CYTOGENETIC DIVERSITY AND EVOLUTION OF ANDEAN SPECIES OF ELIGMODONTIA(RODENTIA, MURIDAE)

The standard and G-banded chromosomes of northern species of the phyll otine genus Eligmodonita were investigated. E. puerulus showed 2n = 50 , NFa = 48 in bone marrow cells of three males and four females from n orthern Chile, and E. moreni 2n = 34, NFa = 48 in three males from nor thern Argentina. Comparisons showed extensive conservation of G-band p atterns, including those of 15 telocentric chromosomes of the former w ith the arms of eight metacentrics of the latter; these characteristic s suggest seven centric fusions and one pericentric inversion in E. mo reni. C-bands were small in E. puerulus, as well as in the related And inomys edax 2n = 54, NFa = 54 (two males and one female from northern Chile). All these northern species have chromosome arm sizes smaller t han 9% of the total karyotype, in contrast to some longer arms reporte d in the southern E. typus and E. morgani; the latter were probably de rived by tandem fusions. Thus, southern species comprise a derived phy letic line, probably evolved from a primitive northern ancestor having 2n = 50 and NFa = 48. The role of geographic and cytogenetic factors in this speciation pattern, similar to that of the related Auliscomys species living in the same area, is discussed.