Overview
I am interested in the evolution of social traits, life-history traits and host-parasite interactions in spatially structured populations. I develop mathematical models to try to understand the interplay between spatial structuring and evolutionary dynamics.
General context
Evolutionary ecology
Evolutionary ecology deals with studying how ecological parameters affect evolutionary dynamics, and how in turn the evolution of traits shapes ecological features such as population dynamics, parasite virulence, population structure, and so on.
Space
Spatial structure is an important component of this feedback loop between ecology and evolution. However, the interplay of spatial dynamics and evolution is still poorly understood. Models often assume that the population has no spatial structure (well-mixed population). In a viscous population, however, spatial heterogeneities can dramatically modify the selective pressures. For instance, spatial structure can promote the evolution of altruism whereas the corresponding non-spatial models predict selfishness to be the sole evolutionary endpoint. Spatial structure can also affect the selective pressures on reproductive effort or host-parasite interactions. In general, evolution will depend on the interplay between genetic and demographic structuring processes.
Methods
Spatial moment equations (aka ‘pair approximation’ techniques) are an analytical framework for deriving analytical deterministic equations for the dynamics of spatial moments (spatial average, spatial covariance...). This provides an analytical alternative (or rather a complement) to spatial stochastic simulations. In these models, space is typically represented as a network of sites (usually a lattice), and updating rules are stochastic. These ecological models can be combined with evolutionary approaches such as adaptive dynamics or quantitative genetics. I am working on various extensions of this theoretical framework (class structure, connections with quantitative genetics, continuous space...).
Evolution of host-parasite interactions
Over the past years, my main interest has been the evolution of spatially structured host-parasite interactions.Parasite life-history traits
Most diseases are transmitted across a network of contacts, resulting in local infections. However, recent changes in human societies and trade have increased the likelihood of global infection events. How do those changes in host and parasite dispersal affect the evolution of parasite life history traits, such as virulence (or strategies of host exploitation more generally)? I have worked on this topic with Mike Boots and Sylvain Gandon. A key insight of this work is that, when dispersal is local, parasites will often evolve more prudent strategies of host exploitation than they would under global dispersal, but only if the relatedness between parasites infecting neighbouring hosts is above a threshold determined by epidemiological structuring. Recent extensions of this work include taking into account the effects of treatments in the host population.
Host defence
Host and parasite dispersal may also affect the evolution of strategies of host defence. Interestingly, spatial structure may select for "altruistic" host defence strategies such as reduced transmissibility or suicide upon infection. Florence Débarre, in a paper co-authored by Minus van Baalen, Sylvain Gandon and I, has shown how this could be explained by a combination of genetic and epidemiological effects.
Parasite manipulation of host dispersal
A long time ago, I worked on a spatial model of a host-parasite interaction in which the parasite is able to manipulate its host's dispersal behaviour. Together with Will Wilson and Minus van Baalen, we have shown that increasing host dispersal can lead to a higher transmission for the parasite, and that spatial structure has an important impact on the benefits that can be reaped from such manipulative strategies.
Evolution of bacteria-phage interactions
I have been involved in several experimental projects aiming at testing theoretical predictions in bacteria-phage systems. This is work in collaboration with Thomas Berngruber and Sylvain Gandon. Other experimental projects are also ongoing as part of Héléne Chabas' PhD thesis, which is co-supervised by Sylvain Gandon and myself.
Evolution of social traits
I am also interested in the evolution of helping and harming behaviours.Kin selection
Kin selection is a key process for the evolution of helping (or harming) behaviours in viscous populations, because population viscosity (e.g. limited dispersal) creates positive assortment between related individuals. Thus, if you help your neighbours, you tend to help relatives. Spatial moment equations provide an alternative way to explicitly incorporate more ecological ‘realism’ (such as demographic or epidemiological fluctuations) into kin selection theory.
Habitat saturation and helping
Together with Sylvain Gandon, we have used this approach to study the effect of habitat saturation on the evolution of helping behaviours. In particular, we have shown that the effect of habitat saturation depends crucially on the details of the life cycle (such as density-dependence or fecundity vs. survival helping).
Evolution of parental care and cannibalism
Most studies on the evolution of altruism in spatially structured populations have focussed on populations with no age or class structure. I have investigated with Minus van Baalen the evolution of between-class altruism (in the form of care for juveniles by adults).
Other projects
Other interests include the evolution of other life-history traits in spatially structured populations and the evolutionary ecology of multiple infections.Life history traits as social traits
Although the previous discussion has focussed on helping behaviours, virtually any trait can be thought of as social in a spatial context. Many life history traits expressed by an individual, such as reproductive effort or senescence, can be expected to affect the reproductive success or survival of the individual's neigbours. I'm interested in understanding how demography and the characteristics of the life cycle will affect the selective pressures on such traits.
Reproductive effort
How should an organism divide its resources between fecundity and survival? And how should population viscosity affect the optimal strategy? I have developed models to investigate this question under different ecological scenarios.
Multiple infections and parasite evolution
I am interested in how other forms of structure in host populations may affect the evolution of parasite traits. In particular, I have worked on various models of coinfections and superinfection to try to understand how multiple infections affect the epidemiological feedbacks shaping parasite evolution. This is work in collaboration with Samuel Alizon and Sarah Kada. I have crazy ideas for further developments of this theoretical framework.