Ould B I, Chatti N, Britton-Davidian J, Saïd K
Laboratoire de Biologie Cellulaire et Génétique, Unité de Recherche, Génétique (Biodiversité et Environnement) UR/09-30 Faculté de Médecine Dentaire de Monastir, Laboratoire de Biochimie, Faculté de Médecine de Monastir, 5000 Tunisie.
Arch Inst Pasteur Tunis. 2001;78(1-4):33-40.
The Robertsonian phenomenon in house mice (Mus musculus domesticus) from Tunisia consists in the presence of only one 22-chromosome Robertsonian race (22Rb) carrying the maximum number of fusions observed until now. The 22Rb populations exclusively occupy urban centers in the Eastern-Central region of Tunisia where standard population with 40-all acrocentric chromosomes (40Std) occur in surrounding neighborhoods and rural environments. In addition to the habitat partition, allozyme and mitochondrial DNA analyses showed that the 22Rb populations were genetically differentiated from the 40Std ones. This differentiation mostly stemmed from an important decrease in genetic variability in the 22Rb populations from the Sahel towns. The extent of morphological, ecological and genetical divergence observed between these chromosomal races in Tunisia is in agreement with the predictions of the chromosomal speciation model of White which advocates that karyotypic differentiation between taxa can lead to their reproductive isolation and independent evolution. Such a process is verified if the Rb process in Tunisia results from local differentiation which is supported by both the genetic and morphological data. However, the hypothesis of an origin by introduction of these mice from another region of Tunisia or from another country cannot be totally dismissed. In this study, an allozymic analysis of mice (22Rb and 40Std) from the geographically distant city of Kairouan was performed. Results showed that 22Rb and 40Std mice from Kairouan shared the same high degree of variability, and were not genetically differentiated. This contrasts with the results registered in the two chromosomal races in the Sahel towns. Such data argue in favor of a local differentiation of the Robertsonian process in Tunisia and suggest that the decrease in variability of the structural nuclear genes in the Sahel 22Rb populations can be related to an introduction from Kairouan into a Sahel locality resulting in a founder effect or followed by a severe bottleneck prior to its dispersion throughout the Sahel region.
突尼斯家鼠（小家鼠）中的罗伯逊易位现象表现为仅存在一个22条染色体的罗伯逊易位种群（22Rb），该种群携带了迄今为止观察到的最大融合数。22Rb种群仅分布在突尼斯中东部地区的城市中心，而周围社区和农村环境中则存在具有40条全近端着丝粒染色体的标准种群（40Std）。除了栖息地分隔外，等位酶和线粒体DNA分析表明，22Rb种群与40Std种群在遗传上存在差异。这种差异主要源于萨赫勒地区城镇22Rb种群遗传变异性的显著降低。突尼斯这些染色体种群之间观察到的形态、生态和遗传分化程度与怀特染色体物种形成模型的预测一致，该模型主张分类群之间的核型分化可导致它们的生殖隔离和独立进化。如果突尼斯的罗伯逊易位过程是由局部分化导致的，且遗传和形态数据均支持这一点，那么这一过程就得到了验证。然而，从突尼斯其他地区或其他国家引入这些小鼠的起源假说也不能被完全排除。在本研究中，对来自地理上遥远的凯鲁万市的小鼠（22Rb和40Std）进行了等位酶分析。结果表明，来自凯鲁万的22Rb和40Std小鼠具有相同的高度变异性，且在遗传上没有分化。这与萨赫勒地区城镇两个染色体种群的结果形成对比。这些数据支持突尼斯罗伯逊易位过程的局部分化，并表明萨赫勒地区22Rb种群结构核基因变异性的降低可能与从凯鲁万引入到萨赫勒地区有关，从而导致奠基者效应，或者在其扩散到整个萨赫勒地区之前经历了严重的瓶颈效应。
