PhD defence David Ekkers
David Ekkers (TRÊS)
Promotores: Prof. F.J. Weissing, Prof. O.P. Kuipers (GBB), Prof. G.S. van Doorn
Life is a trade-off
The interplay between selection and constraints in Lactococcus cremoris
Evolution is often portrayed as a process in which natural selection makes organisms increasingly well adapted to their environment. But evolution cannot simply produce every conceivable solution. Organisms are bound by their structure, physiology, and genetic and metabolic systems. This creates evolutionary constraints and trade-offs: becoming better at one thing can come at the expense of another. Such trade-offs can be an important driver of biological diversity because they force organisms to follow different evolutionary paths and evolve into distinct specialists.
Many of these ideas are already well developed in evolutionary theory, but experimental tests remain relatively scarce. What makes this research distinctive is that evolution was actually followed in the laboratory. Populations of the lactic acid bacterium Lactococcus cremoris evolved for hundreds of generations under precisely controlled conditions, with food resources varying across space or over time. This made it possible to directly test how selection, migration, and metabolic constraints interact to shape evolutionary outcomes.
The experiments show that the structure of metabolism imposes predictable trade-offs. Adaptation to different food resources therefore did not produce a single “jack-of-all-trades,” but instead promoted the evolution of different specialized strategies. These trade-offs also strongly influenced how populations responded to spatial and temporal environmental variation.
This research highlights that evolutionary constraints may play a larger role in directing evolution than is currently recognized. Selection is relatively straightforward to study, whereas the underlying constraints are embedded within complex biological networks and are therefore much harder to uncover experimentally. By putting these constraints at the center of evolutionary research, we can better understand which evolutionary solutions are possible—and which are not.