PhD ceremony: Ms. S.V. Schaper, 11.00 uur, Academiegebouw, Broerstraat 5, Groningen
Dissertation: Seasonal timing in a changing climate. The physiological basis of phenotypic plasticity and its evolutionary potential
Promotor(s): prof. M.E. Visser
Faculty: Mathematics and Natural Sciences
Sonja Schaper has investigated mechanisms underlying the seasonal timing of reproduction in great tits, with a focus on the use of temperature cues. Due to climate change, spring temperatures have increased in central Europe. As a consequence the bud burst of trees and emergence of caterpillars that forage on the young leaves have advanced substantially. The period in which great tits (Parus major) lay their eggs has also advanced, but not sufficiently to keep track of this phenological change. Being mismatched with the peak in food biomass reduces fitness, which leads to selection for earlier laying in the birds. Pairs of great tits were kept in climate-controlled aviaries under different temperature scenarios. Under controlled conditions mean temperature was not the relevant cue determining the onset of egg laying, but rather the pattern of temperature increase explained variation in laying dates. The use of genetically related females made it possible to identify a family resemblance in the onset and termination of egg laying in response to temperature cues, which indicates a genetic basis. Linked avian life-cycle stages were thus to a higher or lower degree fine-tuned to the seasonal environment by temperature cues: while the onset of egg laying was determined by patterns of temperature change, temperature differences did not affect the underlying reproductive physiology or the onset of moult. The research of Schaper increases our understanding of how heritable variation in the physiological mechanisms underlying seasonal timing allows adaptation to a changing climate.
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