Wielstra Lab

Crested newts comprise four ‘morphotypes’: 1) the Triturus karelinii-group, 2) T. carnifex + T. macedonicus, 3) T. cristatus, and 4) T. dobrogicus. These four morphotypes range from sturdy to slender bodies. Body build is reflected by the number of rib-bearing pre-sacral vertebrae (NRBV), running from NRBV=13 (most sturdy) to NRBV=16 (most slender). Hence, NRBV approximates body build in crested newts. A final fun fact is that crested newt morphotypes differ ecologically. Body build is related to the duration of the annual aquatic period, which runs from three months for NRBV=13 to six months for NRBV=16. This suggest that ecology might have driven the crested newt radiation.

Representatives of the four crested newt morphotypes, ordered from sturdy to slender: 1) T. anatolicus – NRBV=13 – aquatic 3 months; 2) T. macedonicus – NRBV=14 – aquatic 4 months; 3) T. cristatus – NRBV=15 – aquatic 5 months; 4) T. dobrogicus – NRBV=16 – aquatic 6 months. Pictures are by Michael Fahrbach.

To understand how this radiation of body shapes originated in crested newts, we should look at their evolutionary tree (their phylogeny). However, despite several previous attempts, employing a variety of molecular markers, phylogenetic relationships among crested newt morphotypes have never been resolved. For four morphotypes, 15 topologies are possible. The number of additions or subtractions of rib-bearing vertebrae during crested newt evolution differs between these topologies. So how flexible was NRBV during crested newt evolution?

All possible topologies for a phylogeny for four crested newt morphotypes. The four letter abbreviations refer to the morphotypes and the NRBV value for each is between parentheses. The upper left topology requires the least amount of evolutionary change to explain the radiation in NRBV observed today.

In a paper in BMC Evolutionary Biology we finally manage to obtain a well-supported, fully resolved crested newt phylogeny, by using complete mitochondrial genome sequences. We can now look at the evolution of the radiation in body build in crested newts, in the context of the new phylogeny. By taking a step back and looking at NRBV values in other salamanders, we can give NRBV evolution a direction. Most salamanders have a relatively low NRBV=13. Therefore, the root of the crested newt tree, furthest back in time, can be set at NRBV=13 as well. This means that the proto crested newt likely had a low NRBV value, like the T. karelinii-group today (which is also 13), while the higher NRBV values seen in crested newts probably evolved at a later stage.

The crested newt phylogeny based on complete mitochondrial genome sequences. The colours reflect the NRBV values of the four crested newt morphotypes. The changes in NRBV over the course of the evolution of the crested newts are noted along the branches of the tree.

A basal dichotomy separates the T. karelinii-group (NRBV=13) from the remaining crested newts. The next split divides T. carnifex + T. macedonicus (NRBV=14) versus the rest. Finally there is a divide between T. cristatus (NRBV=15) and T. dobrogicus (NRBV=16). To explain the evolution of NRBV, given the new phylogeny, three additions of a rib-bearing vertebrae are required. This actually is the minimal number of steps possible to explain the variation in NRBV observed today (in technical terms, the new phylogeny supports a maximally parsimonious interpretation of NRBV evolution). The new phylogeny makes sense!

Reference: Wielstra, B., Arntzen, J.W. (2011). Unraveling the rapid radiation of crested newts (Triturus cristatus superspecies) using complete mitogenomic sequences. BMC Evolutionary Biology 11: 162.

Note: T. dobrogicus has an NRBV count of 16 or 17 at about equal frequency, but to keep it simple I only used NRBV=16 in this post. The principle is the same.

In a paper in the Journal of Zoological Systematics and Evolutionary Research we explore the evolution of body form in crested newts. In general crested newts started out with large bodies with a short trunk and a wide head. Over time smaller bodies with a longer trunk and narrower had were added to the crested newt repertoire. Ecology likely played an important role in the radiation of body shapes in crested newts.

Reference: Vukov, T.D., Sotiropoulos, K., Wielstra, B., Džukić, G., Kalezić, M.L. (2011). The evolution of the adult body form of the crested newt (Triturus cristatus superspecies, Caudata, Salamandridae). Journal of Zoological Systematics and Evolutionary Research 49(4): 324-334.

Within the crested newt assemblage, known as the Triturus cristatus superspecies, T. karelinii has been severely understudied. Limited data suggests there might me more than one species involved and the systematic position within the crested newt superspecies is unclear. Furthermore, T. karelinii occurs in a region that is understudied from a biogeographical point of view: the Near East. Time to take a closer look!

This ‘geophylogeny’ shows a mitochondrial DNA phylogeography for Triturus karelinii plotted on a map. Note that there are three distinct clades, with their approximate range in different shades of blue.

In a paper published in Molecular Phylogenetics and Evolution, we present a range-wide mitochondrial DNA phylogeography. We show that T. karelinii is a monophyletic group that comprises three very distinct, geographically structured lineages. They are as different from one another as recognized crested newt species are. We also provide a historical biogeographical scenario to explain the origin of these lineages.

In the paper we explain the origin of the genetic variation in T. karelinii in the context of the paleogeology of Eurasia.

Reference: Wielstra, B., Espregueira Themudo, G., Güclü, Ö., Olgun, K., Poyarkov, N.A., Arntzen, J.W. (2010). Cryptic crested newt diversity at the Eurasian transition: the mitochondrial DNA phylogeography of Near Eastern Triturus newts. Molecular Phylogenetics and Evolution 56(3): 888-896.

Male crested newt of the T. karelinii-group (now called T. ivanbureschi). Picture by Michael Fahrbach.

The Triturus karelinii-group of crested newts has sometimes been considered to comprise two species, ‘T. karelinii proper’ in the east and ‘T. arntzeni’ in the west. Three hypotheses on the position of the boundary between the two have been suggested 1) somewhere in Thrace, 2) aligning with the sea strait system separating Europe and Asia, or 3) somewhere in western Anatolia. In a paper published in Amphibia-Reptilia we analysed allozyme data from Europe and north-western Turkey. We identified an eastern and a western group, in line with a two species treatment. These two groups show genetic admixture in western Anatolia, in line with hypothesis 3. However, the transition between the species is messy and unfortunately the eastern group is undersampled. Furthermore, two deeply divergent mitochondrial DNA clades suggest the transition between the two groups should be positioned further to the east. More questions than answers! Obviously, a more detailed survey on the crested newts of the Triturus karelinii-group is required.

Reference: Arntzen, J.W., Wielstra, B. (2010). Where to draw the line? A nuclear genetic perspective on proposed range boundaries of the crested newts Triturus karelinii and T. arntzeni. Amphibia-Reptilia 31(3): 311-322.

As the crested newts radiated in a short temporal interval, a relatively long time ago, it has proven extremely difficult to resolve their phylogenetic relationships. This might mean they truly did split simultaneously, or the amount of data studies may not have been sufficient. In a paper in Molecular Phylogenetics and Evolution we take another attempt to resolve the crested newt phylogeny. This time around we use sequence data for several nuclear and mitochondrial genes. I don’t think it actually got us much closer to a resolved phylogeny!

Reference: Esprequeira Themudo, G., Wielstra, B., Arntzen, J.W. (2009). Multiple nuclear and mitochondrial genes resolve the branching order of a rapid radiation of crested newts (Triturus, Salamandridae). Molecular Phylogenetics and Evolution 52(2): 321-328.

The genus Triturus comprises the marbled newts (such as T. pygmaeus on the left) and the crested newts (such as T. karelinii on the right). Pictures by Michael Fahrbach.

Despite the genus Triturus (in my humble opinion) being a model system in evolutionary research , the phylogenetic relationships among the different crested newt species have never been resolved. In a paper published in Contributions to Zoology, we consulted allozyme and mitochondrial DNA data to try and rectify this situation. However, despite the large amount of data, we did not manage to improve on the situation. The fuzziness of crested newt relationships might well reflect an actual simultaneous split. We compare time estimates of the crested newt radiation for the allozyme and mitochondrial DNA dataset. We conclude that only the latter can be brought in line with potential geological drivers and provide a biogeographical scenario. This paper was a good opportunity to split the distinct T. macedonicus from T. carnifex, we thought.

Reference: Arntzen, J.W., Esprequeira Themudo, G., Wielstra, B. (2007). The phylogeny of crested newts (Triturus cristatus superspecies): nuclear and mitochondrial genetic characters suggest a hard polytomy, in line with the paleogeography of the centre of origin. Contributions to Zoology 76(4): 261-278.