Miniature masterminds : neurobiology of brain scaling in the parasitic wasp Nasonia vitripennis

The parasitic wasp <em>Nasonia vitripennis</em> is a small insect that can vary over ten times in adult body weight, ranging from 40 to 438 µg. Due to this interesting characteristic and due to its overall small size (1.5-2.5 mm in length), <em>N. vitripennis</em> is an ideal candidate for the study of brain scaling and its relation with the miniaturization of insects in general. The peculiar adaptations by which insects and other arthropods manage to miniaturize their body but still maintain behavioral complexity have long fascinated many researchers. In addition, <em>N. vitripennis</em> and related <em>Nasonia</em> species provide a novel hymenopteran model system poised to be the “new <em>Drosophila</em>”, which allows for the placing of such knowledge in a wider theoretical context. In this thesis, I aimed to gain further understanding of brain scaling at the limits of miniaturization, as well as to provide the research community with fundamental knowledge of the brain of <em>N. vitripennis</em>. To this end, this thesis provides a morphological description and a standardized average atlas of its brain: the Jewel Wasp Standard Brain. This new tool is available for the overall neuroscience community and the <em>Nasonia</em> community in particular, which will likely benefit from its use as a framework to consolidate results from past and future studies, but also as an interactive tool for educational purposes. In addition, this thesis discusses the differences in brain morphology involved with extreme brain and body size variation in <em>N. vitripennis</em> wasps (likely caused by partially isometric brain scaling), differences between the dopaminergic neurons of <em>N. vitripennis</em> and <em>N. giraulti</em>, and the effects of selection for brain size on memory, brain morphology, and longevity.