Lewis Stevens

Postdoctoral Fellow

Using state-of-the-art genomics and novel bioinformatic approaches to understand animal genome evolution

I am an evolutionary biologist with a decade of experience using state-of-the-art genomics approaches to understand how genomes evolve. I use nematodes as my primary study system, and combine large-scale comparative and population genomics across both free-living and parasitic species.

Causes and consequences of hyperdiversity in parasitic nematodes

Parasitic nematodes infect billions of humans and animals worldwide and are a major cause of chronic disease, food insecurity, and economic loss. Despite their impact, we know surprisingly little about how genetic variation within parasite populations shapes infection, immune evasion, and responses to control. Using single-parasite genomics enabled by low-input long-read sequencing, I study the origins and consequences of extreme genetic diversity in these worms. My work has revealed that individuals of the same species can differ profoundly in genome content, particularly in genes involved in host interaction. By exploring how this parasite “hyperdiversity” is generated, maintained, and deployed during infection, I aim to uncover fundamental principles of host–parasite evolution and assess how genomic diversity influences the success of drugs and vaccines.

The evolution of programmed DNA elimination 

Programmed DNA elimination (PDE) is a fascinating process in which some organisms reproducibly remove specific regions of their genomes from somatic cells during early development, generating distinct germline and somatic genomes. Although first described over a century ago, PDE has long been considered a rare and taxonomically restricted curiosity. My work has revealed that PDE is far more widespread than previously appreciated, and was even present in the ancestors of the model organism Caenorhabditis elegans. By drawing on genome sequences from over a hundred free-living nematode species, I am investigating how this remarkable process has evolved, how it operates mechanistically, and why these species delete large portions of their genome during early development.

Highlighted publications

For an up-to-date list of publications, please see my Google Scholar. Here’s some highlights:

• Programmed DNA elimination was present in the last common ancestor of Caenorhabditis nematodes
  Stevens L, Sun S, Haruta N, et al. bioRxiv (2025). https://doi.org/10.1101/2025.10.23.681605

• The genome of Litomosoides sigmodontis illuminates the origins of Y chromosomes in filarial nematodes
  Stevens L, Kieninger M, Chan B, et al. PLoS Genetics (2024) 20(1): e1011116. https://doi.org/10.1371/journal.pgen.1011116

• Comparative genomics reveals the dynamics of chromosome evolution in Lepidoptera
  Wright CJ, Stevens L, Mackintosh A, et al. Nature Ecology & Evolution (2024) 8: 777–790. https://doi.org/10.1038/s41559-024-02329-4

• Ancient diversity in host–parasite interaction genes in a model parasitic nematode
  Stevens L, Martínez-Ugalde I, King E, et al. Nature Communications (2023) 14: 7776. https://doi.org/10.1038/s41467-023-43556-w

• Balancing selection maintains hyper-divergent haplotypes in Caenorhabditis elegans
  Lee D*, Zdraljevic S*, Stevens L*, et al. Nature Ecology & Evolution (2021) 5: 794–807. https://doi.org/10.1038/s41559-021-01435-x

• The genome of Caenorhabditis bovis
  Stevens L, Rooke S, Falzon LC, et al. Current Biology (2020) 30: 1023–1031.e4. https://doi.org/10.1016/j.cub.2020.01.074

• Comparative genomics of 10 new Caenorhabditis species
  Stevens L, Félix MA, Beltran T, et al. Evolution Letters (2019) 3(2): 217–236. https://doi.org/10.1002/evl3.110

My timeline

• Research By-Fellow, Hughes Hall, University of Cambridge

• Postdoctoral Fellow, Blaxter Lab, Tree of Life @ Wellcome Sanger Institute

• Postdoctoral Fellow, Andersen Lab, Department of Molecular Biosciences @ Northwestern University

• PhD in Evolutionary Genomics, Blaxter Lab, IEE @ University of Edinburgh