CHROMOSOMAL SPECIATION AND ADAPTIVE RADIATION OF MOLE-RATS IN ASIA-MINOR CORRELATED WITH INCREASED ECOLOGICAL STRESS

The evolutionary forces causing chromosomal speciation and adaptation are still enigmatic. Here we tested the Israeli evolutionary model of positive association of diploid chromosome number (2n) and genetic div ersity with aridity stress in subterranean mole rats, on a 30-times-la rger scale in Asia Minor. We analyzed both karyotype and allozyme dive rsity across Turkey, based on 37 allozymic loci in 20 localities of th e Spalax leucodon and 4 localities of the Spalax ehrenbergi superspeci es. We found extensive chromosomal speciation in S, leucodon (2n = 38, 40, 50, 54, 60, and 62) and in S. ehrenbergi (2n = 52, 56, and 58), p resumably representing from 14 to >20 additional biological species. G enetic diversity indices were low, but, like the chromosome number (2n ), positively correlated with aridity stress, increasing centripetally from the periphery toward geologically young, arid, and climatically unpredictable central Anatolia. Nei's genetic distance D across all po pulations averaged 0.174 (range 0.002-0.422), supporting, combined wit h 2n and ecogeography, the biological species status of most tested po pulations. Chromosome evolution is the basis of speciation and adaptat ion in Spalax; it provides both postmating reproductive isolation, as well. as higher levels of recombination with increased 2n. A mathemati cal model shows that a Robertsonian fission of a single metacentric co nsiderably increases haplotype diversity. This haplotype diversity may contribute to population adaptation to climatic stress and ecological unpredictability in space and time. The increase in diversity corrobo rates the niche-width genetic-variation hypothesis.