Genetic Variability of Earthworms Populations in Soils with Different Perturbation Levels

Agricultural and cattle-raising practices disturb the soil ecosystem and impact on the density and genetic variability of both the macrofauna and mesofauna. This study aimed to analyze the genetic diversity and genetic structure of populations of the earthworm Aporrectodea caliginosa caliginosa (Briones 1996) in two sites of the Argentine Pampa under different levels of perturbation: natural grassland, livestock raising soil with sheeps grazing on natural pasture for 7 years without pesticide application, two agriculture-livestock plots (ALU 1 and ALU 2 ), agriculture soils with alternation of cattle grazing for more than 30 years and agricultural field, a plot with exclusively agricultural use for 17 years. Last plot is considered the most disturbed soil due to continuous agriculture use and higher concentration of pesticide applications. We used the inter-simple sequence repeat (ISSR-PCR) technique, which analyzes the polymorphism generated by random amplification of sequences between repeated DNA regions. The genetic diversity of each soil was determined based on the allele number, polymorphism percentage and Similarity Index. The genetic differentiation between populations was estimated using F ST , ɸ PT and θ II . Allele number and polymorphism percentage showed differences between earthworms from soils with different levels of perturbation. The population with lowest polymorphism was that from the soil with agriculture-livestock 1 (0.57%), while that with the highest polymorphism was the population from natural grassland of Universidad Nacional de Luján soil (UNLu: 0.76%). The smallest genetic distances between individuals were recorded in the agricultural field and agriculture-livestock 1. Population structure was low although significant in both sites. We concluded that the genetic variability of Aporrectodea caliginosa caliginosa populations inhabiting soils with different disturbance cycles and levels could be recorded. The alleles number and polymorphism can be used to record this genetic variability. Genetic variables may be very useful to provide historical and functional information of soils. Further studies are needed to understand the multi-causality (historical and recent) of genetic differences registered. The stability of environmental conditions along with the degree of disturbance must be considered to understand their impact on population genetic structure.