An isolated crested newt population in Dutch coastal dunes: distribution relict or introduction?

Abstract

Isolated distribution patches may represent local remnants of a formerly wider range or could have originated by human-mediated expansion beyond the natural range. Distinguishing between these two scenarios is not always straightforward. Northern crested newts (Triturus cristatus) in the Dutch coastal dunes are disconnected from the main species range by over 40 kilometres and whether they have been present historically is unclear. We genotyped crested newts from throughout the Netherlands for an mtDNA marker to determine the provenance of the coastal dune population. Because a closely related species, the Italian crested newt (T. carnifex), has an introduction history in the Netherlands, we also screened eight nuclear DNA SNP markers diagnostic for T. cristatus vs. T. carnifex. The crested newts from the coastal dunes carry a single T. cristatus mtDNA haplotype that naturally occurs in the south, but not the east, of the Netherlands. Therefore, we cannot distinguish if the population represents a natural distribution relict or is derived from an introduction. We find no evidence of genetic admixture with T. carnifex in the coastal dunes, but such admixture is apparent at another Dutch locality (far removed from a previously known genetically admixed population). Our study illustrates how difficult it can be to determine the origin of isolated populations.

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

“…1). There is a similar finding for the great crested newt, where a haplotype otherwise only known from northwestern Romania was recovered in Belgium as well (in the locality Temse, located c. 50 kilometers away from Meerle) (de Brouwer et al, 2023). Except for a laboratory error (which we consider unlikely because the relevant samples were not processed together with Iberian samples), there are three scenarios that could explain an outlier palmate newt haplotype in Belgium: (1) the haplotype occurs naturally north of the Iberian Peninsula, albeit at low frequency; (2) the same haplotype has independently evolved locally, given that it is only one substitution different from the widespread haplotype Lhel016; or (3) newts carrying this haplotype have been introduced in Belgium.…”

“…Therefore, the accuracy with which mtDNA barcoding can pinpoint the provenance of invasive species strongly depends on the source locality of the introduced population. As a consequence, their origin can be determined with high spatial resolution in some cases (Dubey et al, 2019;Dufresnes et al, 2019a;Koster et al, 2023;Kuijt et al, 2023;Robbemont et al, 2023), but remains imprecise in others (de Brouwer et al, 2023;Vliegenthart et al, 2023).…”

“…The palmate newt (Lissotriton helveticus) occurs in the Iberian Peninsula and in western and (a small part of) central Europe (Sillero et al, 2014). In the Netherlands, the species is native to the south, in the provinces Limburg and Noord-Brabant, but has been introduced north of the Rhine river, with around a dozen introduced localities currently known (Creemers and van Delft, 2009; https://www. ravon.nl/Soorten/Soortinformatie/vinpootsala mander; fig.…”

“…This means that the provenance of these introduced localities cannot be determined with a high degree of accuracy. A similar lack of phylogeographic resolution has hampered the ability to determine the provenance of other amphibian populations introduced in the Netherlands, namely the alpine newt Ichthyosaura alpestris, the great crested newt Triturus cristatus, the common tree frog Hyla arborea and the common midwife toad Alytes obstetricans (de Brouwer et al, 2023;Kuijt et al, 2023;Robbemont et al, 2023;Vliegenthart et al, 2023).…”