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.

The genomic basis of adaptation to pathogens in an asexual

It remains unclear why sex is so ubiquitous among animals and plants. The Red Queen hypothesis posits that asexuals fail to adapt to the strong and continually changing selection imposed by coevolving parasites and pathogens. Evidence is hard to obtain given the long timescales involved. We will test the predictions of the Red Queen in a uniquely long-lived lineage of asexual animals, the bdelloid rotifers, by identifying the evolutionary and genetic basis of their interactions with virulent fungal pathogens. Does this apparent exception challenge or affirm the proposed rule?

Selected Publications

• Peck LD, Nowell RW, Flood J, Ryan MJ & Barraclough TG. Historical genomics reveals the evolutionary mechanisms behind multiple outbreaks of the host-specific coffee wilt pathogen Fusarium xylarioides. BMC Genomics (in press)

• Nowell RW, Wilson CG, Almeida P, Schiffer PH, Fontaneto D, Becks L, Rodriguez F, Arkhipova IR, Barraclough TG. Evolutionary dynamics of transposable elements in bdelloid rotifers. Elife 10, e63194 (2021)

• Jaron KS, Bast J, Nowell RW, Rhyker Ranallo-Benavidez T, Robinson-Rechavi M, Schwander T. Genomic features of parthenogenetic animals. J. Hered. 112, 19–33 (2021)

• Pathak A, Nowell RW, Wilson CG, Ryan MJ & Barraclough TG. Comparative genomics of Alexander Fleming’s original Penicillium isolate (IMI 15378) reveals sequence divergence of penicillin synthesis genes. Sci. Rep. 10, 15705 (2020)

• Scheuerl T, Hopkins M, Nowell RW, Rivett DW, Barraclough TG, Bell T. Bacterial adaptation is constrained in complex communities. Nat. Commun. 11, 1–8 (2020)

• Yoshida Y, Nowell RW, Arakawa K & Blaxter M. Horizontal Gene Transfer in Metazoa: Examples and Methods. in Horizontal Gene Transfer: Breaking Borders Between Living Kingdoms (eds. Villa, T. G. & Viñas, M.) 203–226 (Springer International Publishing, 2019). doi:10.1007/978-3-030-21862-1_7

• Nowell RW, Almeida P, Wilson CG, Smith TP, Fontaneto D, Crisp A, Micklem G, Tunnacliffe A, Boschetti C, Barraclough TG. Comparative genomics of bdelloid rotifers: Insights from desiccating and nondesiccating species. PLoS Biol. 16, e2004830 (2018).

• Wilson CG, Nowell RW & Barraclough TG. Cross-Contamination Explains ‘Inter and Intraspecific Horizontal Genetic Transfers’ between Asexual Bdelloid Rotifers. Curr. Biol. 28, 2436–2444.e14 (2018).

• Jay P, Whibley A, Frézal L, Rodríguez de Cara MÁ, Nowell RW, Mallet J, Dasmahapatra KK & Joron M. Supergene Evolution Triggered by the Introgression of a Chromosomal Inversion. Curr. Biol. 28, 1839–1845.e3 (2018).

• 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.

Other

• Github

• ResearchGate