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Marine invasive species and their bioactive metabolites have become critical ecological issues in the Mediterranean Sea. In particular, the highly invasive green algae Caulerpa taxifolia and Caulerpa cylindracea are known to contain the bioactive sesquiterpene caulerpenyne (1) and the bisindolic alkaloid caulerpin (2), potentially acting as chemical stressors for native species. The recent spread of a variety of C. taxifolia, Caulerpa taxifolia var. distichophylla, also raises urgent questions about its chemical composition. Indeed, the only chemical data available for this alga are limited to the seasonal variations of caulerpenyne (1) in samples collected in the Eastern Mediterranean. In this study, we confirmed the presence of 1 also in C. taxifolia var. distichophylla collected along the Sicilian coast, while 2 was not detected in the alga. However, caulerpin(2) was found both in a Mediterranean specimen of C. taxifolia, and at a much higher level in the congeneric C. cylindracea. This suggests that C. taxifolia var. distichophylla differs from C. taxifolia in its secondary metabolism, potentially exerting dissimilar chemically mediated impacts on native biota. Further chemical investigations on the terpenoidic content of C. taxifolia var. distichophylla led to isolate and identify squalene 2,3 oxide (3), phytol (4), and plastoquinone (5), along with the two unreported sesquiterpene lactones 6 and 7. Finally, chemoecological assays clarified that caulerpenyne (1) at its natural concentration in C. taxifolia var. distichophylla elicits avoidance responses in native shrimp, although sensitization was a prerequisite to significantly induce food rejection.

Among the factors affecting community dynamics, bioactive natural products act as mediators of key biological processes, including competition, predation, defense, and reproduction. Their chemical diversity thus critically contributes to the stability of ecological systems. Accordingly, research in chemical ecology provides useful information for a better understanding of ecosystem functioning and biodiversity. On the other hand, the potential of bioactive molecules produced by invasive species to become disruptive to native communities has been recently emphasized in the literature, raising novel and urgent questions about the interactions of invasive metabolites with macromolecular counterparts of ecological and ecotoxicological interest. Relevant issues strongly emerged in the Mediterranean Sea where the green alga Caulerpa cylindracea and the seagrass Halophila stipulacea, both exotic macrophytes containing peculiar bioactive compounds, have become invasive. In particular, the study of these two species has led to the production of a recent literature focusing on "alien biomolecules" and their potential impact on the native community. The present article summarizes the obtained results by giving special emphasis to the urgent need for individuating molecular interactions that are likely to exert cascade effects at all levels of biological organization, from molecules to ecosystems.

Fish have proven to be valuable models in the study of the endocrine control of appetite in response to peripheral signals of energetic and nutritional status. In parallel, a growing body of literature points to the importance of sensory experiences as factors affecting food choice in fish, with a special focus on visual and chemical signals allowing discrimination of potential foods within a 3D environment. Accordingly, waterborne compounds, such as monosaccharides or amino acids, are regarded as the main "olfactory" cues driving fish alimentary behavior. However, we recently suggested that hydrophobic molecules also allow food identification in aquatic environments and that fish actually explore a larger variety of chemosensory cues, including the olfactory/volatile compounds, when determining food palatability. In this study, we show that both homeostatic and chemosensory mechanisms involved in food intake are highly conserved in vertebrates and that the chemosensory world of fish is less different from that of terrestrial mammals than commonly thought. As a result, we support a more integrated and synthetic view of the mechanisms of chemical communication in both terrestrial and aquatic systems, which could help to ensure greater translatability of the fish models, such as the zebrafish (Danio rerio), the turquoise killifish (Nothobranchius furzeri), the goldfish (Carassius auratus), or the Japanese medaka fish (Oryzias latipes) to terrestrial vertebrates when approaching complex dynamic patterns in alimentary behavior.

Although the chemical warfare between invasive and native species has become a central problem in invasion biology, the molecular mechanisms by which bioactive metabolites from invasive pests influence local communities remain poorly characterized. This study demonstrates that the alkaloid caulerpin (CAU)&mdash, a bioactive component of the green alga Caulerpa cylindracea that has invaded the entire Mediterranean basin&mdash, is an agonist of peroxisome proliferator-activated receptors (PPARs). Our interdisciplinary study started with the in silico prediction of the ligand-protein interaction, which was then validated by in vivo, ex vivo and in vitro assays. On the basis of these results, we candidate CAU as a causal factor of the metabolic and behavioural disorders observed in Diplodus sargus, a native edible fish of high ecological and commercial relevance, feeding on C. cylindracea. Moreover, given the considerable interest in PPAR activators for the treatment of relevant human diseases, our findings are also discussed in terms of a possible nutraceutical/pharmacological valorisation of the invasive algal biomasses, supporting an innovative strategy for conserving biodiversity as an alternative to unrealistic campaigns for the eradication of invasive pests.