Map of sample locations included in this study.

<p>Map of sample locations included in this study.</p

Abundance of <i>Cerastoderma glaucum</i> with relation to salinity and LOI both in the North/Baltic Sea and in the Mediterranean.

<p>Relative bubble size: density (absent - ca. 10000 ind/m²). Note that the symbol shading used in Figures 2, 3 and 5 is not consistent as different issues are shown.</p

Abundance of <i>Ampharete baltica</i> in relation to bottom salinity and organic sediment content in three sea areas.

<p>The relative bubble size indicates the density of the species with smallest dots referring to species absence and largest bubble size to ca. 1700 ind/m². Note that the symbol shading used in Figures 2, 3 and 5 is not consistent as different issues are shown.</p

Abundance of <i>Travisia forbesii</i> along the full salinity gradient combining the North and Baltic Sea data set and along median grain size.

<p>Relative bubble size: species density (absent – ca. 670 ind/m²). Note that the symbol shading used in Figures 2, 3 and 5 is not consistent as different issues are shown.</p

Extreme genetic depletion upon postglacial colonization hampers determining the provenance of introduced palmate newt populations

Abstract MtDNA barcoding is regularly applied to determine the provenance of invasive species. Variation in spatial genetic structuring across a species’ range, typically high within glacial refugia and low in postglacially colonized areas, influences the precision of this approach. The palmate newt (Lissotriton helveticus) has been introduced north of its native range inside the Netherlands. We conduct mtDNA barcoding to try and retrace the origin of the introduced localities. A large increase in sample size, particularly focusing on temperate Europe, emphasizes that the palmate newt shows practically no genetic variation outside the Iberian Peninsula glacial refugium. While we find a haplotype previously only known from the Iberian Peninsula inside the native range in Belgium, the haplotype present in the introduced Dutch populations occurs widely throughout the native range north of the Iberian Peninsula. Although mtDNA barcoding can be a powerful tool in invasion biology, the palmate newt case exposes its limitations