Graduate

Urodele Amphibien besitzen außergewöhnliche Regenerationsfähigkeiten, die es ihnen ermöglichen, verlorene Körperteile vollständig nachzubilden. Besonders der Axolotl ist aufgrund seiner einfachen Haltung im Labor ein wichtiger Modellorganismus für die Regenerationsforschung. Allerdings schränkt seine pädomorphe Lebensweise – das Ausbleiben einer natürlichen Metamorphose – die Übertragbarkeit der Ergebnisse auf andere Salamanderarten ein. Um Unterschiede und Gemeinsamkeiten in zugrundeliegenden Mechanismen von Regenerationsprozessen zu entschlüsseln sowie evolutionäre und ökologische Einflüsse besser zu verstehen, sind vergleichende Studien mit weiteren Salamanderarten entscheidend. Kapitel I vergleicht die Regenerationsfähigkeit des Axolotls mit der des metamorphosierenden Tigersalamanders. Dabei zeigen larvale Tigersalamander ähnlich beeindruckende Regenerationsfähigkeiten wie Axolotl, während postmetamorphe Individuen eine unvollständige Frakturheilung und verzögerte Regeneration mit Skelettanomalien aufweisen. Kapitel II untersucht die Schwanzregeneration des Tigersalamanders während der Metamorphose und zeigt, dass sie in und auch nach diesem Entwicklungsstadium fortgesetzt wird, obwohl die Geschwindigkeit und die strukturelle Qualität der Regeneration in den verschiedenen Entwicklungsstadien variieren, was den Einfluss der Metamorphose auf den Regenerationsprozess unterstreicht. Kapitel III analysiert die Gliedmaßenregeneration bei sechs plethodontiden Salamanderarten mit verschiedenen Lebensweisen und Habitaten. Alle Arten zeigen erhebliche Regenerationsfähigkeiten, wenngleich häufig anatomische Anomalien auftreten. Zudem werden Korrelationen zwischen der Regenerationsgeschwindigkeit und dem jeweiligen Habitat festgestellt. Kapitel IV untersucht die Flossenregeneration bei Lungenfischen. Dabei auftretende Anomalien ähneln denen von Salamandern und stützen damit die Hypothese, dass epimorphe Regenerationsfähigkeiten einen tiefen evolutiven Ursprung besitzen. / Urodele amphibians possess remarkable regenerative abilities, allowing them to fully restore lost body parts. The axolotl, in particular, has become a key model organism for regeneration research due to its easy maintenance in laboratory settings. However, its paedomorphic life history pattern—the absence of natural metamorphosis—limits the generalizability of findings to other salamander species. To decipher differences and similarities in the underlying mechanisms of regeneration processes and to better understand evolutionary and ecological influences, comparative studies with other salamander species are essential. Chapter I compares the regenerative abilities of the axolotl with those of the metamorphosing tiger salamander. Larval tiger salamanders exhibit similarly impressive regenerative capacities as axolotls, while post-metamorphic individuals show incomplete fracture healing and delayed regeneration with skeletal anomalies. Chapter II investigates tail regeneration in the tiger salamander during metamorphosis, demonstrating that regeneration continues both during and after this developmental stage, although its speed and structural quality vary. This highlights the impact of metamorphosis on the regeneration process. Chapter III analyzes limb regeneration in six plethodontid salamander species with different lifestyles and habitats. All species exhibit significant regenerative abilities, though anatomical anomalies are common after regeneration. Additionally, correlations between regeneration speed and habitat are identified. Chapter IV examines fin regeneration in lungfish. The observed anomalies resemble those found in salamanders, supporting the hypothesis that epimorphic regenerative abilities have a deep evolutionary origin.

A major goal of evolutionary biology and ecology is to understand why species richness varies among clades. Previous studies have suggested that variation in richness among clades might be related to variation in rates of morphological evolution among clades (e.g., body size and shape). Other studies have suggested that richness patterns might be related to variation in rates of climatic-niche evolution. However, few studies, if any, have tested the relative importance of these variables in explaining patterns of richness among clades. Here, we test their relative importance among major clades of Plethodontidae, the most species-rich family of salamanders. Earlier studies have suggested that climatic-niche evolution explains patterns of diversification among plethodontid clades, whereas rates of morphological evolution do not. A subsequent study stated that rates of morphological evolution instead explained patterns of species richness among plethodontid clades (along with "ecological limits" on richness of clades, leading to saturation of clades with species, given limited resources). However, they did not consider climatic-niche evolution. Using phylogenetic multiple regression, we show that rates of climatic-niche evolution explain most variation in richness among plethodontid clades, whereas rates of morphological evolution do not. We find little evidence that ecological limits explain patterns of richness among plethodontid clades. We also test whether rates of morphological and climatic-niche evolution are correlated, and find that they are not. Overall, our results help explain richness patterns in a major amphibian group and provide possibly the first test of the relative importance of climatic niches and morphological evolution in explaining diversity patterns.

The genus Aneides (Caudata: Plethodontidae) is an arboreal salamander with a prehensile tail and a distribution that spans North America. It is hypothesized that adaptations for arboreality will be visible in the osteology of the sacral vertebra either by qualitative analysis or linear and morphometric analysis in comparison with other plethodontid salamanders. This study demonstrates that while qualitative and quantitative analyses are successful at making genus-level distinctions between taxa, identification to lower taxonomic levels remains inconclusive. Linear morphometrics and dorsal Procrustes landmarks were the most successful metrics to identify known taxa. Two unidentified fossil salamander sacral vertebrae from Oregon Caves National Monument are examined with the same techniques and are tentatively identified as Hydromantes based on qualitative similarities to modern Hydromantes specimens, as the quantitative analyses were unable to confidently diagnose the unknown specimens.

The salamander diversity in the southern Appalachian Mountains is now being threatened, with lungless salamanders (family Plethodontidae) likely the most vulnerable. Multiple environmental factors threaten Plethodontids, and environmental changes uniquely affect each species within this family. Unfortunately, there is a lack of understanding about the current status of salamanders in Greene County, TN that severely limits conservation efforts for lungless salamanders. This study examined local salamander populations’ current distributions and connected salamander abundance and species richness with a subset of environmental factors to determine what areas represent suitable habitat for different Plethodontids. This information was used to develop species distribution models, which were used to identify potential areas of salamander habitat to focus management and conservation efforts. Area constrained surveys were completed at 42 transects within four main areas using a robust, random sampling design. Abiotic and biotic data, along with salamander identification, were documented at each site. Four additional variables were acquired by geographic information system (GIS 10.6). Salamanders were present at 69% of the transects. Our results indicate that salamanders tend to be located at higher elevations, in ravines, and in thicker canopy cover areas. This work will be useful in long-term monitoring and future research as salamander population, habitat, and environmental changes continue to be monitored.

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