Miloš L. Kalezić

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.

Testing the hypothesis of morphological integration on a skull of a vertebrate with a biphasic life cycle: a case study of the alpine newt

In this article, we explore the possible influences of the developmental and functional relationships between skeletal elements on the pattern of morphological integration in the adult skull of the alpine newt. Like many tailed amphibians, the alpine newt has a biphasic life cycle, which implies the possibility that two distinct sets of constraints on development and function of the cranial skeleton may act at different times. We study how trait covariation, resulting from processes early in development, affects patterns of covariation at the adult stage. We test whether the observed patterns of integration are consistent with those predicted from three a priori hypothesized sources of integration: developmental timing, hormonally mediated growth/remodeling during metamorphosis, and developmental and functional relationships. The analyses of the covariation among the landmarks in the dorsal and ventral alpine newt craniums yield somewhat contrasting results. Our results do not indicate a clear correspondence between the observed variations in the skull shape and any of the three proposed hypotheses. No traceable reflection of hypothesized developmental relationships in the pattern of morphological integration/modularity in the adult skull indicate that covariation structure is continually restructured by overlaying variation introduced through developmental and environmental factors at different stages of development. This finding supports the recently elaborated palimpsest view of morphological integration. Also, our results indicate that the allometry-free shape data have an even higher level of morphological integration than the data that contain the allometric component of the shape variation.

Evolutionary and paleogeographical effects on the distribution of the Triturus cristatus superspecies in the central Balkans

A synthesis of all known data on the crested newt group assigns the Balkan peninsula as the center of origin or, at least, the area where the basic lineage of its species was limited in the late Miocene. According to the recent literature, the geological structure of the Balkan region changed considerably during the Tertiary. These geological processes could have had a considerable impact on crested newt divergence and on the recent distribution of species. Using the number of rib-bearing vertebrae (RBVN), recently suggested as a simple and powerful tool for distinguishing four taxa of the T cristatus superspecies, we analysed 36 population samples collected all over former Yugoslavia. The hypothesised recent distribution of the crested newt species, based on frequency distribution of RBVN, appears to correspond well to neotectonic events in the past.

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.

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.

Morphological integration of cranium and postcranial skeleton during ontogeny of facultative paedomorphic European newts ( Triturus vulgaris and T. alpestris )

The patterns of ontogenetic and interspecific variation of morphological integration (the relationships and correlation patterns of functionally and developmentally related morphological traits) in facultative paedomorphic species of two European newts ( Triturus vulgaris and T. alpestris ) were examined. The degree of morphological integration differed among ontogenetic stages. Variation in the level of morphological integration of cranium and postcranial skeleton during ontogeny of paedomorphic newts had the same pattern in both analysed species. The lowest level of cranium morphological integration characterises the larvae and the juveniles. Individuals that follow alternative life-history path (paedomorphs) remain at a relatively low level of morphological integration, while integration highly increased in metamorphosed adult individuals. Limb skeleton also showed a lower level of integration in paedomorphs in comparison with metamorphosed individuals. The hypothesis of morphological integration was confirmed for all stages of T. vulgaris , while the same hypothesis was confirmed only for larval and paedomorphic stages of T. alpestris . In T. vulgaris , metamorphosis changes the pattern of correlation among the cranial traits, while in T. alpestris , the patterns of phenotypic correlation among the cranial traits remain substantially similar for all analysed ontogenetic stages.

Morphological integration and ontogenetic niche shift: a study of crested newt limbs

This study deals with the ontogenetic and evolutionary aspects of integration patterns in the limbs of crested newt species, which, like most amphibians, have a biphasic life history with two morphologically distinct stages (larval vs. juvenile and adult) that occupy different environments (aquatic vs. terrestrial). We analyzed the structure and pattern of correlation between limb skeletal elements at three ontogenetic stages (larval, juvenile, and adult) of four closely related species that differ in their preferences of aquatic habitats (more terrestrial and more aquatic). We found dynamic changes in the pattern of morphological integration between successive ontogenetic stages, as well as changes over the course of crested newt phylogeny. Generally, equivalent ontogenetic stages of different species of crested newts show higher concordance in the correlation pattern than successive ontogenetic stages within species. Among species, two opposing correlation patterns were observed: in more terrestrial species, homologous limb elements are less correlated and within-limb elements are more correlated; in aquatic species, the reverse pattern occurs. These results indicate that the function seems to be the covariance-generating factor, which has shaped the patterns of morphological integration of crested newt limbs.