The smell of Panulirus argus virus 1 (PaV1) infection: Disease-induced changes in metabolites in urine and hemolymph of Caribbean spiny lobsters Panulirus argus

The Caribbean spiny lobster Panulirus argus is a social species in which individuals aggregate for protection during the day using chemicals in their urine as guiding cues. This behavior changes when animals are infected by Panulirus argus virus 1 (PaV1), such that healthy animals avoid the urine of diseased conspecifics. The aim of this study was to identify the molecules responsible for this switch in aggregation behavior. Urine and hemolymph were collected from healthy and diseased animals, and their metabolites were identified and quantified using proton nuclear magnetic resonance (¹H NMR) spectroscopy equipped with cryoprobe. Hemolymph was examined in addition to urine because it can infiltrate the urine of diseased animals and thus might be a source of the disease-specific cues. Overall differences in NMR spectra of urine and hemolymph of healthy and diseased animals were analyzed using principal component analysis of binned spectra. Differences in each chemical shift bins were identified by univariate analysis. Overall comparison of the spectra of healthy and diseased animals showed significant differences broadly across the spectra. Major compounds in the spectra were identified by NMR spectroscopy and mass spectrometry (MS) after high performance liquid chromatography (HPLC) separation as amino acids, organic acids, nucleotides, nucleosides, amines, and betaines. Comparative analysis identified six molecules that differed quantitatively in urine of healthy and diseased animals: lactate was higher in urine of healthy animals, and citrate, homarine, 2′-deoxyadenosine, 2′-deoxycytidine, and thymidine were higher in urine of diseased animals. Earlier studies have demonstrated that these or related metabolites are sensed by the chemosensory systems of spiny lobsters or other marine crustaceans. Together, these findings suggest that these six molecules are candidate chemical cues that healthy lobsters might use to avoid diseased conspecifics and thus infection.