Brine shrimp larval photoresponses involved in diel vertical migration: Activation by fish mucus and modified amino sugars

Abstract

Photoresponses involved in the descent phase of nocturnal diel vertical migration of brine shrimp (Artemia franciscana) naupliar larvae were measured in a laboratory system that mimicked the underwater angular light distribution. The test hypothesis was that kairomones from fish that activate photoresponses involved in DVM include degradation products of polysaccharides in their external mucus. Studies focused on the glycosaminoglycans heparin, chondroitin sulfate A, and hyaluronic acid and their repeating disaccharide units. Active molecules were identified by their activation of the descent photoresponse. Mucus from the mummichog (Fundulus heteroclitus) activated photoresponses at concentrations down to 10-5 g wet weight of mucus L-1. Water that had previously contained this species had (1) active molecules that were <10 kDa in size, (2) polysaccharides in the >10-kDa, <30-kDa fraction that could be acted upon by heparinase and chondroitinase to produce active molecules, and (3) enzymes in the >30-kDa, <100-kDa fraction that acted on heparin and chondroitin sulfate polysaccharides to produce active molecules. The repeating disaccharide subunits of heparin, chondroitin sulfate A, and hyaluronic acid-induced photoresponses. The disaccharide subunit of hyaluronic acid was the most potent disaccharide, as it activated photoresponses at concentrations as low as 10-9 M. Tests with different subunits found that compounds with the most potent biological activity were disaccharides with either a sulfamino or acetylamino group on carbon 2 of the hexoseamine. Collectively, the results support the hypothesis and indicate that enzymatic degradation products of sulfated and acetylated fish mucus can serve as kairomones.