Abstract
The involvement of chromosome changes in the initial steps of speciation is controversial. Here we examine diversification trends within the mole voles Ellobius, a group of subterranean rodents. The first description of their chromosome variability was published almost 40 years ago. Studying the G-band structure of chromosomes in numerous individuals revealed subsequent homologous, step-by-step, Robertsonian translocations, which changed diploid numbers from 54 to 30. Here we used a molecular cytogenetic strategy which demonstrates that chromosomal translocations are not always homologous; consequently, karyotypes with the same diploid number can carry different combinations of metacentrics. We further showed that at least three chromosomal forms with 2n = 34 and distinct metacentrics inhabit the Pamir-Alay mountains. Each of these forms independently hybridized with E. tancrei, 2n = 54, forming separate hybrid zones. The chromosomal variations correlate slightly with geographic barriers. Additionally, we confirmed that the emergence of partial or monobrachial homology appeared to be a strong barrier for hybridization in nature, in contradistinction to experiments which we reported earlier. We discuss the possibility of whole arm reciprocal translocations for mole voles. Our findings suggest that chromosomal translocations lead to diversification and speciation.
Highlights
The role of chromosome changes in speciation has been discussed for many years [1,2,3,4,5,6]
This study aims to describe the karyotype structure of all currently known chromosomal forms of E. tancrei from the Pamir-Alay, the zone of greatest chromosomal variation, using chromosome painting and G-banding comparison to determine their paths of evolution
The karyotype structure was determined for 379 mole voles from 80 localities across the Pamir-Alay mountains, mostly the Surkhob and Vakhsh rivers valleys (Figures 1 and 2)
Summary
The role of chromosome changes in speciation has been discussed for many years [1,2,3,4,5,6]. There seem to be no radical changes in the development of morphological traits, but reproductive isolation appears, which makes such species a good prospective model for studying evolution [10,11,12,13]. E. talpinus and E. tancrei share the same diploid number, 2n = 54, but differ by the fundamental number, NF = 54 and 56, respectively. The centromere reposition which changed the fundamental number probably led to their reproductive isolation [22]. E. tancrei has one of the most variable karyotypes among mammalian species with diploid numbers varying from 54 to 30 [16,20,24,25,26]. White [2] hypothesized that the evolution of karyotypes in mammals was directed towards a reduction of chromosome number, which Robertsonian translocations can affect
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