DEMOGRAPHIC-CHANGES AND GENETIC LOSSES IN POPULATIONS OF A SUBTERRANEAN RODENT (CTENOMYS-MAULINUS BRUNNEUS) AFFECTED BY A NATURAL CATASTROPHE

Studied the demographic and genetic effects of a volcanic eruption on two local populations (Rio Colorado, Las Raices) of the fossorial rode nt Ctenomys maulinus brunneus, in the Andes. Our data represent a uniq ue contribution because the pre-existing demographic data and levels o f genetic variation were contrasted with the changes monitored afterwa rds. Comparative census data of the breeding population size before an d after the volcanic eruption, revealed a population decline of about 90% in Rio Colorado. An electrophoretic survey of 23 presumptive enzym e loci detected a considerable reduction of genetic variability in bot h populations. In Rio Colorado, the proportion of polymorphic loci (P) decreased from 47.8% to 17.4%, and the expected heterozygosity (H) fr om 8.9% to 2.8%. In Las Raices, P decreased from 50% to 0% and H from 13.2% to 0%. Although low genetic variability in fossorial mammals is generally assumed to reflect an adaptation to the stable subterranean niche, in some cases it may be merely the result of genetic drift.