Brain anatomy of the marine isopod Saduria entomon Linnaeus, 1758 (Valvifera, Isopoda) with special emphasis on the olfactory pathway

Abstract

Representatives of at least six crustacean taxa managed to establish a terrestrial life style during their evolutionary history and the Oniscidea (Isopoda) are currently held as the most successfully terrestrialized malacostracan crustaceans. The brain architecture of terrestrial isopods is fairly well understood and studies on this field suggest that the evolutionary transition from sea to land in isopods coincided with a considerable size reduction and functional loss of their first pair of antennae and associated brain areas. This finding suggests that terrestrial isopods may have no or poor abilities to detect volatile substances but that their chemosensory ecology is most likely restricted to contact chemoreception. In this study, we explored how the brain of a marine isopod and particularly its olfactory system compares to that of terrestrial relatives. Using histochemical and immunohistochemical labeling, brightfield and confocal laser-scan microscopy, we show that in the marine isopod Saduria entomon aesthetascs on the first pair of antennae provide input to a well defined deutocerebrum (DC). The deutocerebral chemosensory lobes (DCL) are divided into spherical neuropil compartments, the olfactory glomeruli (og). Secondary processing areas in the lateral protocerebrum (lPC) are supplied by a thin but distinct projection neuron tract (PNT) with a contralateral connection. Hence, contrary to terrestrial Isopoda, S. entomon has at least the neuronal substrate to perceive and process olfactory stimuli suggesting the originally marine isopod lineage had olfactory abilities comparable to that of other malacostracan crustaceans.

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“…The neuroanatomical nomenclature used in this manuscript is based on Sandeman, Sandeman, Derby, and Schmidt () and Richter et al () with modifications adopted from Harzsch and Hansson (), Kenning and Harzsch (), Loesel, Wolf, Kenning, Harzsch, and Sombke (), Krieger et al (), Schmidt () and Harzsch and Krieger (). For simplification, the neuroanatomical descriptions are limited to only one side of the brain and hold true for all specimens studied if not stated otherwise.…”

“…Rath (née Richter) and M. K. Hörnig. Drawings were modified from Kenning and Harzsch () Saduria entomon (Isopoda), and Krieger et al () ( Carcinus maenas —Brachyura); Pagurus bernhardus (Anomala) was redrawn from our own photographs and Cherax (Astacidea) after https://australianadaptations.wikispaces.com/as under a creative common license (CC BY‐SA 3.0). Other species: Nebalia bipes (Leptostraca); Erugosquilla massavensis (Stomatopoda); Neomysis integer (Mysida); Leptochelia dubia (Tanaidacea); Diastylis glabra (Cumacea); Caprella mutica (Amphipoda); Anaspides tasmaniae (Anaspidacea); Euphausia superba (Euphausiacea); Stenopus hispidus (Stenopodidea) in (a–c); Pasiphaea sivado (Caridea); and Paribaccus antarcticus (Achelata).…”

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“…Studies on the morphology of the antennae as well as the underlying neuronal network suggest that S. entomon is able to perceive, process and use odors (Pynnönen 1985;Kenning and Harzsch 2013). Ablation experiments by Pynnönen (1985) showed that the aesthetasc equipment of antenna 1 is necessary for S. entomon to react to chemical stimuli.…”

“…The eyes of S. entomon possess a high sensitivity with maximum absorption close to the wavelength of maximum light transmittance in their habitat (Lindström et al 1991), which, however, features rather low ambient light conditions (Lindström 2000). Poor light conditions in the habitat, dorsal position of the eyes and relatively small optic neuropils underlying the eyes (Kenning and Harzsch 2013) argue against vision being an important factor in foraging. However, similar to other environmental factors (Pynnönen 1996;Johansson 1999), our results suggest that light may have a distinctive influence on the behavior of S. entomon and further attention should be paid to the aspect of lightinduced modulations of behavior.…”

“…We analyzed the ability of the omnivorous isopod Saduria entomon (Valvifera) to localize a broad range of waterborne stimuli using a custom made Y-maze bioassay. In previous studies, it was shown that S. entomon possesses both the sensory (Pynnönen 1985) and central nervous equipment (Kenning and Harzsch 2013) required for receiving and processing olfactory stimuli. In order to document the efficiency of our setup, we used the same bioassay to examine olfactoryguided behavior in the marbled crayfish Procambarus fallax forma virginalis (Decapoda).…”