Karyotypic evolution of the family Sciuridae: inferences from the genome organizations of ground squirrels

Abstract

Cross-species chromosome painting has made a great contribution to our understanding of the evolution of karyotypes and genome organizations of mammals. Several recent papers of comparative painting between tree and flying squirrels have shed some light on the evolution of the family Sciuridae and the order Rodentia. In the present study we have extended the comparative painting to the Himalayan marmot (Marmotahimalayana) and the African ground squirrel (Xerus cf. erythropus), i.e. representative species from another important squirrel group – the ground squirrels –, and have established genome-wide comparative chromosome maps between human, eastern gray squirrel, and these two ground squirrels. The results show that 1) the squirrels so far studied all have conserved karyotypes that resemble the ancestral karyotype of the order Rodentia; 2) the African ground squirrels could have retained the ancestral karyotype of the family Sciuridae. Furthermore, we have mapped the evolutionary rearrangements onto a molecular-based consensus phylogenetic tree of the family Sciuridae.

Chromosomal evolution in Rattini (Muridae, Rodentia)

“…This contrasts with non-murid rodents such as squirrels (Sciuridae), where karyotypes (i.e. Menetes berdmorei, Sciurus carolinensis and Callosciurus erythraeus; Richard et al 2003;Stanyon et al 2003;Li et al 2004Li et al , 2006 show extensive conservation with that of human (i.e. ~0.3 R/my).…”

Chromosomal evolution in Rodentia

“…The HSA 1/8 and HSA 2/17 associations previously found in sciuromorphs (and considered to represent the sciurid ancestral condition) are absent in the Eurasian ground squirrels-sousliks and woodchucks-while HSA 10/ 13 and HSA 8/4/8/12/22 are disrupted in four Spermophilus species. Some ground squirrels (Xerus, Menetes) and the flying squirrel (Petaurista) have highly conserved karyotypes that are probably very similar to the ancestral squirrel karyotype and do not differ significantly from that of Rodentia (Richard et al, 2003;Stanyon et al, 2003;Li et al, 2004Li et al, , 2006aBeklemisheva et al, 2011). In contrast to the general conservation of syntenic groups, most sciurid genomes are characterized by variation in the size and distribution of heterochromatin; additionally, multiple centromeric shifts have been reported in some species (Beklemisheva et al, 2011).…”

“…The consensus is that this comprised 38 elements corresponding to the following human chromosomes and/or segmental associations: HSA 9/11, 1/ 10p, 3/21, 16q/19q, 7/16p, 20/15/14, 1pq/8q, 10q/13, 2q/17, 7/ 22qprox/12qdist, 8p/4q/8p/12pq/22qdiss, 3/19p (Supplement Data 3) (Li et al, 2004(Li et al, , 2006aBeklemisheva et al, 2011). The karyotypes of Gliridae are also relatively conserved.…”

“…The fusion HSA 8/12 (resulting in the HSA 8/ 4/8/12/22 association) could be the single rearrangement distinguishing the Ancestral Sciuromorpha Karyotype from RAK. All sciurids share following associations: HSA 1/8, 2/17, 7/22, 10/13, 15/20 (Richard et al, 2003;Li et al, 2004Li et al, , 2006aGraphodatsky et al, 2008;Beklemisheva et al, 2011). Thus, only five fusions are needed to explain the derivation of the Sciuridae Ancestral Karyotype from that of the putative ancestral Sciuromorpha karyotype.…”

A review of bristly ground squirrels Xerini and a generic revision in the African genus Xerus

“…Such differences provide little useful information for phylogenetic reconstructions of interrelationships in Sciuridae because of convergent and reverse rearrangements of the karyotype (Romanenko et al 2011, Richard andDutrillaux 2012). Evidently, Xerini have retained a conservative karyotype which remains similar to the ancestral condition in squirrels (Li et al 2006, Beklemisheva et al 2011). …”