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Group Chapuisat - Social Evolution.

| Causes and consequences of variation in social organization | Social defences against parasites | Social evolution in sweat bees
 

We study the evolution of social behaviour, with a focus on the structure, function and evolution of insect societies. We are currently working on the causes and consequences of social structure variation in ants, and on social defences against parasites. We combine genomic, behavioural, ecological and experimental approaches, in the field and laboratory.

Causes and consequences of variation in social organization

The social organization of insect societies varies greatly, from simple families headed by one queen to large social groups containing many reproductive individuals. 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 Alpine silver ant Formica selysi, single- and multiple-queen colonies occur in the same populations. We investigate the genetic, behavioural and ecological bases of this polymorphism. We have been monitoring field colonies over a period of 15 years. We explore how the two social forms differ and which factors and processes contribute to the maintenance of the social polymorphism. Using a genotyping-by-sequencing approach, we have identified a social chromosome associated with colony queen number. We are currently investigating the origin and maintenance of this genetic polymorphism controlling social organization, and exploring which ecological factors and behavioural processes favour each social form.

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A lab colony of Formica selysi

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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