Bottleneck events and allele surfing shape genetic differentiation in the septentrional range of European lobster

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Abstract The long history of exploitation and overexploitation of the European lobster (Homarus gammarus) underscores the importance of understanding its genetic structure to inform sustainable management. A set of 12 microsatellites was used to investigate population genetic structure across 20 samples (Ntotal = 2 304 individuals) collected throughout most of the species’ range. Results confirmed a previously suggested bottleneck in the Dutch coast together with a pronounced genetic break in the northernmost fringe of the distribution (at 68°N in Stefjord/Tysfjord system). The three samples from the northern area displayed the lowest genetic diversity as well as the highest levels of genetic differentiation relative to all other samples (mean FST = 0.07), exceeding the differentiation across the Atlantic-Mediterranean phylogeographic discontinuity (mean FST = 0.03). This pattern aligns with the expectations under range expansion scenarios, where populations at the leading edge often undergo founder effects resulting in reduced genetic variation and increased genetic differentiation. Some 6% of the non-private alleles—mapping to different loci—significantly contributed to spatial genetic structure and showed signatures compatible with allele surfing where latitude was a better predictor than temperature for their allele frequencies despite certain correlation between both variables (r2 = 0.5). The northern limit of the European lobster’s distribution lies beyond its thermal optimum of 10°C–20°C. Consequently, ongoing climate change—superimposed on already challenging environmental conditions at the species’ expansion front—may intensify the effects of directional selection in the northern populations. Future genomic analyses will therefore be essential to disentangle demographic from selection-driven processes.

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