Genetic changes in a population of fieldmice (Apodemus sylvaticus) during one winter

Making the right conclusions based on wrong results and small sample sizes: interpretation of statistical tests in ecotoxicology

In environmental risk assessments statistical tests are a standard tool to evaluate the significance of effects by pesticides. While it has rarely been assessed how likely it is to detect effects given a specific sample size, it was never analysed how reliable results are if the test preconditions, particularly of parametric tests, are not fulfilled or how likely it is to detect deviations from these preconditions. Therefore, we analyse the performance of a parametric and a non-parametric test using Monte Carlo simulation, focussing on typical data used in ecotoxicological risk assessments. We show that none of the data distributions are normal and that for typical sample sizes of N<20 it is very unlikely to detect deviations from normality. Non-parametric tests performed markedly better than parametric tests, except when data were in fact normally distributed. We finally discuss the impact of using different tests on pesticide risk assessments.

Genetic differentiation among populations of Myopus schisticolor (the wood lemming)--isozyme variation

To investigate genetic differentiation among populations of the wood lemming Myopus schisticolor (Muridae, Rodentia) isozyme variation in 10 populations from three regions, Fennoscandia, Western and Eastern Siberia, was examined. From 20 loci examined, the two most polymorphic ones, Idh-1 and Pgi-1, were used in the complete survey. The results of hierarchical F-statistics analysis showed significant differentiation among all populations; single locus FPT values agreed well (Idh-1, FPT = 0.20; Pgi-1, FPT = 0.20). However, allele frequencies at each locus demonstrated different patterns of subdivision among populations within regions and between regions. Thus, significant values of F-statistics within (FPR = 0.10) and between (FRT = 0.10) regions were found at Idh-1. Pgi-1 showed no significant differentiation among populations within regions (FPR = 0.01). The subdivision among populations at Pgi-1 was based on differentiation between regions (FRT = 0.19). The lack of differentiation among populations within a geographical region at the Pgi-1 locus is surprising for any rodent species, and the discrepancy between single-locus patterns of subdivision seems likely to result from selection at the Pgi-1 locus.