Schilthuizen Menno, Lombaerts Marcel
Systematic Zoology Group, Institute of Evolutionary and Ecological Sciences, University of Leiden, P.O. Box 9516, NL-2300 RA Leiden, The Netherlands.
Evolution. 1994 Jun;48(3):577-586. doi: 10.1111/j.1558-5646.1994.tb01345.x.
The amount of gene flow among local populations partly determines the relative importance of genetic drift and natural selection in the differentiation of such populations. Land snails, because of their limited powers for dispersal, may be particularly likely to show such differentiation. In this study, we directly estimate gene flow in Albinaria corrugata, a sedentary, rock-dwelling gastropod from Crete, by mark-recapture studies. In the same area, 23 samples were taken and studied electrophoretically for six polymorphic enzyme loci. The field studies indicate that the population structure corresponds closely to the stepping-stone model: demes are present on limestone boulders that are a few meters apart, and dispersal takes place mainly between adjacent demes. Average deme size (N) is estimated at 29 breeding individuals and the proportion of migrants per generation at 0.195 (Nm = 5.7). We find no reason to assume long-distance dispersal, apart from dispersal along occasional stretches of suitable habitat. Genetic subdivision of the population, as derived from F values, corresponds to the direct estimate only at the lowest spatial level (distance between sample sites < 10 m), where values for Nm of 5.4 and 17.6 were obtained. In contrast, at the larger spatial scales, F values give gene-flow estimates that are incompatible with the expected amount of gene flow at these scales. We explain these discrepancies by arguing that gene flow is in fact extremely limited, making correct estimates of Nm from F impossible at the larger spatial scales. In view of these low levels of gene flow, it is concluded that both genetic drift and natural selection may play important roles in the genetic differentiation of this species, even at the lowest spatial scales.
当地种群间基因流动的数量在一定程度上决定了遗传漂变和自然选择在这些种群分化过程中的相对重要性。陆地蜗牛由于其扩散能力有限，可能特别容易出现这种分化。在本研究中，我们通过标记重捕研究直接估计了阿尔比纳里亚波纹螺（Albinaria corrugata）的基因流动，这是一种来自克里特岛、定居于岩石上的腹足纲动物。在同一区域采集了23个样本，并对六个多态性酶位点进行了电泳研究。野外研究表明，种群结构与踏脚石模型密切对应：deme存在于相距几米的石灰岩巨石上，扩散主要发生在相邻的deme之间。平均deme大小（N）估计为29个繁殖个体，每代迁移者的比例为0.195（Nm = 5.7）。除了沿着偶尔的适宜栖息地片段扩散外，我们没有理由假设存在远距离扩散。从F值得出的种群遗传细分仅在最低空间水平（样本位点之间的距离<10米）与直接估计值相符，在该水平获得的Nm值为5.4和17.6。相比之下，在较大的空间尺度上，F值给出的基因流动估计与这些尺度上预期的基因流动量不相符。我们认为这些差异的原因是基因流动实际上极其有限，使得在较大空间尺度上从F值正确估计Nm成为不可能。鉴于这些低水平的基因流动，可以得出结论，即使在最低空间尺度上，遗传漂变和自然选择可能在该物种的遗传分化中都发挥重要作用。
