A chromosomal analysis of some water beetle species recently transferred from Agabus Leach to Ilybius Erichson, with particular reference to the variation in chromosome number shown by I-montanus Stephens (Coleoptera: Dytiscidae)
A chromosomal analysis of some water beetle species recently transferred from Agabus Leach to Ilybius Erichson, with particular reference to the variation in chromosome number shown by I-montanus Stephens (Coleoptera: Dytiscidae)
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DOI：
10.1111/j.1601-5223.2004.01837.x
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发表时间：
2004-01-01
期刊：
影响因子：
2.7
通讯作者：
Angus, RB
中科院分区：
文献类型：
--
作者：
Aradottir, GI;Angus, RB
本文描述了七种伊比乌斯属植物的核型。除了我瓦氏沙蚕的基本核型为34条常染色体和性染色体，性染色体为X 0（雄性），XX（雌性），其中X染色体是细胞核中最大的染色体之一。这种核型似乎是伊里比乌斯的标准核型，并支持有关物种从阿加布斯转移到伊里比乌斯。I. Wasastjerelus有36个常染色体，X染色体是细胞核中最小的，其核型不同于任何其他已知的Ilybius或Agabus的核型。在大多数物种的研究没有种内变异已被检测到。Chalconatus，其中一个常染色体上有一个倒位多态性，I。montanus，其常染色体数目已被发现在29至34之间变化。这种变异在鞘翅目昆虫中极为罕见。这种变异是由涉及三对不同常染色体的融合-分裂多态性引起的。在每种情况下，融合体可以是纯合的、杂合的或不存在的。调查的所有人群的多态性的一些融合，但只有一个（La Salceda，西班牙）包括个人缺乏所有的融合。融合和非融合的染色体的频率进行了分析，在三个英国人口。只有一种情况下，偏离了哈迪-温伯格平衡的预期值，而且这一群体也与其他两个群体有显著差异。融合杂合子雄性的减数分裂涉及在第一次分裂中产生三价体，但导致产生大量精子，没有证据表明第二中期染色体异常，或由于减数分裂失败而导致细胞退化。这三个融合位点在所有研究的人群中是一致的，可以得出结论，这些融合代表了独特的历史事件，而不是目前的染色体不稳定性。
The karyotypes of seven Ilybius species are described and illustrated. All except I. wasastjernae have a basic karyotype of 34 autosomes plus sex chromosomes which are X0 (male), XX (female), with the X chromosome among the largest in the nucleus. This karyotype appears to be the norm for Ilybius and supports the transfer of the species concerned from Agabus to Ilybius. I. wasastjernae has 36 autosomes and the X chromosome is the smallest in the nucleus and its karyotype is unlike any other known karyotype in either Ilybius or Agabus. In most of the species studied no intraspecific variation has been detected. Exceptions are T chalconatus, where there is one inversion polymorphism in one of the autosomes, and I. montanus whose autosome number has been found to vary from 29 to 34. Such variation is highly unusual among Coleoptera. The variation results from fusion-fission polymorphisms involving three different pairs of autosomes. In each case the fusions may be homozygous, heterozygous or absent. All populations investigated were polymorphic for some of the fusions, but only one (La Salceda, Spain) included individuals lacking all fusions. The frequencies of fused and unfused chromosomes were analysed in three English populations. In only one case was there a departure from the values expected from the Hardy-Weinberg equilibrium, and this population also showed a significant difference from the other two. Meiosis in males heterozygous for fusions involves the production of trivalents in first division, but results in the production of abundant sperm, with no evidence of chromosomal abnormalities in second metaphase, or of degenerating cells as a result of failed meiosis. The three fusions sites are consistent in all the populations studied, and it is concluded that these fusions represent unique historical events rather than current chromosomal instability.