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THE FLEXIBLE PHENOTYPE                                                                                   

A common feature of living organisms is the ability to adjust to different environmental circumstances. A more precise way to view this is that in some cases the same genotype can produce different patterns of gene expression and trait development depending on the environment in which it is expressed. This flexibility (or plasticity, depending on your viewpoint...I use the terms interchangably here for simplicity) runs the gamut from epigenetic changes in gene expression, to physiological responses to external stimuli, to learning, to the development of divergent structural and behavioural traits in response to variation in resources or social interactions.

Despite the ubiquitous nature of this flexibility, studying its evolution poses many challenges. I am interested in two broad questions. The first is how phenotypic plasticity evolves. When is it adaptive and when is it an evolutionary byproduct? What genes and proteins underlie flexible responses to environmental cues? How does selection act to change the frequency of those genes in populations? The second question is how social flexibility alters selection through indirect genetic effects (IGEs), which arise when genes in one individual alter the phenotype of an interacting partner. I am particularly interested in how IGEs impact
the evolution of reproductively isolating traits.

DEVELOPMENTAL GENOMICS                                                                              


I want to catch evolution in the act.


What happens when novel mutations 'invade' a genome? In 1954, Earnst Mayr proclaimed that 'genes do not exist in "splendid isolation," but are parts of an integrated system.' How strong is that integration, after all? Mayr's remarks were not exactly uncontroversial, but we now have excellent opportunities to investigate whether and how the emergence and spread of an 'invading' allele under selection provokes changes in the expression of other genes, what genes and protiens are involved and the mechanistic basis of those changes. Understanding how phenotypic variation becomes available to the action of selection - and the degree to which it is underpinned by genetic variation - can provide powerful insights into how a single de novo mutation can rapidly provoke a cascade of evolutionary changes.

With colleagues at St Andrews and UC Riverside, m
y lab is studying the rapid evolution of an adaptive wing mutation in a population of Hawaiian field crickets. Male crickets ordinarily sing to attract females for mating, but about one decade ago, a novel mutation--flatwing--arose and spread in a population of Teleogryllus oceanicus (below). The mutation erases sound-producing structures on male wings, essentially feminising them, but protects males that carry it from attack by an acoustically-orienting parasitoid fly. Mutant males increased in abundance from 0% to over 90% in just a couple of years, and they appear to achieve mating success by acting as satellites to the remaining singing males. The flatwing morph is caused by a sex-linked single-locus mutation.

An added twist is that the wing morph exists on two different islands, but the mutant morphology is significantly different between them (left). Is this a result of different epistatic interactions when the same mutation is expressed in different genomic backgrounds? Or is it a completely different mutation with a similar phenotypic effect?

We are using RAD-seq to try and isolate causative changes in DNA sequence that produce the mutant wing morphology, and identify candidate genes involved. RAD-seq is a inexpensive technique (well, relatively speaking) for chopping up the genome into tiny bits and developing thousands of markers for use in mapping and association studies.



 
SEXUAL SELECTION AND REPRODUCTIVE ISOLATION                                  

Reproductive isolation contributes to population divergence and speciation, and I am interested in how social interactions within and between species can affect the direction and strength of sexual selection on reproductively isolating traits. I study the evolution of acoustic signals and courtship behaviour using two sister species of field crickets, Teleogryllus oceanicus (right) and Teleogryllus commodus. These species overlap in a hybrid zone in eastern Australia and are the focus of work on the genetics of sexual selection in hybrid zones.



PHENOTYPIC PLASTICITY AND SOCIAL ENVIRONMENTS                          

The social environment is one of the most dynamic and intense sources of environmental variation many animals experience during their lifetime, even in animals that we do not typically think of as being particularly social.
I use field cricket, Drosophila and katydid systems to study how behavioural flexibility evolves, but also  how plasticity resulting from social interactions feeds back to affect the evolution of other traits. In particular, my lab seeks to understand and characterise responses to social input. To what extent do animals retain information about their social environment and shape subsequent behavioural interactions or decision-making processes? And is social flexibility in behaviour adaptive?

PHYLOGEOGRAPHY                                                               

Behavioural plasticity can have far-reaching evolutionary impacts. Mormon crickets (Anabrus simplex), exist in a low-density sedentary form, and a high-density outbreak form. My work with this system untangles how biotic factors, like plasticity in migratory behaviour, interact with geographic features to produce distinct population genetic signatures. The network diagram to the right shows distinct popultion genetic patterns in a clade of low-density crickets (yellow) versus a clade of high-density migratory populations (red). Historical migration patterns affected by plastic responses are reflected in current population genetic structuring, with genetic distance accumulating more rapidly between populations of low-density, sedentary crickets. 



SAME-SEX SEXUAL BEHAVIOUR                                                      


Same-sex sexual behavior occurs in many species, from nematodes to insects to primates.  Why?  I am interested in the evolutionary forces that generate and maintain this behavior, and I am also interested in its evolutionary consequences. I study this empirically using Teleogryllus oceanicus and Drosophila melanogaster, both of which show infrequent but persistent levels of same-sex sexual behaviour. I am particularly interested in testing genetic models for the maintenance of the behaviour in model systems, and also in unravelling the intricate social influences on the expression of same-sex behaviour.





ECOLOGICAL IMMUNOLOGY                                                   

Higher population density leads to higher disease and parasite transmission rates, so selection should favor individuals that can invest more in immunity when population density is high. I study this phenomenon--density dependent prophylaxis--in Mormon crickets, which experience profound density fluctuations (see "Videos" and "Photos" pages). In accordance with theoretical predictions, high-density populations of Mormon crickets tend to show higher investment in a number of immune parameters.