Amphibians

Triturus - phylogeny, phylogeography and hybrid zones

The taxonomic status of the marbled newts, the northern marbled newt and the pygmy marbled newt, as full species was once disputed. Our results helped elucidate the matter, giving support for the species status of the two entities [P1]. A detailed survey of a portion of the contact zone between the two species also revealed a complex history of migration, with one of the species completely surrounding a small pocket of the other one, with little interbreeding between them [P2]. Despite its importance in terms of nature conservation, the demonstration of enclaves in natural populations of organisms with low dispersal capability has been a largely neglected topic.

We further modelled the ecological requirement of the two species on their entire range, revealing that those varied in time and space [P4]. This prompted us to examine whether the symmetry, strength and direction of gene flow in different sections of the contact zone would follow predictions derived from the local ecological conditions. The study of interactions between related species particularly at hybrid or contact zones elucidate speciation itself, now seen largely as a process rather than an event. Our work in particular highlights the influence that local conditions have on this process. This has a considerable impact on the way that studies are carried out in the future, as findings may not apply to other areas with dissimilar conditions. Conservation efforts should also take into consideration the dynamics of the contact between species to maintain natural processes.

To clarify the relationships between species in the genus Triturus, we developed a set of nuclear DNA markers variable enough to resolve the phylogeny of the group. As there were few published sequences of nuclear genes of anywhere near closely related to this genus this was extremely difficult at the time. After testing 50+ markers, we settled on five genes that showed some promise [P5]. An initial study using only mitochondrial DNA (mtDNA) pointed to a very fast speciation process at the end of the Miocene that originated most of the crested newt species [P3]. The extension of this study into the nuclear genome required the use of cutting edge algorithms that could tackle the ‘gene tree vs. species tree’ problem. The use of the computer-intensive program BEST (Bayesian Estimates of Species Trees), even though it relied on a very parameter rich molecular evolution model, produced an almost fully resolved species tree. The calibration of this tree with fossil dates allowed us to confirm that species of the group originated from a fast succession of events around 11 million years ago [P6]. The resolution of phylogenetic relationships within the Triturus genus provides a temporal framework for study of the evolution of particular traits such as morphological and physiological characteristics, such as body size and adaptation to aquatic/terrestrial environments, and tissue regeneration, as newts in general are able to regenerate even full limbs and eyes.

Collaborators:

• Pim Arntzen
• Ben Wielstra
• Wieslaw Babik
• Aline Nieman