Dr. Reuben Nowell

Research Overview

I am an evolutionary biologist with broad interests in the processes of adaptation, diversification and speciation. I use whole-genome sequence data in conjunction with population genomics and comparative phylogenetics to provide insights into how these mechanisms contribute to the evolutionary process. I am continually fascinated by how patterns in molecular and genomic data can be used to infer the evolutionary histories of both prokaryotic and eukaryotic organisms.

Current Research

Population genomics of ecological speciation in the bdelloid rotifers

Sexual reproduction is nearly ubiquitous among animals – most require at least some parts of their life-cycle to involve the shuffling of genes from different individuals to produce genetically mixed offspring. This genetic recombination allows natural selection to act more efficiently in both removing harmful mutations from the population as well as allowing good combinations of mutations to spread. These long-term benefits of sex mean that, even though asexuality may have some short-term benefits, asexuality is considered an “evolutionary dead-end”, and most asexual animals quickly go extinct.

The bdelloid rotifers seemingly defy the conventional requirement of a sexual stage in their lifecycle. Bdelloid rotifers are tiny animals that live in a variety of freshwater habitats, including lakes and ponds but also in more temporary wet habitats such as puddles and moss. These animals have been apparently existing without sex for at least 40 million years: no males have ever been seen, and the structure of their genome is such that conventional meiosis, through which gametes such as eggs and sperm are normally produced, is thought to be impossible.

Given the evolutionary benefits of sex, how then is it possible for the bdelloids to have maintained an apparently asexual lifestyle for such a long time? Are bdelloid rotifers truly asexual, or do they have some as-yet unknown mechanism by which they can shuffle their genes without the need for males and meiosis? And just what impact does such long-term “asexuality” have on other evolutionary processes, such as adaptation, divergence and speciation?

This project aims to answer some of these questions by looking in depth at the genomes of bdelloid rotifers from the genus Rotaria. Comparing genome sequences between individuals will allow us to look for evidence of between-individual recombination (i.e., sex), which might indicate that gene-shuffling is occurring despite no males or meiosis. In addition, we can determine how important are other evolutionary processes, such as horizontal gene transfer (HGT), in the evolutionary history of these amazing animals.

Previous Research

Genomic basis of adaptation in the plant-pathogenic bacterium Pseudomonas syringae

During my PhD I used a range of comparative genomics and phylogenetics methods to investigate:

  1. The contribution HGT and genome fluctuation towards evolutionary processes such as adaptation, diversification and (perhaps even) speciation in bacteria
  2. The effect of HGT on synonymous codon usage
  3. The association between the “flexible genome” and niche adaptation in relation to adaptation onto woody host plants
  4. The adaptation of P. syringae pv. aesculi onto the European horse chestnut

Genome assembly of the Mycalesine butterfly Bicyclus anynana

I have also cut my teeth in the world of eukaryotic genome assembly and annotation, working on the genome of the African squinting bush brown butterfly Bicyclus anynana.


Having graduated from Edinburgh University with a BSc (Hons) in Evolutionary Biology in 2008, I then completed an MSc in Quantitative Genetics and Genome Analysis before getting my hat-trick of degrees all from Edinburgh with a PhD, supervised by Prof. Paul Sharp and Dr. Sarah Green, looking at the genomic basis of adaptation in the plant-pathogenic bacterium Pseudomonas syringae. I then did a short Post-Doc in the lab of Prof. Mark Blaxter before joining the Barralab in late 2015.


  • Wilson CG, Nowell RW, Barraclough TG. Evidence for “inter- and intraspecific horizontal genetic transfers” between anciently asexual bdelloid rotifers is explained by cross-contamination. bioRxiv. 2017. p. 150490. doi:10.1101/150490
  • Nowell RW, Elsworth B, Oostra V, Zwaan BJ, Wheat CW, Saastamoinen M, et al. A high-coverage draft genome of the mycalesine butterfly Bicyclus anynana. Gigascience. 2017; doi:10.1093/gigascience/gix035
  • Nowell RW, Laue BE, Sharp PM, Green S. Comparative genomics reveals genes significantly associated with woody hosts in the plant pathogen Pseudomonas syringae. Mol Plant Pathol. 2016;17: 1409–1424.
  • Nowell RW, Green S, Laue BE, Sharp PM. The extent of genome flux and its role in the differentiation of bacterial lineages. Genome Biol Evol. 2014;6: 1514–1529.
  • Green S, Laue BE, Nowell RW & Steele H. 2014. Horse chestnut bleeding canker: a twenty-first century tree pathogen. In T. Fenning (Ed.), Challenges and Opportunities for the World’s Forests in the 21 st Century (pp. 784–794). Forestry Sciences 81, doi:10.1007/978-94-007-7076-8_35.
  • Nowell RW, Charlesworth B, Haddrill PR. Ancestral polymorphisms in Drosophila pseudoobscura and Drosophila miranda. Genet Res. 2011;93: 255–263.