SENSE · Social evolution: novel insights from the neglected sphecid wasps

Social evolution: novel insights from the neglected sphecid wasps

Project context and objectives SENSE was a 24-month research project addressing the evolution of social behaviour in the Hymenoptera, integrating field experiments with molecular genetic laboratory studies of a Mediterranean ground-nesting wasp whose females sometimes nest alone and sometimes share with other females. The main objective of the research was to open up an empirical study of a major evolutionary transition from solitary to social lifestyles, in the understudied 'sphecid' wasps, which the project has achieved in part through the successful development of novel genetic markers. The project simultaneously aimed to enhance the scientific and generic skills of a promising European researcher, Dr Manuela Giovanetti, an Italian national who undertook the research project in the United Kingdom. One of the most amazing phenomena in the animal kingdom is the evolution of true sociality (eusociality), as exemplified by the ants, some bees, some vespid wasps and termites. The phenomenon is of interest to all of us because of the parallels that social insects share with human social behaviour and human society. Among these well-known social insect societies, nest-mates co-operate for the successful growth and reproduction of the colony, with the workers often foregoing all reproduction and sometimes even dying to defend the colony. In the vast majority of these insect societies, there is just one or maybe a few mother queens who lay most or all of the eggs, and therefore all the worker individuals of a single colony show a close genetic relationship (high relatedness) to one another. The queen is also the dominant individual in the colony. Theories have been developed to justify the success of such mother-daughter eusocial systems. Central among these theories is 'inclusive fitness' or 'kin selection' theory, which explains why workers act altruistically and co-operate for the good of the colony: they do so because they help their close relatives and thereby enhance the transmission to future generations of their own genes, if not directly then indirectly through the enhanced reproductive success of relatives. The Sphecidae is a large family of wasps that is found across the world. Studies made so far on the group have often been descriptive and anecdotal, with some species of sphecid wasps labelled as social or potentially eusocial. This is surprising as they are only distantly related to the ants, bees, vespid wasps and termites. Sphecid wasps would therefore represent an independent origin of eusociality in the insects. Yet the group has rarely been investigated. Since sphecid wasp societies comprise only small groups of females, they provide an ideal model to test hypotheses related to the evolution of social behaviour, especially the role therein of kin selection (inclusive fitness) in favouring the transition from solitary nesting to eusocial nesting. Cerceris rubida (Jurine) is a very small but social member of the Sphecidae. Females are active during the hot Mediterranean summer, dig tunnels in the soil and hunt small beetles to feed to their larvae. They were the focus of this project. There were three specific research objectives: - to evaluate the degree to which nest-mate females co-operate and share in worker activities, such as foraging versus egoistic reproduction (i.e. are they eusocial); - to determine whether nest-mates are related (i.e. could kin selection explain their sociality); - to demonstrate experimentally the factors that modulate co-operation and reproductive division of labour, particularly relatedness, nest-mate number (colony size), age and size of individuals (i.e. can we demonstrate experimentally that kin selection is important in favouring co-operation).

Data: CORDIS, © European Union