群的个体完成定殖，理论上可带来遗传变异的流入。我们针对一场森林鼠疫（sylvatic plague）暴发期间的7年采样数据，对草原犬鼠（prairie dog）集合种群（metapopulation）中的15个聚居点开展分析，以此检验上述两种对立假说。此次采样覆盖了疫病暴发的前、中、后三个阶段，得以全程监测种群遗传多样性的动态变化。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未发生显著变化。但在发生局部灭绝的聚居点中，遗传模式呈现出分化：半数聚居点恢复后的等位基因丰富度（allelic richness）低于鼠疫暴发前的水平，而另一半聚居点的等位基因丰富度则高于暴发前。此外，对个体内遗传变异的分析表明，经再定殖形成的聚居点中的草原犬鼠，其杂合度（heterozygosity）显著高于鼠疫暴发前的种群个体。我们还确认了6个奠基者个体（founders）的鼠疫存活情况，这些个体的杂合度显著高于随机预期水平。综合来看，本研究结果表明，即便邻近种群同时发生局部灭绝，高迁入率仍可维持区域尺度的遗传变异。因此，高致病性疫病或可通过形成空置生境、促进遗传变异流入，提升宿主种群的遗传多样性。此外，即便是高致病性疫病，也并非随机清除宿主个体：这类疫病或可选择性移除近交程度最高的个体。