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Group Chapuisat - Social Evolution.

| From simple families to complex societies | Social defences against parasites | Social evolution in sweat bees
 

We study the evolution of social behaviour, with a special focus on the structure, function and evolution of insect societies. We are working on the evolution of altruism, the resolution of within group conflicts, the causes and consequences of social structure variation, and the social mechanisms of defence against parasites in ants and wild bees. Our approach combines genetic data from molecular markers, behavioural observations and experiments in the field and laboratory.

From simple families to complex societies

The structure of animal societies varies greatly, from small family groups to large networks of unrelated individuals. For example, the number of queens per colony varies within and among species of ants. A long-term goal of our research is to understand the causes and consequences of social structure variation in insect societies.

In our main model system, the ant Formica selysi, single- and multiple-queen colonies occur in the same populations. The variation in the number of queens changes the genetic diversity and the relatedness within groups, which in turn may affect multiple aspects of social life, from social conflicts to parasite resistance. We aim at determining which environmental and social factors favour each social structure and how the two social forms can co-occur in the same sites. We also draw on genetic data that we have been collecting over a 10-year period to explore whether this social polymorphism is stable through time.

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A lab colony of Formica selysi

In another long-term project, we study the evolution of unicoloniality, an extraordinary social organisation characterised by a very high number of queens per nest and extensive movements of workers between neighbouring nests.

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A large mound of the unicolonial wood ant Formica paralugubris

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Social defences against parasites

Social life is generally associated with an increased exposure to pathogens and parasites, due to factors such as high population density, frequent physical contact and the use of perennial nest sites. However, social life also permits the evolution of collective behavioural defences and the emergence of novel group-level adaptations to resist parasites. We study these social defences against parasites in ants.

Wood ants collect pieces of solidified coniferous resin that they incorporate into their nests. We have shown that the presence of resin protects the ants against bacterial and fungal pathogens. We are further investigating the mode of action and economics of resin use.

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A wood ant carrying a big piece of resin



Fungal pathogens may have a large impact on insect societies. In field surveys and lab experiments, we investigate how ant colonies of various degrees of complexity resist to fungal pathogens, with a special interest in their behavioural and collective defences.

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A Formica selysi worker that died from an infection by the fungus Metarhizium anisopliae

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Social evolution in sweat bees

Sweat bees (family Halictidae) are highly variable in their social organisation, which can range from solitary (one female breeds alone) to eusocial (the first generation of females becomes non-reproductive workers). Such variation provides a great opportunity to study the evolution of altruism and the costs and benefits of alternative social behaviours.

We study the social organisation, social behaviour and population genetics of the sweat bee Halictus scabiosae, which is common on the campus. The methods combine manipulative field experiments, behavioural observations, and genetic analyses with microsatellite markers. Our long-term goal is to unravel the selective pressures acting on alternative social behaviours such as of joint colony founding, drifting or helping at the nest.

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A female sweat bee, Halictus scabiosae, nectaring on Knapweed flower.
Photo credit: Francis Ratnieks

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Biophore - CH-1015 Lausanne  - Switzerland  -  Tel. +41 21 692 41 60  -  Fax +41 21 692 41 65
Swiss University