Karyotypie diversity and taxonomic problems in the genus Arvicanthis (Rodentia,Muridae)

The analyses of R- and C-banding patterns of chromosomes of Arvicanthis niloticus originating from two different localities (Egypt and Central African Republic) revealed karyotypic differences caused by one pericentric inversion and three translocations, one being reciprocal and the others Robertsonian. There were also some differences in centromeric heterochromatin patterns.The data indicate that these two forms are distinct species, cytogenetically isolated, and that a revision of the taxonomic status of the genus Arvicanthis is needed.     

Patterns of karyotype evolution in complexes of sibling species within three genera of African murid rodents inferred from the comparison of cytogenetic and molecular data

Here we report on the analysis of three rodent sibling species complexes belonging to the African genera Arvicanthis, Acomys and Mastomys. Using cytogenetic and molecular approaches we set out to investigate how karyotype and molecular evolution are linked in these muroid sibling species and, in particular, to what extent chromosomal changes are relevant to cladogenic events inferred from molecular data. The study revealed that each complex is characterized by a distinct pattern of karyotype evolution (karyotypic orthoselection), and a specific mutation rate. However we found that the general pattern may be considerably modified in the course of evolution within the same species complex (Arvicanthis, Acomys). This observation suggests that karyotypic orthoselection documented in numerous groups is not so much a reflection of selection of a definite type of chromosomal mutation, as suggested by the classical concept, but is due to genome structure of a given species. In particular, karyotypic change appears related to the quantity and chromosomal location of repeated sequences. The congruence between the chromosomal and molecular data shows that chromosomal changes are often valuable phylogenetic characters (Arvicanthis and Mastomys, but not Acomys). However, most importantly the approach underscores the value of incorporating both in order to gain a better understanding of complex patterns of evolution. Moreover, the fact that every cladogenetic event in Mastomys is supported by two pericentric inversions allowed us to hypothesize that genetic differentiation is initiated by the suppression of recombination within inverted segments, and that the accumulation of multiple pericentric inversions reinforces genetic isolation leading to subsequent speciation. Finally, the low sequence divergences distinguishing karyotypically distinct sibling species within Arvicanthis and Mastomys emphasizes the power of combining cytogenetic and molecular approaches for the characterization of unrecognized components of biodiversity.     

Karyotype identity of two subspecies of Eld's deer [Cervus eldi (Cervinae, Artiodactyla)] and its consequences for conservation

Among the three subspecies generally recognized within the Eld's deer (Cervus eldi)--C. e. eldi, C. e. thamin, and C. e. siamensis--C. e. siamensis is considered to be particularly endangered following its disappearance from a major portion of its original range. The only captive breeding population of this subspecies is in the zoological parks at the Paris Museum of Natural History. Taking into account its low effective population size (Ne = 7) and the increasing levels of inbreeding, the continued breeding of this "micropopulation" in isolation from closely related subspecies and in particular from C. e. thamin, which is much more common in zoos as well as in the nature, is questioned. As an initial step in determining if crosses between these subspecies could be performed without risk of outbreeding depression due, in part, to gross differences in their karyotypes, a comparative chromosome banding analysis (RBG-bands) of C. e. siamensis and C. e. thamin was undertaken. No chromosomal differences were identified between the taxa at the level of resolution obtained. The study suggests that, at least from a karyotypic perspective, no obvious differences delimit the two subspecies, and hybridization between endangered C. e. siamensis and C. e. thamin is not likely to lead to impaired fertility in hybrid animals.     

Karyotype of the rare Johnston’s genet<Emphasis Type="Italic">Genetta johnstoni</Emphasis> (Viverridae) and a reassessment of chromosomal characterization among congeneric species

We present herein new data on karyotypes of members of the genusGenetta. G- and C-banded chromosomes of the Johnston’s genetGenetta johnstoni Pocock, 1908 (2n = 50 / FNa = 92) are described for the first time, and compared with those ofG. genetta (2n = 54 / FNa = 92). In addition, the standard karyotype ofG. maculata (2n = 52 / FNa = 96) was studied. A reassessment of taxonomic attribution of previously published material allowed us to characterize (2n, FNa, and chromosome morphology) the karyotypes of three genets, previously unknown (G. pardina, G. letabae andG. tigrina). Our results show that despite a rather low interspecific variability in 2n and FNa, all the species of genets (exceptG. pardina andG. maculata) appear differentiated when chromosomal morphology is taken into account. Although chromosomal banding data are limited, confrontation of G-band karyotypes with preliminary molecular phylogenetic results reveals that karyotypic evolution within the genusGenetta might involve various rearrangements like Robertsonian and tandem translocations, pericentric inversions, and centromere fissions; thus providing at least for some taxa a solid postzygotic isolation. Finally, our study suggests that cytogenetic analyses might constitute a useful tool for questioning interspecific boundaries, especially within the taxonomically debated complex of large-spotted genets.     

Reciprocal chromosome painting between three laboratory rodent species

The laboratory mouse (Mus musculus, 2n = 40), the Chinese hamster (Cricetulus griseus, 2n = 22), and the golden (Syrian) hamster (Mesocricetus auratus, 2n = 44) are common laboratory animals, extensively used in biomedical research. In contrast with the mouse genome, which was sequenced and well characterized, the hamster species has been set aside. We constructed a chromosome paint set for the golden hamster, which for the first time allowed us to perform multidirectional chromosome painting between the golden hamster and the mouse and between the two species of hamster. From these data we constructed a detailed comparative chromosome map of the laboratory mouse and the two hamster species. The golden hamster painting probes revealed 25 autosomal segments in the Chinese hamster and 43 in the mouse. Using the Chinese hamster probes, 23 conserved segments were found in the golden hamster karyotype. The mouse probes revealed 42 conserved autosomal segments in the golden hamster karyotype. The two largest chromosomes of the Chinese hamster (1 and 2) are homologous to seven and five chromosomes of the golden hamster, respectively. The golden hamster karyotype can be transformed into the Chinese hamster karyotype by 15 fusions and 3 fissions. Previous reconstructions of the ancestral murid karyotype proposed diploid numbers from 2n = 52 to 2n = 54. By integrating the new multidirectional chromosome painting data presented here with previous comparative genomics data, we can propose that syntenies to mouse Chrs 6 and 16 were both present and to hypothesize a diploid number of 2n = 48 for the ancestral Murinae/Cricetinae karyotype.     

Unusually extensive karyotype reorganization in four congeneric Gerbillus species (Muridae: Gerbillinae)

Comparative analysis of the G- and C-banding patterns in four morphologically poorly differentiated Gerbillus species (G. pyramidum, G. perpallidus, G. tarabuli and G. occiduus) was carried out. These gerbils have similar karyotype morphology with 2n and NF equal to 38/76, 40/76, 40/78 and 40/80, respectively. Our study revealed that possibly 70 Robertsonian (Rb) fusions, two pericentric inversions, one tandem translocation and at least 13 non-identified rearrangements have occurred during the karyotypic evolution of these species. The number of chromosomal changes by which any of these species differ from each other ranges from 33 to 49. One Rb fusion was common to two of the species, with only a single autosome-gonosome translocation shared by all four, suggesting a monophyletic origin of these karyotypically highly divergent species. Based on the chromosomal data obtained here, the systematic and geographic implications for these North African species are also discussed.     

Flying lemurs – The 'flying tree shrews'? Molecular cytogenetic evidence for a Scandentia-Dermoptera sister clade

Background  

Flying lemurs or Colugos (order Dermoptera) represent an ancient mammalian lineage that contains only two extant species. Although molecular evidence strongly supports that the orders Dermoptera, Scandentia, Lagomorpha, Rodentia and Primates form a superordinal clade called Supraprimates (or Euarchontoglires), the phylogenetic placement of Dermoptera within Supraprimates remains ambiguous.     

Characterization and chromosomal location of two repeated DNAs in three Gerbillus species

Two tandemly repeated DNA sequences of Gerbillus nigeriae (Rodentia) (GN1 and GN2) were isolated and characterized. Both share a 36 bp repeated unit, which includes a 20 bp motif also found in primate alphoid and other repeated DNAs. The localization of GN1 and GN2 sequences on metaphase chromosomes of three Gerbillus species, G. nigeriae, G. aureus and G. nanus, was studied by fluorescence in situ hybridization (FISH). In the G. nigeriae and G. aureus karyotypes, which were shown to possess large amounts of heterochromatin and to have undergone multiple rearrangements during evolution, both GN1 and GN2 sequences were observed at various chromosomal sites: centromeric, telomeric and intercalary. In contrast, the karyotypically stable G. nanus, which does not possess large amounts of heterochromatin and seems to be a more ancestral species, possesses only GN1 sequences, localized in the juxtacentromeric regions.