Social Species in their Environments : Adaptation and Evolution "ESEAE" Team - iEES Paris

Caption : From left to right: Temnothorax nylanderi ants © T.Colin. Nasutitermes ephratae termites © D.Sillam-Dussès. Expression of the engrailed gene (green: in situ hybridization) in an imaginary disc of the larvae of the ant Mystrium rogeri © M.Molet. Thorax of an ant worker, large muscles of the head and abdomen © A.Khalife

Axis 1. Social life and the adaptation to habitats

In social species, adaptation to the environment is achieved not only through individuals but also through the society. Recent changes in climate and in soil use (agriculture, forestry, pollution, urbanization) lead to the loss, fragmentation and degradation of habitats. This can affect biodiversity at every level. We study how these changes affect communities, populations, reproductive strategies and dispersal of insect societies.

Species found in natural and anthropized habitats are identified using morphological and molecular approaches. We describe their diversity and features. The effect of ecosystem disruption on communities is assessed through the study of species composition and richness, and their structuration in terms of trophic regimes. We also quantify genetic and morphological differentiation between urban and forest populations. We expose colonies to stressful environments in the laboratory in order to test whether urban colonies are better adapted. This is done in collaboration with Claudie DOUMS (MNHN).

We describe reproductive and dispersal strategies of colonies (number of mating, number and origin of reproductives, independent colony founding, fission, investment in growth and reproduction) in relation with environmental changes using molecular methods, landscape genetics, and agent-based modeling in spatially explicit environments.

In contrast with solitary organisms, individuals of social species do not fully face the external environment, because the latter is buffered by the society. The social environment could thus play a major role in the adaptation of social species to environmental changes. We manipulate the external and social environments as well as genetic diversity within colonies in order to quantify the contribution of these factors to colony fitness.

 

Axis 2. Diversity of life history traits

The diversity of colonial life cycles, adult phenotypes, and their production mechanisms are studied based on several examples :

Colony founding by fission is studied using agent-based modeling and experiments in semi-natural conditions.

We describe the biomecanics of weight transport and the evolutionary diversification of muscular and cuticular adaptations, using microtomography imaging in collaboration with Evan P. ECONOMO (Okinawa Institute of Science & Technology).

We assess the effects of miniaturization. We are also interested in the differences between large-headed soldiers and smaller workers. We consider central place foraging and nest defense.

A rearing method of ant larvae with few or no workers is under development in order to quantify the role of the social environment in the phenotypic diversity produced by colonies, in collaboration with Brian L. FISHER (California Academy of Sciences).

With an experimental device developed at the Bois de Vincennes, we manipulate colonial traits of ant societies, and measure the consequences of these manipulations on the fitness of society in nature. For example, we manipulated worker size diversity and mean worker size in order to quantify the adaptive value of size in the ant Temnothorax nylanderi.

Axe 3. Interactions within communities

The diversity and ecological success of social insects result in part from their interactions with other species, especially micro-organisms.

In termites, digestive endo- and exosymbionts are essential. The mechanisms that allow for the maintenance of such symbionts across generation based on horizontal transmission through the environment or vertical transmission through reproductives are characterized using pyrosequencing and behavioural ecology on our laboratory colonies.

A preliminary study of the interaction between ants and aphids is being carried out, with special focus on its plasticity. We manipulate the benefits gained by ants when they monopolize an aphid group or when they exploit it, in order to assess whether the interactions are mutualist or predatory.

We describe new examples of ecological interactions including predation, herbivory, parasitoidism and symbiosis among social insects and other species.

 

Axis 4. The termites, an original model to study ageing

The fact that ageing is partly genetically programmed explains why different mechanisms related to ageing can be found in the diversity of living things, from the Caenorhabditis elegans worm to the fruit fly Drosophila melanogaster or the mouse, which are the most widely used laboratory models. In many organisms, longevity is negatively correlated with reproduction. Social insects represent a major exception to the classic fecundity/longevity trade-off and provide a suitable model for understanding the mechanisms involved. Our team, M. Vasseur-Cognet and her collaborators HS. Sul, W. De Beer, E. Bornberg-Bauer, T. Van Dooren and S. Séité, granted by the Human Frontier Science Program (HFSP), studies a new natural model, the Macrotermes queen termite. In this species, queens and kings can live more than 30 years while remaining highly fecund. Using an integrative biology approach, we study the impact of energetic metabolic reprogramming on the reproductive rate during the sequential stages of queen differentiation, and we compare the obtained data to those of short-lived nonreproductive female workers, long-lived reproductive kings and very short-lived queen species. Comparison of our results with other model organisms will help to identify the molecular components universally conserved or modified, and will highlight the signaling pathways involved in an increased longevity and/or reproduction.

Axis 5. Applications

In addition to fundamental research, some of our studies have direct applications.

We develop biological pest control methods that are both sustainable and environment-friendly. They are directed against some termite and ant species that are harmful for agriculture. They rely on baits that directly target the development of colonies instead of foragers only. Workers are tricked towards baits using specific artificial trail pheromones.

The termite gut microbiota is highly original and efficient at degrading lignin and cellulose, making it a key element to develop new biotechnologies with industrial partners.

We develop a cell line from an ant species that will be used to study cell cycle. Better knowledge of cell division has applications to study cancer. This is done in collaboration with Alain DEBEC (Institut Jacques Monod).

These five axes rely on our rearing infrastructures. Our tropical and temperate rooms allow us to keep live colonies of various termite and ant species.

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