Data from: Patterns of range-wide genetic variation in six North American bumble bee (Apidae: Bombus) species

The increasing evidence for population declines in bumble bee (Bombus) species worldwide has accelerated research efforts to explain losses in these important pollinators. In North America, a number of once widespread Bombus species have suffered serious reductions in range and abundance, although other species remain healthy. To examine whether declining and stable species exhibit different levels of genetic diversity or population fragmentation, we genotyped a set of microsatellite markers from populations sampled across the geographic distributions of two declining (B. occidentalis; B. pensylvanicus) and four stable (B. bifarius; B. vosnesenskii; B. impatiens; B. bimaculatus) Bombus species. Populations of declining species generally have reduced levels of genetic diversity throughout their range compared to co-distributed stable species. Genetic diversity can be affected by overall range size and degree of isolation of local populations, potentially confounding comparisons among species in some cases. We find no evidence for consistent differences in gene flow among stable and declining species, with all species exhibiting weak genetic differentiation over large distances (e.g., >1,000 km). Populations on islands and at high elevations experience relatively strong genetic drift, suggesting that some conditions lead to genetic isolation in otherwise weakly differentiated species. Bombus bifarius and B. occidentalis exhibit stronger genetic differentiation than the other species, indicating more complex phylogeographic histories consistent with their broader geographic distributions across western North America. Screening genetic diversity in North American Bombus may prove to be useful for identifying species that warrant monitoring, and developing management strategies that promote high levels of gene flow will be a key component in efforts to maintain healthy bumble bee populations.

全球范围内熊蜂属（Bombus）物种种群衰退的相关证据日益增多，推动了针对这类关键传粉昆虫种群衰退机制的研究工作。在北美地区，诸多曾广泛分布的熊蜂物种种群的分布范围与种群丰度均出现了显著缩减，但仍有部分物种种群保持健康状态。为探究衰退型与稳定型熊蜂物种是否存在遗传多样性（genetic diversity）或种群破碎化（population fragmentation）水平的差异，我们针对两种衰退型（B. occidentalis、B. pensylvanicus）与四种稳定型（B. bifarius、B. vosnesenskii、B. impatiens、B. bimaculatus）熊蜂物种的地理分布范围内采集的种群样本，对一组微卫星标记（microsatellite markers）进行了基因分型。相较于同分布区域内的稳定型物种，衰退型物种的种群在其整个分布范围内普遍表现出更低水平的遗传多样性。遗传多样性水平会受整体分布范围大小以及局域种群的隔离程度影响，在部分研究场景中可能会干扰不同物种间的比较分析。我们未发现稳定型与衰退型物种间的基因流（gene flow）存在显著一致性差异的证据；所有物种在大尺度地理距离（如超过1000公里）下均表现出较弱的遗传分化（genetic differentiation）水平。岛屿与高海拔区域的熊蜂种群则经历了相对较强的遗传漂变（genetic drift），这表明部分环境条件会在原本遗传分化较弱的物种中引发遗传隔离（genetic isolation）。B. bifarius与B. occidentalis的遗传分化程度高于其余物种，这与其在北美西部广泛的地理分布特征相符，暗示二者拥有更为复杂的谱系地理历史（phylogeographic history）。对北美地区熊蜂物种的遗传多样性进行筛查，或可用于甄别需要开展监测的物种；而制定能够促进高水平基因流的管理策略，则是维持健康熊蜂种群的核心举措之一。