A three-dimensional immunofluorescence atlas of the brain of the hackled-orb weaver spider, Uloborus diversus

Spider orb-web building is a captivating, rare example of animal construction, whose neural underpinnings remain undiscovered. We created a three-dimensional atlas for the hackled-orb weaver, Uloborus diversus , based on immunostaining for the presynaptic component, synapsin, in whole-mounted spider synganglia. Whereas spider neuroanatomy has thus far been most comprehensively studied in cursorial species, this optically sectioned atlas contributes a continuous, finely resolved model of the central nervous system of an orb-web building spider. Aligned to this volume, we examined the expression patterns of neuronal populations representing many of the classical neurotransmitters and neuromodulators (GABA, acetylcholine, serotonin, and octopamine/tyramine), as well as a subset of neuropeptides (allatostatin A, crustacean cardioactive peptide (CCAP), FMRFamide, proctolin) – detailing immunoreactivity in an unbiased fashion throughout the synganglion to reveal co-expression in known structures (such as the arcuate body), as well as novel neuropils not readily apparent in prior spider research, including the tonsillar neuropil as well as a potential protocerebral bridge. These structures provide targets for future functional studies, and taken together, could represent a spider equivalent of the central complex, contributing to behaviors such as web-building.