DIFFERENTIAL SURVIVORSHIP OF EVOLVING CHROMOSOMAL SPECIES OF MOLE RATS, SPALAX: AN UNPLANNED LABORATORY EXPERIMENT

Biological species are unique genetic and ecological systems. Closely related species may differ on multiple levels and part of the genetic component of this variation may be unveiled by keeping them under a common standardized environment. Subterranean mole rats of the Spalax ehrenbergi complex in Israel involve four, morphologically indistinguishable (except in mean differences) homozygous chromosomal species (2n = 52, 54, 58 and 60). They represent four dynamically evolving species undergoing ecological speciation related to four different climatic regimes in Israel: cool and humid Upper Galilee Mts. (2n = 52), cool and drier Golan Heights (2n = 54), warm and humid central Mediterranean Israel (2n = 58), and warm and dry Samaria, Judea and northern Negev (2n = 60). These chromosomal species are reproductively isolated in varying degrees and represent different adaptive systems genetically, physiologically, ecologically, and behaviorally (Nevo, 1982). The multidisciplinary studies of the S. ehrenbergi complex have involved hundreds of individuals that were each caught in the field and housed separately in identical tin cages at the Institute of Evolution, University of Haifa, under standardized conditions (19-21 C; 70% R.H.) with the same vegetable food (carrots, potatoes, lettuce, etc.) and sawdust bedding. The present note represents a survivorship analysis of 860 individuals representing 16 populations of the four chromosomal species that were caught in the field from 1974 through 1980 and housed under the above mentioned conditions. We demonstrate that the four chromosomal species differ significantly in their survivorship and life span patterns as well as in acclimatization to the laboratory conditions largely in accord with their adaptive patterns to their climatic origins.