Wielstra Lab

The awesome banded newt genus comprises three cryptic species that are really old and have little to no genetic exchange between them. However, the ancestral banded newt appears to have radiated into three species in a relatively short time span. Under such conditions, it is notoriously difficult to retrace the order in which species split. We certainly tried before – and failed. But now, in a paper led by my former MSc students Konstantinos Kalaentzis and Stephanie Koster and out in Molecular Phylogenetics and Evolution, we finally manage to resolve the banded newt phylogeny. The Anatolian banded newt, (currently) in contact with the Caucasian banded newt, is the first offshoot, whereas the Caucasian banded newt is the sister species of the (at the moment) geographically isolated Southern banded newt. Resolving the banded newt phylogeny was only possible because of the Triturus sequence capture protocol, which allows us to get genome-scale data for any newt!

Reference: Kalaentzis, K., Koster, S., Arntzen, J.W., Bogaerts, S., France, J., Franzen, M., Kazilas, C., Litvinchuk, S.N., Olgun, K., de Visser, M.C., Wielstra, B. (2025). Phylogenomics resolves the puzzling phylogeny of banded newts (genus Ommatotriton). Molecular Phylogenetics and Evolution 203: 108237.

Understanding how crested and marbled newt embryos develop inside the egg is critical for my research. During this period, body shape is determined, hybrid unfitness would be expected to reveal itself, and half of the embryos are killed by a balanced lethal system! In a paper published in Journal of Experimental Zoology Part B: Molecular and Developmental Evolution, led by my postdoc Tijana Vučić, we present a ‘staging table’ for crested newt embryonic development. A staging table is basically a summary of embryonic development, in which this continuous process is partitioned into a certain number of stages, based on outside appearance. We focus on a single crested newt species: the Balkan crested newt, Triturus ivanbureschi. Our new crested newt staging table serves as a baseline against which we can compare the embryonic development of individuals that belong to another Triturus species, that are hybrid, or that express arrested development due to the balanced lethal system. Take a look, the pictures and movies are gorgeous! You can download a high resolution PDF version of the poster below here.

Reference: Vućič, T., Drobnjaković, M., Ajduković, M., Bugarčić, M., Wielstra, B., Ivanović, A., Cvijanović, A. (2024). A staging table of Balkan crested newt embryonic development to serve as a baseline in evolutionary developmental studies. Journal of Experimental Zoology Part B: Molecular and Developmental Evolution 342(7): 465-482.

This work was supported by the Serbian Ministry of Science, Technological Development and Innovation (grants nos. 451-03-47/2023-01/200007, 451-03-47/2023-01/200178, 451-03-847/2021-14/2830), the Dutch Research Council – NWO (ENW-M1 grant OCENW.M20.090), and the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. [802759]).

In my lab we are using mtDNA barcoding to try to determine from where within the natural range introduced amphibian populations derive from. In the palmate newt, there is basically no genetic variation north of the Pyrenees Mountains. This also means that when people move newts around within this genetically depleted area, you cannot infer that from mtDNA barcoding. This is what we see in the Netherlands: the introduced populations we scanned are genetically indistinguishable from the native populations. However, if people move newts from the Iberian Peninsula to western Europe this immediately stands out. We see this in Belgium, where we detected an Iberian mtDNA barcode inside the native palmate newt range. For more details, check the paper in Amphibia-Reptilia.

Reference: Elfering, R., Mannix, S., Allain, S., Ambu, J. Crochet, P.-A., van Doorn, L., Dufresnes, C., Jehle, R., Julian, A., Kirkpatrick Baird, F., ‘O Brien, D., Secondi, J., Speybroeck, J., Theodoropoulos, A., Stark, T., Wielstra, B. (2024). Extreme genetic depletion upon postglacial colonization hampers determining the provenance of introduced palmate newt populations. Amphibia-Reptilia 45(3): 349-356.

A male pygmy marbled newt (left) and a male marbled newt. Pictures by Michael Fahrbach.

Although my work is heavily focused on crested newts, there are two marbled newt species in the genus Triturus as well. In a new paper out in Molecular Phylogenetics and Evolution, led by my former MSc student Christos Kazilas, we present a ‘next-generation phylogeography’ of marbled newts. There is remarkable little gene flow between the two marbled newt species compared to crested newts. This finding strongly supports the species status of the two marbled newts – in case anyone was still in doubt. Furthermore, both marbled newt species are composed of two genetically distinct groups. We could expose these intricate patterns thanks to the massive amount of DNA data that is easily generated with the Triturus sequence capture protocol.

Reference: Kazilas, C., Dufresnes, C., France, J., Martínez-Solano, Í., Kalaentzis, K., de Visser, M.C., Arntzen, J.W., Wielstra, B. (2024). Spatial genetic structure in European marbled newts revealed with target enrichment by sequence capture. Molecular Phylogenetics and Evolution 194: 108043.

In an article aimed at high school students for the journal Frontiers for Young Minds my former student Nienke Prins and I explain hybrid zone movement. Obviously we also mention the best example of hybrid zone movement there is: crested newts. Please have a look here.

(You can also see a previous Frontiers for Young Minds piece from our lab on balanced lethal systems here.)

Reference: Prins, N., Wielstra, B. (2024). Moving hybrid zones; when two species meet, mate, and compete. Frontiers for Young Minds 12: 1207354.

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 655487.

In the Dune area of Meijendel, close to Leiden, a population of crested newts occurs. The history of this population is dodgy. While genetic data could not confirm that this population is introduced, the isolated position and apparent rapid expansion speak in favor of such a scenario. Previously we reported on an aberrantly colored newt from this population, with a pattern reminding of a Koi carp. Last spring we caught another odd individual, this time almost completely pale yellow.

Catching two of these weird newts in rapid succession in the same area: surely that cannot be a coincidence? I suspect this high freak-frequency fits with an introduction history for the Meijendel crested newts. The establishment of an introduced population involves similar genetic bottlenecking and inbreeding dynamics as the establishment of island populations and island populations also tend to show a higher incidence of color deviations.

Reference: Elfering, R., Bijlsma, L., Mannix, S., Plomp, S., Theodoropoulos, A., Wielstra, B. (2023). Kamsalamanders met kleurafwijking uit Meijendel. Holland’s Duinen 83: 38-39.

Three banded newt species are currently recognized. However, this was not always the case. Previously, my lab has shown that these morphologically similar species are genetically super distinct. That is why we suggested their treatment as distinct species – despite their morphological similarity. The term ‘cryptic species’ is regularly used in such a case.

But is being genetically distinct enough to qualify as a species? If cryptic species meet in nature, it is possible to perform the ultimate test of species status: hybrid zone analysis. Selection against hybrids allows species to persist. Hybrid zone analysis can tell you if natural selection favors purebreds of either species over their genetically mixed offspring.

In a new paper published in Ecology and Evolution, we show that two of the banded newt species meet at a hybrid zone in northern Türkiye. At this hybrid zone, selection against hybrids is evidently very strong. As a consequence, the hybrid zone is extremely narrow. Our study shows that the two banded newts truly are proper species. We have already shown that, with the benefit of hindsight, it is actually possible to distinguish them based on morphological characteristics.

Reference: Kalaentzis, K., Arntzen, J.W. Avcı, A., van den Berg, V., Beukema, W. France, J., Olgun, K., van Riemsdijk, I., Üzüm, N., de Visser, M.C., Wielstra, B. (2023). Hybrid zone analysis confirms cryptic species of banded newt and does not support competitive displacement since secondary contact. Ecology and Evolution 13(9): e10442.

_{This project has received funding from the European Union’s Horizon 2020 research and innovation programme (under the Marie Skłodowska-Curie grant agreement No. 655487) and the ‘Nederlandse organisatie voor Wetenschappelijk Onderzoek’ (NWO Open Programme 824.14.014)}

Befitting its intimidating scientific name, Ichthyosaura, the alpine newt is an interesting beast. The alpine newt is characterized by hugely divergent mtDNA lineages that may well reflect cryptic species (genetically distinct but morphologically similar species). The distribution of these cryptic species is still incompletely understood. On top of that, alpine newts have been introduced outside their natural range on a massive scale. While the alpine newt has even colonized New Zealand, it is in the Netherlands, the UK and Ireland where the introduced population has truly exploded.

In the context of their BSc research project in my lab, Jody Robbemont and Sam van Veldhuijzen studied an enormous number of samples, from both the native and introduced alpine newt range. Many international collaborators contributed to this dataset. Furthermore, we relied on a large network of volunteers for NGO RAVON to collect skin swabs of alpine newts – a nice example of citizen science.

In a paper out in Amphibia-Reptilia we use the mtDNA barcoding technique to take a closer look at the alpine newt. We manage to delineate the geographical distribution of the cryptic alpine newt species in much more detail then before and home in on the regions where they presumably meet in nature. Our improved alpine newt mtDNA phylogeography also allows us to determine the provenance of many introduced populations. Four out of seven of the highly distinct alpine newt mtDNA lineages are implicated! The alpine newt provides a textbook example of the uncoordinated and simply chaotic nature of species invasion.

Reference: Robbemont, J., van Veldhuijzen, S., Allain, S.J.R., Ambu, J., Boyle, R., Canestrelli, D., Ó Cathasaigh, É., Cathrine, C., Chiocchio, A., Cogalniceanu, D., Cvijanović, M., Dufresnes, C., Ennis, C., Gandola, R., Jablonski, D., Julian, A., Kranželić, D., Lukanov, S., Martínez-Solano, I., Montgomery, R., Naumov, B., O’Neill, M., North, A., Pabijan, M., Pushendorf, R., Salvi, D., Schmidt, B., Sotiropoulos, K., Stanescu, F., Stanković, D., Stapelton, S., Šunje, E., Szabolcs, M., Vacheva, E., Willis, D., Zimić, A., France, J., Meilink, W.R.M., Stark, T., Struijk, R.P.J.H., Theodoropoulos, A., de Visser, M.C., Wielstra, B. (2023). An extended mtDNA phylogeography for the alpine newt illuminates the provenance of introduced populations. Amphibia-Reptilia 44(3): 347-361.

Reference: Wielstra, B., Boer, I. den, France, J., de Visser, M., Struijk, R. (2023). MtDNA barcoding van exotische amfibieën in de duinen. RAVON 89(2): 26-29.

Reference: de Visser, M., Prins, N., France, J., Struijk, R., Wielstra, B. (2023). Exotische amfibieën in de duinen ontmaskerd met mtDNA barcoding. Holland’s Duinen 82(1): 25-29.

Reference: Struijk, R.P.J.H., Prins, N., Koster, S., Putters, N., Jansen, N., Esselaar, J., de Visser, M., France, J., Wielstra, B. (2024). Verspreiding, voortplanting en geografische herkomst van de knoflookpad in Callantsoog. RAVON 26(1): 2-5.

The job of immune genes is to fight off pathogens. However, pathogens don’t take this beating lying down. Pathogens adapt to evade the immune genes, forcing the immune genes to counter-adapt in return. To improve your chances against infection in this evolutionary arms race, would it not be neat if you could borrow immune genes that evolved in another species? Hybridization could facilitate this. Through repeated hybridization, genes can flow between species: a process known as introgression. In a study led by Tomasz Gaczorek and Wiesław Babik, published in Molecular Ecology, we test to what extent the important immune genes of the major histocompatibility complex (MHC) are exchanged between different crested newt species. It turns out that MHC genes introgress more extensively than random genes – exactly what you would expect if natural selection were to favor exotic immune genes.

Reference: Gaczorek, T., Marszałek, M., Dudek, K., Arntzen, J.W., Wielstra, B., Babik, W. (2023) Interspecific introgression of MHC genes in Triturus newts: evidence from multiple contact zones. Molecular Ecology 32(4): 867-880.