Effective population size and temporal genetic change in stream resident brown trout (Salmo trutta, L.)

Abstract

Temporal genetic data may be used for estimating effective population size (Ne) and for addressing the 'temporal stability' of population structure, two issues of central importance for conservation and management. In this paper we assess the amount of spatio-temporal genetic variation at 17 di-allelic allozyme loci and estimate current Ne in two populations of stream resident brown trout (Salmo trutta) using data collected over 20 years. The amount of population divergence was found to be reasonably stable over the studied time period. There was significant temporal heterogeneity within both populations, however, and Ne was estimated as 19 and 48 for the two populations. Empirical estimates of the probability of detecting statistically significant allele frequency differences between samples from the same population separated by different numbers of years were obtained. This probability was found to be fairly small when comparing samples collected only a few years apart, even for these particular populations that exhibit quite restricted effective sizes. We discuss some implications of the present results for brown trout population genetics and conservation, and for the analysis of temporal genetic change in populations with overlapping generations in general.