RELATIVE ABUNDANCE AND RESISTANCE TRAITS OF 2 COLLEMBOLA SPECIES UNDER METAL STRESS

1. Population differentiation was studied in Onychiurus armatus (Tullb.) and Isotoma notabilis Schaffer from a reference site and two highly polluted (Cu, Zn) sites (long-term and short-term exposed, respectively) in the Gusum area, SE Sweden. 2. Growth, survival and reproduction were followed in a Fl generation of O. armatus reared on a diet of the fungus Verticillium bulbillosum (W. Gams and Malla) grown on a series of Cu + Zn amended agar plates. Survival and reproduction were observed in a P generation of I. notabilis incubated in soils with enhanced concentrations of Cu and Zn. 3. Metals affected growth rate but not mean maximum length of O. armatus. The growth rates of both populations decreased significantly with increasing metal concentrations. Animals from the polluted site were less affected by metals and attained reproductive size earlier than those from the reference site. 4. Survival decreased with increasing metal exposure in both species, but there was no significant difference in survival between populations within the species. 5. Reproduction in terms of egg production (O. armatus) and number of juveniles (I. notabilis) was significantly reduced by metals. 6. Higher overall reproduction rates were recorded for O. armatus and I. notabilis from polluted sites compared with the reference sites. The difference between populations of both species reached a maximum in the most polluted treatments. 7. The rareness of I. notabilis in comparison with O. armatus in the polluted soil could not be explained from a weaker phenotypic response to metals. In neither of the species was the population from the polluted site inferior to the reference population. 8. Selection for metal resistance in O. armatus is suggested to operate on the body growth rate and for both species on the reproductive rate.