The chemical sense of marine isopod crustaceans
Final Report Abstract
Studies on the chemical senses of crustaceans so far have mostly centered on large decapod crustaceans such as spiny lobsters, crayfish and crabs. In the current project we analysed the central olfactory pathway and odor-guided behavior in a representative of another group of malacostracan crustaceans, the isopod Saduria entomon. Our anatomical analyses combined classical histology, 3D reconstruction, immunohistochemistry and confocal laser-scan microscopy. Concerning the olfactory glomeruli as fundamental units in the primary olfactory processing centers, we have to conclude that S. entomon represents a rather early stage of an evolutionary trajectory towards more and more effective olfactory systems as we see them in Decapoda. Furthermore, our analysis showed that also in terms of numbers of sensory afferences, glomerular numbers, and glomerular volume, Isopoda would rank rather low in a direct competition of olfactory performance with their decapod relatives, as far as we can judge from anatomical features. We conclude that the level of structural complexity both in the peripheral and central chemosensory pathways indicate a lower discriminative performance in S. entomon compared to Decapoda. Next, we analysed odor tracking behavior in two different setups, a Y-maze and an arena. Crayfish used as a control in one of these bioessays were able to locate food related stimuli with a high fidelity as was previously demonstrated in numerous behavioral studies. However, S. entomon did not show any meaningful odor-tracking behavior in these experimental situations. Nevertheless, we found that the presence of food-related stimuli does stimulate the animal’s search behavior in the arena setup. We conclude that experimental environments that are spatially and temporally restrictive do not represent an ecologically relevant situation for S. entomon (i.e., we did not ask any ecologically relevant question with our bioassay). Alternatively, ‘‘long-distance’’ odor tracking as tested in our bioassay is not ecologically relevant for these animals, and a directed orientation toward food-related odor sources is not part of their foraging strategy. Another explanation may be that the animals’ chemosensory systems do not permit the extraction of directional information from odor plumes under the tested conditions. In our behavioral studies with Saduria entomon, we did not observe any flicking behavior of antenna 1, a behavior which in decapod crustaceans is thought to be essential for extracting spatial and temporal information from odor plumes. Therefore, it remains completely unclear what kind of information S. entomon is able to extract from odor plumes. In summary, using their long-distance chemosensory system does not seem to be an essential element of their foraging strategy. Given enough time, even completely random movements will at some point lead an animal to a target. With regard to their natural habitat which provides sufficient resources to maintain population densities as high as 120 individuals per square meter, making use of sophisticated olfactory systems might not be as vital as in nutrient poor areas such as the deep sea. Thus, by patrolling its habitat without cease, finding food through fortuitous encounters might be an appropriate foraging strategy for S. entomon.
Publications
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(2013) Brain anatomy of the marine isopod Saduria entomon Linnaeus, 1758 (Valvifera, Isopoda) with special emphasis on the olfactory pathway. Frontiers in Neuroanatomy 7:32
Kenning M, Harzsch S
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(2014) Adaptive trends in malacostracan brain form and function related to behavior. In: The Natural History of Crustacea - Nervous Systems and Control of Behavior. Edited by Charles Derby and Martin Thiel, Oxford University Press; pp. 11-48
Sandeman DC, Kenning M, Harzsch S
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(2015) Heading which way? Y-maze chemical assays: not all crustaceans are alike. Helgoland Marine Research 69:305–311
Kenning M, Lehmann P, Lindström M, Harzsch S
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(2016) An Ancestor‘s Tale: Woodlice, Slater and the conquest of land. Dissertation, Zoological Institute and Museum, University of Greifswald, pp. 1 - 148
Kenning M
