Browsing by Author "Castiglia, Riccardo"

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The origin of an unusual sex chromosome constitution in Acomys sp. (Rodentia, Muridae) from Tanzania
(Springer Science+Business Media B.V. 2006, 2007) Castiglia, Riccardo; Makundi, Rhodes H.; Corti, Marco
This paper describes a case which presents an evident variation from the ‘‘standard’’ XX/XY sex chromosomal constitution in a rodent, Acomys sp. This species known to be found in three localities of East Africa has only recently been separated from A. spinosissimus, its closest relative. In our study, five specimens of Acomys sp. and eight specimens of A. spinosissimus were live-trapped in five localities. Comparisons between the two taxa assed by G- banding show a complete homology in the chromosomal shape and banding pattern for 29 pairs of chromosomes corresponding to the complete autosomal set of A. spinosissimus. However, while all the A. spinosissimus analysed have 2n = 60 and a XY-XX system, in Acomys sp. males and females constitute mosaics for sex chromosomes in the bone marrow cells. Females (2n = 59, 60) have an excess (97%) of aneuploid cells with one single giant X chromosome, and males (2n = 60, 61) show X0/XY cells occurring in somatic tissues and XY cells in the germinal lineage. In addition, an odd heterochromatic submetacentric chromosome was identified in all the cells examined in two males and a female of Acomys sp. Since this chromosome was not related to sex determination and it is not present in all the analysed specimens, it can be considered as a B chromosome. Finally, the in situ fluorescence hybridisation (FISH) with telomeric probes showed a very intense interstitial telomeric signal (ITS) at the medial part on the long heterochromatic arm of the X chromosome. This could be due to recent chromosomal rearrangement.
Rapid chromosomal evolution in the mesic four-striped grass rat rhabdomys dilectus (rodentia, muridae) revealed by mtDNA phylogeographic analysis
(Blackwell Verlag GmbH, 2011-04-27) Castiglia, Riccardo; Solano, Emanuela; Makundi, Rhodes H.; Hulselmans, Jan; Verheyen, Erik; Colangelo, Paolo
The mesic four-striped grass rat Rhabdomys dilectus De Winton, 1897 is distributed in mesic regions of southern and eastern Africa. We carried out a molecular and chromosomal study of the northernmost populations of the species to provide insight into the subspecific boundaries identified within the species and to describe its genetic structure in Eastern Africa. Maximum likelihood, maximum parsimony and neighbour- joining methods were used to construct phylogenetic relationships among all the haplotypes belonging to the large part of the species range. Times of divergences were estimated assuming a relaxed molecular clock with two calibration points. We identified three well-supported clades within R. dilectus. One basal clade corresponding to Rhabdomys d. chakae (2n = 48) is found in South Africa. Two additional sister clades corresponding to R. d. dilectus (2n = 48 and 2n = 46) are allopatrically distributed in southern and northern parts of the species range. Genetic divergence among the three clades is relatively high (ranges 4.2–5.7%). A very divergent new karyotype 2n = 38, FNa = 60 was found in two high-altitude populations on Mt. Meru and Mt. Kilimanjaro. The karyotype differences consist in three Robertsonian fusions and one whole-arm reciprocal translocation. Interestingly, the mtDNA phylogeny does not match with the diploid numbers. In fact, the 2n = 38 specimens form a monophyletic group within a clade that includes specimens with the 2n = 46 karyotype that appears as paraphyletic. We estimated the new karyotype originated in peripatric condition during the last phases of the Pleistocene. This study confirms the importance of chromosomal analysis in detecting taxonomic units and cryptic diversity in rodents.
Rapid chromosomal evolution in the mesic four-striped grass rat rhabdomys dilectus (rodentia, muridae) revealed by mtDNA phylogeographic analysis
(Blackwell Verlag GmbH, 2011-04-27) Castiglia, Riccardo; Solano, Emanuela; Makundi, Rhodes H.; Hulselmans, Jan; Verheyen, Erik; Colangelo, Paolo
The mesic four-striped grass rat Rhabdomys dilectus De Winton, 1897 is distributed in mesic regions of southern and eastern Africa. We carried out a molecular and chromosomal study of the northernmost populations of the species to provide insight into the subspecific boundaries identified within the species and to describe its genetic structure in Eastern Africa. Maximum likelihood, maximum parsimony and neighbour- joining methods were used to construct phylogenetic relationships among all the haplotypes belonging to the large part of the species range. Times of divergences were estimated assuming a relaxed molecular clock with two calibration points. We identified three well-supported clades within R. dilectus. One basal clade corresponding to Rhabdomys d. chakae (2n = 48) is found in South Africa. Two additional sister clades corresponding to R. d. dilectus (2n = 48 and 2n = 46) are allopatrically distributed in southern and northern parts of the species range. Genetic divergence among the three clades is relatively high (ranges 4.2–5.7%). A very divergent new karyotype 2n = 38, FNa = 60 was found in two high-altitude populations on Mt. Meru and Mt. Kilimanjaro. The karyotype differences consist in three Robertsonian fusions and one whole-arm reciprocal translocation. Interestingly, the mtDNA phylogeny does not match with the diploid numbers. In fact, the 2n = 38 specimens form a monophyletic group within a clade that includes specimens with the 2n = 46 karyotype that appears as paraphyletic. We estimated the new karyotype originated in peripatric condition during the last phases of the Pleistocene. This study confirms the importance of chromosomal analysis in detecting taxonomic units and cryptic diversity in rodents.