Department of Biology, CSU Dominguez Hills, Carson, California, USA.
Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, Michigan, USA.
Mol Ecol. 2022 Aug;31(16):4242-4253. doi: 10.1111/mec.16589. Epub 2022 Jul 14.
For many species, both local abundance and regional occupancy are highest near the centre of their geographic distributions. One hypothesis for this pattern is that niche suitability declines with increasing distance from a species geographic centre, such that populations near range margins are characterized by reduced density and increased patchiness. In these smaller edge populations, genetic drift is more powerful, leading to the loss of genetic diversity. This simple verbal model has been formalized as the central-marginal hypothesis, which predicts that core populations should have greater genetic diversity than edge populations. Here, we tested the central-marginal hypothesis using a genomic data set of 25 species-level taxa of Australian scincid lizards in the genera Ctenotus and Lerista. A majority of taxa in our data set showed range-wide patterns of genetic variation consistent with central-marginal hypothesis, and eight of 25 taxa showed significantly greater genetic diversity in the centre of their range. We then explored biological, historical, and methodological factors that might predict which taxa support the central-marginal hypothesis. We found that taxa with the strongest evidence for range expansion were the least likely to follow predictions of the central-marginal hypothesis. The majority of these taxa had range expansions that originated at the range edge, which led to a gradient of decreasing genetic diversity from the range edge to the core, contrary to the central-marginal hypothesis.
对于许多物种来说，其地理分布中心附近的局部丰度和区域占有率最高。对于这种模式，有一种假说认为，随着与物种地理中心的距离增加，生态位适宜性下降，因此，分布范围边缘的种群密度降低，斑块性增加。在这些较小的边缘种群中，遗传漂变更为强大，导致遗传多样性的丧失。这个简单的口头模型已经被形式化为中心-边缘假说，该假说预测核心种群的遗传多样性应该大于边缘种群。在这里，我们使用澳大利亚石龙子属 Ctenotus 和 Lerista 中 25 个种级分类群的基因组数据集来检验中心-边缘假说。我们数据集中的大多数分类群表现出与中心-边缘假说一致的遗传变异的广泛范围模式，并且 25 个分类群中有 8 个在其分布范围的中心显示出显著更高的遗传多样性。然后，我们探讨了可能预测哪些分类群支持中心-边缘假说的生物、历史和方法因素。我们发现，具有最强范围扩展证据的分类群最不可能遵循中心-边缘假说的预测。这些分类群中的大多数都有起源于分布范围边缘的范围扩展，这导致从分布范围边缘到核心的遗传多样性逐渐降低，与中心-边缘假说相反。
