Wielstra Lab

In a big chunk of France, the crested newt Triturus cristatus and the marbled newt T. marmoratus live alongside one another. Sometimes things get frisky: about one in 25 adult Triturus newts here is a first generation (F1) hybrid between the two species. The fitness of these F1 hybrids is pretty lousy, but it turns out they are not a complete evolutionary dead end either. In a paper just out in Evolutionary Applications we show that deeper generation hybrids do exist, albeit very rarely. The non-zero fitness of hybrids provides a window of opportunity for gene flow between the two parent species. This gene flow appears to be skewed from marbled toward crested newts (confirming a previous finding that linked this pattern to hybrid zone movement). There are also some weird biases in which F1 hybrids survive (expanding upon a previous finding). If the mother is a crested newt, the majority of offspring is female (meaning more males die). On the other hand, offspring of marbled newt mothers are mostly males (so here more females die). You really need DNA to unveil all this stuff!

Reference: Arntzen, J.W., Jehle, R., Wielstra, B. (2021). Genetic and morphological data demonstrate hybridization and backcrossing in salamanders at the far end of the speciation continuum. Evolutionary Applications 14(12): 2784-2793.

This spring we conducted fieldwork in the Dutch dune area Meijendel, close to Leiden. One of our target species was the northern crested newt (Triturus cristatus). There is a crested newt population in Meijendel that is completely isolated from the rest of the species’ range. While dipnetting away in a pond full of crested newts, my student Bas Helder caught his first crested newt ever. And it was a weird one: a partially flavistic male, reminiscent of a Koi carp. We wrote a little note about it (in Dutch) in RAVON’s newsletter Schubben & Slijm.

Reference: Helder, B., de Brouwer, J., Ouwehand, J., de Visser, M., Wielstra, B. (2021). Koi-kamsalamander. Schubben & Slijm 48: 8.

In an article aimed at high school students for the journal Frontiers for Young Minds we introduce the evolutionary mystery posed by balanced lethal systems. We use crested newts as an example throughout. Please have a look here.

Reference: Meilink, W.R.M., France, J., de Visser, M.C., Wielstra, B. (2021). Balanced lethal systems: an evolutionary mystery. Frontiers for Young Minds 9: 632945.

I have been awarded an ENW-M-1 grant in NWO’s Open Competition ENW. With this project I will expand my research line on the balanced lethal system in Triturus newts. We know that only those Triturus offspring that possess two different forms of chromosome 1 survive, while those that receive the same form twice from their father and mother, exactly half of the total number, die. We will study developing embryos and their genes simultaneously, to figure out what exactly goes wrong in the unfortunate embryos.

In the 1970s Jozef F. Schmidtler noticed that crested newts in the Berchtesgadener Land, in the extreme southeast of Germany, show morphological characteristics of the Italian crested newt (Triturus carnifex). A particular striking feature was the bright yellow stripe along the back of some juveniles. While this stripe is typical for the Italian crested newt, it is not usually found in the crested newt species that is widely distributed throughout Germany: the northern crested newt (T. cristatus). Schmidtler published his findings in the journal Salamandra.

In a new paper also published in Salamandra we employ a genetic toolkit that was originally designed to screen for ‘genetic pollution’ from the Italian into the northern crested newt. For some reason the Italian crested newt has repeatedly been introduced inside the range of the northern crested newt. Hybridization between the two species poses a complicated conservation concern. The genetic toolkit should be able to pick up ‘Italian alleles’ in the natural hybrid zone just as well. Our results are obvious: alleles of the Italian crested newt are indeed present in the Berchtesgadener Land. In other words, the natural hybrid zone between the northern and Italian crested newts just reaches Germany.

Reference: Fahrbach, M., de Visser, M., Wielstra, B. (2021). The hybrid zone between the Italian and Northern crested newts (Triturus carnifex and T. cristatus) reaches Germany. Salamandra 57(1): 428-434.

A beautiful banded newt because why not (Michael Fahrbach)

A follow-up study on the evolution of the immune system in salamanders, again led by Gemma Palomar and Wiesław Babik, is just out in Molecular Biology and Evolution. We conduct an analysis, recommended in our previous collaboration, in which we test if the diversity of two important players in the immune system, namely the major histocompatibility complex class I and the antigen-processing genes, is correlated across the salamander tree of life. Such correlation is expected if the two coevolve. Coevolution could make the salamander immune response more effective, but would come at the cost of its flexibility. Analysis of an enormous genetic dataset indeed supports co-evolution in the salamander immune system. However, this co-evolution also coincides with extensive duplication of major histocompatibility complex class I genes, increasing flexibility in dealing with new pathogens. Therefore, the salamander immune response reflects a best of both worlds situation.

Reference: Palomar, G., Dudek, K., Migalska, M., Arntzen, J.W., Ficetola, G.F., Jelić, D., Jockusch, E., Martínez-Solano, I., Matsunami, M., Shaffer, H.B., Vörös, J., Waldman, B., Wielstra, B., Babik, W. (2021). Coevolution between MHC class I and Antigen Processing Genes in salamanders. Molecular Biology and Evolution 38(11): 5092-5106.

In an article in Dutch for the journal RAVON we discuss chromosome 1 syndrome – the balanced lethal system ravaging Triturus eggs. You can read it here.

Reference: de Visser, M., France, J., Meilink, W., Wielstra, B. (2021). Een evolutionair raadsel: het dodelijke chromosoom 1 syndroom in Triturus salamanders. RAVON 23(1): 9-12.

Hybrid zones are a main focal point of my work on newts. The genomes of distinct populations are brought together in the genetically admixed offspring that are produced in a hybrid zone. This means that any evolved incompatibility between the genomes, hampering cooperation inside a single organism, are exposed in the hybrid zone. Hence, hybrid zones provide crucial insight into the genetic barriers that underlie the origin of species. In a new ‘quick guide’ published in Current Biology I introduce hybrid zones. Follow this link for temporary free access.

A hybrid zone between the two crested newt species: Triturus ivanbureschi in the west (yellow) and T. anatolicus in the east (blue). The graph depicts the proportion of alleles diagnostic for the eastern species from east to west. A value of 0 corresponds to the western species and a value of 1 to the eastern species. Intermediate frequencies are observed in the hybrid zone (in green on the map). (As usual, thanks to Michael Fahrbach for use of his pictures.)

Reference: Wielstra, B. (2021). Hybrid zones. Current Biology 31(3): PR108-R109.

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.

Male T. karelinii. Picture by Michael Fahrbach.

The southern crested newt (Triturus karelinii) has a striking distribution pattern. It is endemic to the Pontocaspian region and its range comprises three disconnected sections: a Crimean, a Caucasian and a Caspian one. A previous mtDNA phylogeographical survey suggested that the Caucasian range section was colonized from the Caspian one and that the Crimean range section was subsequently colonized from the Caucasian one.

The three disjunct range sections of Triturus karelinii.

In a paper published in Amphibia-Reptilia we look into this proposed colonization history in a bit more detail. Nuclear DNA shows little genetic differentiation between the three range sections and species distribution modelling suggests that they only recently became isolated. While the Crimean range section was indeed only recently colonized, the Caspian and Caucasian ones have been inhabited long-term. Our findings support extensive gene flow between the currently isolated range sections and little genetic diversity across the southern crested newt range.

Reference: Wielstra, B., Arntzen, J.W. (2021). Genetic homogeneity in a Pontocaspian crested newt suggests recent isolation of its three allopatric range sections. Amphibia-Reptilia 42(2) 179-187.