Generally, we are interested in social evolution and multi-level selection. Our research focus is in the combined experimental and theoretical study of evolutionary dynamics, i.e., feedbacks between evolutionary and ecological processes — nowadays called eco-evolutionary dynamics — and the role of genetic factors in determining these dynamics. In this context we have mainly worked on 1) the evolution of specialization in herbivorous arthropods, and 2) the evolution of cooperation and altruism in humans and arthropods (elaborated below).

Also, we are involved in the larger NWA projects “Predicting Evolution” (based at the University of Amsterdam (UvA), with Karen Bisschop, Thomas Blankers, Meike Wortel, Ken Kraaijeveld, co-supervised by Astrid Groot, Jacintha Ellers and Marcel Visser) and “Metahealth” (a consortium coordinated by ACTA (Amsterdam) on health in a microbial, sociocultural and care context in the first 1000 days of life, wherein we collaborate with microbiologists and bio-informatics to analyze eco-evolutionary coexistence in oral and gut microbiomes). We collaborate with Karline Janmaat (UvA) to gain insight in the foraging cognition of primates in the rain forest, and compare that with foraging cognition of endemic human rain forest tribes. In the future, we hope to work on the role of musicality in human cooperative behavior in the same hunter-gatherer setting. With Isabel Smallegange (Newcastle University, UK), we investigated the effect of developmental plasticity on eco-evolutionary dynamics in general and on the evolution of male dimorphism in particular. We have also worked on alternative male mating tactics in the two-spotted spider mite, Tetranychus urticae, with Yukie Sato (University of Tsubuka, Japan).

Since the COVID pandemic unfolded, we started a new collaborative research group with international colleagues, within the theme “Predicting Evolution”, on the evolution of the genetic code (with Astrid Groot (UvA), Peter van der Gulik (CWI Amsterdam), Ken Kraaijeveld (Applied University Leiden), Wouter Hoff ((Oklahoma State University, USA), and Jenna Gallie (Max Planck Institute for Evolutionary Biology, Plön, Germany). We have been working online, meeting once per week, on bio-informatic “big-data” analysis of available genome data, in order to study variation in the use of tRNA gene repertoires within and among the three domains of life. We started by focusing on the variation in tRNA repertoire of Archaea, figuring out not only which tRNAs are mandatory for a functioning organism and which are auxiliary, but also why some taxa lost many auxiliary tRNA genes and others did not.

1) Specialization is a widespread biological phenomenon, particularly among herbivorous arthropods, and its evolutionary explanation therefore poses important questions. We developed theoretical and experimental evidence (using T. urticae) for the role of adaptive learning and foraging behaviour in facilitating the evolution of resource specialization. With Sara Magalhaes and Isabelle Olivieri (University of Montpellier), we studied patterns of local adaptation to new host plants using an experimental evolution approach with T. urticae. Our main findings were that local adaptation builds up trade-offs between performance on two new host plants and that phenotypic plasticity (in the form of maternal effects) plays a large role in the evolutionary response to new host plants. With Nicola Tien (PhD awarded November 2010), we studied the evolutionary genetics of life-history traits of T. urticae, such as development time, juvenile survival or egg-laying rate. Of all life-history traits, egg-laying rate stood out as a trait with high additive genetic variance (resulting in a high degree of heritability) as well as strong effects of (partly recessive) deleterious variation. The latter finding suggests that host-plant specialization in this species may be explained by “mutation accumulation” rather than fitness trade-offs, a theoretical possibility that has not been tested in herbivorous arthropods. With Bram Knegt (PhD awarded June 2019) we studied aspects of host plant specialization of the spider mite Tetranychus evansi, which is on record as a specialist on solanaceous plants. We assessed genetic variation in the ability of this mite to suppress direct defence mechanisms in its host plant tomato.

2) Explaining the evolution and maintenance of cooperation among unrelated individuals is one of the fundamental problems in biology and the social sciences. To study this problem, we have collaborated with Aljaz Ule, Eva van den Broek, Matthijs van Veelen and Arthur Schram (Experimental Economics, UvA) and Arno Riedl (Behavioural Economics, Maastricht University) to study the interactive evolution of social norms and cooperation. Our experiments confirmed a role for group competition in within-group cooperation. Also, we showed that humans use both personal experience and reputation information about others in helping decisions, and that humans show distinct moral rules in assessing reputation information (with Eva van den Broek, PhD awarded January 2014, and Lucas Molleman, PhD awarded at Groningen University, February 2014). Theoretical study focused on the role of mutation in the maintenance of cooperation by direct reciprocity, and on sexual selection for cooperative behaviour (with Mathias Spichtig, PhD awarded June 2013). We also studied spiteful behaviour (male killing) in social spider mites (with Yukie Sato), and alarm communication in thrips (with Paulien de Bruijn, PhD awarded June 2015). We have shown that thrips larvae exhibit context-dependent communication of predation danger (relating to predator nearby vs actual predator attack) by means of varying the ratio of two chemical components in their alarm pheromone, and showing appropriate responses to the various alarm signals. We also showed that thrips larvae can recognize kin. This means that we now have a lab system to study the evolutionary mechanisms that in theory can maintain such a communication system, a topic of general interest that is so far only investigated in prairie dogs, ground squirrels and several other mammals under natural conditions.

Currently, we are studying the theoretical question under which conditions cooperative and altruistic behaviour can be promoted by sexual selection, for instance as a handicap signal of high quality as a mate. PhD student Dajo Boog is analyzing individual-based models on this topic, supervised by Martijn Egas and by Matthijs van Veelen (Experimental Economics, UvA) and Annemie Ploeger (Evolutionary Psychology, UvA). Results so far suggest that there are indeed conditions, such as the way in which the partner expresses preference for one mate over another, under which cues with a fitness cost – and hence altruistic behaviour – can be selected for, even when there is no link with mate quality.