RESEARCH LINES
Evolution of resource specialization and foraging behaviour
Diet specialization, i.e. the description of realized diet compared with null hypothesis of generalism, has been the subject of numerous studies. However, in depth-studies on the relative importance of the different factors accounting for specialization, or promoting specialization over generalism (or vice-versa) are still few. Furthermore, very few studies analyzed simultaneously these patterns at both individual- and population-level, despite it is now widely recognized that apparent generalist populations (i.e. using resource types in accordance with their environmental availability) may be composed by specialized individuals (i.e. individual diets represent only a portion of the whole population diet). Similarly, a species may be composed of more or less specialized populations. Hymenoptera are interesting model insects to investigate in deep this topic. First, many lineages of both wasps and bees include generalist and specialist species. Second, central-place foraging species nest in restricted areas, allowing researchers to monitor the resource use of many individuals. Third, brood-parasitic species often forage in the restricted nesting areas of their hosts. I am using a variety of populations and species of wasps, bees and their hymenopteran brood parasites (e.g. cuckoo wasps, velvet ants) to study the ecology and evolution of specialization, through field sampling, behavioural tests, network analysis, and chemical communication' analysis of the interactions between consumers and resources.
Evolution of nesting strategies and cooperative behaviour
The major transitions in evolution are characterised by cooperation and division of labour among biological entities. Studying solitary and primitively social species within lineages where a more complex sociality arose (eusociality: one or few reproductive queens live with their non-reproductive daughters) helps in understanding the evolution of cooperation. Within Apoidea, eusociality arose several times in bees but apparently only once in the (basal) wasps. The lack of nestmate recognition ability and the harder task-related investment for progeny due to using large prey rather than pollen were invoked as possible causes for the rarity of eusociality in apoid wasps compared to bees, though evidence for these hypothesis is lacking. On the other side, female-female attraction and philopatry are responsable in solitary species for nest aggregation and nest-sharing. I am using a variety of solitary as well as primitively eusocial apoid wasps and bees to investigate which factors would have promoted, and which factors would have limited, the evolution of complex societies in the Apoidea. Though the study involves species from many lineages, main models are digger wasps in the genus Cerceris and digger bees in the genus Lasioglossum, since both genera are known to include species varying in their social life-style, from strictly solitary, to communal, to eusocial. I am approaching this evolutionary question with behavioral observations, manipulative experiments in the field, genetic analysis of relatedness, and chemical ecology of recognition.
Morphological adaptations to life-history traits
Wasps and bees should evolve the best “design” to efficiently exploit their resources, which can be as various as concealed hosts, quick-flying prey, plant tissues, and nest material. I am explicitly testing the links between phenotypical adaptations and resource specialization in different lineages of Hymenoptera, including parasitic wasps, gall wasps, predatory wasps, and bees. Target phenotypes include the sensory equipment (antennal sensilla and visual morphology) and hardness of the organs used to attack hosts or dig substrates (ovipositor/sting and mandibles). Thus, for example, a more sensitive visual system could be advantageous for wasps hunting for elusive, quickly mobile prey, while certain chemical sensory systems would be more important for wasps searching prey through non-body odour cues (e.g. faeces). Once host/prey is found, consumers have to successfully subdue it. Thus, ovipositor/sting properties, such as hardness (via incorporating metals) and size/shape, may change with hardness of resource attacked. Strict specialization on determinate food resource (e.g. oligolectic bees, monophagous wasps) may also present specific sensorial equipment. On the other hand, different types of nest material may require different morphologies of structures involved in its collection and manipulation (e.g. mandibles). To achieve my goal, I am carrying out comparative studies in order to discriminate if a given phenotype is the result of the evolutionary responses to resource type.
Mating strategies and sexual communication
Hymenoptera have evolved a remarkable variety of mating strategies and thus represent exceptional models to study the evolution of mating systems and inter-sexual communication. Males of wasps and bees are guided by visual and/or chemical cues or signals to find suitable females to mate, or alternatively males wait on mating sites for a suitable female to intercept, after having attract it by releasing pheromones or because perching at locations where females find resources (e.g. pollen, prey). At such sites, males monopolize access to mates by either defending females or their resources (e.g., foraging sites or nesting sites), establishing territories, or, alternatively, a system of scramble competition between males evolves. Furthermore, males are under strong competitive pressure because females mate only once or few times during their lifetime. Despite a great amount of studies were carried out on mating behaviour of bees and wasps, information still almost lack or its very poor for entire lineages (e.g. cuckoo wasps, velvet ants). Furthermore, the study of chemical communication between sexes, which is extremely important in the evolution of mating strategies, is still largely ignored for most of aculeate lineages. I aim to study in a comparative framework the mating system of model species within unexplored lineages of aculeate Hymenoptera, and reconstruct the evolution of inter-sexual communication within such a large and diverse group.