Evolutionary ecology of newts

Sammanfattning: Doktorsavhandling för filosofie doktorsexamen i biologi med inriktningen ekologi framlagd vid Örebro universitet, november 2001 Abstract Malmgren, J. C. 2001. Evolutionary Ecology of Newts. Örebro Studies in Biology 1Department of Natural Sciences, Örebro University, SE–701 82 Örebro, Sweden Sexual dimorphism, predator avoidance and migratory behaviour are adaptive traits that show variation at the population and species level. Such features respond to the environment in the broad sense, that is, when both abiotic and biotic components are included. Newts of the genus Triturus have several unique features and therefore make interesting model organisms.I use multivariate methods to test predictions about the evolution of sex differences in morphological traits. There was no evidence for dimorphism due to diverging feeding niche specialisation between the sexes in great crested and smooth newts (Triturus cristatus and T. vulgaris, respectively). The sexes, on the other hand, diverged in traits related to female fecundity and male reproductive success. Within the genus Triturus, there was no overall allometry for sexual size dimorphism (SSD), but subgenus Triturus, a lineage comprised by medium- to large-bodied species, were significantly allometric, and SSD decreased with increasing body size for male-biased taxa and increased with size for female-biased taxa. Species in the marmoratus-cristatus species group were almost perfectly isometric, but female-biased. With respect to an ancestral state, I suggest that differences in mating system have caused medium- and small-bodied species (subgenus Palaeotriton) to decrease SSD with smaller body size, whereas subgenus Triturus have evolved larger body size with a reversal from male- to female-biased SSD. Several peculiar traits are common to the latter group. I argue, and present a conceptual model, that the reversal is an adaptation to genetic constraints posed by a balanced lethal system (the developmental arrest syndrome). Several life history traits, as well as morphological and reproductive traits, may be interpreted as evidence for the scenario. Predictions from the model are presented and future research to test the validity of the model is encouraged.Newts are threatened by the introduction of fish and predictions from a predator-prey model on the evolution of predator avoidance behaviour, are tested. The results suggest that the great crested newt may be able to detect chemical cues from the ninespined stickleback, Pungitius pungitius, and adjust its behaviour accordingly. The response could be a predator avoidance response that enables adults to increase reproductive success by eliminating predation risk. I also studied migration behaviour in response to surrounding landscape elements after breeding and metamorphosis in great crested and smooth newts. Fragmentation effects reduce the chance for newts to disperse to suitable habitat patches in the landscape. I demonstrate that newts appear to orientate towards forest non-randomly, regardless of age-class or species, and their responses may be used to predict where critical elements for population persistence are located, in relation to a breeding pond. Overall, the results from my studies suggest that the great crested newt may be more prone to local extinction than previously believed, much due to genetic constraints and possible habitat specialisation. I use the results to present avenues for future research and discuss implications from my studies for management and conservation of newts and newt-friendly landscapes.Key words: Evolution, adaptation, amphibians, salamanders, predation, migration, sexual dimorphism, sex differences, behaviour, conservation