Supplementary Material for: Tracking Chromosome Evolution in Southern African Gerbils Using Flow-Sorted Chromosome Paints

Desmodillus and Gerbilliscus (formerly Tatera) comprise a monophyletic group of gerbils (subfamily Gerbillinae) which last shared an ancestor approximately 8 million years ago; diploid chromosome number variation among the species ranges from 2n = 36 to 2n = 50. In an attempt to shed more light on chromosome evolution and speciation in these rodents, we compared the karyotypes of 7 species, representing 3 genera, based on homology data revealed by chromosome painting with probes derived from flow-sorted chromosomes of the hairy footed gerbil, Gerbillurus paeba (2n = 36). The fluorescent in situ hybridization data revealed remarkable genome conservation: these species share a high proportion of conserved chromosomes, and differences are due to 10 Robertsonian (Rb) rearrangements (3 autapomorphies, 3 synapomorphies and 4 hemiplasies/homoplasies). Our data suggest that chromosome evolution in Desmodillus occurred at a rate of ∼1.25 rearrangements per million years (Myr), and that the rate among Gerbilliscus over a time period spanning 8 Myr is also ∼1.25 rearrangements/Myr. The recently diverged Gerbillurus (G. tytonis and G. paeba) share an identical karyotype, while Gerbilliscus kempi, G. afra and G. leucogaster differ by 6 Rb rearrangements (a rate of ∼1 rearrangement/Myr). Thus, our data suggests a very slow rate of chromosomal evolution in Southern African gerbils.

德沙鼠属（Desmodillus）与沙跳鼠属（Gerbilliscus，原名为Tatera）构成单系群沙鼠（隶属于沙鼠亚科（Gerbillinae）），二者的最近共同祖先可追溯至约800万年前；该类群各物种的二倍体染色体数（2n）变异范围为2n=36至2n=50。为进一步阐明这类啮齿动物的染色体演化与物种形成机制，研究人员以多毛足沙鼠（Gerbillurus paeba，2n=36）的流式分选染色体探针开展染色体涂染实验，获取同源性数据，进而对代表3个属的7个物种的核型进行了比较分析。荧光原位杂交（fluorescent in situ hybridization, FISH）数据显示出极高的基因组保守性：这些物种共享大量保守染色体，其核型差异仅由10次罗伯逊易位（Robertsonian, Rb）重排导致，其中3次为独有衍征、3次为共有衍征，另有4次为半同态/同态。研究数据表明，德沙鼠属的染色体演化速率约为1.25次重排/百万年（Myr）；而在跨度达800万年的演化时间内，沙跳鼠属的染色体演化速率同样约为1.25次重排/Myr。新近分化的毛足沙鼠属（Gerbillurus）物种（G. tytonis与G. paeba）核型完全一致，而沙跳鼠属的G. kempi、G. afra与G. leucogaster之间存在6次罗伯逊易位重排差异，对应演化速率约为1次重排/Myr。综上，本研究数据显示南非沙鼠的染色体演化速率极为缓慢。