Modulatory capacity correlates with dietary diversity in three species of decapod crustaceans

Abstract

The central nervous systems of decapod crustaceans contains numerous amines, amino acids, and peptides that modulate the central pattern generating (CPG) circuits found within its stomatogastric nervous system (STNS) and cardiac ganglion (CG); over 30 modulators have been identified in one species of crab (C. borealis). CPGs in the STNS are responsible for internally chewing (Gastric Mill CPG) and filtering food (Pyloric CPG) into the midgut, while the CG drives the heartbeat. Neuromodulation allows these CPGs to flexibly produce a variety of output patterns; however, the variety of modulators exceeds the variety of induced output, leading us to ask why so many modulators are present. Although modulatory capacity, a measure of the extent to which a neuronal circuit can be modulated, may be solely an inherited trait, we hypothesize a functional correlation: decapods that need more behavioral flexibility utilize a broader range of modulators than those with more stereotyped behaviors. We thus predicted that decapods with broad diets would have a larger modulatory capacity in the STNS, but not the CG, than those with limited diets. To test this, we compared responses of the STNS and CG CPGs in three species of majoid crabs (Pugettia producta, Libinia emarginata, and Chionoecetes opilio) to the same neuromodulators. L. emarginata and C. opilio both have broad diets, while P. producta primarily eats kelp. With one exception, each species’ CG exhibited similar responses to all modulators. The STNS of crabs with broader diets responded similarly to all modulators, whereas the P. producta STNS showed limited responses to the same set of neuromodulators. CG responses did not follow this trend, as all crabs showed varied CG response to modulation. Modulators: Cancer borealisTachykinin Related Peptide (CabTRP), Crustacean Cardioactive Peptide (CCAP), Red Pigment Concentrating Hormone (RPCH), Myosuppressin (Myo), Oxotremorine (Oxo), Dopamine (DA), Proctolin (Proc).