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HERGEN Report Summary

Project ID: Q5RS-2001-01370
Funded under: FP5-LIFE QUALITY
Country: Sweden

Allozyme population structure

Genotyping of 11 polymorphic allozyme loci was performed using muscle, liver, and eye tissue samples of 2064 herring collected at 12 localities including the Baltic, Kattegat, Skagerrak, and North Seas. Sampling was repeated two consecutive years (2002 and 2003) for seven of these localities. Five of the 12 localities were included in a study of allozyme variability in herring that was carried out c. 20 years ago (Ryman et al. 1984, Heredity 53(3), 687-704), and the intention of including these localities in the present study was to create a possibility for long term temporal comparisons. Genotypic data from the Ryman et al. (1984) study is available and permit statistical comparisons between present day variability patterns and that observed two decades ago.

The sampling was not exclusively concentrated to spawning aggregations in the Ryman et al. study and only parts of the material from that study consisted of spawning individuals. In contrast, the sampling within HERGEN was concentrated to spawning aggregations. There were 1681 spawners out of the 2064 fish genotyped at allozyme loci. The observed levels of genetic variation, including expected heterozygosity and number of observed alleles in the present day material are comparable to that of Ryman et al. (1984). Similar to what was reported by Ryman et al. (1984), there are no indications of deviations from Hardy-Weinberg proportions in the present day material. Of a total of 407 individual tests for each sample and locus only two significant deviations were observed. No test remained significant when loci or populations were combined. Combining all samples into a single one resulted in genotype frequencies not significantly different from Hardy-Weinberg expectations.

Pairwise FST between sampling localities in 2002-2003 range from -0.003 to 0.003. Eight cases of significant differences between localities were observed, but none of these remain significant after Bonferroni correction. Overall spatial FST among present day localities is 0.0001 (P<0.001). No short-term genetic change could be observed when comparing samples collected in 2002 with those of 2003. The amount of spatial divergence appears to have remained consistent over the short and long term time periods examined; overall FST among the localities remain at c. 0.001 over the entire period. No long-term temporal differentiation can be observed at four of the five examined localities. At Fehmarn there is a statistically significant difference between the 1979 and 2002 collections, most likely reflecting sampling from different spawning stocks in 1979 vs. 2002.

The statistical power for detecting an FST of 0.005 is about 95% when using the present set of allozyme markers and sampling conditions (n = 100 and sampling from five populations). As we detect only limited occurrences of statistically significant heterogeneity it appears unlikely that the true degree of spatial or temporal divergence at the present allozyme markers is substantially larger than estimated in our study. Thus, the HERGEN sampling in 2002/03 has not changed the previous picture of very restricted spatial differentiation at allozyme loci in this species. The sampling of spawning aggregations has not affected the overall conclusion drawn twenty years ago.

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