The periwinkle Echinolittorina punctata (Mollusca: Gastropoda) tracked the warming of the Mediterranean Sea following the Last Glacial Maximum

Distribution shifts of intertidal species have been thoroughly described for several organisms on the Atlantic coasts of Europe, but comparatively less work has been conducted in the Mediterranean Sea. However, such semi-enclosed basins react faster to global change. The periwinkle Echinolittorina punctata is a littorinid gastropod which has shown a remarkable range expansion during the last few decades. Moreover, its unambiguous taxonomy, accessible habitat and ease of identification qualify it as an ideal descriptor of biotic changes in the Mediterranean Sea. We investigated genetic differentiation among 17 Mediterranean and Atlantic populations covering its current distributional range, using the mitochondrial cox1 marker to test the hypothesis that it experienced a significant range expansion triggered by sea warming after the Last Glacial Maximum (LGM). This would confirm its suitability as descriptor of climatic fluctuations. E. punctata has a weak population structure along its distributional range, with greater haplotype diversity in the western African populations than in the Mediterranean Sea, suggesting a recent population expansion following a bottleneck event. Such range expansion is dated ca. 15,000 years BP, and is, thus, related to the end of LGM. E. punctata planktotrophic development lasts 3-4 weeks, likely triggering the weak population structure and enhanced ability to track environmental change.