Morfološka varijabilnost, evolucija i razviće kičmenice kod velikih mrmoljaka (Triturus, Salamandridae, Caudata)

Analize intra- i interspecijske varijabilnosti u ontogeniji morfoloških struktura (npr. razlike u vremenu diferencijacije, stopi i pravcu ontogenetskih promena u veličini i obliku), kao i varijabilnosti na adultnom stupnju, omogućavaju utvrđivanje obrazaca morfološke varijabilnosti i sagledavanje procesa i mehanizma koji dovode do evolucionih promena morfoloških struktura. U ovoj tezi izučavana je morfološka varijabilnost osovinskog skeleta u okviru monofiletske grupe velikih mrmoljaka koju čine devet vrsta roda Triturus. Različit stepen izduživanja tela, varijabilnost u broju trupnih pršljenova kao i poznati filogenetski odnosi čine ovu grupu izuzetno pogodnim model-organizmima za studije razvića kičmenice i evolucije kičmenih pršljenova. Histološkim metodama praćeno je postembrionsko razviće trupnih pršljenova, radi utvrđivanja eventualnih razlika u vremenu formiranja, osifikacionim sekvencama kao i stopi njihove diferencijacije. Za ove analize odabrane su dve vrste velikih mrmoljaka koje se razlikuju u stepenu izduživanja tela, odnosno u broju trupnih pršljenova. Utvrđeno je da nema razlika u vremenu i načinu formiranja pršljenova između vrsta. Tokom formiranja kičmenih pršljenova zabeležena su tri tipa osifikacije: 1) perihordalna osifikacija, 2) perihondrijalna osifikacija i 3) endohondralna osifikacija. Takođe, zabeleženo je i prisustvo intravertebralne (notohordalne) hrskavice unutar tela pršljena pri čemu je razviće kičmenih pršljenova roda Triturus veoma slično razviću kod drugih vrsta repatih vodozemaca. Homeotske transformacije predstavljaju transformacije pri kojima jedan deo tela preuzima identitet drugog dela tela (npr. transformacija trupnog u sakralni pršljen) usled mutacije ili promena u ekspresiji određenih Hox gena. Studija variabilnosti u broju trupnih pršljenova i tipova homeotskih transformacija urađena je na uzorku koji pokriva celokopnu genetičku i geografsku varijabilnost roda Triturus. Uočeno je odsustvo korelacije između nepotpunih homeotskih transformacija sakralnog pršljena i varijabilnosti u broju trupnih pršljenova što može biti rezultat razvojnih mehanizama koji favorizuju kompletan broj presakralnih pršljenova ili favorizovanje selekcije protiv tranzicionih pršljenova kod ove grupe repatih vodozemaca... 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...