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dr. C.J.M. (Martijn) Egas

Assistant Professor
Faculty of Science
Institute for Biodiversity and Ecosystem Dynamics
Photographer: onbekend

Visiting address
  • Science Park 904
  • Room number:C3.214
Postal address
  • Postbus 94240
    1090 GE Amsterdam
Contact details
  • Profile

    Visit the website of the research institute IBED


    Welcome to my personal webpages at the University of Amsterdam.
    I am associate professor in Evolution and Behaviour at the Institute for Biodiversity and Ecosystem Dynamics.
    Currently, I am supervising two PhD students:

    • Pedro Branco
    • Dajo Boog


    Graduated PhD students:

    • Bram Knegt (thesis defence: June 2019)
    • Alexandra Revynthi (thesis defence: December 2017)
    • Paulien de Bruijn (thesis defence: June 2015)
    • Eva van den Broek (thesis defence: January 2014)
    • Mathias Spichtig (thesis defence: June 2013)
    • Nicola Tien (thesis defence: November 2010)
    • Beata Sznajder (thesis defence: September 2010)


    Please do refer to the information on my research, teaching activities and publications, which can be accessed through the navigation bar at the top of this page.

    Overview of the Department of Evolutionary and Population Biology

  • Research



    Generally, I am interested in social evolution and multi-level selection, and have worked on projects related to: effects of learning on the evolution of exploitation strategies of mite predators (with Beata Sznajder; PhD awarded September 2010), evolution of prudent predation in the predatory mite Phytoseiulus persimilis (with Alexandra Revynthi; PhD awarded December 2017), evolution of diapause (with Annemarie Kroon, postdoc), communicating the nature of danger in thrips (with Paulien de Bruijn - see also below; PhD awarded June 2015), and evolution of the interaction between cytoplasmic bacteria and the animal hosts they infect (with Filipa Vala and Hans Breeuwer). More recently, I have also worked on alternative male mating tactics in the two-spotted spider mite, Tetranychus urticae, with Yukie Sato. My 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 I have worked with various collaborators on 1) the evolution of specialization in herbivorous arthropods, and 2) the evolution of cooperation and altruism in humans and arthropods.

    Specialization is a widespread biological phenomenon, particularly among herbivorous arthropods, and its evolutionary explanation therefore poses important questions. With Sara Magalhaes and Isabelle Olivieri (University of Montpellier), I 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), I 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 student, UvA) I currently study aspects of host plant specialization of the spider mite Tetranychus evansi, which is on record as a specialist on solanaceous plants. We are assessing genetic variation in the ability of this mite to suppress direct defence mechanisms in its host plant tomato.

    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, I have set up collaboration 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. 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). I also study 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. Taken together this means that we now have a lab system for studying 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.

    My expertise in both theory and experiments on specialization has led to collaboration with the group of Jef Huisman (Aquatic Microbiology, University of Amsterdam) on the evolution of specialization and life-history traits in phytoplankton and their herbivores (with Jef Huisman). This collaboration is ongoing with the daily supervisor of one of the PhD students of Jef Huisman (Pedro Branco) on evolution of ecological stochiometric relationships in phytoplankton and zooplankton.

  • Teaching


    I am involved in the following courses and other teaching activities:

    Bachelor programme Biology

    • Course: "Neurobiology and Behaviour" (for biologists)
    • Course: "Evolutionary Biology" (for biologists)
    • Course: "Dynamical Systems in Biology" (for biologists)
    • Course: "Evolution and Behaviour" (for psychobiologists)
    • Course: "Thema I: de Handelende Mens" (for beta-gamma students)
    • Course: "Thema III: interdisciplinary research project - domain Evolution" (for beta-gamma students)
    • Literature thesis supervision
    • Bachelor thesis supervision

    Master programme Biological Sciences

    • Coordinator of the MSc track General Biology
    • Courses: "Masterclasses in Ecology & Evolution", involved in "Experimental Design and Analysis"
    • Supervision of MSc projects and literature theses

    PhD courses

    • "Evolutionary Dynamics"


    • Chairman Examination Committee Psychobiology (2019-present)
    • Chairman IBED Advisory Committee on Teaching and Education (IBED-ACTE)


  • Publications













    • Magalhães, S., Blanchet, E., Egas, M., & Olivieri, I. (2009). Are adaptation costs necessary to build up a local adaptation pattern? BMC Evolutionary Biology, 9, 182. [details]
    • Tien, N. S. H., Sabelis, M. W., & Egas, M. (2009). Heritability of defence and life-history traits in the two-spotted spider mite. Evolutionary Ecology Research, 11(8), 1271-1281. [details]


    • Egas, M., & Riedl, A. (2008). The economics of altruistic punishment and the maintenance of cooperation. Proceedings of the Royal Society B-Biological Sciences, 275(1637), 871-878. [details]
    • Kroon, A., Veenendaal, R. L., Bruin, J., Egas, M., & Sabelis, M. W. (2008). "Sleeping with the enemy"—predator-induced diapause in a mite. Naturwissenschaften, 95(12), 1195-1198. [details]
    • Stomp, M., van Dijk, M. A., van Overzee, H. M. J., Wortel, M. T., Sigon, C. A. M., Egas, M., ... Huisman, J. (2008). The timescale of phenotypic plasticity and its impact on competition in fluctuating environments. American Naturalist, 172(5), E169-E185. [details]


    • Sabelis, M. W., van Baalen, M., Bakker, FM., Bruin, J., Drukker, B., Egas, C. J. M., ... Brown, VK. (Ed.) (1998). Evolution of direct and indirect plant defence against herbivorous arthropods. In Herbivores: Between Plants and Predators (pp. 109-166). London: Blackwell.



    • Knegt, B., Alba, J. M., Ataide, L. M. S., Barbosa, T. A., Bernardo, A. M. G., Chafi, R., ... Egas, M. (2017). Meta-analysis reveals intraspecific variation in herbivores for plant-mediated interactions. Poster session presented at Gordon Research Conference "Plant - Herbivore Interactions", Ventura, CA, USA, United States.

    Journal editor

    • Egas, M. (editor) (2020-2026). ANIMAL BIOLOGY (Journal).


    This list of publications is extracted from the UvA-Current Research Information System. Questions? Ask the library or the Pure staff of your faculty / institute. Log in to Pure to edit your publications. Log in to Personal Page Publication Selection tool to manage the visibility of your publications on this list.
  • Ancillary activities
    • No ancillary activities