Research Interests

My research interests span quite a diverse range of topics within the general realm of evolutionary genetics, but basically I use population genetics approaches to understand the fundamental evolutionary and demographic processes that determine the genetic make-up of populations. My recent work has focused on human migration and settlement history, patterns of colonization and sex-biased dispersal in animal populations, the evolution of sex chromosomes, and the evolutionary biology of invasive and recipient species.

NEWS FLASH!

This year, as part of the UK ladybird group, Cathleen, Joe and myself exhibited at the Royal Society Summer Exhibition. It was a fantastic experience, and thank you to everyone that came to visit us and chat about ladybirds! To find out more about the exhibition or read Jim Bacon's excellent blog, click here!

Projects

Evolutionary biology of invasive and recipient species

Biological invasions are a major threat to global biodiversity, agriculture, the economy and human health. Together with Cathleen Thomas, a PhD student in my group, we are investigating the evolutionary genetics of the harlequin ladybird, Harmonia axyridis, a species that is currently invading the British Isles and posing a potentially devastating risk to native ladybird populations. We hope that this unique case study will contribute significantly to our understanding of the evolutionary biology of species invasions. The harlequin, which is native to Asia, was first found in the UK in 2004. Since then it has become widespread throughout south-east England, and is now found as far as Cornwall, Wales, Lancashire, and North Yorkshire. The harlequin has been monitored rigorously since its initial discovery in the UK by our collaborators as part of "The Harlequin Ladybird Survey". Records sent in by the general public are validated and collated within a main database. This information is essential so we can follow the pace and spread of the invasion, so please do keep on sending your records and samples. More information and an on-line recording form can be found at http://www.harlequin-survey.org/.

Figs: top- native seven-spot ladybird, left- harlequin ladybird larva, middle- harlequin ladybird (form Succinea), right- harlequin ladybird (form Spectabilis).

Collaborators: Mike Majerus (deceased) Remy Ware and LJ Michie (University of Cambridge), Helen Roy (Centre for Ecology and Hydrology, CEH), Pete Brown (Anglia Ruskin University), Arnaud Estoup and Eric Lombaert (CNRS, Montpellier and INRA) 

Human migration and settlement history

Geography has played a crucial part in determining the genetic make-up of human populations. In fact, distance from East Africa (the cradle of modern humans) can explain most of the variation within and between human populations, as demonstrated by the smooth decline in neutral genetic diversity, and increase in genetic distance with increasing distance from Africa (See figure below). These "clines" are consistent with a single exit of anatomically modern humans out of Africa and essentially continuous gene-flow over limited distances. I am interested in using these simple patterns as null models to investigate natural selection at particular regions of the genome, and in using geographically explicit frameworks to investigate the influence of geography, environment and culture on global and regional-scale patterns of human genetic variation. This was reviewed in the September 2007 issue of Trends in Genetics.

Collaborators: François Balloux, Irene Gallego Romero (Leverhulme Centre for Human Evolutionary Studies), Andrea Manica (University of Cambridge), Jérôme Goudet (University of Lausanne), Maziar Ashrafian-Bonab (University of Portsmouth).

Fig: Human genetic variation is largely clinal

a) Gene diversity within the human populations decreases with increasing distance from East Africa.

b) Pair-wise genetic distance between human populations increases with geographic distance

The figures are based on data from autosomal microsatellite markers typed in populations from the Human Genome Diversity Project cell line panel. The figure is adapted from Trends in Genetics, September 2007

Patterns, causes and consequences of mammalian sex-biased dispersal

Dispersal is arguably one of the most important events in an organism's life and is influenced by interactions among kin, such as competition for mates or resources, cooperation, and inbreeding avoidance. I am interested in understanding the relative importance of these factors in determining which sex disperses, and their influence on the timing and distance of dispersal (see Lawson Handley and Perrin 2007). Consistent with evolutionary predictions, dispersal is male-biased in the majority of species. Investigations of exceptional species can therefore be particularly enlightening for studying the evolution of dispersal. We recently provided genetic evidence for female-biased dispersal in Hamadryas baboons, which is contrary to predictions based on this species' polygynous mating system, and likely to be linked to its' unique hierarchical social structure, with which dispersal has evolved (Hammond et al. 2006). Dispersal is also a trait that evolves in response to natural selection. An area of my current interest is therefore to understand the effects of landscape and environmental variables on dispersal over different spatial scales, since this has important implications due to changing climatic conditions and increased habitat fragmentation.

Collaborators: Rob Hammond (University of Hull), Nicolas Perrin (University of Lausanne).

I am interested in the progressive evolution of sex chromosomes from their autosomal progenitors, and in more fine scale molecular evolutionary processes on the Y chromosome. First, by analyzing data from birds, which have ZZ males and ZW females (the opposite system to mammals), we demonstrated that progressive and stepwise cessation of recombination is a general feature behind sex chromosome evolution (Lawson Handley et al. 2004). Second, the Y chromosome seems to have very low levels of genetic variation, but the reasons why are poorly understood (Lawson Handley et al. 2006 a, b). One possibility is that this is linked to natural selection on the Y, but this is difficult to determine because confounding factors such as effective population size (Ne, note there is only one Y chromosome to 3X chromosomes or 4 autosomes in a male-female pair) and demographic effects can be tricky to tease apart. To address this we compared patterns of Y and X chromosome variation in ancestral and derived populations of a monogamous shrew (the greater white-toothed shrew). After accounting for mutation rate, Ne and demographic history, the Y chromosome still displays a deficit in variation relative to the X in both populations, which suggests that selection may have played a role in lowering Y chromosome diversity.

Collaborators: Nicolas Perrin and Laura Berset-Braendli (University of Lausanne), Hans Ellegren (Uppsala University), Rob Hammond (University of Hull).

Publications

Balloux F, Lawson Handley LJ, Jombart T, Liu H, and Manica A. (2009) Climate shaped the worldwide distribution of human mitochondrial DNA sequence variation. Proc R Soc B doi: 10.1098/rspb.2009.0752 (on line 8th July 2009)

Romero IG, Manica A, Goudet J, Lawson Handley, LJ, and Balloux F. (2009) How accurate is the current picture of human genetic variation? Heredity 102: 120-126.

Lawson Handley L-J, Manica A, Goudet J, Balloux F. (2007) Going the distance: Human population genetics in a clinal world. Trends in Genetics 23(9): 432-439.

Lawson Handley L-J, Byrne K, Santucci F, Townsend S, Taylor M, Bruford MW, Hewitt GM. (2007) Genetic structure of European sheep breeds. Heredity 99:620-631

Lawson Handley L-J, Perrin N. (2007) Advances in our understanding of mammalian sex-biased dispersal. Molecular Ecology 16:1559-1578

Ashrafian-Bonab M, Lawson Handley L-J, Balloux F. Is urbanization scrambling signals of human genetic diversity? A case study. Heredity 98:151-156

Lawson Handley L-J, Berset-Brandli L, Perrin N (2006a) Disentangling Reasons for Low Y Chromosome Variation in the Greater White-Toothed Shrew (Crocidura russula). Genetics 173:935-942.

Lawson Handley L-J*, Hammond RL*, Emaresi G, Reber A, Perrin N (2006b) Low Y chromosome variation in Saudi-Arabian hamadryas baboons (Papio hamadryas hamadryas). Heredity 96:298-303. (*Joint first authors)

Hammond RL*, Lawson Handley L-J*, Winney BJ, Bruford MW, Perrin N (2006) Genetic evidence for female-biased dispersal and gene flow in a polygynous primate. Proceedings of the Royal Society B-Biological Sciences 273:479-484 (*Joint first authors)

Lawson Handley L-J, Perrin N (2006) Y chromosome microsatellite isolation from BAC clones in the greater white-toothed shrew (Crocidura russula). Molecular Ecology Notes 6:276-279

Sazanov AA, Sazanova AL, Stekolnikova VA, Trukhina AV, Kozyreva AA, Smirnov AF, Romanov MN, Lawson Handley L-J, Malewski T, Dodgson JB (2006) Chromosomal localization of the UBAP2Z and UBAP2W genes in chicken. Animal Genetics 37:72-73

Brändli L, Lawson Handley, L-J, Vogel P, and Perrin N (2005) Evolutionary history of the greater white-toothed shrew (Crocidura russula) inferred from analysis of mtDNA, Y, and X chromosome markers. Molecular Phylogenetics and Evolution 37: 832-844

Lawson Handley L-J, Ceplitis H, and Ellegren H (2004) Evolutionary strata on the chicken Z chromosome: Implications for sex chromosome evolution. Genetics 167:367-376

Lawson L-J, and Hewitt GM (2002) Comparison of substitution rates in ZFX and ZFY introns of sheep and goat related species supports the hypothesis of male-biased mutation rates.  Journal of Molecular Evolution 54: 54-61