Phylogenetic Trends Of The Salamanders Of The Family Plethodontidae As Indicated By Their Cranial Morphology PDF Download

Sexual dimorphism (SD) i.e., the difference in morphology between males and females, is a common phenomenon in the animal kingdom. SD can be observed in various forms such as gender-dependent differences in size, colouration or the presence of ornaments. While warm-blooded vertebrates are well investigated in the context of SD, cold-blooded vertebrates i.e., amphibians and reptiles are still neglected. Often sexes are differentiated in terms of size, termed sexual size dimorphism (SSD) or even in terms of shape differences, so termed sexual shape dimorphism (SShD). Sexual size and shape dimorphisms are often rather subtle and hard to capture when employing traditional analysing methodology. The evolutionary mechanism underlying those features are still under debate. An integrative approach in a phylogenetic context including different patterns of SD connected to the ecology of a respective species can help to reconstruct and understand the evolutionary historical patterns leading to differences between males and females. This is of significant interest for the reconstruction of ancient life in a paleontological sense. The most prominent remains of fossil vertebrates are hard tissues e.g., bones and teeth. Hence, more knowledge on the osteology of extant taxa is needed to allow conclusions on their fossil relatives. True salamanders of the family Salamandridae are a perfectly suited model system for the investigation of SD and its evolutionary history, because this group exhibits diverse reproductive modes and life history strategies linked to different patterns of SD. In this thesis, I investigated extensively patterns of sexual size and shape dimorphism in basal salamandrid salamanders. Further, I wanted to set morphology into context with a species' ecology to allow conclusions on the ecology of extinct salamander taxa. In the first chapter, I used the spectacled salamander Salamandrina perspicillata (SAVI, 1821), the phylogenetically most basal genus of the Salamandridae, to extensively investigate patterns of sexual size and shape dimorphism in the external morphology and osteology by linear measurements. Therefore, I employed a novel integrative statistical approach. The results showed that comparable characters in the soft and hard tissue revealed similar patterns of SD. The osteology harbours also so far unknown pattern of SD. In the second chapter, I used geometric morphometrics (GM), which represents a novel upcoming technique in morphology research, to reveal even more subtle shape differences. To this end, I used the same set of specimens as in chapter one. This enabled me to compare GM with the traditional approach of capturing morphological differences. Generally, the outcome of both methods is similar if appropriate data is gathered, but via GM, smaller shape differences were revealed. Especially, the pelvic girdle harboured size independent shape differences likely corresponding to the different roles of males and females during reproduction. In the third chapter, I investigated the cranial morphology of the ribbed and crocodile newts (Pleurodelini) and set it into context to selected reproductive traits. Ribbed and crocodile newts bear an extensive fossil record spanning from the Eocene towards the Pliocene. Consequently I included the closely related but extinct genus Chelotriton into my analyses to obtain further hints on the relationship of extinct and extant taxa and to draw conclusions on the ecology of Chelotriton based on morphology-ecology correlations. European ribbed newts were well separated from the Asian crocodile newts. For the first time it was possible to define clear-cut morphological differences for the two subgenera of crocodile newts i.e., Tylototriton and Yaotriton. Regarding the selected reproductive traits, the mating mode affected the cranial shape evolution. Fossil Chelotriton likely represents several species exhibiting a rather terrestrial lifestyle and reproduction. In the fourth chapter, I investigated patterns of SSD and SShD in several species of crocodile newts and in relation with their mating mode, which variably includes an amplexus or mating dances. Trajectories of shape changes from males to females differed interspecifically. The mating mode could explain interspecific SD trajectory differences in cranial but not humerus morphology. Nevertheless, humerus morphology differed also in shape among species exhibiting different mating modes, indicating other selective forces are acting on limb morphology. An interaction of allometric trajectories different between species but similar between the sexes are likely responsible for the variable SD patterns among polymorphic crocodile newts.