Niklas Janz

Niklas Janz

Associate Professor, Docent

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Works at Department of Zoology
Telephone 08-16 40 22
Visiting address Svante Arrheniusväg 18 B
Room D521
Postal address Zoologiska institutionen: Ekologi 106 91 Stockholm

About me

I am a Lecturer in Evolutionary insect Ecology and head of the Ecology division at the Department of Zoology


I am director of studies in Ecology at the Department of Zoology and coordinator for the Master program in Ecology & Biodiversity. Currently, I also give two courses, ”Ecology 1” on the Bachelor program in Biology and the Master course ”Science in Biological Research and Investigation”. In adition to these I also give stray lectures on various other courses.


In my group, we study the ecological and evolutionary interaction between butterflies and their host plants.

Most of our research focuses on understanding the evolutionary dynamics of host plant range, host shifts, and speciation. And in particular how these phenomena are interrelated.

You can find more info on my home page:


A selection from Stockholm University publication database
  • 2011. Niklas Janz. Annual Review of Ecology, Evolution and Systematics 42, 71-89

    After almost 50 years of scrutiny, the ideas that Ehrlich and Raven presented in their classical paper on the coevolution between butterflies and plants are still very much alive. Much of this interest has involved the potential for codiversification, both in how the interaction itself diversifies and how the interaction affects modes and rates of speciation. Despite high levels of conservatism and specialization, diversification of the interaction appears to be mainly a consequence of host shifts, but this somewhat paradoxical conclusion can be understood by an appreciation of the ecological as well as genetic mechanisms behind host shifts. There are several ways that the interaction can influence speciation, with or without host-plant-based di-vergent selection on reproductive barriers. One current debate is over the relative importance of radiations following shifts to new adaptive zones and elevated rates of speciation in groups with plastic and diverse host use.

  • 2010. Salvatore J Agosta, Niklas Janz, Daniel R Brooks. Zoologia 27 (2), 151-162

    The parasite paradox arises from the dual observations that parasites (broadly construed, including phy- tophagous insects) are resource specialists with restricted host ranges, and yet shifts onto relatively unrelated hosts are common in the phylogenetic diversification of parasite lineages and directly observable in ecological time. We synthe- size the emerging solution to this paradox: phenotypic flexibility and phylogenetic conservatism in traits related to resource use, grouped under the term ecological fitting, provide substantial opportunities for rapid host switching in changing environments, in the absence of the evolution of novel host-utilization capabilities. We discuss mechanisms behind ecological fitting, its implications for defining specialists and generalists, and briefly review empirical examples of host shifts in the context of ecological fitting. We conclude that host shifts via ecological fitting provide the fuel for the expansion phase of the recently proposed oscillation hypothesis of host range and speciation, and, more generally, the generation of novel combinations of interacting species within the geographic mosaic theory of coevolution. Finally, we conclude that taxon pulses, driven by climate change and large-scale ecological perturbation are drivers of biotic mixing and resultant ecological fitting, which leads to increased rates of rapid host switching, including the agents of Emerging Infectious Disease.

  • 2008. Niklas Janz, Sören Nylin. Specialization, speciation and radiation, 203-215
  • 2016. Maria de la Paz Celorio-Mancera (et al.). BMC Evolutionary Biology 16

    Background: Although most insect species are specialized on one or few groups of plants, there are phytophagous insects that seem to use virtually any kind of plant as food. Understanding the nature of this ability to feed on a wide repertoire of plants is crucial for the control of pest species and for the elucidation of the macroevolutionary mechanisms of speciation and diversification of insect herbivores. Here we studied Vanessa cardui, the species with the widest diet breadth among butterflies and a potential insect pest, by comparing tissue-specific transcriptomes from caterpillars that were reared on different host plants. We tested whether the similarities of gene-expression response reflect the evolutionary history of adaptation to these plants in the Vanessa and related genera, against the null hypothesis of transcriptional profiles reflecting plant phylogenetic relatedness. Result: Using both unsupervised and supervised methods of data analysis, we found that the tissue-specific patterns of caterpillar gene expression are better explained by the evolutionary history of adaptation of the insects to the plants than by plant phylogeny. Conclusion: Our findings suggest that V. cardui may use two sets of expressed genes to achieve polyphagy, one associated with the ancestral capability to consume Rosids and Asterids, and another allowing the caterpillar to incorporate a wide range of novel host-plants.

  • 2013. Maria de la Paz Celorio-Mancera (et al.). Molecular Ecology 22 (19), 4884-4895

    Transcriptome studies of insect herbivory are still rare, yet studies in model systems have uncovered patterns of transcript regulation that appear to provide insights into how insect herbivores attain polyphagy, such as a general increase in expression breadth and regulation of ribosomal, digestion- and detoxification-related genes. We investigated the potential generality of these emerging patterns, in the Swedish comma, Polygonia c-album, which is a polyphagous, widely-distributed butterfly. Urtica dioica and Ribes uva-crispa are hosts of P. c-album, but Ribes represents a recent evolutionary shift onto a very divergent host. Utilizing the assembled transcriptome for read mapping, we assessed gene expression finding that caterpillar life-history (i.e. 2nd vs. 4th-instar regulation) had a limited influence on gene expression plasticity. In contrast, differential expression in response to host-plant identified genes encoding serine-type endopeptidases, membrane-associated proteins and transporters. Differential regulation of genes involved in nucleic acid binding was also observed suggesting that polyphagy involves large scale transcriptional changes. Additionally, transcripts coding for structural constituents of the cuticle were differentially expressed in caterpillars in response to their diet indicating that the insect cuticle may be a target for plant defence. Our results state that emerging patterns of transcript regulation from model species appear relevant in species when placed in an evolutionary context.

  • 2016. Niklas Janz (et al.). Evolution 70 (5), 1150-1155

    The diversification of plant-feeding insects is seen as a spectacular example of evolutionary radiation. Hence, developing hypotheses to explain this diversification, and methods to test them, is an important undertaking. Some years ago, we presented the oscillation hypothesis as a general process that could drive diversification of this and similar interactions, through repeated expansions and contractions of host ranges. Hamm and Fordyce recently presented a study with the outspoken intention of testing this hypothesis where they concluded that the oscillation hypothesis was not supported. We point out several problems with their study, owing both to a misrepresentation of our hypothesis and to the methods. We provide a clarifying description of the oscillation hypothesis, and detail some predictions that follow from it. A reanalysis of the data demonstrated a troubling sensitivity of the "SSE" class of models to small changes in model specification, and we caution against using them for tests of trait-based diversification. Future tests of the hypothesis also need to better acknowledge the processes behind the host range oscillations. We suspect that doing so will resolve some of the apparent conflicts between our hypothesis and the view presented by Hamm and Fordyce.

Show all publications by Niklas Janz at Stockholm University

Last updated: February 20, 2018

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