Direct selection on allozymes is not required to explain heterogeneity among marker loci across a Mytilus hybrid zone
Direct selection on allozymes is not required to explain heterogeneity among marker loci across a Mytilus hybrid zone
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DOI：
10.1046/j.1365-294x.2003.01936.x
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发表时间：
2003-09-01
影响因子：
4.9
通讯作者：
Borsa, P
中科院分区：
文献类型：
--
作者：
Bierne, N;Daguin, C;Borsa, P
两种类型的位点（同工酶和DNA标记）之间的不平等分化最近被认为是对某些同工酶位点进行直接选择的证据。我们在这里提供了一个反例：一个非编码DNA位点，表现出与受牵连的同酶一样多的分化。等位酶和非编码DNA标记之间的遗传分化水平差异很大，两类标记之间没有明显差异。这表明，遗传分化中强烈的位点间差异与标记类型之间的差异相混淆，这是由于基因座采样不足和不平衡造成的。中性基因座间分化的异质性可由异源分化前的二次接触期间的随机方差造成。在杂交区，变异的另一个来源是继发性接触后染色体区域之间的差异渐渗，这是由于所选基因对或多或少遥远标记的局部影响。然而，仅凭分化程度无法区分间接的伪选择（杂交带的规则和普遍特征）和直接选择。更一般地说，我们建议，当怀疑基因交换存在半渗透性遗传障碍时，必须谨慎应用基于标记类型差异的比较中性测试。
Unequal differentiation between two types of loci (allozyme and DNA markers) across a Mytilus hybrid zone has recently been claimed as evidence for direct selection on some allozyme loci. We provide here a counter-example: a noncoding DNA locus that exhibits as much differentiation as the incriminated allozymes do. The levels of genetic differentiation varied widely among both allozymes and noncoding DNA markers and no clear difference emerged between the two types of markers. This suggests that the strong interlocus variance in genetic differentiation has been confounded with a discrepancy between marker types as a result of an insufficient and unbalanced locus sampling. Heterogeneity in differentiation among neutral loci can be created by stochastic variance during the allopatric divergence preceding a secondary contact. In hybrid zones, a further source of variance is differential introgression among chromosomal regions after the secondary contact owing to the local influence of selected genes on more or less distant markers. However, the degree of differentiation alone gives no way to distinguish indirect pseudo-selection (a regular and ubiquitous feature of hybrid zones) from direct selection. More generally, we suggest that comparative neutrality tests based on discrepancies among marker types have to be applied with caution when the presence of semi-permeable genetic barriers to gene exchange is suspected.