Working with Tim Connallon at Monash University gives me the opportunity to learn to formulate my ideas and questions about the evolution of sexual dimorphism in a population genetic framework. This is something I always wanted to add to my toolbox as an evolutionary biologist, in order to force me to articulate my research questions very precisely and to get testable quantitative predictions, based on the wealth of modelling techniques developed in the mathematical framework of population and quantitative genetics. My theoretical explorations will be accompanied by experimental work on the good old fruit fly, and on a lizard species, the poetically named rainbow skink (Lampropholis delicata), which seems to have a very intriguing way of sexually dimorphic trait expression.
My work with Mollie Manier at the Department of Biological Sciences of The George Washington University in Washington, D.C., centres around two topics.
First, I study sexual conflict through antagonistic alleles for male sperm lengths and female reproductive tract morphology, using D. melanogaster artifical selection lines, selected for short and long sperm cells, and for short and long seminal receptacles, the primary sperm storage organ in female fruit flies.
Second, I work on transgenerational epigenetic effects of diet and age on postcopulatory sexual selection. These studies involve extensive profiling of gene expression through RNA-Seq.
At the Evolutionary Biology Centre of the University of Uppsala, I work on diet effects on life-history and ageing in the fruit fly, Drosophila melanogaster. This includes experiments on the interaction between reproduction and low or high yeast diet, acting on age-dependent mortality and reproductive patterns. Evolutionary trajectories of mortality and reproductive fitness, including the late life phase, in response to restricted and ‘obese’ diets are my main experimental focus at the moment. To study the longer term evolutionary consequences of extreme diets during adulthood, I set up experimental evolution lines in mixed-sex population cages which have had time to evolve since late 2012.
I’m also working on the integration between laboratory and field studies, especially in invertebrate species (think about the lack of field studies on D. melanogaster, that could complement the vast number of studies conducted in the lab).
RESEARCH on CRICKETS
cricket in the field
Crickets kept in individual
containers in a
temperature controlled room
Life-history theory provides ultimate causes of why traits like development time, mortality before and after maturation, or fecundity should be shaped in a specific way, depending on what species or even population we look at. It is obvious that lifespan of an organism does affect its fitness. Maximum potential lifespan is not the same in organisms with similar metabolic rates, therefore a purely mechanistic explanation of senescence (‘wear and tear’) is not sufficient. Rates of ageing and senescence should depend on the genetic architecture and the evolutionary forces, mainly selection, that shaped them.
To investigate the genetic architecture underlying age-dependent fitness traits, I performed a quantitative genetic study, where I looked at the genetic correlations between the expression of fitness related traits early and late in life. These kinds of correlations are an important tenet in evolutionary theory of ageing, more exactly in the antagonistic pleiotropy theory. I tested not only for genetic relationships within the two separate sexes, but also between the sexes. This allowed me to evaluate whether sexual conflict is potentially important in constraining sex-specific independent evolution of increased fitness.
More estimates of the effect of intra-locus sexual conflict on ageing in various different taxa are needed to assess the importance and ubiquity of this mechanism for the evolution of sex-specific senescent phenotypes.
Caloric or, better, dietary restriction is another area I am interested in. Theory predicts that sexually selected traits should be costly, and that does not only mean in an immediate physiological way (e.g. ‘the more a cricket calls, the more energy it spends, the higher its immediate resource intake has to be’), rather with a life-history background of some kind of lifetime balance between acquisition and allocation of resources. So, by combining this assumption with the fact that dietary restriction has been shown to prolong lifespan in a wide range of organisms, I would like to further explore the interface between sexual selection and ageing. Especially in the last two years, evidence for the importance of other characteristics of diet, rather than simply caloric intake, has emerged. Accordingly, to tease out what component or composition of the diet is responsible for a potential increase in longevity, is of major interest.
Ageing and senescence in animals in the wild has been neglected for a long time, because animals that show senescent signatures were thought not to occur in nature. After studies showed senescence in vertebrate, longer-lived animals, this belief was still held up for short-lived animals like insects. We know now from a handful of studies that invertebrate species can show senescence in their natural environment. In the field cricket, I used capture-mark-recapture methodology to show a senescent increase in mortality rate for males and females. To design and carry out good experiments on ageing in natural populations is very hard, because there are many confounding environmental variables, and because the sample sizes have to be substantial in order to estimate mortality rates or other age-dependent fitness correlates (especially in older age-groups). But most often, study species have evolved for hundreds and thousands of generations in a fluctuating environment where external mortality risk is high, compared to lab environments. This means that testing findings from the lab in the wild can tell us about their adaptive significance, and, vice versa, results from the wild can be used to design experiments in the lab, under more controlled circumstances, allowing to further disentangle the results from nature.
Female cricket in the field,
A spider with a
cricket as its prey
LINKS to present and past COLLABORATORS
- Timothy Connallon – Population genetics of sexual dimorphism
- Mollie Manier – Sexual conflict over reproductive traits, Transgenerational epigenetic inheritance
- Fernando Colchero – Bayesian estimation of age-specific mortality
- Alexei Maklakov – Sexual conflict, dietary restriction and ageing
- Susanne Zajitschek – haplotype selection in zebrafish, Condition-dependent dispersal and temperaturedependent performance in lizards, Population effects of inbreeding in guppies
- Russell Bondurianky – Ageing and quantitative genetics in natural insect populations
- Jean Clobert – Consequences of personality traits and dispersal variability on meta-population dynamics; sibling dispersal; maintenance of colour polymorphism
- Ruth Archer – Sexual conflict over ageing in decorated crickets
- Don Miles – Physiological performance in lizards
- Rob Brooks– Genetic architecture underlying ageing, dietary restriction, ageing in the wild
- Simon Lailvaux – Sex-effects of mating and diet on performance and demography
- John Hunt – Maintenance of genetic variarion, dietary restriction, demography, ageing
- Hwei-yen Chen – Late-life mortality plateaus in nematodes
- Matt Hall– Statistics of non-normal longitudinal data
- Mike Jennions – Dietary restriction, genetic architecture underlying ageing
- Chad Brassil – Mathematical modelling of ageing in natural populations
- Steve Simpson’s lab – Geometric framework of feeding and nutrition