Doctoral Defense in Biology - Alessandra Schnider

Doctoral candidate:
Alessandra Schnider

Title of thesis:
Phenotypic plasticity in Mývatn threespine stickleback (Gasterosteus aculeatus): response to temperature and diet within and across generations

Opponents:
Dr. Lisa N. S. Shama, Senior Scientist at Helmholtz center for polar and Marine Research, Alfred Wegener institute, Germany
Dr. Antti P. Eloranta, Academic Research Fellow at the Faculty of Mathematics and Science, University of Jyväskylä, Finland

Administrative supervisor:
Dr. Zophonías O. Jónsson, Professor at the Department of Life- and Environmental Sciences, University of Iceland

Academic supervisor:
Dr. Bjarni Kristófer Kristjánsson, Professor at the Department of Aquaculture and Fish Biology, Hólar University

Other members of the doctoral committee:
Dr. Katja Räsänen, Professor at Faculty of Mathematics and Science, University of Jyväskylä, Finland
Dr. Blake Matthews, Professor at Swiss Federal Institute of Aquatic Science and Technology, Switzerland
Dr. Catherine Peichel, Professor at Faculty of Science, University of Bern, Switzerland

Chair of Ceremony:
Dr. Gunnar Þór Jóhannesson, Professor in Tourism studies at
Faculty of Life and Environmental Sciences, University of Iceland 

Abstract:
Phenotypic plasticity, the ability of a single genotype to produce different phenotypes in response to environmental stimuli, can mitigate effects of adverse environmental conditions within and across generations and be an important source of adaptation in response to natural selection. The aim of this thesis was to study how environmental drivers shape the phenotype of threespine stickleback, within and across generations, in the spatio-temporally varying system, Lake Mývatn, Iceland. Firstly, my study of diet and morphology of wild juvenile Mývatn stickleback revealed a dietary niche shift from Cladocera to midge larvae with increasing body size and diverging head morphology in response to varying diet composition. Secondly, I conducted a multigenerational plasticity experiment, rearing offspring from stickleback originating from two contrasting habitats under varying temperature and diet conditions. I analysed phenotypic information of juveniles and sexually mature females and males across two generations. I further collected liver samples of sexually mature experimental and wild individuals for transcriptomic analyses, to further our understanding of the underlying molecular mechanisms. I found clear environmental effects on traits directly associated with fitness. Thus, transgenerational effects appear crucial in shaping biological fitness in this highly dynamic system. I also identified differentially expressed genes in response to temperature and diet, potentially reducing environmental stress and support habitat expansion. This thesis enhances our understanding of phenotypic plasticity and transgenerational effects in dynamic systems. Integrating multiple environmental factors over biologically relevant timeframes is rare, making my findings crucial for understanding how phenotypic plasticity contributes to biological diversity.

About the doctoral candidate:
Alessandra Schnider grew up in Switzerland and earned her B.Sc. in Biology and M.Sc. in Biological Anthropology from the University of Zuirch. In her master’s thesis she studied how relatedness shaped sociopositive behaviours among female vervet monkeys and how seasonal changes in food availability affected this relationship. After taking a break from her studies to travel and explore the world, Alessandra accepted a PhD position at the University of Iceland and subsequently moved to the wild, cold north of Skagafjörður in August 2019. Many people were surprised by this perceived change in field, but for Alessandra the question remained the same: How does the interaction between genes and environment shape an individual’s phenotype. To this end, her PhD thesis focuses on the importance of phenotypic plasticity in shaping the phenotype in threespine stickleback within and across generations. In a laboratory experiment she specifically tested the effects of temperature and diet on key life history traits such as size, parental investment and reproductive success as well as investigating molecular mechanisms underlying these responsesthrough gene expression patterns. After graduation Alessandra will be producing a podcast on fish research in Iceland, as part of her work in science communication, and looks forward to exploring new opportunities and continuing to contribute to the field through research and collaboration.