Debes, Paul Vincent (2007) Phylogeographie und Populationsstruktur der Europäischen Sprotte (Sprattus sprattus) mittels Sequenzdaten der mitochondrialen Kontrollregion. (Diploma thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 120 pp.

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Abstract

The population structure and phylogeography of the European sprat (Sprattus sprattus) was investigated using molecular markers. 210 individuals from seven sampling sites (each n=30) along the European coast from the Baltic to the Black Sea were screened. 82 polymorphic sites within a 530-nucleotide fragment of the mitochondrial control region defined 128 putative haplotypes. Overall haplotype and nucleotide diversity was high (h = 98.5 %, n = 1.54 %). Analysis of molecular variance (AMOV A) and pairwise calculated <l>sT-values did not yield a significant difference among the northern sampling sites from the Baltic Sea, the North Sea and the Bay of Biscay (<ΦST = 0.003 to 0.027, P > 0.05) and between two sampling sites from the Black Sea/Bosporus (<ΦST = -0.018, P = 0.85). Two sampling sites from within the Mediterranean Sea (Gulf of Lyon and Adriatic Sea) were shown to be highly divergent populations according to all pairwise comparisons (<ΦST = 0.411 to 0.789, P < 0.001). Whenthe samples with no observed significant differentiation were pooled to populations, a highly significant differentiation between all populations with an overall <ΦST of 0.59 (P < 0.001) was demonstrated by AMOV A. Genetic diversity within the Northern and the Black Sea population was higher (Northern: mean h = 97.3 %, mean n = 0.95 %; Black Sea: mean h = 93.7 %, mean n = 1.43 %) than that observed within the Mediterranean Sea samples (Gulf of
Lyon: h = 89.4 %, n = 0.44 %; Adriatic Sea: h = 78.4 %, n = 0.89 %). Phylogenetic relationship between haplotypes was analysed using Bayesian analysis, maximum parsimony and statistical parsimony. Two phylogroups, separated by five mutational steps and three fixed differences, could be defined. When the distribution of haplotypes was taken into account, an incomplete geographic separation between both phylogroups was apparent. Haplotypes of both phylogroups and one intennediate haplotype occurred only within the Adriatic sample, suggesting either gene flow from the Northern population or the occurrence of ancestral haplotypes within this population. The hypothesis of isolation by distance was rejected by a Mantel test carried out on pairwise genetic and geographic distances. The largest genetic distance (net nucleotide differences, Da) was observed between the neighbouring samples from the Gulf of Lyon and the Adriatic Sea (Da = 13.261). Phylogeographic analysis indicated a northward range expansion into the Baltic Sea, the North Sea and the Gulf of Biscay of a large stable population of unknown origin. The population of the Gulf of Lyon contained only private haplotypes and showed signs of a bottleneck or a founder event. Within the Black Sea and Bosporus population only relatively divergent private haplotypes were observed. All samples showed signs of recent demographic expans10ns. Possibilities for the genetic structure of sprat are discussed with regards to historical changes throughout the region. Further sampling is needed to evaluate probabilities of possible demographic scenarios.

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