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Abstract

Animal nervous systems utilize a wide array of neuropeptides for signal transmission and neural modulation. Contrary to classical neurotransmitters, which only transfer action potentials, neuropeptides can act in different ways and are often involved in triggering or altering physiological and behavioral responses. Since most studies of marine protostomes have focused on annelids or molluscs, so far nothing is known about neuropeptides in brachiopods and nemerteans. Using an integrative approach that combines comparative genmics, transcriptomics, mass spectrometry, molecular biology and behavioral studies, we identified and characterized a set of neuropeptides in the larvae of two brachiopod species (Novocrania anomala and Terebratalia transversa) and two nemertean species (Lineus longissimus and Lineus ruber), and identified their neurosecretory regions. Behavioral assays show the specific involvement of the FMRFamide-like peptide (FLP) FLRFamide in the defense behavior of T. transversa larvae that are triggered by muscular contraction. This mirrors the role of FLPs in the myoactivity of other metazoans. We also examined the trochozoan specific "excitatory peptide" that is connected with myoactivity in annelids and molluscs, and demonstrate that it specifically influences the ciliary beating of L. longissimus larvae. These two examples demonstrate that neuropeptides show a high variation regarding their utilization during evolution. Although broadly conserved functions can be found throughout metazoans, we also demonstrate that even lineage specific neuropeptides can be recruited for different functions, which indicates rapid evolution of these essential molecules.