Georg Džukić

Ontogeny of skull size and shape changes within a framework of biphasic lifestyle: a case study in six Triturus species (Amphibia, Salamandridae)

As with many other amphibians, Triturus species are characterized by a biphasic life cycle with abrupt changes in the cranial skeleton during metamorphosis. The post-metamorphic shape changes of the cranial skeleton were investigated using geometric morphometric techniques in six species: Triturus alpestris, T. vulgaris, T. dobrogicus, T. cristatus, T. carnifex, and T. karelinii. The comparative analysis of ontogenetic trajectories revealed that these species have a conserved developmental rate with divergent ontogenetic trajectories of the ventral skull shape that mainly reflect phylogenetic relatedness. A striking exception in the ontogenetic pattern was possibly found in T. dobrogicus, characterized by a marked increase in the developmental rate compared to the other newt species. The size-related shape changes explained a large proportion of shape change during post-metamorphic growth within each species, with marked positive allometric growth of skull elements related to foraging.

The Biodiversity of Amphibians and Reptiles in the Balkan Peninsula

Biologists have long recognised that the circum-Mediterranean region, and the Balkans in particular, contains an extraordinary variety of life forms in both plant and animal groups (Gaston & David, 1994), which is expressed in terms of biogeographical diversity, including that of amphibians and reptiles. The Mediterranean region of Europe comprises three large southern peninsulas and their archipelagoes. The amphibians and reptiles in this part of Europe exhibit complex biogeographic patterns, with large numbers of endemic taxa, dynamism, and the presence of certain general biological phenomena (see below). Distinguished by a high level of heterogeneity and of mosaicism, and natural fragmentation due to mountain ranges, the Balkan Peninsula is particularly intriguing in this respect.

Sexual size dimorphism in the evolutionary context of facultative paedomorphosis: insights from European newts

BackgroundSexual size dimorphism (SSD) is a key evolutionary feature that has been studied in many organisms. In a wide range of species, this pattern is more complex because of polymorphism within each sex. However, it is not known whether the magnitude and direction of SSD could be affected by alternative developmental trajectories within sexes. Our aim was to test whether an intrasexual polymorphism, facultative paedomorphosis (a process in which the development of somatic and gonadal tissues differs in alternative morphs), could affect SSD variation patterns in European newts.ResultsWe report here the first evidence that SSD varies depending on the paedomorphic or metamorphic ontogenetic pathway. In species with a consistent female-biased SSD, paedomorphosis decreased the SSD level, but did not affect its direction. In species with moderate female-biased SSD or variable SSD patterns, paedomorphosis changed the magnitude, or both the magnitude and the direction, of SSD.ConclusionOur study highlights the importance of developmental processes for shaping SSD patterns in populations in which contrasting life-history pathways evolved. European newts express different SSD patterns depending on their developmental pathway (i.e., metamorphosis versus paedomorphosis), as well as their species and population. These findings emphasize the importance of studying alternative morphotypes, which are found in a wide range of animal groups, to understand the evolution of SSD.

Skull size and shape variation versus molecular phylogeny: a case study of alpine newts (Mesotriton alpestris, Salamandridae) from the Balkan Peninsula

We explored the phylogenetic signal of skull size and shape in alpine newts from the Balkans, a group of European newts that, in spite of their considerable phylogeographic substructuring (as inferred from previous DNA analyses), maintain a conserved phenotype. In terms of skull shape disparity, geometric morphometrics show that the dorsal cranium carries a significant phylogenetic signal, the most notable evidence in this present study. On the contrary, no phylogenetic signal in the shape of the ventral cranium was found. This result indicates that the variation in the shape of the ventral cranium is more prone to other factors and processes, such as adaptations to local environments rather than phylogenetic constraints. Variation in skull size within alpine newts seems to be independent from phylogenetic constraints.

Geographic variability and taxonomy of the nose-horned viper, Vipera ammodytes (L. 1758), in the central and eastern parts of the Balkans: A multivariate study

A multivariate analyses of various morphological characters (morphometric, meristic and qualitative) of nose-horned viper ( Vipera ammodytes ) revealed a complex morphological differentiation of populations from the central and the eastern Balkan Peninsula. Analyses of quantitative data showed no clear morphological discrimination or well-defined taxonomical units. On the contrary, analyses of qualitative traits separated two discrete taxa in the analysed area. One, inhabiting the eastern and the southern part of the Balkans, includes samples from most parts of Bulgaria, Former Yugoslav Republic of Macedonia and south-eastern Serbia, whereas the other ranges from north-western Bulgaria through the main part of Serbia (except the south-east) to Montenegro.

Contrasting evolutionary histories of the legless lizards slow worms (Anguis) shaped by the topography of the Balkan Peninsula

BackgroundGenetic architecture of a species is a result of historical changes in population size and extent of distribution related to climatic and environmental factors and contemporary processes of dispersal and gene flow. Population-size and range contractions, expansions and shifts have a substantial effect on genetic diversity and intraspecific divergence, which is further shaped by gene-flow limiting barriers. The Balkans, as one of the most important sources of European biodiversity, is a region where many temperate species persisted during the Pleistocene glaciations and where high topographic heterogeneity offers suitable conditions for local adaptations of populations. In this study, we investigated the phylogeographical patterns and demographic histories of four species of semifossorial slow-worm lizards (genus Anguis) present in the Balkan Peninsula, and tested the relationship between genetic diversity and topographic heterogeneity of the inhabited ranges.ResultsWe inferred phylogenetic relationships, compared genetic structure and historical demography of slow worms using nucleotide sequence variation of mitochondrial DNA. Four Anguis species with mostly parapatric distributions occur in the Balkan Peninsula. They show different levels of genetic diversity. A signature of population growth was detected in all four species but with various courses in particular populations. We found a strong correlation between genetic diversity of slow-worm populations and topographic ruggedness of the ranges (mountain systems) they inhabit. Areas with more rugged terrain harbour higher genetic diversity.ConclusionsPhylogeographical pattern of the genus Anguis in the Balkans is concordant with the refugia-within-refugia model previously proposed for both several other taxa in the region and other main European Peninsulas. While slow-worm populations from the southern refugia mostly have restricted distributions and have not dispersed much from their refugial areas, populations from the extra-Mediterranean refugia in northern parts of the Balkans have colonized vast areas of eastern, central, and western Europe. Besides climatic historical events, the heterogeneous topography of the Balkans has also played an important role in shaping genetic diversity of slow worms.

The crested newt (Triturus carnifex) in the Submediterranean: Reproductive biology, body size, and age

Abstract The annual reproductive cycle of both sexes of Triturus carnifex from the Submediterranean was analysed, as well as complex relationships between fecundity, body size, and age. Highly significant seasonal variations in snout‐vent length‐adjusted gonads, fat bodies, and liver weight were found in both sexes. Variations in cycle due to geographic location and climate were recorded. Newts exhibited extended residence in water and lengthening of breeding period. Body size was significantly correlated with age in males, contrary to females. All organ weights were significantly correlated to body size, except for fat body weight in females. In both sexes, fecundity parameters showed a highly significant effect of season, while the effect of age was insignificant (testes weight and total number of oocytes) or barely significant (ovaries weight).

Evolutionary Diversification of the Limb Skeleton in Crested Newts (Triturus cristatus Superspecies, Caudata, Salamandridae)

We explored the interspecific variation patterns in the limb skeleton of four crested newts that underwent an extensive evolutionary diversification. All studied species shared the same basipodial pattern, within which the carpus exhibited much more variation than the tarsus. Morphometric analysis of stylopodium, zeugopodium, and the third metapodial element showed that the species differed in the size of skeletal elements, but they shared common allometric slopes. In comparison to the other crested newts, T. dobrogicus appeared as the outlier due to (1) significantly shorter stylopodium and zeugopodium relative to body size and (2) rather different anatomical designs regarding ossification level of the basipodium. Based on these results, it is suggested that the observed T. dobrogicus uniqueness originates from allometric heterochrony paralleled by a profound switch in habitat preference.

A Phenotypic Point of View of the Adaptive Radiation of Crested Newts (Triturus cristatus Superspecies, Caudata, Amphibia)

The divergence in phenotype and habitat preference within the crested newt Triturus cristatus superspecies, examined across different ontogenetic stages, provides an excellent setting to explore the pattern of adaptive radiation. The crested newts form a well-supported monophyletic clade for which at least the full mitochondrial DNA phylogeny is resolved. Here we summarise studies that explored the variation in morphological (larval and adult body form, limb skeleton, and skull shape) and other phenotypic traits (early life history, developmental sequences, larval growth rate, and sexual dimorphism) to infer the magnitude and direction of evolutionary changes in crested newts. The phenotypic traits show a high level of concordance in the pattern of variation; there is a cline-like variation, from T. dobrogicus, via T. cristatus, T. carnifex, and T. macedonicus to the T. karelinii group. This pattern matches the cline of ecological preferences; T. dobrogicus is relatively aquatic, followed by T. cristatus. T. macedonicus, T. carnifex, and the T. karelinii group are relatively terrestrial. The observed pattern indicates that phenotypic diversification in crested newts emerged due to an evolutionary switch in ecological preferences. Furthermore, the pattern indicates that heterochronic changes, or changes in the timing and rate of development, underlie the observed phenotypic evolutionary diversification.

Female life‐history characteristics of the Mosor rock lizard, Dinarolacerta mosorensis (Kolombatović, 1886) from Montenegro (Squamata: Lacertidae)

Analysis of the female life history of the poorly studied endemic Balkan lizard species Dinarolacerta mosorensis was conducted on three population samples from Montenegro. One clutch is produced annually. Females mature at body sizes of 56–57 mm snout–vent length (SVL), attained at age 3–4 years. SVL increases with age. The average clutch size ranged from 4.3 to 5.2 eggs, and was significantly positively correlated with maternal SVL in two population samples. There were no trade‐offs between egg size/offspring size and clutch size, nor between variation in egg size/offspring size and maternal SVL. The incubation period averaged 26.5 days, while hatching success in captivity was 72%. Significant positive correlations were found between the hatchling mass and egg mass and size, and also between the hatchling total length and egg width and volume. There was a significant negative relationship between the hatchling mass and incubation duration.