Abstract
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.
Highlights
Karyotype comparisons between many species of plants and animals have revealed large-scale chromosomal differences [1,2,3,4,5,6,7]
We investigated a sample of 137 scorpions, all of which belonged to the subgenera Tityus (Archaeotityus), T. clathratus, T. maranhensis, T. mattogrossensis, T. paraguayensis, T. pusillus and T. silvestris
Diploid number variability occurred within populations of T. clathratus from Amajari, T. mattogrossensis from Cuiaba, and T. paraguayensis from Campo Grande and between populations of T. silvestris
Summary
Karyotype comparisons between many species of plants and animals have revealed large-scale chromosomal differences [1,2,3,4,5,6,7]. New technologies, such as genome scanning have shown that submicroscopic chromosomal variants are more common than previously thought [8,9,10]. Rearrangements that give rise to chromosome variants frequently reduce the fertility of hybrids due to problems related to chromosome segregation in meiosis and the generation of unbalanced gametes via duplication or deletion. In holocentric, all chromosome segments arising from rearrangements might segregate normally to the poles due to the attachment of microtubules along the entire chromosome length [19,20,21]
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