Experimental approaches to dispersal – a visit to the Metatron facility

It has been a while since the last post here. Hopefully, in the next year we will be able to keep up a more constant flow of posts.

However, a couple of months ago some members of our research group went to a workshop on dispersal organized by the Experimental Ecology Research station in Moulis, more precisely Jean Clobert, Michel Baguette and Virginie Stevens. Besides the highly interesting meeting with many stimulating talks on the “importance of inter-individual variation of dispersal”, “dispersal, life-histories and meta-communities” and “the causes and consequences of dispersal”, we had the opportunity to visit the Metatron facility which was recently created as part of the Experimental station.

Metatron? Behind that slightly cryptic name hides a really fascinating approach to study dispersal. Generally, dispersal is the process that leads to exchange of individuals between populations which can ultimately lead to gene flow between populations. Therefore, its understanding is crucial to the fields of ecology and evolutionary biology and many aspects of applied ecology such conservation biology or the management of invasive species. The objective of the Metatron is indicated by the prefix “meta”, which points in the direction of the highly influential concepts of metapopulations and –communities, while the “-tron” is a hint to the influential and pioneering Ecotron facility. Since ecologists have realized how important the incorporation of the spatial component is to understand for example population dynamics, the literature on dispersal really exploded and lead to own subfields such as dispersal or movement ecology.

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The Metatron facility with its 48 population cages connected by S-shaped corridors.

However, dispersal is notoriously difficult to study in the field: in our team many members work or worked with capture-recapture techniques among others to trace the dispersal of individuals and to infer which factors influence dispersal decisions. Although such techniques work quite fine, they are quite demanding in terms of man power and sometimes, even though a huge amount of time was spent on data collection, the information is insufficient for certain conclusions. Moreover, field studies often suffer from the large spatial and temporal scales involved. To really understand which factors drive the dispersal, one needs replication in space and time to get generality, and manipulation of conditions to rule out confounding factors. However, how can you possibly replicate whole landscapes and manipulate them to infer causal mechanisms? All these drawbacks lead to the development of miniature versions of field study systems such as the bryophyte microcosms of Andrew Gonzalez and his co-workers or the protist microcosms of Marcel Holyoak. Our own Tetrahymena microcosms were developed in a similar fashion as complementary systems to the field research on butterflies. These approaches proved to be very valuable; however, there are still certain objections against the use of microcosms, including the simplicity of the model organisms employed which may not be representative for higher organisms such as vertebrates.

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The interior of the population cage. Shades and sprinklers are used to control the temperature and humidity within the cage.

One of the resident researchers explains how to control the corridor permeability

This is where the Metatron comes in, which is basically a full-fledged field study system where you can replicate whole populations or even communities and manipulate the environmental conditions for model species such as butterflies or small vertebrates such as the Common Lizard. It consists of 48 population cages of about 100m² surface each, which are connected by corridors allowing the autonomous exchange of individuals between populations. The feature which makes this different from other large scale experimental sites such as the Savannah River Site or the Biological dynamics of forest fragments in the Amazonian forest, is the possibility to regulate the environmental conditions such as temperature or humidity independently in each cage, thereby one can either control for these factors or study their effect on dispersal. There is a strong interest in understanding the impact of climate change on animal dispersal, which may be easier to test in such a facility or at least complemented by additional experiments performed there. Moreover, the dispersal process may be manipulated by changing the hostility of the corridor and then the consequences for population dynamics studied. While there are also arguments which limit the applicability of the Metatron, e.g. the spatial extent is indeed much smaller than dispersal ability of certain butterflies, this facility has great potential to test certain theoretical models under standardized conditions.

Julien Cote shows the Common Lizard, which perfecly suits the Metatron as model organism.

Julien Cote shows the Common Lizard, which perfecly suits the Metatron as model organism.

When I visited the facility I was really quite impressed and could not help thinking that this may be a kind of Large Hadron Collider for Ecologists. But of course, the money invested is ridiculously small in comparison (1.6 Million vs. 3.1 Billion EUR). I am really curious to see the first results coming out of this facility. For those interested in the technical details and some results of two pilot studies, please refer to Legrand et al. (2012).

References:

Legrand, D., Guillaume, O., Baguette, M., Cote, J., Trochet, A., Calvez, O., Zajitschek, S., Zajitschek, F., Lecomte, J., Bénard, Q., Galliard, J.-F.L. & Clobert, J. (2012) The Metatron: an experimental system to study dispersal and metaecosystems for terrestrial organisms. Nature Methods, 9, 828–833.

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