The Polyommatus butterflies have holocentric chromosomes, which are characterized by kinetic activity distributed along the entire chromosome length, and the highest range of haploid chromosome numbers (n) known within a single eukaryotic genus (from n = 10 to n = 226). Previous analyses have shown that these numbers most likely evolved gradually from an ancestral karyotype, in accordance with the Brownian motion model of chromosome change accumulation. Here we studied chromosome sets within a monophyletic group of previously non-karyotyped Polyommatus species. We demonstrate that these species have a limited interspecific chromosome number variation from n = 16 to n = 25, which is consistent with the Brownian motion model prediction. We also found intra- and interpopulation variation in the chromosome numbers. These findings support the model of karyotype evolution through the gradual accumulation of neutral or weakly underdominant rearrangements that can persist in the heterozygous state within a population. For Polyommatus poseidonides we report the phenomenon of flexible meiosis in which the chromosome multivalents are able to undergo either conventional or inverted meiosis within the same individual. We hypothesise that the ability to invert the order of the meiotic events may be adaptive and can facilitate proper chromosome segregation in chromosomal heterozygotes, thus promoting rapid karyotype evolution.

中文翻译：

---

具有全中心染色体的昆虫的核型进化和柔性（常规与反向）减数分裂：一个基于Polyommatus蝴蝶的案例研究

所述眼灰蝶属蝴蝶有holocentric染色体，其特征为沿整个染色体长度分布动力学活性，和单倍体染色体数目（最高范围Ñ单个真核属内已知的（从）Ñ = 10至Ñ = 226）。先前的分析表明，根据染色体变化积累的布朗运动模型，这些数目最有可能从祖先的核型逐渐演化而来。在这里，我们研究了以前非核型的多鞭毛虫物种的单系群内的染色体组。我们证明这些物种具有有限的种间染色体数目变异，范围从n = 16到n= 25，这与布朗运动模型预测一致。我们还发现染色体数目内群体内和群体间的差异。这些发现通过逐渐积累的中性或弱优势性重排逐渐积累，可在群体内保持杂合状态，从而支持核型进化模型。对于Polyommatusposeidonides，我们报道了柔性减数分裂现象，其中多价染色体能够在同一个体内经历常规减数分裂或倒数减数分裂。我们假设反转减数分裂事件顺序的能力可能是适应性的，并且可以促进染色体杂合子中正确的染色体分离，从而促进快速核型进化。