The olfactory system of closely related wild bee species (families: Halictidae, Colletidae and Megachilidae) - neuroanatomical correlations to social organization and host-plant preference

• Applicant: Dr. Christina Kelber
• Subject Area: Sensory and Behavioural Biology
• Term: from 2011 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 198005794

Among Hymenoptera (bees, wasps, ants), many ecologically successful species can be found with a eusocial lifestyle. However, there are also many bee and wasp species which stayed solitary. Previous studies show that eusocial Hymenoptera have a complex brain. Two main hypotheses exist about the evolution of eusociality concerning the insect brain: First, the brain complexity may have evolved as the result of eusocial lifestyles (eusocial brain Hypothesis). Second, a complex brain could have evolved in response to other selective pressures and became a precondition for the evolution of eusociality. Many studies show that both the sensory input regions and the higher integration centers of eusocial Hymenoptera brains exhibit large interspecific variance and both developmental and adult plasticity. The goal of the proposed project is to analyze specific neuroanatomical traits in selected species within the Hymenoptera with different grades of sociality. Two groups of species will be investigated: 1) Sweat bee species (Halictidae), a family where closely related species show different grades of eusociality. 2) Mason bee species (Megachilidae), a family where none of the species developed any social forms of living. Olfaction plays a prominent role in social organization of Hymenoptera. Therefore, the main focus of the proposed study will be on the first olfactory neuropile, the antennal lobe and the periphery of the olfactory system, the olfactory sensilla on the antennae. Major neuroanatomical structures of the antennal lobe will be analyzed: the number of input and output tracts, the number and size of the functional units for odor processing (glomeruli) and neuromodulators in the antennal lobe. Furthermore, I will analyze the numbers and types of olfactory sensilla on the antennae and their equipment with olfactory receptor neurons. Comparison of these neuroanatomical traits in closely related wild bees with different grades of eusociality will be a crucial step for supporting one of the two hypotheses concerning the evolution of eusociality and of a social brain.

• DFG Programme: Research Grants