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大苇莺和噪大苇莺在同域种群中的杂交但没有回交和渐渗的证据。

Hybridization but no evidence for backcrossing and introgression in a sympatric population of great reed warblers and clamorous reed warblers.

机构信息

Department of Biology, Lund University, Lund, Sweden.

出版信息

PLoS One. 2012;7(2):e31667. doi: 10.1371/journal.pone.0031667. Epub 2012 Feb 27.

Abstract

Hybridization is observed frequently in birds, but often it is not known whether the hybrids are fertile and if backcrossing occurs. The breeding ranges of the great reed warbler (Acrocephalus arundinaceus) and the clamorous reed warbler (A. stentoreus) overlap in southern Kazakhstan and a previous study has documented hybridization in a sympatric population. In the present study, we first present a large set of novel microsatellite loci isolated and characterised in great reed warblers. Secondly, we evaluate whether hybridization in the sympatric breeding population has been followed by backcrossing and introgression.We isolated 181 unique microsatellite loci in great reed warblers. Of 41 loci evaluated, 40 amplified and 30 were polymorphic. Bayesian clustering analyses based on genotype data from 23 autosomal loci recognised two well-defined genetic clusters corresponding to the two species. Individuals clustered to a very high extent to either of these clusters (admixture proportions ≥ 0.984) with the exception of four previously suggested arundinaceus-stentoreus hybrid birds that showed mixed ancestry (admixture proportions 0.495-0.619). Analyses of simulated hybrids and backcrossed individuals showed that the sampled birds do not correspond to first-fourth-generation backcrosses, and that fifth or higher generation backcrosses to a high extent resemble 'pure' birds at this set of markers.We conclude that these novel microsatellite loci provide a useful molecular resource for Acrocephalus warblers. The time to reach reproductive isolation is believed to be very long in birds, approximately 5 Myrs, and with an estimated divergence time of 2 Myrs between these warblers, some backcrossing and introgression could have been expected. However, there was no evidence for backcrossing and introgression suggesting that hybrids are either infertile or their progeny inviable. Very low levels of introgression cannot be excluded, which still may be an important factor as a source of new genetic variation.

摘要

杂交在鸟类中很常见,但通常不知道杂种是否可育,以及是否发生回交。大苇莺(Acrocephalus arundinaceus)和噪大苇莺(A. stentoreus)的繁殖范围在哈萨克斯坦南部重叠,先前的研究记录了同域种群中的杂交现象。在本研究中,我们首先提出了一套在大苇莺中分离和鉴定的新微卫星基因座。其次,我们评估了同域繁殖种群中的杂交是否已经发生了回交和基因渗入。我们从大苇莺中分离出 181 个独特的微卫星基因座。在评估的 41 个基因座中,有 40 个基因座扩增,30 个基因座具有多态性。基于 23 个常染色体基因座的基因型数据进行的贝叶斯聚类分析识别出了两个与两个物种相对应的明确遗传聚类。个体非常倾向于这两个聚类中的任何一个(混合比例≥0.984),除了四只先前被认为是大苇莺-噪大苇莺杂交鸟的个体,它们显示出混合祖先(混合比例 0.495-0.619)。对模拟杂种和回交个体的分析表明,所采样的个体与第一代至第四代回交个体不对应,而第五代或更高代的回交个体在这套标记中很大程度上与“纯”个体相似。我们得出结论,这些新的微卫星基因座为大苇莺属的鸟类提供了一个有用的分子资源。在鸟类中,达到生殖隔离的时间被认为非常长,大约为 500 万年,而这两种苇莺的估计分化时间为 200 万年,因此可以预期会发生一些回交和基因渗入。然而,没有回交和基因渗入的证据表明,杂种要么是不育的,要么是它们的后代是不可存活的。不能排除非常低水平的基因渗入,这仍然可能是一个重要的因素,作为新遗传变异的来源。

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