Cryptic crested newt diversity at the Eurasian transition: The mitochondrial DNA phylogeography of Near Eastern Triturus newts
Introduction
Historical biogeography seeks to understand the processes governing the spatio-temporal distribution of biodiversity. Patterns in biodiversity can be established objectively by exploring the genotype (Avise, 2004, Riddle et al., 2008). Phylogeography refers to the section of historical biogeography that aims to uncover the geographical distribution of genealogical lineages within (groups of related) species (Avise, 2000). Present-day distribution patterns are the result of past processes and, aided by gene geography, factors responsible for former vicariance and dispersal can be inferred.
Although each species will have had unique evolutionary responses, similarities in genetic patterns are expected to be present among the components of a region’s contemporary biodiversity (Arbogast and Kenagy, 2001, Avise, 2004). The phylogeographic approach provides the foundation for formulating biogeographical hypotheses, initially for individual model species and ultimately for entire communities. It can be seen as a tool for reconstructing paleogeological scenario’s, analogous to, for example, paleontology and palynology (Riddle et al., 2008).
The Mediterranean region serves as a natural laboratory for phylogeographically oriented studies. The area has experienced a turbulent geological and climatological history, resulting from the continental collision of Eurasia and Africa–Arabia (e.g. Meulenkamp and Sissingh, 2003, Popov et al., 2004, Rögl, 1998). This dynamic past is reflected by the rich biodiversity characterizing the region today (Mittermeier et al., 2005, Myers et al., 2000). The accumulation of phylogeographical information enables the extraction of prevailing biogeographical patterns in the Mediterranean region. However, phylogeographic research has been biased towards the southern European peninsulas (e.g. Beheregaray, 2008).
Amphibians provide an excellent model system for phylogeographical studies (Avise, 2004, Zeisset and Beebee, 2008). The crested newt Triturus cristatus superspecies is distributed in a large segment of the Mediterranean region (e.g. Arntzen, 2003). Crested newts have been subjected to previous phylogeographic analyses, but the emphasis lay on the Balkan Peninsula (e.g. Wallis and Arntzen, 1989, Arntzen et al., 2007). The range of the crested newts traditionally referred to as ‘T. karelinii’ encompasses, next to an isolated Serbian enclave and Thrace on the Balkan Peninsula, the regions Anatolia, Caucasia, Crimea and the southern shore of the Caspian Sea (Fig. 1).
Wallis and Arntzen (1989), based on limited sampling, already hinted at the presence of substantial genetic variation in ‘T. karelinii’. Subsequently, Steinfartz et al. (2007) suggested that ‘T. karelinii’ actually constitutes a paraphyletic grouping. Recently, Espregueira Themudo et al. (2009) uncovered two distinct clades in ‘T. karelinii’, which were postulated to represent two distinct species (elevating the subspecies arntzeni to species level). The phylogenetic scope of these studies – reflected in geographically restricted, low density sampling – hinders the translation of taxonomical interpretation to geographical population; firstly, it is not settled how many distinct forms are included, and secondly, it is not clear how these forms would be distributed (cf. Arntzen and Wielstra, in press). For ease of communication, we refer to the ‘T. karelinii’ crested newts as the T. karelinii group throughout this paper.
We present a range-wide phylogeographic analysis for the T. karelinii group, based on mitochondrial DNA sequence data. We (1) investigate the phylogenetic position of the T. karelinii group in the genus Triturus, (2) explore the distribution and structuring of genetic variation within the T. karelinii group and (3) formulate a hypothesis on the biogeographical history of the T. karelinii group, based on a qualitative comparison of gene geography and paleo-reconstructions.
Section snippets
Sampling strategy
Sampling covers the entire distribution range of the T. karelinii group and includes 144 individuals from 34 georeferenced localities (Table 1, Fig. 1 and Supplementary data Appendix 1). Representatives of the other Triturus species – the four remaining crested newt species (T. carnifex, T. cristatus, T. dobrogicus and T. macedonicus) and the two marbled newt species (T. marmoratus and T. pygmaeus) – are included (Supplementary data Appendix 1). The Pyrenean brook newt Calotriton asper, being
Results
The 144 T. karelinii group individuals comprise 61 haplotypes, the other Triturus samples and the C. asper outgroup each represent unique haplotypes (for details and GenBank Accession Numbers see Supplementary data Appendices 1 and 2). Sequences could be unambiguously aligned; the only length variation is observed at the 3′ end of ND2, with a one or two triplet deletion in the crested newts, relative to the marbled newts and the outgroup C. asper. The total alignment comprises 1699 bp (1035–1041
Systematic position
The T. karelinii group composes one of four mitochondrial DNA lineages (the others being T. carnifex plus T. macedonicus, T. cristatus and T. dobrogicus) that form a basal polytomy in the T. cristatus superspecies (Fig. 2; cf. Arntzen et al., 2007). This means that either the mitochondrial data analyzed here contain too little information to resolve the order of speciation events (a soft polytomy), or that the four lineages truly split simultaneously (a hard polytomy). Espregueira Themudo et
Acknowledgments
B.W. thanks the ‘J.J. ter Pelkwijk fund’ for support. G.E.T. was financed through a Ph.D. grant from the Fundação para a Ciência e a Tecnologia, Lisbon, Portugal (SFRH/BD/16894/2004). N.A.P. was supported by a Naturalis ‘Martin fellowship’ and by a grant from the ‘Pieter Langerhuizen Lambertuszoon Fonds’, allocated by the ‘Koninklijke Hollandsche Maatschappij der Wetenschappen’. Permits for Turkey were made available by TÜBITAK. The authors thank W. Babik, J. Badridze, S. Carranza, D.
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