Contributions to Zoology, 68 (3) ..-.. (1999)J. W. Arntzen; Graham P. Wallis: Geographic variation and taxonomy of crested newts (Triturus cristatus superspecies): morphological and mitochondrial DNA data
Discussion

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Distribution and biogeography

Crested newts appear to be absent from the largest part of Bosnia-Hercegovina (see for example Schmidtler and Schmidtler, 1983; Kalezi’c, D’zuki’c and Tvrtkovi’c, 1990; Kalezi’c et al., 1997). The southeasternmost localities of T. carnifex to the northeast of the perceived gap in the species distribution are sites 21 - 23 [Belovar Moravce (Table 2); Plitvice (Fejervary-Langh, 1943) and Licki Osik (Kalezi’c et al, 1990). Further to the southeast T. carnifex is found at sites 24 - 27 [Donja Dubrava (Kalezi’c et al., 1990), Sarajevo (Bolkay, 1929; communicated by G. D’zuki’c), the Zelengora Mountain (Bolkay, 1928) and Dobrsko Selo (Kalezi’c and D’zuki’c, 1990). The easternmost recorded locality is site 29 at Dimitrovgrad (Radovanovi’c, 1964). Crested newts of unknown taxonomic affinity were recorded at the Dalmatian coast [site 28, situated in between Sebenico (= S’ibenik) and Spalato (= Split) (Werner, 1897, also mentioned by Buresh and Zonkov, 1941), but with no clearly independent confirmation for over a century we doubt the validity of this record. Dzuki’c (1993) considers the distribution of T. carnifex not to be interrupted but continuous, following a strip of land to the south of the Sava river, without, however, presenting data supporting this view. The area where crested newts are absent coincides with the core area of the karst (Sket, 1994), where most natural water bodies are ephemeral and do often not support the larval development of species with a prolonged larval phase, such as crested newts. The small-bodied newts such as T. alpestris and T. vulgaris in contrast are widespread and locally abundant. They may reproduce successfully in shallow and temporary ponds such a wheel ruts (Winkler and Brauns, 1990) and the dispersal rate for the small newt T. vulgaris is estimated to be higher than that for the big newt T. cristatus (Stensjö, 1998). While most contemporary newt ponds are man-made and rarely desiccate (i.e., watering holes for cattle), the puddles formed by fallen trees and springs may originally have been the typical breeding habitat for the small bodied species.

The distribution of the four crested newt species in F. R. Yugoslavia is complex (Fig. 3c). Triturus dobrogicus is found all over the Pannonian and Dobrogean Plains. Both parts of the range are probably connected by the Danube where flowing through the Iron Gate (Arntzen et al., 1997). Triturus cristatus has a wide European range, is widespread over Romania and reaches southwards over the Iron Gate into Yugoslavia. Triturus carnifex macedonicus is widespread over most of Yugoslavia, the Former Yugoslavian Republic of Macedonia, Albania, and northern Greece. Triturus karelinii is found immediately south and southeast of Belgrade. The available evidence suggests that the local distribution is in a small pocket - an enclave, geographically isolated from the main T. karelinii distribution in Bulgaria, Thrace, and Turkey (Fig. 3c). However, a link between the parts, along a narrow strip in northeastern Yugoslavia (as in Arntzen, 1995 and in Kalezi’c et al, 1997: Fig. 6), cannot be excluded. The further surveying of eastern Yugoslavia and northwestern Bulgaria is required to settle this issue.

On a gross geographic scale, phenotype distributions, and mtDNA haplotype distributions are concordant. However, in northern Yugoslavia the ‘KAR?’ mtDNA haplotype is more widespread than the T. karelinii phenotype distribution would suggest (Fig. 3) (Wallis and Arntzen, 1989). The ‘KAR?’ mtDNA haplotype is locally found in T. dobrogicus, T. cristatus, and T. carnifex macedonicus populations. The reverse situation, with a foreign haplotype in T. karelinii, has been observed once (the ‘DOB’ haplotype in population 15). Populations with foreign haplotypes possess either two haplotypes - the original plus an alien, such as at site 15 and 34 in T. karelinii and T. dobrogicus),or just the alien haplotype [‘KAR?’ in T. cristatus (site 30 and 37, N = 5) and in T. carnifex macedonicus (site 35 and 36, N = 16; Wallis and Arntzen, 1989). To account for these observations we suggest the following scenario. In former times T. karelinii was more widespread than at present, with a range approximately coinciding to the present day distribution of the ‘KAR?’ haplotype. By dispersing southwards and northwards, respectively T. cristatus and T. carnifex macedonicus superseded T. karelinii, in which process the range of T. karelinii south of Belgrade became isolated from the main stock (see the arrows in Fig. 3c). The genetic interactions between T. karelinii at one side and T. cristatus and T. carnifex macedonicus at the other where such that the formation of F1 hybrids was asymmetric, with hybrid offspring and the subsequent backcrosses possessing the (maternally inherited) T. karelinii mtDNA. This scenario is surprisingly similar to the one we described for T. cristatus - T. marmoratus interactions in western France (Arntzen and Wallis, 1991). In France, T. cristatus supersedes T. marmoratus, forming T. marmoratus enclaves in the process. Hybridisation between the species is strongly asymmetric, with F1 adults derived from matings of T. cristatus mothers and T. marmoratus fathers significantly outnumbering the reverse combination. The facts responsible for this phenomenon are largely unknown but may involve the genetic incompatibility of the nuclear and mtDNA genomes (J. W. Arntzen et al., in prep.). By comparing past and present distributions, the rate at which T. cristatus takes over from T. marmoratus has been estimated as averaging one km a year. The process may be triggered, or accelerated, by the removal of hedgerows, modifying a landscape with terrestrial features favourable to T. marmoratus, the most terrestrial among the big-bodied newt species, into one favourable to the more aquatic T. cristatus. The habitat preferences of the various crested newt species in eastern Europe, with the exception of T. dobrogicus, are poorly understood and it is unclear which ecological parameters affect their distribution or change in distribution. Another area of complexity is that around Vienna, where T. carnifex, T. cristatus and T. dobrogicus meet (Fig. 3b). At sites 12 and 36 newts were found with T. carnifex phenotype and the mtDNA haplotype typical for T. dobrogicus, matching a similar observation at Tasovice in the Czech Republic (48º49’ N, 16º09’ E; J. Pialek, V. Zavadil and J. W. Arntzen, unpubl.).

As noted by Crnobrnja-Isailovi’c et al. (1997), the remarkable variability in Balkan crested newts should provide valuable insights into the evolution of the group. Palaeontological and various molecular methods have provided some clues towards the timing of the radiation of the T. cristatus superspecies (reviewed in Oosterbroek and Arntzen, 1992). This period, which can be placed at 2-5 Ma, was one of great geographical and geological complexity in southeastern Europe (Crnobrnja-Isailovi’c et al., 1997 and references therein). However, our ability to associate the historical patterns of fragmentation, speciation and dispersal with palaeogeography is, as yet, hampered by the absence of a well-supported phylogeny.