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Comparative neuroanatomy of the central nervous system in web-building and cursorial hunting spiders
(2023)
Spiders (Araneae) include cursorial species that stalk their prey and more stationary species that use webs for prey capture. While many cursorial hunting spiders rely on visual cues, web-building spiders use vibratory cues (mechanosensation) for prey capture. We predicted that the differences in primary sensory input between the species are mirrored by differences in the morphology/architecture of the central nervous system (CNS). Here, we investigated the CNS anatomy of four spider species, two cursorial hunters Pardosa amentata (Lycosidae) and Marpissa muscosa (Salticidae), and two web-building hunters Argiope bruennichi (Araneidae) and Parasteatoda tepidariorum (Theridiidae). Their CNS was analyzed using Bodian silver impregnations, immunohistochemistry, and microCT analysis. We found that there are major differences between species in the secondary eye pathway of the brain that pertain to first-order, second-order, and higher order brain centers (mushroom bodies [MB]). While P. amentata and M. muscosa have prominent visual neuropils and MB, these are much reduced in the two web-building species. Argiope bruennichi lacks second-order visual neuropils but has specialized photoreceptors that project into two distinct visual neuropils, and P. tepidariorum lacks MB, suggesting that motion vision might be absent in this species. Interestingly, the differences in the ventral nerve cord are much less pronounced, but the web-building spiders have proportionally larger leg neuropils than the cursorial spiders. Our findings suggest that the importance of visual information is much reduced in web-building spiders, compared to cursorial spiders, while processing of mechanosensory information requires the same major circuits in both web-building and cursorial hunting spiders.
In mandibulate arthropods, the primary olfactory centers, termed olfactory lobes in crustaceans, are typically organized in distinct fields of dense synaptic neuropils called olfactory glomeruli. In addition to olfactory sensory neuron terminals and their postsynaptic efferents, the glomeruli are innervated by diverse neurochemically distinctive interneurons. The functional morphology of the olfactory glomeruli is understudied in crustaceans compared with insects and even less well understood and described in a particular crustacean subgroup, the Peracarida, which embrace, for example, Amphipoda and Isopoda. Using immunohistochemistry combined with confocal laser scanning microscopy, we analyzed the neurochemistry of the olfactory pathway in the amphipod Parhyale hawaiensis. We localized the biogenic amines serotonin and histamine as well as the neuropeptides RFamide, allatostatin, orcokinin, and SIFamide. As for other classical neurotransmitters, we stained for γ-aminobutyric acid and glutamate decarboxylase and used choline acetyltransferase as indicator for acetylcholine. Our study is another step in understanding principles of olfactory processing in crustaceans and can serve as a basis for understanding evolutionary transformations of crustacean olfactory systems.