Chromosomal evolution in Rodentia

Lagomorpha (rabbits and pikas) and Sciuromorpha (squirrels) are grouped in the Glires superorder. Their chromosome diversification, since their separation from the eutherian mammalian common ancestor, was characterized by a low rate of chromosome rearrangements. Consequently, the structure of some chromosomes was either conserved or only slightly modified, making their comparison easy at the genus, family and even order level. Interspecific in situ hybridization (Zoo-FISH) largely corroborates classical cytogenetic data but provides much more reliability in comparisons, especially for distant species. We reconstructed common ancestral karyotypes for Glires, Lagomorpha, Sciuromorpha, and Sciuridae species, and then, determined the chromosome changes separating these ancestors from their common eutherian ancestor. We propose that reticulated evolution occurred during the diversification of Glires, which implies that several pericentric inversions and Robertsonian translocations were conserved in the heterozygous status for an extensive period. Finally, among Lagomorpha and Sciuromorpha, we focused on Leporidae and Sciuridae chromosome evolution. In the various attempts to establish dichotomic evolutionary schemes, it was necessary to admit that multiple homoplasies (convergent and reverse rearrangements) occurred in Sciuridae and in a lesser degree, in Leporidae. In Leporidae, additional rearrangements were sufficient to propose a resolved phylogeny. However, a resolved phylogeny was not possible for Sciuridae because most of the rearrangements occurred in terminal branches. We conclude that a reticulated evolution took place early during the evolution of both families and lasted longer in Sciuridae than in Leporidae. In Sciuridae, most chromosome rearrangements were pericentric inversions involving short fragments. Such rearrangements have only mild meiotic consequences, which may explain the long persistence of the heterozygous status characterizing reticulated evolution.

Section: Diversity and Stability Of Lagomorpha And Sciuromorpha Karyosupporting

confidence: 64%

Low, Complex and Probably Reticulated Chromosome Evolution of Sciuromorpha (Rodentia) and Lagomorpha

Richard

Dutrillaux

2012

“…Still, this is investigated in more detail currently by high-resolution molecular and cytogenetic studies [Carbone et al, 2014]. Yet, in Hylobatidae, 10-20 fold faster chromosome rearrangement rates compared to most mammals were revealed, and similar rates were detected in muroid rodents [Romanenko et al, 2012] and equids . The possible mechanisms responsible for such an increased genome evolution might be due to LAVA (gibbon specific retrotransposon)-induced premature transcription termination of chromosome segregation genes [Carbone et al, 2014].…”

Section: Genomic Sequence and Karyotype Evolutionmentioning

confidence: 99%

Comprehensive Analyses of White-Handed Gibbon Chromosomes Enables Access to 92 Evolutionary Conserved Breakpoints Compared to the Human Genome

Weise

Kosyakova

Voigt

et al. 2015

Gibbon species (Hylobatidae) impress with an unusually high number of numerical and structural chromosomal changes within the family itself as well as compared to other Hominoidea including humans. In former studies applying molecular cytogenetic methods, 86 evolutionary conserved breakpoints (ECBs) were reported in the white-handed gibbon (Hylobates lar, HLA) with respect to the human genome. To analyze those ECBs in more detail and also to achieve a better understanding of the fast karyotype evolution in Hylobatidae, molecular data for these regions are indispensably necessary. In the present study, we obtained whole chromosome-specific probes by microdissection of all 21 HLA autosomes and prepared them for aCGH. Locus-specific DNA probes were also used for further molecular cytogenetic characterization of selected regions. Thus, we could map 6 yet unreported ECBs in HLA with respect to the human genome. Additionally, in 26 of the 86 previously reported ECBs, the present approach enabled a more precise breakpoint mapping. Interestingly, a preferred localization of ECBs within segmental duplications, copy number variant regions, and fragile sites was observed.

“…There are significant variations in diploid number both between and within species as well as variations in the number and distribution of heterochromatin blocks and other cytogenetic features. Many findings of comparative cytogenetic studies using FISH have recently been summarized and analyzed in a review by Romanenko et al [2012].…”

mentioning

confidence: 99%

Non-Sciuromorph Rodent Karyotypes in Evolution

Romanenko

Volobouev

2012

Rodents are, taxonomically, the most species-rich mammalian order. They display a series of special genomic features including the highest karyotypic diversity, frequent occurrence of complex intraspecies chromosome variability, and a variety of unusual chromosomal sex determination mechanisms not encountered in other mammalian taxa. Rodents also have an abundance of cytochemically heterogeneous heterochromatin. There are also instances of extremely rapid karyotype reorganization and speciation not accompanied by significant genetic differentiation. All these peculiarities make it clear that a detailed study of rodent genomic evolution is indispensable to understand the mode and tempo of mammalian evolution. The aim of this review is to update the data obtained by classical and molecular cytogenetics as well as comparative genomics in order to outline the range of old and emerging problems that remain to be resolved.