Autosome and Sex Chromosome Diversity Among the African Pygmy Mice, Subgenus Nannomys (Murinae; Mus)

Abstract

The African pygmy mice, subgenus Nannomys, constitute the most speciose lineage of the genus Mus with 19 recognized species. Although morphologically very similar, they exhibit considerable chromosomal diversity which is here confirmed and extended by the G-banding analysis of 65 mice from West and South Africa. On the basis of their karyotype and distribution area, the specimens were assigned to at least five species. Extensive differentiation both within and between species was observed that involved almost exclusively Robertsonian translocations, 23 of which are newly described. Two of the rearrangements were sex chromosome-autosome translocations, associated in some cases with partial deletions of the X or Y chromosomes. Several authors have predicted that the highly deleterious effect of this rearrangement would be reduced if the sex and autosomal segments were insulated by a block of centromeric heterochromatin. The C-banding analyses performed showed that among the species carrying X-autosome translocations, one followed the expected pattern, while the other did not. In this case, functional isolation of the sex and autosome compartments must involve other repetitive sequences or genomic traits that require further molecular characterization. Such studies will provide insight into the causes and consequences of the high diversity of sex chromosome rearrangements in this subgenus.

New data on the taxonomy and distribution of Rodentia (Mammalia) from the western and coastal regions of Guinea West Africa

“…However, from a morphological point of view they are difficult to separate from M. haussa and M. minutoides. Veyrunes et al (2004) karyotyped 31 specimens of M. mattheyi from Burkina Faso, Mali (Farabana, Samaya) and Senegal (Bandia) and found a chromosomal formula close to ours, 2n536, NFa536. This is the first record of M. mattheyi in Guinea and its distribution could correspond to the so-called Guinean savannas zone.…”

“…Veyrunes et al (2004Veyrunes et al ( , 2005, in their revision of Nannomys cytogenetics and phylogeny, provided a clarification in the Nannomys complex of West Africa in distinguishing M. minutoides from M. musculoides. They also sequenced Guinean Nannomys from Bantou and Gbetaya villages close to Faranah that belong clearly to the M. minutoides clade.…”

Steps in the evolution of heteromorphic sex chromosomes

“…Neo-sex chromosome systems are known in many plants and animals, including XY 1 Y 2 in the plant Rumex acetosa (Rejó n et al, 1994), and multiple sex chromosomes due to translocations in African misteltoes (Barlow and Wiens, 1976), termites (Syren and Luykx, 1977), African pygmy mice (Veyrunes et al, 2004) and monotremes (Rens et al, 2004). As we shall describe below, the sex chromosomes of eutherian mammals represent an ancient case of neo-sex chromosomes, established after the divergence of eutherians and marsupials (Waters et al, 2001).…”

The house fly Y Chromosome is young and minimally differentiated from its ancient X Chromosome partner

“…The recycling of differentiated sex chromosomes into a neo-sex chromosome pair in house fly appears to have happened without a fusion to an autosome. In comparison, most previously documented sex chromosome transitions involved autosomes transforming into sex chromosomes through either the evolution of a novel sex-determining locus on the autosome or a fusion of the autosome with a sex chromosome (e.g., Patterson and Stone 1952;Steinemann and Steinemann 1998;Filatov et al 2000;Liu et al 2004;Veyrunes et al 2004;Carvalho and Clark 2005;Vallender and Lahn 2006;Ross et al 2009;Bachtrog 2013, 2015). There are other examples of sex chromosome transformations involving only X, Y, Z, and W Chromosomes (i.e., no autosomes) in platyfish, Rana rugosa, and Xenopus tropicalis (Kallman 1984;Miura 2007;Roco et al 2015).…”