Mattos Viviane Fagundes, Carvalho Leonardo Sousa, Carvalho Marcos André, Schneider Marielle Cristina
Universidade Estadual Paulista "Júlio de Mesquita Filho", UNESP, Departamento de Biologia, Rio Claro, São Paulo, Brazil.
Universidade Federal do Piauí, UFPI, Campus Almícar Ferreira Sobral Floriano, Piauí, Brazil.
PLoS One. 2018 Feb 21;13(2):e0192070. doi: 10.1371/journal.pone.0192070. eCollection 2018.
Scorpions represent an intriguing group of animals characterized by a high incidence of heterozygous chromosomal rearrangements. In this work, we examined six species of Tityus (Archaeotityus) from Brazilian fauna with a particular focus on elucidating the rearrangements responsible for the intraspecific variability of diploid number and the presence of long chromosomal chains in meiosis. To access any interpopulation diversity, we also studied individuals from four species representing distinct localities. Most species demonstrated intraspecific polymorphism in diploid number (2n = 19 and 2n = 20 in T. clathratus, T. mattogrossensis, and T. pusillus, 2n = 16, 2n = 17 and 2n = 18 in T. paraguayensis, and 2n = 16 and 2n = 24 in T. silvestris) and multi-chromosomal associations during meiosis I, which differed even among individuals with the same chromosome number. In some species, the heterozygous rearrangements were not fixed, resulting such as in Tityus clathatrus, in 11 different chromosomal configurations recognized within a same population. Based on meiotic chromosome behaviour, we suggested that independent rearrangements (fusion/fission and reciprocal translocations), occurring in different combinations, originated the multi-chromosomal chains. To evaluate the effects of these chromosome chains on meiotic segregation, we applied the chi-square test in metaphase II cells. The non-significant occurrence of aneuploid nuclei indicated that non-disjunction was negligible in specimens bearing heterozygous rearrangements. Finally, based on our analysis of many chromosome characteristics, e.g., holocentricity, achiasmate meiosis, endopolyploidy, ability to segregate heterosynaptic or unsynapsed chromosomes, (TTAGG)n sequence located in terminal regions of rearranged chromosomes, we suggest that the maintenance of multi-chromosomal associations may be evolutionarily advantageous for these species.
蝎子是一类有趣的动物，其特点是杂合染色体重排的发生率很高。在这项研究中，我们检查了六种来自巴西动物区系的蒂尤斯（古蒂尤斯）蝎子，特别关注阐明导致二倍体数目种内变异以及减数分裂中长染色体链存在的重排。为了探究种群间的多样性，我们还研究了来自四个不同地区的四个物种的个体。大多数物种在二倍体数目上表现出种内多态性（在克氏蒂尤斯、马托格罗索蒂尤斯和小蒂尤斯中2n = 19和2n = 20，在巴拉圭蒂尤斯中2n = 16、2n = 17和2n = 18，在森林蒂尤斯中2n = 16和2n = 24），并且在减数分裂I期间存在多染色体联会，即使在具有相同染色体数目的个体之间也有所不同。在一些物种中，杂合重排并未固定，例如在克氏蒂尤斯中，在同一个种群内识别出了11种不同的染色体构型。基于减数分裂染色体行为，我们认为以不同组合发生的独立重排（融合/裂变和相互易位）产生了多染色体链。为了评估这些染色体链对减数分裂分离的影响，我们在中期II细胞中应用了卡方检验。非整倍体核的非显著出现表明，在具有杂合重排的标本中，不分离现象可以忽略不计。最后，基于我们对许多染色体特征的分析，例如全着丝粒、无交叉减数分裂、核内多倍体、分离异突触或未联会染色体的能力、位于重排染色体末端区域的(TTAGG)n序列，我们认为多染色体联会的维持可能对这些物种具有进化优势。
