Dowle Eddy J, Morgan-Richards Mary, Trewick Steven A
Ecology Group, IAE, Massey University, Private Bag 11222, Palmerston North, 4442, New Zealand.
Coastal and Freshwater Group, Cawthron Institute, Nelson, New Zealand.
BMC Evol Biol. 2014 Oct 16;14:216. doi: 10.1186/s12862-014-0216-x.
Gene flow is traditionally considered a limitation to speciation because selection is required to counter the homogenising effect of allele exchange. Here we report on two sympatric short-horned grasshoppers species in the South Island of New Zealand; one (Sigaus australis) widespread and the other (Sigaus childi) a narrow endemic.
Of the 79 putatively neutral markers (mtDNA, microsatellite loci, ITS sequences and RAD-seq SNPs) all but one marker we examined showed extensive allele sharing, and similar or identical allele frequencies in the two species where they co-occur. We found no genetic evidence of deviation from random mating in the region of sympatry. However, analysis of morphological and geometric traits revealed no evidence of morphological introgression.
Based on phenotype the two species are clearly distinct, but their genotypes thus far reveal no divergence. The best explanation for this is that some loci associated with the distinguishing morphological characters are under strong selection, but exchange of neutral loci is occurring freely between the two species. Although it is easier to define species as requiring a barrier between them, a dynamic model that accommodates gene flow is a biologically more reasonable explanation for these grasshoppers.
传统上认为基因流是物种形成的一个限制因素，因为需要选择来对抗等位基因交换的同质化效应。在此，我们报告新西兰南岛的两种同域分布的短角蝗虫物种；一种（南方西格蝗）分布广泛，另一种（基氏西格蝗）是狭窄分布的特有物种。
在79个假定的中性标记（线粒体DNA、微卫星位点、ITS序列和RAD-seq单核苷酸多态性）中，除一个标记外，我们检测的所有标记都显示出广泛的等位基因共享，并且在两种物种共发生的区域中，它们的等位基因频率相似或相同。我们没有发现同域分布区域内偏离随机交配的遗传证据。然而，对形态和几何特征的分析没有发现形态渐渗的证据。
基于表型，这两个物种明显不同，但到目前为止它们的基因型没有显示出差异。对此的最佳解释是，一些与区分形态特征相关的基因座受到强烈选择，但中性基因座在这两个物种之间自由交换。虽然将物种定义为需要它们之间存在一个屏障更容易，但一个适应基因流的动态模型对于这些蝗虫来说在生物学上是更合理的解释。
