Morfološka varijabilnost, evolucija i razviće kičmenice kod velikih mrmoljaka (Triturus, Salamandridae, Caudata)
Morphological variability, evolution and development of vertebral column in crested newts (Triturus, Salamandridae, Caudata)
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Analyses of intra- and interspecific morphological variation through ontogeny (e.g. difference in the time of differentiation, rate and direction of ontogenetic changes in size and shape), as well as variability at the adult stage, enable determination of morphological patterns and mechanism which lead to evolution of morphological structures. In this thesis, morphological variability of axial skeleton was studied within monophyletic group of crested newts which comprises nine species of the genus Triturus. Crested newts are suitable model organisms for studies of vertebral development and evolution. They are closely related group of species with known phylogenetic relations, different rate of body elongation and great variability in the number of trunk vertebrae. Histological techiques were used in tracing postembrionic development of trunk verteberae to test difference in the time of vertebral development, ossification sequences and rate of vertebral differentiation. For these analyses, two species of crested newts which differ in rate of body elongation and number of trunk vertebrae were chosen. Results show that there is no difference between analysed species of Triturus newts in development time and formation of vertebrae. Three modes of the ossification process were recorded during vertebral formation: 1) perichordal ossification, 2) perichondrial ossification and 3) endochondral ossification. Also, the presence of intravertebral (notochordal) cartilage was recorded at centrum which makes vertebral development in Triturus newts very similar to other species of tailed amphibians. Homeotic transformations are replacements of one body part by another (e.g. transformation of trunk into sacral vertebra) due to the mutation or changes in expression of certain Hox genes. The studies of variability in the number of trunk vertebrae and types of homeotic transformations were done on sample that represents all genetical and geographical variability in the genus Triturus. The absence of correlation between the frequency of incomplete homeotic transformation of sacral vertebrae and variation in the number of trunk vertebrae could be a result of developmental mechanisms that favour complete numbers of presacral vertebrae or selection against transitional vertebrae in this group of tailed amphibians. Also, in this thesis, evolutionary changes in number, size and shape of trunk vertebrae of adult specimens were studied across nine species of Triturus newts. The employed methods of computed microtomography and three-dimensional geometric morphometrics with construction of phylomorphospace enabled us to analyze changes in shape and size of vertebrae, i.e. to which extent evolutionary changes in vertebral size are correlated with changes in vertebral shape. These results show significant difference in number, size and shape of trunk vertebrae among Triturus species. Body elongation, which is related to more aquatic lifestyle, was achieved through an increase in the number of trunk vertebrae, and interspecific differences in vertebral shape are correlated with this pattern of elongation. Species-specific differences in vertebral shape are such that single trunk vertebra can be used for the identification of species, which enables eventual use of these methods for identification of fossil and subfossil material.
Keywords:Triturus sp.; Vertebra; Development; Modes of ossification; Inter- and inbtravertebral cartilage; Homeotic transformation; Vertebral number; Size; Shape; Geometric morphometric
Source:University of Belgrade, Faculty of Biology, 2018, 1-160
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